Electrical Designing

ELECTRICAL DESIGNING

ECDL - KELTRON

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CONTENTS

1. Safety Rules 2. Basic Electrical 3. Measuring Instruments

4. Generation Transmission & Distribution of Electricity 5. Power Triangle & Power Factor 6. Illumination 7. Wiring Concepts 8. Transformers 9. Switch Gear & Protection 10. Generators & Inverters 11. Motor Starters 12. Cables & Bus Bars 13. Power Factor Improvement 14. Earthing 15. CCTV & Fire Alarm 16. Standards & Charts

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CHAPTER - 1 SAFETY RULES Why Electricity Can Be Dangerous to You Electricity always seeks the shortest path to the ground. It tries to find a conductor, or something that it can pass through to get to the ground, like metal, wet wood or water. Your body is about 70% water, so that makes you a good conductor, too. For example, if you touch an energized bare wire or faulty appliance while your feet are touching the ground, electricity will automatically pass through you to the ground, causing a harmful, or even fatal shock. Shock The minimum current a human can feel depends on the current type (AC or DC) and frequency. A person can feel at least 1 mA (rms) of AC at 60 Hz, while at least 5 mA for DC. At around 10 mill amperes, AC current passing through the arm of a 68 kg (150 lb) human can cause powerful muscle contractions; the victim is unable to voluntarily control muscles and cannot release an electrified object.[2] This is known as the "let go threshold" and is a criterion for shock hazard in electrical regulations. The current may, if it is high enough, cause tissue damage or fibrillation which leads to cardiac arrest; more than 30 mA[3] of AC (rms, 60 Hz) or 300 – 500 mA of DC can cause fibrillation. A sustained electric shock from AC at 120 V, 60 Hz is an especially dangerous source of ventricular fibrillation because it usually exceeds the let-go threshold, while not delivering enough initial energy to propel the person away from the source. However, the potential seriousness of the shock depends on paths through the body that the currents take.[4] If the voltage is less than 200 V, then the human skin, more precisely the stratum corneum, is the main contributor to the impedance of the body in the case of a macro shock—the passing of current between two contact points on the skin. The characteristics of the skin are non-linear however. If the voltage is above 450–600 V, then dielectric breakdown of the skin occurs. The protection offered by the skin is lowered by perspiration, and this is accelerated if electricity causes muscles to contract above the let-go threshold for a sustained period of time.

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Burns

SECOND-DEGREE DEGREE BURN AFTER A HIGH TENSION LINE ACCIDENT

A person who was struck by lightning. Heating due to resistance can cause extensive and deep burns. Voltage levels of 500 to 1000 volts tend to cause internal burns due to the large energy (which is proportional to the duration multiplied by the square of the voltage divided by resistance) available from the source. Damage due to current is through tissue heating.

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21 SAFETY RULES FOR WORKING WITH ELECTRICAL EQUIPMENT Posted dec. 12 2012 by Edvard in energy and power, protection with 7 comments

A safe work environment is not always enough to control all potential electrical hazards. You must be very cautious and work safely. Safety rules help you control your and others risk of injury or death from workplace hazards. If you are working on electrical circuits or with electrical tools and equipment, you need to use following golden safety rules: 21 Golden Safety Rules Rule no. 1 Avoid contact with energized electrical circuits. Please don’t make fun of this rule if you already know this (and you probably already know if you are reading these lines) and remember that if something bad occurs – you probably won’t have second chance. That’s not funny. Rule no. 2 Treat all electrical devices as if they are live or energized. You never know. Rule no. 3 Disconnect the power source before servicing or repairing electrical equipment. The only way to be sure.

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Rule no. 4 Use only tools and equipment with non-conducting handles when working on electrical devices. Easy to check. Rule no. 5 Never use metallic pencils or rulers, or wear rings or metal watchbands when working with electrical equipment. This rule is very easy to forget, especially when you are showing some electrical part pointing with metallic pencil. Always be aware. Rule no. 6 When it is necessary to handle equipment that is plugged in, be sure hands are dry and, when possible, wear nonconductive gloves, protective clothes and shoes with insulated soles. Remember: gloves, clothes and shoes.

Safety clothes, gloves and shoes Rule no. 7 If it is safe to do so, work with only one hand, keeping the other hand at your side or in your pocket, away from all conductive material. This precaution reduces the likelihood of accidents that result in current passing through the chest cavity. If you ever read about current passing through human body you will know, so remember – work with one hand only. If you don’t clue about electric current path through human body, read more in following technical articles: • •

Do You Understand What Is Electric Shock? What psychological effect does an electric shock?

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Rule no. 8 Minimize the use of electrical equipment in cold rooms or other areas where condensation is likely. If equipment must be used in such areas, mount the equipment on a wall or vertical panel. Rule no. 9 If water or a chemical is spilled onto equipment, shut off power at the main switch or circuit breaker and unplug the equipment. Very logical. NEVER try to remove water or similar from equipment while energized. After all, it’s stupid to do so. Rule no. 10 If an individual comes in contact with a live electrical conductor, do not touch the equipment, cord or person. Disconnect the power source from the circuit breaker or pull out the plug using a leather belt. Tricky situation, and you must be very calm in order not to make the situation even worse. Like in previous rules – Always disconnect the power FIRST.

Always disconnect the power FIRST Rule no. 11 Equipment producing a “tingle” should be disconnected and reported promptly for repair. Rule no. 12 Do not rely on grounding to mask a defective circuit nor attempt to correct a fault by insertion of another fuse or breaker, particularly one of larger capacity.

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Rule no. 13 Drain capacitors before working near them and keep the short circuit on the terminals during the work to prevent electrical shock. Rule no. 14 Never touch another person’s equipment or electrical control devices unless instructed to do so. Don’t be too smart. Don’t try your luck. Rule no. 15 Enclose all electric contacts and conductors so that no one can accidentally come into contact with them. If applicable do it always, if not be very care full. Rule no. 16 Never handle electrical equipment when hands, feet, or body are wet or perspiring, or when standing on a wet floor. Remember: Gloves and shoes Rule no. 17 When it is necessary to touch electrical equipment (for example, when checking for overheated motors), use the back of the hand. Thus, if accidental shock were to cause muscular contraction, you would not “freeze” to the conductor. Rule no. 18 Do not store highly flammable liquids near electrical equipment. Rule no. 19 Be aware that interlocks on equipment disconnect the high voltage source when a cabinet door is open but power for control circuits may remain on. Read the single line diagram and wiring schemes – know your switchboard. Rule no. 20 De-energize open unattended.

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Rule no. 21 Do not wear loose clothing or ties near electrical equipment. Act like an electrical engineer, you are not on the beach.

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CHAPTER - 2 BASIC ELECTRICAL
ELECTRIC CURRENT
VOLTAGE
CIRCUIT ELEMENTS
DIRECT CURRENT
ALTERNATING CURRENT
POWER & ENERGY
OHMS LAW 1. Electric Current While a potential difference is applied across a conductor, electrical charge flows through it and electrical current is the measure of the quantity of the electrical charge transferred through the conductor per unit time. Let's explain in little bit detail the definition of electric current. The general concept of electric current is very simple. Every conducting substance in this universe consists of some free electrons in side it. These free electrons move with a random manner at room temperature. Whenever a potential difference is applied across the substance, an electric field appears inside the substance due to which the negatively charged free electrons experience an attraction toward higher potential terminal or relatively positive terminal of the substance. As a result the electrons start drifting from lower potential terminal to higher potential terminal. Flow of electrons means transfer of charge from one point to other in the substance. Electric current is nothing but measure of rate of this transferring charge. So it is measured as transferred charge per unit time. Mathematically it can be represented as

Unit of Electric Current As in the definition of electric current we have already told, that this is nothing but transferring charge per unit time in other view it can be seen as

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amount of charge crossing the perpendicular cross section of a conductor per unit time. So due to application of potential difference, if δQ Coulomb charge crosses a particular cross section of any conductor at ∆t second then,

Hence, unit of electric current is Coulomb per Second and it is named as Ampere. After name of famous French mathematician Andre-Marie Ampere. SI unit of electric current is Ampere and it abbreviated as A or Amp. In CGS system its unit is biot and abbreviated as Bi. 1 Bi = 10 A.

Electric Current Formula The most simple formula of electric current can be determined by Ohm's law. As per this low,

Current Density We can derive mathematical expression for electric current from current density. Think about the movements of charge carriers in a conductor. They have the same kind of random velocities as we explained in last paragraph. So the drift velocity at any location in a conductor can be calculated. If we consider a unit volume of space in the conductor where concentration of charge carriers is ′n′ number of similar charge carriers and ′q′ is the charge of each similar charge carrier, the rate of charge transferring to a particular direction through the surface, (particular to the direction of drift velocity) of the said space is nothing but product of ′n′, ′q′ and the drift velocity Vd of that location to the said direction. The rate of charge transferring through a

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surface, particular to the direction of drift velocity is known as current density of that location to the said direction.

Let us again assume a small surface area of the space is dA. If the current density of the space is J, then obviously current passing through this small surface is J.dA. Therefore, total current through an area A is,

Explanation of electric current as a phenomenon Current is associated with charge carried by charged particles. Electrical current means the charge flows to one end from other by means of charged particles. The phenomenon of transferring charge from one place to another is referred as electric current.

Electric Current It can be assumed that a beam of positively charged holes moving from one side to another. If that beam of holes moving from left to right, the current would be assumed, directed from left to right. As the holes are associated with atoms generally they cannot move. Then what we mean by movement of positive holes? Actually negatively charged free electrons move from right to left, which is assumed as if positive holes are moving in opposite direction of electrons movement that is from left to right. According to the general agreement the direction of current is chosen to coincide with the direction in

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which positive charge carriers or holes move even the actual movable carriers of charge are electrons and they move in opposite direction. So direction of conventional current flow is in opposite of electrons movement. So it can be concluded like this, if potential difference is applied across a conductor, then due to electrical field, free electrons in the conductor start moving toward positive or higher potential end of the conductor. The direction of the electric current is considered to be flowing from higher potential end to lower, as the relative motion of static positive charges is assumed to be in that direction. Explanation of current as a physical quantity Let us consider a conductor and assume one surface across the cross section of the conductor. By definition, electrical current is the rate of transferring electric charge through this surface in respect of time or alternatively, current across a surface is defined as the rate at which charge is transferred through this surface. Therefore, current

So, whenever we will think about current, we should always keep in mind the surface of cross - section of the conductor and current is nothing but, the amount of charge is transferred through this surface for unit time. If 1 Coulomb of charge is transferred through any surface in 1 second, then current would be

2. VOLTAGE Charge moving in an electric circuit gives rise to a current, as stated in the preceding section. Naturally, it must take some work, or energy, for the charge to move between two points in a circuit, say, from point a to point b. The total work per unit charge associated with the motion of charge between two points is called voltage. Thus, the units of voltage are those of energy per unit charge; they have been called volts in honor of Alessandro Volta. Voltage (or potential difference) is the energy required to move charge from one point to the other, measured in volts (V). Voltage is denoted by the letter v or V.

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3. CIRCUIT ELEMENTS As we discussed in the Introduction, an element is the basic buildings block of a circuit. An electric circuit is simply an interconnection of elements there are two types of elements found in electric circuits: passive elements and active elements. An active element is capable of generating energy while a passive element is not. Our aim in this section is to gain familiarity with some important passive and active elements. Passive elements (loads) A load generally refers to a component or a piece of equipment to the output of an electric circuit. In its fundamental form, the load is represented by one or a combination of the following circuit elements: 1. Resistor (R). 2. Inductor (L). 3. Capacitor (C). A load can either be resistive, inductive or capacitive nature or a blend of them. For example, a light bulb is a purely resistive load whereas a transformer is both inductive and resistive. Active elements The most important active elements are voltage or current sources that generally deliver power to the circuit connected to them. There are two kinds of sources: independent and dependent sources. An ideal independent source is an active element that provides a specified voltage or current that is completely independent of other circuit variables. An ideal dependent (or controlled) source is an active element in which the source quantity is controlled by another voltage or current. It should be noted that an ideal voltage source (dependent or independent) will produce any current required to ensure that the terminal voltage is as stated; whereas an ideal current source will produce the necessary voltage to ensure the stated current flow.

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.

Electrical Resistance Electrical resistance may be defined as the basic property of any substance due to which it opposes the flow of electric current through it While an electric potential difference is applied across any substance, electric current starts to flow through it. But if we observe carefully the current flows through the all substances are not equal even when the same potential difference is applied across each of the substances. This is because current carrying capacities of all substances are not equal. Electric current is defined as the quantity of charge transferred through a cross - section of any substance per unit time. This change transferring depends upon the number of electrons crosses the cross - section per unit time. Again this number of electrons crossing the cross - section is dependable on the free electrons available in the substances. If free electrons are plenty in a substance the amount of current is more and if the availability of free electrons is less then, the current through the substance is less for same voltage applied across the substances. The

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current through a substance not only depends upon the number of free electrons in it, but also depends upon the length of path an electron has to travel to reach from lower potential end to higher potential end of the substance. In addition to that every electron has collide randomly with other atoms and electrons in numbers of times during its traveling. So, every substance has a resistance against the electric current flows through it. So as stated earlier that electrical resistance is a property of a substance which opposes flow of current. If one volt across a conductor produces one ampere of current through it then, the resistance of the conductor is said to be one ohm (Ω). Laws of resistance There are mainly two laws of resistance from which the resistivity or specific resistance of any substance can easily be determined. One law is related to cross - sectional area of the conductor and other law is related with its length. As stated earlier, the current through any conductor depends upon numbers of electrons passes through a cross - section per unit time. So if cross section of any conductor is large then more electrons can cross it that means more current can flow through the conductor. For fixed voltage, more current means less electrical resistance. So it can be concluded like that resistance of any conductor is inversely proportional to its cross - sectional area. If length of the conductor is increased, the path traveled by the electrons is also increased. If electrons travel long they collide more and consequently the number of electron passing through the conductor becomes less hence current through the conductor is reduced. In other word resistance of the conductor increases with increase in length of the conductor.

Current flows through unit cube of material

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The laws of resistance state that, electrical resistance R of a conductor or wire is 1) directly proportional to its length, l i.e. R ∝ l 2) inversely proportional to its area of cross - section, a i.e.

Combining these two laws we get,

Where ρ (rho) is the proportionality constant and known as resistivity or specific resistance of the material of the conductor or wire. Now if we put, l = 1 and a = 1 in the equation,

We get, R = ρ. That means resistance of a material of unit length having unit cross - sectional area is equal to its resistivity or specific resistance. Resistivity of a material can be alliteratively defined as the electrical resistance between opposite faces of a unit cube of that material. Hence we have seen that laws of resistance are very simple. Unit of Resistivity The unit of resistivity can be easily determined form its equation

The unit of resistivity is Ω - m in MKS system and Ω - cm in CGS system and 1 Ω - m = 100 Ω - cm. Capacitance The property of an electric circuit or its element that permits it to store charge, and is defined by the ratio of the stored charge to potential over that element or circuit (q/v); is known as the capacitance of the given circuit.

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A capacitor is basically a component made of two or more sets of conductive plates, placed within a thin insulator material between them and then it’s wrapped in a ceramic or a plastic container. Whenever the capacitor receives a direct current (DC), a positive charge builds up on one of the plates (or set of plates) while an equal amount of negative charge builds up on the other.

Capacitor Capacitance is one of the basic parameters of electric circuit. Any circuit element showing the property of yielding a current which is directly proportional to the rate of change of voltage across its terminal is called a capacitor. It consists of two plates and the dielectrics in between. In general capacitance can be characterized as that property of a circuit element in which energy is capable of being stored in an electric field i.e the ability to accumulate the charge from the circuit and give up charge back to the circuit. Physics of Capacitor We know, when we apply a potential difference(V) across the two plates of a capacitor, a concentrated field flux is generated between the plates, allowing quite a significant difference in the numbers free electrons (or charge) to develop between the two plates. This particular phenomenon is illustrated in the diagram given below.

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As an electric field is established due to the voltage being applied, excess free electrons are accumulated on the negatively charged conductor, while at the same instance free electrons are essentially robbed from the positively charged conductor, to compensate for the excess in its negative counterpart, thus leaving the positive conductor deprived of charge. This difference in the charge storage can be equated to storage of energy in the capacitor, representing the potential of the electrons between the two charged capacitor plates. The greater the difference of electrons on opposing plates of a capacitor, the greater will be the field flux, and thus the value for energy storage in the capacitor will also be more. Capacitance in DC Circuit Current will flow in a capacitive circuit only long enough to charge the capacitor, as with a dc voltage source. The current that charges a capacitor flows only for the first moment after the switch is closed. After this momentary flow the current stops, since the plates of the capacitor are separated by an insulator which does not allow the electrons to pass through it. Thus, capacitor does not allow dc current to flow continuously through a circuit. Thus, Capacitance is manifested only when there exists a changing potential difference across the terminals of the circuit element i.e in AC only. Circuit View Point: Capacitance is introduced as the proportionality factor relating the charge between two metals surfaces to the corresponding potential difference existing between them.

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This expression shows the manner in which the current flowing through a capacitance parameter is related to the potential difference appearing across it. Thus

When there is no initial voltage on the capacitor then,

Capacitor in series and parallel Series capacitance formula

Parallel Capacitance formula

Energy View Point: The Capacitor absorbs the amount of energy which is proportional to the capacitance parameter and the square of the instantaneous value of the voltage appear across the capacitor. The absorbed energy in turn is stored by the capacitor in an electric field existing between its two plates. The energy delivered to the capacitor is given as Phase relationship: In a pure capacitive circuit current leads voltage by 90o. This property is used to improve the power factor using capacitor banks at the sending end of the voltage. The capacitive reactance Xc is given as

In a pure capacitive circuit, the true power is Zero but the apparent power is E x I.

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Geometrical View Point: The amount of charge that accumulates on the plates of the capacitor is expressed as q = CV. By means of gauss theorem it can also be expressed in terms of electric field intensity i.e q = kAE

k denotes permittivity or Dielectric Constant of the material between the plates. A denotes area of the plates; and E denotes electric field intensity

d is the distance between the plates

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Thus from the above expression we can conclude that changing the Dielectric Material change s the capacitance. The dielectric constants and the dielectric strengths of some common materials are listed in the table: Single Phase Power A single phase transmission system is practically not available but still we should know first the basic concept of single phase power before going through modern three phase power system. Before going to details about single phase power, let's try to understand different Parameters Three basic parameters of electrical power system are resistance, inductance and capacitance. Resistance The resistance of power circuit or simply resistor consumes ohmic energy. While electric current flows through a resistor there will not be any phase difference between the voltage and current, that means electric current and voltage are in same phase the phase angle between them is zero. If I current flows through an electrical resistance R for t seconds then total energy consumed by the resistor is I2.R.t. This power is known as active power Inductance Inductance of the system or simply inductor stores magnetic field energy during positive half cycle and gives away during negative half cycle of single phase power supply. If a current 'I' flows through a coil of inductance L Henri, the energy stored in the coil in form of magnetic field is given by

The power associated with an inductance is reactive power. Capacitance Capacitance of the system or simply capacitor, stores electric field energy during positive half cycle and give away during negative half cycle of supply. The energy stored between two parallel metallic plates of potential difference V and capacitance across them C, is expressed as

This energy is stored in form of electric field. The power associated with a capacitance is also reactive power.

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4. DIRECT CURRENT Direct current (DC) is the unidirectional flow of electric charge. Direct current is produced by sources such as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current (AC). A term formerly used for direct current was galvanic current. The abbreviations AC and DC are often used to mean simply Alternating and direct, as when they modify current or voltage. [2][3] Direct current may be obtained from an alternating current supply by use of a current-switching arrangement called a rectifier, which contains electronic elements (usually) or electromechanical elements (historically) that allow current to flow only in one direction. Direct current may be made into alternating current with an inverter or a motor-generator set. The first commercial electric power transmission (developed by Thomas Edison in the late nineteenth century) used direct current. Because of the significant advantages of alternating current over direct current in transforming and transmission, electric power distribution is nearly all alternating current today. In the mid-1950s, HVDC transmission was developed, and is now an option instead of long-distance high voltage alternating current systems. For long distance under seas cables (e.g. between countries, such as Nor Ned) is the only technical feasible option. For applications requiring direct current, such as third rail power systems, alternating current is distributed to a substation, which utilizes a rectifier to convert the power to direct current. See War of Currents. Direct current is used to charge batteries, and in nearly all electronic systems, as the power supply. Very large quantities of direct-current power are used in production of aluminum and other electrochemical processes. Direct current is used for some railway propulsion, especially in urban areas. High-voltage direct current is used to transmit large amounts of power from remote generation sites or to interconnect alternating current power grids.

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A direct current circuit is an electrical circuit that consists of any combination of constant voltage sources, constant current sources, and resistors.. In this case, the circuit voltages and currents are independent of time. A particularr circuit voltage or current does not depend on the past value of any circuit voltage or current. This implies that the system of equations that represent a DC circuit do not involve integrals or derivatives with respect to time. If a capacitor or inductor is added to a DC circuit, the resulting circuit is not, strictly speaking, a DC circuit. However, most such circuits have a DC solution. This solution gives the circuit voltages and currents when the circuit is in DC steady state. state. Such a circuit is represented by a system of differential equations.. The solution to these equations usually contains a time varying or transient part as well as constant or steady state part. It is this steady state part that is the DC solution. There are some circuits that do not have a DC solution. Two simple examples are a constant current source connected to a capacitor and a constant constant voltage source connected to an inductor. In electronics, it is common to refer to a circuit that is powered by a DC voltage source such as a battery or the output of a DC power supply as a DC circuit even though what is meant is that the circuit is DC powered 5. ALTERNATING CURRENT In alternating current (AC, ( also ac), the flow of electric charge periodically reverses direction. In direct current (DC, also dc), ), the flow of electric charge is only in one direction. The abbreviations AC and DC are often used to mean simply alternating and direct,, as when they modify m current or voltage.[1] [2]

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AC is the form in which electric power is delivered to businesses and residences. The usual waveform of an AC power circuit is a sine wave. In certain applications, different waveforms are used, such as triangular or square waves. Audio and radio signals carried on electrical wires are also examples of alternating current. In these applications, an important impo goal is often the recovery of information encoded (or modulated)) onto the AC signal AC voltage may be increased or decreased with a transformer. transformer Use of a higher voltage leads to significantly more efficient transmission of power. The power losses in a conductor are a product of the square of the current curre and the resistance of the conductor, conductor, described by the formula

This means that when transmitting a fixed power on a given wire, if the current is doubled, the power loss will be four times greater. The power transmitted is equal to the product of the current and the voltage (assuming no phase difference); that is, Thus, the same amount of power can be transmitted with a lower current by increasing the voltage. It is therefore advantageous when transmitting large amounts of power to distribute the power with high voltages (often hundreds of kilovolts).

High voltage transmission lines deliver power from electric generation plants over long distances using alternating current. These lines are located in eastern Utah. However, high voltages also have disadvantages, the main one being the increased insulation required, and generally increased difficulty in their safe handling. In a power plant, plant, power is generated at a convenient voltage for the design of a generator, generator and then stepped up to a high voltage for transmission. Near the loads, the transmission voltage is stepped down to the voltages used by equipment. Consumer Consumer voltages vary depending on the country and size of load, but generally motors and lighting are built to use up to a few hundred volts between phases.

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The utilization voltage delivered to equipment such as lighting and motor loads is standardized, with an allowable range of voltage over which equipment is expected to operate. Standard power utilization voltages and percentage tolerance vary in the different mains power systems found in the world. Modern high-voltage direct-current (HVDC) electric power transmission systems contrast with the more common alternating-current systems as a means for the efficient bulk transmission of electrical power over long distances. HVDC systems, however, tend to be more expensive and less efficient over shorter distances than transformers.[citation needed] Transmission with high voltage direct current was not feasible when Edison, Westinghouse And Tesla were designing their power systems, since there was then no way to economically convert AC power to DC and back again at the necessary voltages. Three-phase electrical generation is very common. The simplest case is three separate coils in the generator stator that are physically offset by an angle of 120° to each other. Three current waveforms are produced that are equal in magnitude and 120° out of phase to each other. If coils are added opposite to these (60° spacing), they generate the same phases with reverse polarity and so can be simply wired together. In practice, higher "pole orders" are commonly used. For example, a 12-pole machine would have 36 coils (10° spacing). The advantage is that lower speeds can be used. For example, a 2-pole machine running at 3600 rpm and a 12-pole machine running at 600 rpm produce the same frequency. This is much more practical for larger machines. If the load on a three-phase system is balanced equally among the phases, no current flows through the neutral point. Even in the worst-case unbalanced (linear) load, the neutral current will not exceed the highest of the phase currents. Non-linear loads (e.g., computers) may require an oversized neutral bus and neutral conductor in the upstream distribution panel to handle harmonics. Harmonics can cause neutral conductor current levels to exceed that of one or all phase conductors. For three-phase at utilization voltages a four-wire system is often used. When stepping down three-phase, a transformer with a Delta (3-wire) primary and a Star (4-wire, center-earthed) secondary is often used so there is no need for a neutral on the supply side. For smaller customers (just how small varies by country and age of the installation) only a single phase and the neutral or two phases and the neutral are taken to the property. For larger installations all three phases

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and the neutral are taken to the main distribution panel. From the threephase main panel, both single and three-phase circuits may lead off. Three-wire single-phase systems, with a single center-tapped transformer giving two live conductors, is a common distribution scheme for residential and small commercial buildings in North America. This arrangement is sometimes incorrectly referred to as "two phase". A similar method is used for a different reason on construction sites in the UK. Small power tools and lighting are supposed to be supplied by a local center-tapped transformer with a voltage of 55 V between each power conductor and earth. This significantly reduces the risk of electric shock in the event that one of the live conductors becomes exposed through an equipment fault whilst still allowing a reasonable voltage of 110 V between the two conductors for running the tools. A third wire, called the bond (or earth) wire, is often connected between noncurrent-carrying metal enclosures and earth ground. This conductor provides protection from electric shock due to accidental contact of circuit conductors with the metal chassis of portable appliances and tools. Bonding all non-current-carrying metal parts into one complete system ensures there is always a low electrical impedance path to ground sufficient to carry any fault current for as long as it takes for the system to clear the fault. This low impedance path allows the maximum amount of fault current, causing the over current protection device (breakers, fuses) to trip or burn out as quickly as possible, bringing the electrical system to a safe state. All bond wires are bonded to ground at the main service panel, as is the Neutral/Identified conductor if present. 6. POWER AND ENERGY Electric power is the mathematical product of two quantities: current and voltage. These two quantities can vary with respect to time (AC power) or can be kept at constant levels (DC power). Most refrigerators, air conditioners, pumps and industrial machinery use AC power whereas most computers and digital equipment use DC power (the digital devices you plug into the mains typically have an internal or external power adapter to convert from AC to DC power). AC power has the advantage of being easy to transform between voltages and is able to be generated and utilized by brushless machinery. DC power remains the only practical choice in digital systems and can be more economical to transmit over long distances at very high voltages. The ability to easily transform the voltage of AC power is important for two reasons: Firstly, power can be transmitted over long distances with less loss at higher voltages. So in power networks where generation is distant from

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the load, it is desirable to step-up the voltage of power at the generation point and then step-down the voltage near the load. Secondly, it is often more economical to install turbines that produce higher voltages than would be used by most appliances, so the ability to easily transform voltages means this mismatch between voltages can be easily managed. Solid state devices, which are products of the semiconductor revolution, make it possible to transform DC power to different voltages, build brushless DC machines and convert between AC and DC power. Nevertheless, devices utilizing solid state technology are often more expensive than their traditional counterparts, so AC power remains in widespread use. Electric power is usually produced by electric generators, but can also be supplied by chemical sources such as electric batteries. Electric power is generally supplied to businesses and homes by the electric power industry. Electric power is usually sold by the kilowatt hour (3.6 MJ) which is the product of power in kilowatts multiplied by running time in hours. Electric utilities measure power using an electricity meter, which keeps a running total of the electric energy delivered to a customer. Although current and voltage are the two basic variables in an electric circuit, they are not sufficient by themselves. For practical purposes, we need to know how much power an electric device can handle. We also know that when we pay our bills to the electric utility companies, we are paying for the electric energy consumed over a certain period of time. Thus power and energy calculations are important in circuit analysis. We write this relationship as: p = dwdt Electric Power Formulas P=VI P = R I2 P = V2 / R where P = power (wattsW) V = voltage (voltsV) I = current(ampere) R = resistance(ohm)

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Electrical Energy Electrical energy is energy newly derived from electrical potential energy. When loosely used to describe energy absorbed or delivered by an electrical circuit (for example, one provided by an electric power utility) "electrical energy" refers to energy which has been converted from electrical potential energy. This energy is supplied by the combination of electric current and electrical potential that is delivered by the circuit. At the point that this electrical potential energy has been converted to another type of energy, it ceases to be electrical potential energy. Thus, all electrical energy is potential energy before it is delivered to the end-use. Once converted from potential energy, electrical energy can always be described as another type of energy (heat, light, motion, etc.). The formula that links energy and power is: Energy = Power x Time. The unit of energy is the joule, the unit of power is the watt, and the unit of time is the second. If we know the power in watts of an appliance and how many seconds it is used we can calculate the number of joules of electrical energy which have been converted to sortie other form. E.g. If a 40 watt lamp is turned on for one hour, how many joules of electrical energy have been converted by the lamp? Energy (w)

=

Power x Time

Energy

=

40 x 3600

=

14,400 joules

Note: if an appliance has a rating of one watt it means it converts one joule of electrical energy to some other form every second. Because the joule is such a small unit, quantities of energy are often given in kilojoules. i.e, thousands of joules. Therefore the above answer could be written as 14.4 kJ.

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The Kilowatt Hour (kWh) Because the joule is so small, electrical energy supplied to consumers is bought by the UNIT. The UNIT is the kilowatt hour (kWh). One kilowatt hour is the amount of energy that would be converted by a one thousand watt appliance when used for one hour Example: A consumer uses a 6 kW immersion heater, a 4 kW electric stove and three 100 watt lamps for 10 hours. How many units (kwh) of electrical energy have been converted. Total Power (kw) = 6+4+300 / 1000 = 10.3kw Energy consumed (kwh) = Power in kw x time in hours = 10.3 x 10 = 103 kwh Electrical supply authorities use the kWh as the unit for measuring electrical energy to householders. Revision Exercise 1. How much heat energy is converted by a 1kw heater in half a minute? 2. An electric toaster is rated at 500 watts. Determine the amount of heat energy it converts to heat in one minute. In the calculations of energy so far the values of the power have been given. However, if enough information is given the volume of the power can be calculated first and then the value put into the energy formula. Worked Example - Number 1 • Calculate the heat produced by an electric iron, which has a resistance of 30 ohms and takes a current of 3 amperes when it is switched on for 15 seconds. Power

= 12R = 32 x 30

= 270 watts Energy = Power x Time = 270 x 15 = 4050 joules

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Worked Example - Number 2 A d-c generator has an E.m.f of 200 volts and provides a current of 10 amps. How much energy does it provide each minute? Energy = Power x Time Power

=VxI = 200 x 10 = 2000 watts

Energy = 2000 x 60 = 120,000 Joules 7Ohm's law The most basic quantities of electricity are voltage, current and resistance. Ohm's law shows a simple relation between these three quantities, hence this law can be considered as most basic law of electrical engineering. This simple, easiest to remember three characters law of electrical engineering helps to calculate and analyze, electrical quantities related to power, efficiency and impedance. Ohm's law first appeared in the book written by Georg Simon Ohm (German) in 1827. Statement of Ohm's Law

Georg Ohm The statement of Ohm’s law is simple and it says that, whenever a potential difference or voltage is applied across a resistor of a closed circuit, current starts flowing through it. This current is directly proportional to the voltage applied if temperature and all other factors remain constant. Thus we can mathematically express it as,

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Now putting the constant of proportionality we get,

This particular equation essentially presents, the statement of this law where I is the current through the resistor in unit of Ampere, when the potential difference V is applied across the resistor in unit of volt, and ohm(&Ohm;) is the unit of resistance of the resistor R. It’s important to note, that the resistance R, is the property of the conductor and theoretically it has no dependence on the voltage applied, or on the flow of current. The value of R changes only if the conditions (like temperature, diameter, length etc.) of the material are changed by any means. He performed his experiment with a simple electrochemical cell, as shown in the figure below. 1. There were two copper made electrodes X and Y. 2. Reference electrodes A, B and C are partly immersed in electrolyte as shown. 3. A glass made container is used for electrolyte, as shown.

Ohm's Law Experiment Setup By observing, the results of this experiment, Georg Simon Ohm had defined the fundamental interrelationship between current, voltage and resistance of a circuit, which was later named as Ohm's law. Because of this law and his excellence in the field of science and academics, he got Copley Medal award in 1841. In 1872 the unit of electrical resistance was named as 'OHM" in his honor. Ohm’s law physics To understand the physics behind Ohm's law in the most simplistic manner possible. Let us have a look at this picture below and study it very closely. From here we can draw the analogy that the person at the extreme left is the cause or the external force due to which current (or the person in the

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middle) tends to flows across a particular circuit from one end to the other in the direction of the applied voltage. Where as the one at the top is resistance, as it increases the difficulty for the cause to be fulfilled, in achieving end result. The more powerful the person at the top is, or greater the resistance, more difficulty will be encountered by the current to flow through as a result we will get lesser the amount than expected. Or for the flowing of required amount of current in presence of resistance, greater applied force or voltage needs to be applied. Thus from here we can reach the conclusion that the resistance, which is an inherent property of the conducting material, is an independent parameter. And depending on it are the voltage and current, which are directly and inversely proportional to it respectively.

Ohm's Law This is the exact phenomena that occur even at the molecular level, where the solid conductor contains free electrons as negative charge carriers. The atoms and ions are heavier in weight compared to the electrons and therefore have no contribution towards flow of current. In fact they are the barriers, to the path of the electron flow. These barriers are the real cause behind the resistance in a circuit. Let us look into it in details. When we apply a voltage V, between the leads of a resistor, we can expect a current, I = V/R to flow through it. The way the electrons move through the solid material is a bit like the way toothpaste squeezes along a tube or as shown in the comic picture above. The electrons keep being accelerated by

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the applied electric field or voltage. This means they acquire some kinetic energy as they move towards the + Ve end of the piece of material (resistor). However, before they get very far they collide with an atom or ion, lose some of their kinetic energy and may bounce back. Again due to presence of electric field the free electrons again accelerate. This keeps happening. As a result they tend to "drift" towards the + Ve end, bouncing around from atom to atom on the way. This is illustrated in figure below.

This process of drifting or diffusing of electrons in the presence of static atoms and ions, is the exact reason why does material encounter resistance to the electric current. This is the physics behind Ohm's Law. The average drift velocity of the electrons is proportional to the applied electric field. Hence the electric current, we get is also proportional to the applied voltage. It thus explains why we need to constantly supply the energy to maintain the current. The electrons need to be given the required kinetic energy to move them along, as it keeps being 'lost' every time they interact with an atom. Now from law of conservation of energy we know, that the energy of electrons lost due to collision is not vanished forever, in fact it is taken up by the atoms, as it makes them jiggle around and vibrate more furiously due to increased energy level. Thus increasing the total internal energy of the material and resulting in heat formation. As a result, we see here that electrical energy is being converted into heat energy and dissipated as loss. The rate of energy loss or the power dissipation, P, in the resistor can be calculated from the equation P = VI. This equation makes sense since we can expect a higher voltage to make the electrons speed up more swiftly; hence they have more energy to lose when they strike an atom. Doubling the voltage would double the rate at which each electron picks up kinetic energy and loses it again by banging into the atoms.

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The current we get at any particular voltage depends upon the number of free electrons that are, able to flow across, in response to the applied field. Twice the number of electrons would give us twice the current. So it means twice as many electrons requiring kinetic energy to move them and colliding with atoms. So, the rate at which the resistor 'eats up' electrical energy and converts it into heat is proportional to the current also. I.e. the power dissipation (rate of energy loss) is P = VI. Applications of Ohm’s law. The applications of ohm’s law are that, it helps us in determining either of voltage, current or resistance of a linear circuit, when the other two quantities are known to us. Apart from that, it makes Power calculation a lot more simpler, like when we know the value of the resistance for a particular circuit we need not know both the current and the voltage to calculate the power dissipation since P = VI. Rather we can use Ohm's Law

To replace either the voltage or current in the above expression to produce the result

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These are the applications of Ohm’s law as we can see from the results that the rate of energy loss varies with the square of the voltage or current. When we double the voltage applied to a circuit obeying Ohm’s law the rate at which energy is supplied (or power) gets four times bigger. This phenomenon occurs because increasing the voltage also makes the current rise by the same amount as it has been explained above. Limitation of Ohm’s law The limitations of Ohm’s law are explained as under, 1) This law cannot be applied for unilateral network. The network consisting of unilateral element like, diode, transistor etc, which do not have same voltage current relation for both direction of current. 2) Ohm’s law also not applicable for non – linear elements. Non – linear elements are those which do not give current through ii, is not exactly proportional to the voltage applied, that means resistance value of those element changes for different values of voltage and current. Examples of non – linear elements are thyristors, electric arc etc.

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CHAPTER - 3 MEASURING INSTRUMENTS
AMMETERS


VOLTMETERS AMMETER & VOLTMETER In our day today life, many times we require to measure different electrical quantities like current, voltage, resistance, etc. While doing experiment, there is necessity of multi meter. As we have already discussed about multi meter, how it measures different electrical quantities like electrical current, voltage, resistance, etc. But the basic instruments for the measurement of electric current and voltage are ammeters and voltmeters respectively. Let us discuss these instruments one by one, operating principle (working principle) of ammeters and voltmeters, finally major differences between ammeters and voltmeters. Operating Principle: Analog ammeters and voltmeters are classed together as there are no fundamental differences in their operating principles. The action of all ammeters and voltmeters, with the exception of electrostatic type of instruments, depends upon a deflecting torque produced by an electric current in an ammeter this torque is produced by a current to be measured or by a fraction of it. In a voltmeter this torque is produced by a current which is proportional to the voltage to be measured. Thus all analog voltmeters and ammeters are essentially current measuring devices. The essential requirement of measuring instruments are (i) that its introduction into the circuit, where measurements are to be made, does not alter the circuit conditions; (ii)the power consumed by them for their operation is small. Ammeters: Ammeters are connected in the series with the circuit whose current is to be measured. The power loss in an ammeter is (I^2.Ra) where I is the current to be measured Ra is the resistance of the ammeter therefore ammeter should have low electrical resistance so that they cause a small voltage drop and consequently absorb small power.

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Voltmeters: Voltmeters are connected in parallel with the circuit whose voltage is to be measured .the power loss in voltmeter is (V^2/Rv), where V is the voltage to be measured and Rv is the resistance of the voltmeter. Therefore voltmeters should have a high electrical resistance, in order that the current drawn by them is small and consequently the power consumed is small.

Difference between Ammeters and voltmeters: Parameters

Ammeter

Voltmeter

Connection

It is to be connected in series mode

It is to be connected in parallel mode

Resistance

It has comparatively low resistance

It has high resistance

Uses

It is used to find the amount of current flowing in the circuit

It is used to find the potential difference in the circuit

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Circuit

Accuracy

39

Circuit must be disconnected in order to attach the ammeter

Circuit does not need to be disconnected

Considered as less Accurate

Considered as more accurate compared to ammeter

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

CHAPTER - 4 GENERATION, TRANSMISSION & DISTRIBUTION OF ELECTRICAL ENERGY


THERMAL POWER STATION
HYDRO POWER PLANT
SOLAR POWER PLANT
SERIES AND PARALLEL BATTERY CELL
TRANSMISSION OF ELECTRICAL ENERGY
DISTRIBUTION

1. GENERATING STATIONS 1.1 Thermal Power Station Thermal power generation plant or thermal power station is the most conventional source of electric power. Thermal power plant is also referred as coal thermal power plant and steam turbine power plant. Before going into detail of this topic, we will try to understand the line diagram of electric power generation plant. Theory of thermal power station The theory of thermal power station is very simple. A power generation plant mainly consists of alternator runs with help of steam turbine. The steam is obtained from high pressure boilers. Generally in India, bituminous coal, brown coal and peat are used as fuel of boiler. The bituminous coal is used as boiler fuel has volatile matter from 8 to 33 % and ash content 5 to 16 %. To increase the thermal efficiency the coal is used in the boiler in powder form. In coal thermal power plant the steam is produced in high pressure in the boiler due to burning of fuel (pulverized coal) in boiler furnaces. This steam is further supper heated in a super heater. This supper heated steam then enters into the turbine and rotates the turbine blades. The turbine is

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mechanically so coupled with alternator that its rotor will rotate with the rotation of turbine blades. After entering in turbine the steam pressure suddenly falls and corresponding volume of the steam increases. After imparting energy to the turbine rotator the steam passes out of the turbine blades into the condenser. In the condenser the cold water is circulated with the help of pump which condenses the low pressure wet steam. this condensed water is further supplied to low pressure water heater where the low pressure steam increases the temperature of this feed water; it is again heated in high pressure. For better understanding we furnish every step of function of a thermal power station as follows, 1) First the pulverized coal is burnt into the furnace of boiler. 2) High pressure steam is produced in the boiler. 3) This steam is then passed through the super heater, where it further heated up. 4) This supper heated steam is then entered into a turbine at high speed. 5) In turbine this steam force rotates the turbine blades that means here in the turbine the stored potential energy of the high pressured steam is converted into mechanical energy. 6) After rotating the turbine blades, the steam has lost its high pressure, passes out of turbine blades and enters into a condenser. 7) In the condenser the cold water is circulated with help of pump which condenses the low pressure wet steam. 8) This condensed water is then further supplied to low pressure water heater where the low pressure steam increases the temperature of this feed water; it is then again heated in a high pressure heater where the high pressure of steam is used for heating. 9) The turbine in thermal power station acts as a prime mover of the alternator.

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The total scheme of a typical thermal power station along with different circuits is illustrated below.

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1.2 Hydro Power Plant Power system mainly contains three parts namely generation, transmission and distribution. Generation means how to generate electricity from the available source and there are various methods to generate electricity but in this article we only focused on generation of electricity by the means of hydro or water (hydro power plant). As we know that the power plant is defined as the place where power is generated from a given source, so here the source is hydro that’s why we called it hydro power plant.

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Hydro Power Plant In hydro power plant we use gravitational force of fluid water to run the turbine which is coupled with electric generator to produce electricity. This power plant plays an important role to protect our fossil fuel which is limited, because the generated electricity in hydro power station is the use of water which is renewable source of energy and available in lots of amount without any cost. The big advantage of hydro power is the water which the main stuff to produce electricity in hydro power plant is free, it not contain any type of pollution and after generated electricity the price of electricity is average not too much high. Construction and Working of Hydro Power Plant Fundamental parts of hydro power plant are a) Area b) Dam c) Reservoir d) Penstock e) Storage tank f) Turbines and generators

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1.3 SOLAR POWER PLANT PV Array A photovoltaic array is a linked collection of photovoltaic modules, which are in turn made of multiple interconnected solar cells. By their modularity, they are able to be configured to supply most loads.

A photovoltaic array is a linked assembly of PV modules. The cells convert solar energy into direct current electricity via the photovoltaic effect. The power that one module can produce is seldom enough to meet requirements of a home or a business, so the modules are

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linked together to form an array. Most PV arrays use an inverter to convert the DC power produced by the modules into alternating current that can plug into the existing infrastructure to power lights, motors, and other loads. The modules in a PV array are usually first connected in series to obtain the desired voltage; the individual strings are then connected in parallel to allow the system to produce more current. Solar arrays are typically measured by the peak electrical power they produce, in watts, kilowatts, or even megawatts.

Timber framed house with a photovoltaic array Costs of production have been reduced in recent years for more widespread use through production and technological advances. One source claims the cost in February 2006 ranged $3–10/watt while a similar size is said to have cost $8–10/watt in February 1996, depending on type. For example, crystal silicon solar cells have largely been replaced by less expensive multi crystalline silicon solar cells, and thin film silicon solar cells have also been developed recently at lower costs of production yet. Although they are reduced in energy conversion efficiency from single crystalline "siwafers", they are also much easier to produce at comparably lower costs. Applications

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The solar panels on this small yacht at sea can charge the 12 volt batteries at up to 9 amperes in full, direct sunlight. Urban uses In urban and suburban areas, photovoltaic arrays are commonly used on rooftops to supplement power use; often the building will have a connection to the power grid, in which case the energy produced by the PV array can be sold back to the utility in some sort of net metering agreement. Solar trees are arrays that, as the name implies, mimic the look of trees, provide shade, and at night can function as street lights. In agricultural settings, the array may be used to directly power DC pumps, without the need for an inverter. In remote settings such as mountainous areas, islands, or other places where a power grid is unavailable, solar arrays can be used as the sole source of electricity, usually by charging a storage battery. There is financial support available for people wishing to install PV arrays. In the UK, households are paid a 'Feedback Fee' to buy excess electricity at a flat rate per kWh. This is up to 44.3p/kWh which can allow a home to earn double their usual annual domestic electricity bill. Note that the current UK feed in tariff system is due for review on 31st March 2012, after this date the current scheme may be no longer available.

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A solar panel on top of a parking meter. Note that this particular installation is shaded, and may not perform as desired. Performance At high noon on a cloudless day at the equator, the power of the sun is about 1 kW/m², on the Earth's surface, to a plane that is perpendicular to the sun's rays. As such, PV arrays can track the sun through each day to greatly enhance energy collection. However, tracking devices add cost, and require maintenance, so it is more common for PV arrays to have fixed mounts that tilt the array and face due South in the Northern Hemisphere (in the Southern Hemisphere, they should point due North). The tilt angle, from horizontal, can be varied for season, but if fixed, should be set to give optimal array output during the peak electrical demand portion of a typical year. Trackers and sensors to optimise the performance are often seen as optional, but tracking systems can increase viable output by up to 100%. PV arrays that approach or exceed one megawatt often use solar trackers. Accounting for clouds, and the fact that most of the world is not on the equator, and that the sun sets in the evening, the correct measure of solar power is insulations – the average number of kilowatt-hours per square meter per day. For the weather and latitudes of the United States and Europe, typical insulations ranges from 4kWh/m²/day in northern climes to 6.5 kWh/m²/day in the sunniest regions. In 2010, solar panels available for customers can have a yield of up to 19%, while commercially available panels can go as far as 27%. Thus, a photovoltaic installation in the southern latitudes of Europe or the United States may expect to produce 1 kWh/m²/day. A typical "150 watt" solar panel is about a square meter in size. Such a panel may be expected to

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produce 1 kWh every day, on average, after taking into account the weather and the latitude. In the Sahara desert, with less cloud cover and a better solar angle, one can obtain closer to 8.3 kWh/m²/day. The unpopulated area of the Sahara desert is over 9 million km², which if covered with solar panels would provide 630 terawatts total power. The Earth's current energy consumption rate is around 13.5 TW at any given moment (including oil, gas, coal, nuclear, and hydroelectric). Other factors affect PV performance. Many Photovoltaic cells' electrical output is extremely sensitive to shading. There are some non-traditional solar cell manufacturers, thin-film a:Si, that have installed bypass diodes between each cell that minimize the effects of shading and only lose the power of the shaded portion of the array. When even a small portion of a cell, module, or array is shaded, while the remainder is in sunlight, the output falls dramatically due to internal 'short-circuiting' (the electrons reversing course through the shaded portion of the p-n junction). Therefore it is extremely important that a PV installation is not shaded at all by trees, architectural features, flag poles, or other obstructions like continuously parked cars. Sunlight can be absorbed by dust, fallout, or other impurities at the surface of the module. This can cut down the amount of light that actually strikes the cells by as much as half. Maintaining a clean module surface will increase output performance over the life of the module. Module output and life are also degraded by increased temperature. Allowing ambient air to flow over, and if possible behind, PV modules reduces this problem. Effective module lives are typically 25 years or more.

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Electrical power is generated at different generating stations. These generating stations are not necessarily situated at the load center. During construction of generating station number of factors to be considered from economical point of view. These all factors may not be easily available at load center; hence generating stations are not normally situated very nearer to load center. Load center is the place where maximum power is consumed. Hence there must be some means by which the generated power must be transmitted to the load center. Electrical Transmission system is the means of transmitting power from generating station to different load centers. Factor to be considered for constructing a generating station During planning of construction of generating station the following factors to be considered for economical generation of electrical power. 1) Easy availability of water for Thermal Power Generating Station. 2) Easy availability of land for construction of power station including it's staff township. 3) For Hydral Power station there must be a dam on river. So proper place on the river must be chosen in such a way that the construction of the dam can be done in most optimum way. 4) For thermal station easy availability of fuel is one of the most important factors to be considered. 5) Better communication for goods as well as employees of the power station also to be kept into consideration. 6) For transporting very big spare parts of turbines, alternators etc, there must be wide road ways, rain communication, and deep and wide river must pass away nearby the power station.

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7) For nuclear power plant, it must be situated in such a distance from common location so that there may be any effect from nuclear reaction the heath of common people. many other factors also to be considered, but there are beyond the scope of our discussion. All the factors listed above are very difficult to be available at load center. The power station or generating station must be situated where all the facilities are easily available. This place may not be necessarily at the load center. The power generated at generating station then transmitted to the load center by means of electrical power transmission system as we said earlier.

The power generated at generating station is in low voltage level as low voltage power generation has some economical values. Low voltage power generation is more economical than high voltage power generation. At low voltage level, both weight and wide of insulation is less in the alternator, this directly reduces the cost and size of alternator. But this low voltage level power cannot be transmitted directly to the consumer end as because this low voltage power transmission is not at all economical. Hence although low voltage power generation is economical but low voltage electrical power transmission is not economical. Electrical power is directly proportional to the product of electrical current and voltage of system. So for transmitting certain electrical power from one place to another, if the voltage of the power is increased then associated electric current of this power is reduced. Reduced current means less I2R loss in the system, less cross sectional area of the conductor means less capital involvement and decreased current causes improvement in voltage regulation of the system and improved voltage regulation indicates quality power. Because of these three reasons electrical power mainly transmitted at high voltage level.

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Again at distribution end for efficient distribution of the transmitted power, it is stepped down to its desired low voltage level. So it can be concluded that first the electrical power is generated at low voltage level then it stepped up to high voltage for efficient transmission of electrical energy. Lastly for distribution of electrical energy or power to different consumers it is stepped down to desired low voltage level. This brief discussion of electrical transmission system and network, but now we will discussed little bit more details about transmission of electrical energy.

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1.4 Series Parallel Battery Cells Battery is an electrical element where electrical potential is produced due to chemical reaction. Every electrochemical reaction has its limit of producing potential difference between two electrodes. Battery cells are those where these electrochemical reactions take place to produce the limited potential difference. For achieving desired potential difference across the battery terminals multiple numbers of cells to be connected in series. Hence it can be concluded like that, a battery is combination of several cells whereas a cell is a unit of a battery. For example, Nickel – Cadmium battery cells normally develop about 1.2 V per cell while lead acid batteries develop about 2 V per cell. So a 12 volt battery will have total 6 number of cells connected in series. EMF of Battery If anyone just measures the potential difference between two terminals of a battery when, load is not connected with the battery, he or she will get the voltage developed in the battery when there is no electric current flowing through it. This voltage is generally referred as electromotive force or emf of battery. It is also referred as no-load voltage of battery. Terminal Voltage of Battery Terminal voltage of battery is the potential difference across its terminals when the current is being drawn from it. Actually when load is connected with the battery, there will be load current flowing through it. As a battery is electrical equipment, it must have some electrical resistance inside it. Because of this internal resistance of battery, there will be some voltage drop across it. So, if any one measures the terminal voltage of the load i.e. terminal voltage of battery when load is connected, he or she will get the voltage which is less than emf of the battery by internal voltage drop of the battery. If E is the emf or no – load voltage of the battery and V is the terminal voltage of load voltage of the battery, then E – V = internal voltage drop of the battery. As per Ohm’s law this internal voltage drop is nothing but the product of resistance offered by the battery and the current flows through it.

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Internal Resistance of Battery

The entire resistance encountered by a current as if it flows through a battery from the negative terminal to the positive terminal is known as internal resistance of battery. Series Parallel Batteries Battery cells can be connected in series, in parallel and as well as mixture both series and parallel. Series Batteries When in a battery, positive terminal of one cell is connected with the negative terminal of succeeding cell, then the cells are said to be series connected or simply series batteries. Here, overall emf of the battery is algebraic sum of all individual cells connected in series. But overall discharge current of the battery does not exceed the discharge current of individual cells.

Series connected Batteries If E is the overall emf of the battery combined by n number cells and E1, E2, E3, …………… En are the emfs of individual cells. Then E = E1 + E2 + E3 + …………… + En. Similarly, if r1, r2, r3, …………… rn are the internal resistances of individual cells. Then the internal resistance of the battery will be equal to the sum of the internal resistance of the individual cells i.e. r = r1 + r2 + r3 + …………… + rn.

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Parallel Connected Batteries Parallel Batteries When positive terminal of all cells are connected together and similarly negative terminals of these cells are connected together in a battery, then the cells are said to be connected in parallel. These combinations are also referred as parallel Batteries. If emf of each cell is identical then the emf of the battery combined by n numbers of cells connected in parallel, is equal to emf of each cell. The resultant internal resistance of the combination is (r1 − 1 + r2 − 1 + r3 − 1 + ……………………… + rn − 1 ) − 1. The current delivered by the battery is sum of currents delivered by individual cells. Mixed Grouping of Battery or Series Parallel Batteries As we said earlier, the cells in a battery can also be connected in mixture of both series and parallel. These combinations are some time referred as series parallel batteries. A load can require both voltage and current more than that of an individual battery cell. For achieving the required load voltage the desired numbers of battery cells can be combined in series and for achieving the required load current, desired numbers of these series combination are connected in parallel. Let m, numbers of series, each containing n numbers of identical cells, are connected in parallel.

Series Parallel Batteries

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Again assume emf of each cell is E and internal resistance of each cell is r. As n numbers of cells are connected in each series, the emf of each series as well as the battery will be nE. The equivalent resistance of the series is nr. 2. Transmission of Electrical Energy Fundamentally there are two systems by which electrical energy can be transmitted (1) High Voltage DC Electrical Transmission System (2) High voltage AC Electrical Transmission System There are some advantages in using DC transmission system i.

ii.

iii.

Only two conductor are required for Dc transmission system. It is further possible to use only one conductor of DC transmission system if earth is utilized as return path of the system. The potential stress on the insulator of DC transmission system is about 70% of same voltage AC transmission system. Hence less insulation cost is involved in DC transmission system. Inductance, capacitance, phase displacement and surge problems can be eliminated in DC system.

Even having these advantages in DC system, generally electrical energy is transmitted by three (3) phase AC transmission system. i. ii. iii.

The alternating voltages can easily be stepped up & down, which is not possible in DC transmission system. Maintenance of AC substation is quite easy and economical compared to DC syte. The transforming in AC substation is much easier than motor generator sets in DC system

But AC transmission system also has some disadvantages like, i. ii. iii. iv.

The volume of conductor used in AC system is much higher than that of DC The reactance of the line, affects the voltage regulation of electrical power transmission system Problems of skin effects and proximity effects only found in AC system. AC transmission system is more likely to be affected by corona than DC system.

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v. vi.

Construction of AC electrical power transmission network is more completed than DC system. Proper synchronizing is required before inter connecting two or more transmission lines together; Synchronizing can totally be omitted in DC transmission system.

POWER SYSTEM Power Engineering deals with the generation, transmission and distribution of electricity as well as the design of a range of related devices. These include transformers, electric generators, electric motors and power electronics. The power grid is an electrical network that connects a variety of electric generators to the users of electric power. Users purchase electricity from the grid avoiding the costly exercise of having to generate their own. Power engineers may work on the design and maintenance of the power grid as well as the power systems that connect to it. Such systems are called ongrid power systems and may supply the grid with additional power, draw power from the grid or do both. Power engineers may also work on systems that do not connect to the grid. These systems are called off-grid power systems and may be used in preference to on-grid systems for a variety of reasons. For example, in remote locations it may be cheaper for a mine to generate its own power rather than pay for connection to the grid and in most mobile applications connection to the grid is simply not practical. Today, most grids adopt three-phase electric power with alternating current. This choice can be partly attributed to the ease with which this type of power can be generated, transformed and used. Often, the power is split before it reaches residential customers whose low-power appliances rely upon single-phase electric power. However, many larger industries and organizations still prefer to receive the three-phase power directly because it can be used to drive highly efficient electric motors such as threephase induction motors. Transformers play an important role in power transmission because they allow power to be converted to and from higher voltages. This is important because higher voltages suffer less power loss during transmission. This is because higher voltages allow for lower current to deliver the same amount of power, as power is the product of the two. Thus, as the voltage steps up, the current steps down. It is the current flowing through the components that result in both the losses and the subsequent heating. These losses, appearing in the form of heat, are equal to the current squared times the

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electrical resistance through which the current flows, so as the voltage goes up the losses are dramatically reduced. For these reasons, electrical substations exist throughout power grids to convert power to higher voltages before transmission and to lower voltages suitable for appliances after transmission. COMPONENTS Power engineering is a network of interconnected components which convert different forms of energy to electrical energy. Modern power engineering consists of three main subsystems: the generation subsystem, the transmission subsystem, and the distribution subsystem. In the generation subsystem, the power plant produces the electricity. The transmission subsystem transmits the electricity to the load centers. The distribution subsystem continues to transmit the power to the customers. 2.1GENERATION Generation of electrical power is a process whereby energy is transformed into an electrical form. There are several different transformation processes, among which are chemical, photo-voltaic, and electromechanical. Electromechanical energy conversion is used in converting energy from coal, petroleum, natural gas, uranium, water flow, and wind into electrical energy. Of these, all except the wind energy conversion process take advantage of the synchronous AC generator coupled to a steam, gas or hydro turbine such that the turbine converts steam, gas, or water flow into rotational energy, and the synchronous generator then converts the rotational energy of the turbine into electrical energy. It is the turbinegenerator conversion process that is by far most economical and consequently most common in the industry today. The AC synchronous machine is the most common technology for generating electrical energy. It is called synchronous because the composite magnetic field produced by the three stator windings rotate at the same speed as the magnetic field produced by the field winding on the rotor. A simplified circuit model is used to analyze steady-state operating conditions for a synchronous machine. The phasor diagram is an effective tool for visualizing the relationships between internal voltage, armature current, and terminal voltage. The excitation control system is used on synchronous machines to regulate terminal voltage, and the turbine-governor system is used to regulate the speed of the machine. The operating costs of generating electrical energy are determined by the fuel cost and the efficiency of the power station. The efficiency depends on generation level and can be obtained from the heat rate curve. We may also

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obtain the incremental cost curve from the heat rate curve. Economic dispatch is the process of allocating the required load demand between the available generation units such that the cost of operation is minimized. 2.2 TRANSMISSION The electricity is transported to load locations from a power station to a transmission subsystem. Therefore we may think of the transmission system as providing the medium of transportation for electric energy. The transmission system may be subdivided into the bulk transmission system and the sub-transmission system. The functions of the bulk transmission are to interconnect generators, to interconnect various areas of the network, and to transfer electrical energy from the generators to the major load centers. This portion of the system is called "bulk" because it delivers energy only to so-called bulk loads such as the distribution system of a town, city, or large industrial plant. The function of the sub-transmission system is to interconnect the bulk power system with the distribution system. Transmission circuits may be built either underground or overhead. Underground cables are used predominantly in urban areas where acquisition of overhead rights of way is costly or not possible. They are also used for transmission under rivers, lakes and bays. Overhead transmission is used otherwise because, for a given voltage level, overhead conductors are much less expensive than underground cables. The transmission system is a highly integrated system. It is referred to the substation equipment and transmission lines. The substation equipment contain the transformers, relays, and circuit breakers. Transformers are important static devices which transfer electrical energy from one circuit with another in the transmission subsystem. Transformers are used to step up the voltage on the transmission line to reduce the power loss which is dissipated on the way. A relay is functionally a level-detector; they perform a switching action when the input voltage (or current) meets or exceeds a specific and adjustable value. A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. A change in the status of any one component can significantly affect the operation of the entire system. There are three possible causes for power flow limitations to a transmission line. These causes are thermal overload, voltage instability, and rotor angle instability. Thermal overload is caused by excessive current flow in a circuit causing overheating. Voltage instability is said to occur when the power required to maintain voltages at or above acceptable levels exceeds the available power. Rotor angle instability is a dynamic problem that may occur following faults, such as short circuit, in the transmission system. It may

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also occur tens of seconds after a fault due to poorly damped or un damped oscillatory response of the rotor motion. 2.3 DISTRIBUTION The distribution system transports the power from the transmission system to the customer. The distribution systems are typically radial because networked systems are more expensive. The equipment associated with the distribution system includes the substation transformers connected to the transmission systems, the distribution lines from the transformers to the customers and the protection and control equipment between the transformer and the customer. The protection equipment includes lightning protectors, circuit breakers, disconnectors and fuses. The control equipment includes voltage regulators, capacitors, relays and demand side management equipment. Electrical Transmission Tower types and design The main supporting unit of overhead transmission line is transmission tower. Transmission towers have to carry the heavy transmission conductor at a sufficient safe height from ground. In addition to that all towers have to sustain all kinds of natural calamities. So transmission tower designing is an important engineering job where all three basic engineering concepts, civil, mechanical and electrical engineering concepts are equally applicable. Main parts of a transmission tower A power transmission tower consists of the following parts, 1) Peak of transmission tower 2) Cross Arm of transmission tower 3) Boom of transmission tower 4) Cage of transmission tower 5) Transmission Tower Body 6) Leg of transmission tower 7) Stub/Anchor Bolt and Base plate assembly of transmission tower

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The main parts among these are shown in the pictures Peak of transmission tower The portion above the top cross arm is called peak of transmission tower. Generally earth shield wire connected to the tip of this peak. Cross Arm of transmission tower Cross arms of transmission tower hold the transmission conductor. The dimension of cross arm depends on the level of transmission voltage, configuration and minimum forming angle for stress distribution. Cage of transmission tower The portion between tower body and peak is known as cage of transmission tower. This portion of the tower holds the cross arms.

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Transmission tower body The portion from bottom cross arms up to the ground level is called transmission tower body. This portion of the tower plays a vital role for maintaining required ground clearance of the bottom conductor of the transmission line.

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Design of transmission tower

During design of transmission tower the following points to be considered in mind, a) The minimum ground clearance of the lowest conductor point above the ground level. b) The length of the insulator string. c) The minimum clearance to be maintained between conductors and between conductor and tower. d) The location of ground wire with respect to outer most conductors. e) The mid span clearance required from considerations of the dynamic behavior of conductor and lightening protection of the line.

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CHAPTER - 5 POWER TRIANGLE AND POWER FACTOR


REAL POWER
REACTIVE POWER
APPARENT POWER
POWER FACTOR

The Power Factor Triangle: Real , Reactive and Apparent Power Power Factor Formulas and the Power Factor Triangle, now that you understand the terminology, are easily within your grasp. The key to the Power Factor Triangle understands vectors. I'll make vectors easy and in a few minutes you'll have it. Vector Analysis Vectors are simply another way to draw sine waves. You'll see its not difficult and actually makes things easier. Vectors, as used in this discussion, are representations of a sine wave of current relative to a sine wave of voltage. Instead of showing the current as a sine wave, the vector shows it as a straight line that point in a direction. The length of the line represents the RMS value of the current (remember, peak value x 0.707) and the direction of the line represents the phase angle of the current relative to the voltage (this is the "offset" as discussed in the "Power Factor" section). The direction of the arrow is simple. It’s like a compass, 0 to 360 degrees. Remember, this is the offset. The compass starts at 3 o'clock and rotates counter-clockwise in a full circle. We establish that the voltage's sine wave peaks at 0 degrees (this is the reference). Lets look at cases where the currents leads or lags voltage by 45 degrees. See the graphic below.

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Current B lags the voltage by 45 degrees so the vector points down and to the right (see below). Current A leads by 45 degrees (it's happening 45 degrees ahead of voltage) so it points up and to the right. Since the peak currents are 1 Amp, the RMS currents are 0.707 Amps.

Adding Vectors This is almost as fun as connecting the dots (an EE's childhood pastime). To add two RMS currents, simply put one vector at the end of the other (remember to point in the correct direction, not 180 degrees out). The resultant, a straight line from where you started to where you ended, is the sum.

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Hopefully that makes sense to you. Now let’s apply what you already know....the load current in motors, which does the actual work, is in-phase with the voltage and therefore the load current vector points at 0 degrees (left to right). The magnetizing current in motors (and transformers), which does no work and lags behind the voltage by 90 degrees, points straight down. Oh yeah, capacitive current, which also does no work and leads voltage by 90 degrees, points straight up. (See below)

Good news! Because the Power Factor Triangle is all about examining the relationship between load currents and reactive currents, we will simply be adding currents that are in-phase with voltage (vectors pointing at 0 degrees) to currents that are 90 degrees out of phase (magnetizing or capacitive). See the graphic below, which only has load and magnetizing currents.

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Back in the Power Factor Terminology section we learned that Load Current multiplied by the system voltage yields Real Load, also called Real Power. The units of Real Power are Watts (i.e. kW, MW, etc.) When we multiply the Reactive Current by the system voltage we get the Reactive Load or Reactive Power (also called Imaginary Load). The units of Reactive Power are VARs, which stands for Volts-Amps-Reactive (i.e. kVAR, MVARS, etc.). If we multiply the Apparent Current by the system voltage we get the Apparent Load or Apparent Power. The units for Apparent Power are VA, for Volt-Amps (i.e. kVA, MVA, etc.). Changing the above graphic into terms of Power yields the Power Factor Triangle, also called the Power Triangle. The Power Factor Triangle (below) shows that (Real Power squared) + (Reactive Power squared) = (Apparent Power squared) Yup! Pythagorean's Theorem....and you thought you were done with that in high school geometry!

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Remember, the units are all in terms of RMS values and RMS values cannot be simply added together unless the components have no phase difference. We use vector addition to add RMS values because Real Power and Reactive Power are 90 degrees apart. The Power Factor Triangle yields some useful equations. This one is very useful and easy to remember. Simply stated, the Power Factor is the percentage of Apparent Power that does real work. Apparent Power x PF = Real Power Or in terms of units, VA x PF = Watts POWER FACTOR In general power is the capacity to do work. In electrical domain, electrical power is the amount of electrical energy that can be transferred to some other form (heat, light etc) per unit time. Mathematically it is the product of voltage drop across the element and current flowing through it. Considering first the DC circuits, having only DC voltage sources, the inductors and capacitors behave as short circuit and open circuit respectively in steady state. Hence the entire circuit behaves as resistive circuit and the entire electrical power is dissipated in the form of heat. Here the voltage and current are in same phase and the total electrical power is given by Electrical Power = Voltage across the element X Current through the element. Its unit is Watt = Joule/sec.

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Now coming to AC circuits, here both inductor and capacitor offer certain amount of impedance given by

The inductor stores electrical energy in the form of magnetic energy and capacitor stores electrical energy in the form of electrostatic energy. Neither of them dissipates it. Further there is a phase shift of 90-°between voltage and current. Hence when we consider the entire circuit consisting of resistor, inductor and capacitor, there exists some phase difference between the source voltage and current. The cosine of this phase difference is called electrical power factor. This factor (0 < cosφ < 1 ) represents the fraction of total power that is used to do the useful work. The other fraction of electrical power is stored in the form of magnetic energy or electrostatic energy in inductor and capacitor respectively. The total power in this case is Total Electrical Power = Voltage across the element X Current through the element This is called Apparent power and its unit is VA (Volt Amp) and denoted by ‘S’ A fraction of this total electrical power which actually does our useful work is called as active power. It is denoted as ‘P’ P = Active power = Total Electrical Power. cos φ and its unit is watt. The other fraction of power is called reactive power. This does no useful work, but it is required for the active work to be done. It is denoted by ‘Q’ and mathematically is given by Q = Reactive power = Total Electrical Power. sinφ and its unit is VAR (Volt Amp Reactive). This reactive power oscillates between source and load. To help understand this better all these power are represented in the form of triangle.

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Power Factor Triangle Mathematically, S2 = P2 + Q2 and Electrical Power Factor is Active power / Apparent power. Power Factor Improvement The term power factor comes into picture in AC circuits only. Mathematically it is cosine of the phase difference between source voltage and current. It refers to the fraction of total power (apparent power) which is utilized to do the useful work called active power.

Need for Power Factor Improvement •

Real power is given by P = VI cosφ. To transfer a given amount of power at certain voltage, the electrical current is inversely proportional to cosφ. Hence higher the pf lower will be the current flowing. A small current flow requires less cross sectional area of conductor and thus it saves conductor and money.

•

From above relation we saw having poor power factor increases the current flowing in conductor and thus copper loss increases. Further large voltage drop occurs in alternator, electrical transformer and transmission & distribution lines which gives very poor voltage regulation.

•

Further the KVA rating of machines is also reduced by having higher power factor as

Hence, the size and cost of machine also reduced. So, electrical power factor should be maintained close to unity.

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Methods of power factor improvement •

Capacitors: Improving power factor means reducing the phase difference between voltage and current. Since majority of loads are of inductive nature, they require some amount of reactive power for them to function. This reactive power is provided by the capacitor or bank of capacitors installed parallel to the load. They act as a source of local reactive power and thus less reactive power flows through the line. Basically they reduces the phase difference between the voltage and current.

•

Synchronous Condenser: They are 3 phase synchronous motor with no load attached to its shaft. The synchronous motor has the characteristics of operating under any power factor leading, lagging or unity depending upon the excitation. For inductive loads, synchronous condenser is connected towards load side and is overexcited. This makes it behave like a capacitor. It draws the lagging current from the supply or supplies the reactive power.

•

Phase Advancer: This is an ac exciter mainly used to improve pf of induction motor. They are mounted on shaft of the motor and is connected in the rotor circuit of the motor. It improves the power factor by providing the exciting ampere turns to produce required flux at slip frequency. Further if ampere turns are increased, it can be made to operate at leading power factor.

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CHAPTER - 6 ILLUMINATION


QUANTITY OF ILLUMINATION
QUALITY OF ILLUMINATION
GLARE
LIGHT SOURCES
DEFINITION
CALCULATION OF ILLUMINATION LEVELS ILLUMINATION • Quantity of Illumination • Quality of Illumination Quantity of Illumination Light Output The most common measure of light output (or luminous flux) is the lumen. Light sources are labeled with an output rating in lumens. For example, a T12 40-watt fluorescent lamp may have a rating of 3050 lumens. Similarly, a light fixture's output can be expressed in lumens. As lamps and fixtures age and become dirty, their lumen output decreases (i.e., lumen depreciation occurs). Most lamp ratings are based on initial lumens (i.e., when the lamp is new). Light Level Light intensity measured on a plane at a specific location is called illuminance. Illuminance is measured in foot candles, which are work plane lumens per square foot. You can measure illuminance using a light meter located on the work surface where tasks are performed. Using simple arithmetic and manufacturers' photometric data, you can predict illuminance for a defined space. (Lux is the metric unit for illuminance, measured in lumens per square meter. To convert foot candles to lux, multiply foot candles by 10.76.)

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Brightness Another measurement of light is luminance, sometimes called brightness. This measures light "leaving" a surface in a particular direction, and considers the illuminance on the surface and the reflectance of the surface. The human eye does not see illuminance; it sees luminance. Therefore, the amount of light delivered into the space and the reflectance of the surfaces in the space affects your ability to see. Refer to the GLOSSARY at the end of this document for more detailed definitions. Quantity Measures • Luminous flux is commonly called light output and is measured in lumens (lm). • Illuminance is called light level and is measured in foot candles (fc). • Luminance is referred to as brightness and is measured in foot lamberts (fL) or candelas/m2 (cd/m2). Determining Target Light Levels The Illuminating Engineering Society of North America has developed a procedure for determining the appropriate average light level for a particular space. This procedure (used extensively by designers and engineers (recommends a target light level by considering the following: • • •

the task(s) being performed (contrast, size, etc.) the ages of the occupants the importance of speed and accuracy

Then, the appropriate type and quantity of lamps and light fixtures may be selected based on the following: • • • • • •

fixture efficiency lamp lumen output the reflectance of surrounding surfaces the effects of light losses from lamp lumen depreciation and dirt accumulation room size and shape availability of natural light (daylight)

When designing a new or upgraded lighting system, one must be careful to avoid over lighting a space. In the past, spaces were designed for as much as 200 foot candles in places where 50 foot candles may not only be adequate, but superior. This was partly due to the misconception that the more light

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in a space, the higher the quality. Not only does over lighting waste energy, but it can also reduce lighting quality. Refer to Exhibit 2 for light levels recommended by the Illuminating Engineering Society of North America. Within a listed range of illuminance, three factors dictate the proper level: age of the occupant(s), speed and accuracy requirements, and background contrast. For example, to light a space that uses computers, the overhead light fixtures should provide up to 30 fc of ambient lighting. The task lights should provide the additional foot candles needed to achieve a total illuminance of up to 50 fc for reading and writing. For illuminance recommendations for specific visual tasks, refer to the IES Lighting Handbook, 1993, or to the IES Recommended Practice No. 24 (for VDT lighting). Quality Measures • Visual comfort probability (VCP) indicates the percent of people who are comfortable with the glare from a fixture. • Spacing criteria (SC) refers to the maximum recommended distance between fixtures to ensure uniformity. • Color rendering index (CRI) indicates the color appearance of an object under a source as compared to a reference source. Quality of Illumination Improvements in lighting quality can yield high dividends for US businesses. Gains in worker productivity may result by providing corrected light levels with reduced glare. Although the cost of energy for lighting is substantial, it is small compared with the cost of labor. Therefore, these gains in productivity may be even more valuable than the energy savings associated with new lighting technologies. In retail spaces, attractive and comfortable lighting designs can attract clientele and enhance sales. Three quality issues are addressed in this section. • glare • uniformity of illuminance • color rendition Glare Perhaps the most important factor with respect to lighting quality is glare. Glare is a sensation caused by luminances in the visual field that are too bright. Discomfort, annoyance, or reduced productivity can result. A bright object alone does not necessarily cause glare, but a bright object in front of a dark background, however, usually will cause glare. Contrast is

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the relationship between the luminance of an object and its background. Although the visual task generally becomes easier with increased contrast, too much contrast causes glare and makes the visual task much more difficult. You can reduce glare or luminance ratios by not exceeding suggested light levels and by using lighting equipment designed to reduce glare. A louver or lens is commonly used to block direct viewing of a light source. Indirect lighting, or up lighting, can create a low glare environment by uniformly lighting the ceiling. Also, proper fixture placement can reduce reflected glare on work surfaces or computer screens. Standard data now provided with luminaire specifications include tables of its visual comfort probability (VCP) ratings for various room geometries. The VCP index provides an indication of the percentage of people in a given space that would find the glare from a fixture to be acceptable. A minimum VCP of 70 is recommended for commercial interiors, while luminaires with VCPs exceeding 80 are recommended in computer areas. Uniformity of Illuminance on Tasks The uniformity of illuminance is a quality issue that addresses how evenly light spreads over a task area. Although a room's average illuminance may be appropriate, two factors may compromise uniformity. •

•

improper fixture placement based on the luminaire's spacing criteria (ratio of maxim recommended fixture spacing distance to mounting height above task height) fixtures that are retrofit with reflectors that narrow the light distribution

Non-uniform illuminance causes several problems: • inadequate light levels in some areas • visual discomfort when tasks require frequent shifting of view from under lit to over lit areas • bright spots and patches of light on floors and walls that cause distraction and generate a low quality appearance Color Rendition The ability to see colors properly is another aspect of lighting quality. Light sources vary in their ability to accurately reflect the true colors of people and objects. The color rendering index (CRI) scale is used to compare the effect of a light source on the color appearance of its surroundings. A scale of 0 to 100 defines the CRI. A higher CRI means better color rendering, or less color shift. CRIs in the range of 75-100 are considered

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excellent, while 65-75 are good. The range of 55-65 is fair, and 0-55 is poor. Under higher CRI sources, surface colors appear brighter, improving the aesthetics of the space. Sometimes, higher CRI sources create the illusion of higher illuminance levels. The CRI values for selected light sources are tabulated with other lamp data in Exhibit 3. LIGHT SOURCES • Characteristics of Light Sources • Incandescent Lamps • Fluorescent Lamps • High-Intensity Discharge Lamps Commercial, industrial, and retail facilities use several sources. Each lamp type has particular advantages; appropriate source depends on installation requirements, color qualities, dimming capability, and the effect wanted. lamps are commonly used: • • • • • • •

different light selecting the life-cycle cost, Three types of

incandescent fluorescent high intensity discharge mercury vapor metal halide high pressure sodium low pressure sodium

Before describing each of these lamp types, the following sections describe characteristics that are common to all of them. Characteristics of Light Sources Electric light sources have three characteristics: efficiency, color temperature, and color rendering index (CRI). Exhibit 4 summarizes these characteristics. Efficiency Some lamp types are more efficient in converting energy into visible light than others. The efficacy of a lamp refers to the number of lumens leaving the lamp compared to the number of watts required by the lamp (and ballast). It is expressed in lumens per watt. Sources with higher efficacy require less electrical energy to light a space.

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Color Temperature Another characteristic of a light source is the color temperature. This is a measurement of "warmth" or "coolness" provided by the lamp. People usually prefer a warmer source in lower illuminance areas, such as dining areas and living rooms, and a cooler source in higher illuminance areas, such as grocery stores. Color temperature refers to the color of a blackbody radiator at a given absolute temperature, expressed in Kelvins. A blackbody radiator changes color as its temperature increases (first to red, then to orange, yellow, and finally bluish white at the highest temperature. A "warm" color light source actually has a lower color temperature. For example, a cool-white fluorescent lamp appears bluish in color with a color temperature of around 4100 K. A warmer fluorescent lamp appears more yellowish with a color temperature around 3000 K. Refer to Exhibit 5 for color temperatures of various light sources. Color Rendering Index The CRI is a relative scale (ranging from 0 - 100). Indicating how perceived colors match actual colors. It measures the degree that perceived colors of objects, illuminated by a given light source, conform to the colors of those same objects when they are lighted by a reference standard light source. The higher the color rendering index, the less color shift or distortion occurs. The CRI number does not indicate which colors will shift or by how much; it is rather an indication of the average shift of eight standard colors. Two different light sources may have identical CRI values, but colors may appear quite different under these two sources. Standard Incandescent Lamp Incandescent lamps are one of the oldest electric lighting technologies available. With efficacies ranging from 6 to 24 lumens per watt, incandescent lamps are the least energy-efficient electric light source and have a relatively short life (750-2500 hours). Light is produced by passing a current through a tungsten filament, causing it to become hot and glow. With use, the tungsten slowly evaporates, eventually causing the filament to break. These lamps are available in many shapes and finishes. The two most common types of shapes are the common "A-type" lamp and the reflectorshaped lamps.

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Tungsten-Halogen Lamps The tungsten halogen lamp is another type of incandescent lamp. In a halogen lamp, a small quartz capsule contains the filament and a halogen gas. The small capsule size allows the filament to operate at a higher temperature, which produces light at a higher efficacy than standard incandescent. The halogen gas combines with the evaporated tungsten, redepositing it on the filament. This process extends the life of the filament and keeps the bulb wall from blackening and reducing light output. Because the filament is relatively small, this source is often used where a highly focused beam is desired. Compact halogen lamps are popular in retail applications for display and accent lighting. In addition, tungsten-halogen lamps generally produce a whiter light than other incandescent lamps, are more efficient, last longer, and have improved lamp lumen depreciation.

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Incandescent A-Lamp More efficient halogen lamps are available. These sources use an infrared coating on the quartz bulb or an advanced reflector design to redirect infrared light back to the filament. The filament then glows hotter and the efficiency of the source is increased. Fluorescent Lamps Fluorescent lamps are the most commonly used commercial light source in North America. In fact, fluorescent lamps illuminate 71% of the commercial space in the United States. Their popularity can be attributed to their relatively high efficacy, diffuse light distribution characteristics, and long operating life. • • • •

Fluorescent lamp construction consists of a glass tube with the following features: filled with an argon or argon-krypton gas and a small amount of mercury coated on the inside with phosphors equipped with an electrode at both ends

Fluorescent lamps provide light by the following process: •

An electric discharge (current) is maintained between the electrodes through the mercury vapor and inert gas.

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This current excites the mercury atoms, causing them to emit nonvisible ultraviolet (UV) radiation. This UV radiation is converted into visible light by the phosphors lining the tube.

Discharge lamps (such as fluorescent) require a ballast to provide correct starting voltage and to regulate the operating current after the lamp has started.

Full-Size Fluorescent Lamps Full-size fluorescent lamps are available in several shapes, including straight, U-shaped, and circular configurations. Lamp diameters range from 1" to 2.5". The most common lamp type is the four-foot (F40), 1.5" diameter (T12) straight fluorescent lamp. More efficient fluorescent lamps are now available in smaller diameters, including the T10 (1.25 ") and T8 (1"). Fluorescent lamps are available in color temperatures ranging from warm (2700(K) "incandescent-like" colors to very cool (6500(K) "daylight" colors. "Cool white" (4100(K) is the most common fluorescent lamp color. Neutral white (3500(K) is becoming popular for office and retail use. Improvements in the phosphor coating of fluorescent lamps have improved color rendering and made some fluorescent lamps acceptable in many applications previously dominated by incandescent lamps. Performance Considerations The performance of any luminaire system depends on how well its components work together. With fluorescent lamp-ballast systems, light output, input watts, and efficacy are sensitive to changes in the ambient temperature. When the ambient temperature around the lamp is significantly above or below 25C (77F), the performance of the system can change. Exhibit 6 shows this relationship for two common lamp-ballast systems: the F40T12 lamp with magnetic ballast and the F32T8 lamp with electronic ballast.

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As you can see, the optimum operating temperature for the F32T8 lampballast system is higher than for the F40T12 system. Thus, when the ambient temperature is greater than 25C (77F), the performance of the F32T8 system may be higher than the performance under ANSI conditions. Lamps with smaller diameters (such as T-5 twin tube lamps) peak at even higher ambient temperatures. Compact Fluorescent Lamps Advances in phosphor coatings and reductions of tube diameters have facilitated the development of compact fluorescent lamps. Manufactured since the early 1980s, they are a long-lasting, energy-efficient substitute for the incandescent lamp. Various wattages, color temperatures, and sizes are available. The wattages of the compact fluorescents range from 5 to 40 (replacing incandescent lamps ranging from 25 to 150 watts (and provide energy savings of 60 to 75 percent. While producing light similar in color to incandescent sources, the life expectancy of a compact fluorescent is about 10 times that of a standard incandescent lamp. Note, however, that the use of compact fluorescent lamps is very limited in dimming applications. The compact fluorescent lamp with an Edison screw-base offers an easy means to upgrade an incandescent luminaire. Screw-in compact fluorescents are available in two types: •

•

Integral Units. These consist of a compact fluorescent lamp and ballast in self-contained units. Some integral units also include a reflector and/or glass enclosure. Modular Units. The modular type of retrofit compact fluorescent lamp is similar to the integral units, except that the lamp is replaceable.

A Specifier Report that compares the performance of various name-brand compact fluorescent lamps is now available from the National Lighting Product Information Program ("Screw-Base Compact Fluorescent Lamp Products," Specifier Reports, Volume 1, Issue 6, April 1993).

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High-Intensity Discharge Lamps High-intensity discharge (HID) lamps are similar to fluorescents in that an arc is generated between two electrodes. The arc in a HID source is shorter, yet it generates much more light, heat, and pressure within the arc tube. Originally developed for outdoor and industrial applications, HID lamps are also used in office, retail, and other indoor applications. Their color rendering characteristics have been improved and lower wattages have recently become available (as low as 18 watts. There are several advantages to HID sources: • • •

relatively long life (5,000 to 24,000+ hrs) relatively high lumen output per watt relatively small in physical size

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However, the following operating limitations must also be considered. First, HID lamps require time to warm up. It varies from lamp to lamp, but the average warm-up time is 2 to 6 minutes. Second, HID lamps have a "restrike" time, meaning a momentary interruption of current or a voltage drop too low to maintain the arc will extinguish the lamp. At that point, the gases inside the lamp are too hot to ionize, and time is needed for the gases to cool and pressure to drop before the arc will re-strike. This process of re-striking takes between 5 and 15 minutes, depending on which HID source is being used. Therefore, good applications of HID lamps are areas where lamps are not switched on and off intermittently. The following HID sources are listed in increasing order of efficacy: • mercury vapor • metal halide • high pressure sodium • low pressure sodium Mercury Vapor Clear mercury vapor lamps, which produce a blue-green light, consist of a mercury-vapor arc tube with tungsten electrodes at both ends. These lamps have the lowest efficacies of the HID family, rapid lumen depreciation, and a low color rendering index. Because of these characteristics, other HID sources have replaced mercury vapor lamps in many applications. However, mercury vapor lamps are still popular sources for landscape illumination because of their 24,000 hour lamp life and vivid portrayal of green landscapes.

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The arc is contained in an inner bulb called the arc tube. The arc tube is filled with high purity mercury and argon gas. The arc tube is enclosed within the outer bulb, which is filled with nitrogen. Color-improved mercury lamps use a phosphor coating on the inner wall of the bulb to improve the color rendering index, resulting in slight reductions in efficiency.

Metal Halide These lamps are similar to mercury vapor lamps but use metal halide additives inside the arc tube along with the mercury and argon. These additives enable the lamp to produce more visible light per watt with improved color rendition. Wattages range from 32 to 2,000, offering a wide range of indoor and outdoor applications. The efficacy of metal halide lamps ranges from 50 to 115 lumens per watt (typically about double that of mercury vapor. In short, metal halide lamps have several advantages. • • •

high efficacy good color rendering wide range of wattages

However, they also have some operating limitations: • The rated life of metal halide lamps is shorter than other HID sources; lower-wattage lamps last less than 7500 hours while high-wattage lamps last an average of 15,000 to 20,000 hours. • The color may vary from lamp to lamp and may shift over the life of the lamp and during dimming.

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Because of the good color rendition and high lumen output, these lamps are good for sports arenas and stadiums. Indoor uses include large auditoriums and convention halls. These lamps are sometimes used for general outdoor lighting, such as parking facilities, but a high pressure sodium system is typically a better choice.

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High Pressure Sodium The high pressure sodium (HPS) lamp is widely used for outdoor and industrial applications. Its higher efficacy makes it a better choice than metal halide for these applications, especially when good color rendering is not a priority. HPS lamps differ from mercury and metal-halide lamps in that they do not contain starting electrodes; the ballast circuit includes a high-voltage electronic starter. The arc tube is made of a ceramic material which can withstand temperatures up to 2372F. It is filled with xenon to help start the arc, as well as a sodium-mercury gas mixture. The efficacy of the lamp is very high (as much as 140 lumens per watt. For example, a 400-watt high pressure sodium lamp produces 50,000 initial lumens. The same wattage metal halide lamp produces 40,000 initial lumens, and the 400-watt mercury vapor lamp produces only 21,000 initially. Sodium, the major element used, produces the "golden" color that is characteristic of HPS lamps. Although HPS lamps are not generally recommended for applications where color rendering is critical, HPS color rendering properties are being improved. Some HPS lamps are now available in "deluxe" and "white" colors that provide higher color temperature and improved color rendition. The efficacy of low-wattage "white" HPS lamps is lower than that of metal halide lamps (lumens per watt of low-wattage metal halide is 75-85, while white HPS is 50-60 LPW). Low Pressure Sodium Although low pressure sodium (LPS) lamps are similar to fluorescent systems (because they are low pressure systems), they are commonly included in the HID family. LPS lamps are the most efficacious light sources, but they produce the poorest quality light of all the lamp types. Being a monochromatic light source, all colors appear black, white, or shades of gray under an LPS source. LPS lamps are available in wattages ranging from 18-180. LPS lamp use has been generally limited to outdoor applications such as security or street lighting and indoor, low-wattage applications where color quality is not important (e.g. stairwells). However, because the color rendition is so poor, many municipalities do not allow them for roadway lighting. Because the LPS lamps are "extended" (like fluorescent), they are less effective in directing and controlling a light beam, compared with "point sources" like high-pressure sodium and metal halide. Therefore, lower

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mounting heights will provide better results with LPS lamps. To compare a LPS installation with other alternatives, calculate the installation efficacy as the average maintained foot candles divided by the input watts per square foot of illuminated area. The input wattage of an LPS system increases over time to maintain consistent light output over the lamp life. The low-pressure sodium lamp can explode if the sodium comes in contact with water. Dispose of these lamps according to the manufacturer's instructions. Back to the Table of Contents BALLASTS • Fluorescent Ballasts • HID Ballasts All discharge lamps (fluorescent and HID) require an auxiliary piece of equipment called ballast. Ballasts have three main functions: • • •

provide correct starting voltage, because lamps require a higher voltage to start than to operate match the line voltage to the operating voltage of the lamp limit the lamp current to prevent immediate destruction, because once the arc is struck the lamp impedance decreases

Because ballasts are an integral component of the lighting system, they have a direct impact on light output. The ballast factor is the ratio of a lamp's light output using standard reference ballast, compared to the lamp's rated light output on laboratory standard ballast. General purpose ballasts have a ballast factor that is less than one; special ballasts may have a ballast factor greater than one. Fluorescent Ballasts The two general types of fluorescent ballasts are magnetic and electronic ballasts: Magnetic Ballasts Magnetic ballasts (also referred to as electromagnetic ballasts) fall into one of the following categories: • • •

standard core-coil (no longer sold in the US for most applications) high-efficiency core-coil cathode cut-out or hybrid

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Standard core-coil magnetic ballasts are essentially core-coil transformers that are relatively inefficient in operating fluorescent lamps. The highefficiency ballast replaces the aluminum wiring and lower grade steel of the standard ballast with copper wiring and enhanced ferromagnetic materials. The result of these material upgrades is a 10 percent system efficiency improvement. However, note that these "high efficiency" ballasts are the least efficient magnetic ballasts that are available for operating full-size fluorescent lamps. More efficient ballasts are described below. "Cathode cut-out" (or "hybrid") ballasts are high-efficiency core-coil ballasts that incorporate electronic components that cut off power to the lamp cathodes (filaments) after the lamps are lit, resulting in an additional 2-watt savings per standard lamp. Also, many partial-output T12 hybrid ballasts provide up to 10% less light output while consuming up to 17% less energy than energy-efficient magnetic ballasts. Full-output T8 hybrid ballasts are nearly as efficient as rapid-start two-lamp T8 electronic ballasts. Electronic Ballasts In nearly every full-size fluorescent lighting application, electronic ballasts can be used in place of conventional magnetic "core-and-coil" ballasts. Electronic ballasts improve fluorescent system efficacy by converting the standard 60 Hz input frequency to a higher frequency, usually 25,000 to 40,000 Hz. Lamps operating at these higher frequencies produce about the same amount of light, while consuming 12 to 25 percent less power. Other advantages of electronic ballasts include less audible noise, less weight, virtually no lamp flicker, and dimming capabilities (with specific ballast models). There are three electronic ballast designs available: Standard T12 electronic ballasts (430 mA) These ballasts are designed for use with conventional (T12 or T10) fluorescent lighting systems. Some electronic ballast that is designed for use with 4' lamps can operate up to four lamps at a time. Parallel wiring is another feature now available that allows all companion lamps in the ballast circuit to continue operating in the event of a lamp failure. Electronic ballasts are also available for 8' standard and high-output T12 lamps. T8 Electronic ballasts (265 mA) Specifically designed for use with T8 (1-inch diameter) lamps, the T8 electronic ballast provide the highest efficiency of any fluorescent lighting system. Some T8 electronic ballasts are designed to start the lamps in the conventional rapid start mode, while others are operated in the instant start

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mode. The use of instant start T8 electronic ballasts may result in up to 25 percent reduction in lamp life (at 3 hours per start) but produces slight increases in efficiency and light output. (Note: Lamp life ratings for instant start and rapid start are the same for 12 or more hours per start.) Dimmable electronic ballasts These ballasts permit the light output of the lamps to be dimmed based on input from manual dimmer controls or from devices that sense daylight or occupancy. Types of Fluorescent Circuits There are three main types of fluorescent circuits: • rapid start • instant start • preheat The specific fluorescent circuit in use can be identified by the label on the ballast. The rapid start circuit is the most used system today. Rapid start ballasts provide continuous lamp filament heating during lamp operation (except when used with a cathode cut-out ballast or lamp). Users notice a very short delay after "flipping the switch," before the lamp is started. The instant start system ignites the arc within the lamp instantly. This ballast provides a higher starting voltage, which eliminates the need for a separate starting circuit. This higher starting voltage causes more wear on the filaments, resulting in reduced lamp life compared with rapid starting. The preheat circuit was used when fluorescent lamps first became available. This technology is used very little today, except for low-wattage magnetic ballast applications such as compact fluorescents. A separate starting switch, called a starter, is used to aid in forming the arc. The filament needs some time to reach proper temperature, so the lamp does not strike for a few seconds. HID Ballasts Like fluorescent lamps, HID lamps require a ballast to start and operate. The purposes of the ballast are similar: to provide starting voltage, to limit the current, and to match the line voltage to the arc voltage. With HID ballasts, a major performance consideration is lamp wattage regulation when the line voltage varies. With HPS lamps, the ballast must

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compensate for changes in the lamp voltage as well as for changes in the line voltages. Installing the wrong HID ballast can cause a variety of problems: • waste energy and increase operating cost • severely shorten lamp life • significantly add to system maintenance costs • produce lower-than-desired light levels • increase wiring and circuit breaker installation costs • result in lamp cycling when voltage dips occur Capacitive switching is available in new HID luminaires with special HID ballasts. The most common application for HID capacitive switching is in occupancy-sensed bi-level lighting control. Upon sensing motion, the occupancy sensor will send a signal to the bi-level HID system that will rapidly bring the light levels from a standby reduced level to approximately 80% of full output, followed by the normal warm-up time between 80% and 100% of full light output. Depending on the lamp type and wattage, the standby lumens are roughly 15-40% of full output and the input watts are 30-60% of full wattage. Therefore, during periods that the space is unoccupied and the system is dimmed, savings of 40-70% are achieved. Electronic ballasts for some types of HID lamps are starting to become commercially available. These ballasts offer the advantages of reduced size and weight, as well as better color control; however, electronic HID ballasts offer minimal efficiency gains over magnetic HID ballasts. Back to the Table of Contents LUMINAIRES • Luminaire Efficiency • Directing Light A luminaire, or light fixture, is a unit consisting of the following components: • lamps • lamp sockets • ballasts • reflective material • lenses, refractors, or louvers • housing

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Luminaire The main function of the luminaire is to direct light using reflective and shielding materials. Many lighting upgrade projects consist of replacing one or more of these components to improve fixture efficiency. Alternatively, users may consider replacing the entire luminaire with one that I designed to efficiently provide the appropriate quantity and quality of illumination. There are several different types of luminaires. The following is a listing of some of the common luminaire types: • • • • • •

general illumination fixtures such as 2x4, 2x2, & 1x4 fluorescent troffers down lights indirect lighting (light reflected off the ceiling/walls) spot or accent lighting task lighting outdoor area and flood lighting

Luminaire Efficiency The efficiency of a luminaire is the percentage of lamp lumens produced that actually exits the fixture. The use of louvers can improve visual comfort, but because they reduce the lumen output of the fixture, efficiency is reduced. Generally, the most efficient fixtures have the poorest visual comfort (e.g. bare strip industrial fixtures). Conversely, the fixture that provides the highest visual comfort level is the least efficient. Thus, a lighting designer must determine the best compromise between efficiency and VCP when specifying luminaires. Recently, some manufacturers have started offering fixtures with excellent VCP and efficiency. These so-called "super fixtures" combine state-of-the-art lens or louver designs to provide the best of both worlds. Surface deterioration and accumulated dirt in older, poorly maintained fixtures can also cause reductions in luminaire efficiency. Refer to Lighting Maintenance for more information. Directing Light Each of the above luminaire types consist of a number of components that are designed to work together to produce and direct light. Because the subject of light production has been covered by the previous section, the text below focuses on the components used to direct the light produced by the lamps.

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Reflectors Reflectors are designed to redirect the light emitted from a lamp in order to achieve a desired distribution of light intensity outside of the luminaire. In most incandescent spot and flood lights, highly spectacular (mirror-like) reflectors are usually built into the lamps. One energy-efficient upgrade option is to install a custom-designed reflector to enhance the light control and efficiency of the fixture, which may allow partial de-lamping. Retrofit reflectors are useful for upgrading the efficiency of older, deteriorated luminaire surfaces. A variety of reflector materials are available: highly reflective white paint, silver film laminate, and two grades of anodized aluminum sheet (standard or enhanced reflectivity). Silver film laminate is generally considered to have the highest reflectance, but is considered less durable. Proper design and installation of reflectors can have more effect on performance than the reflector materials. In combination with de-lamping, however, the use of reflectors may result in reduced light output and may redistribute the light, which may or may not be acceptable for a specific space or application. To ensure acceptable performance from reflectors, arrange for a trial installation and measure "before" and "after" light levels using the procedures outlined in Lighting Evaluations. For specific namebrand performance data, refer to Specifier Reports, "Spectacular Reflectors," Volume 1, Issue 3, National Lighting Product Information Program. Lenses and Louvers Most indoor commercial fluorescent fixtures use either a lens or a louver to prevent direct viewing of the lamps. Light that is emitted in the so-called "glare zone" (angles above 45 degrees from the fixture's vertical axis) can cause visual discomfort and reflections, which reduce contrast on work surfaces or computer screens. Lenses and louvers attempt to control these problems. Lenses Lenses made from clear ultraviolet-stabilized acrylic plastic deliver the most light output and uniformity of all shielding media. However, they provide less glare control than louvered fixtures. Clear lens types include prismatic, batwing, linear batwing, and polarized lenses. Lenses are usually much less expensive than louvers. White translucent diffusers are much less efficient than clear lenses, and they result in relatively low visual comfort probability. New low-glare lens materials are available for retrofit and provide high visual comfort (VCP>80) and high efficiency.

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Louvers. Louvers provide superior glare control and high visual comfort compared with lens-diffuser systems. The most common application of louvers is to eliminate the fixture glare reflected on computer screens. So-called "deepcell" parabolic louvers (with 5-7" cell apertures and depths of 2-4" ( provide a good balance between visual comfort and luminaire efficiency. Although small-cell parabolic louvers provide the highest level of visual comfort, they reduce luminaire efficiency to about 35-45 percent. For retrofit applications, both deep-cell and small-cell louvers are available for use with existing fixtures. Note that the deep-cell louver retrofit adds 2-4" to the overall depth of a troffer; verify that sufficient plenum depth is available before specifying the deep-cell retrofit. Distribution One of the primary functions of a luminaire is to direct the light to where it is needed. The light distribution produced by luminaires is characterized by the Illuminating Engineering Society as follows: • • • • •

Direct (90 to 100 percent of the light is directed downward for maximum use. Indirect (90 to 100 percent of the light is directed to the ceilings and upper walls and is reflected to all parts of a room. Semi-Direct ( 60 to 90 percent of the light is directed downward with the remainder directed upward. General Diffuse or Direct-Indirect (equal portions of the light are directed upward and downward. Highlighting (the beam projection distance and focusing ability characterize this luminaire.

The lighting distribution that is characteristic of a given luminaire is described using the candela distribution provided by the luminaire manufacturer (see diagram on next page). The candela distribution is represented by a curve on a polar graph showing the relative luminous intensity 360 around the fixture (looking at a cross-section of the fixture. This information is useful because it shows how much light is emitted in each direction and the relative proportions of down lighting and up lighting. The cut-off angle is the angle, measured from straight down, where the fixture begins to shield the light source and no direct light from the source is visible. The shielding angle is the angle, measured from horizontal, through which the fixture provides shielding to prevent direct viewing of the light source. The shielding and cut-off angles add up to 90 degrees.

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The lighting upgrade products mentioned in this document are described in more detail in Lighting Upgrade Technologies. 4. Calculation of illumination levels Lumen method For a given room, predicted illumination levels for a given layout, or alternatively the number of luminaires required to give a desired illumination level can be calculated from tables of Utilisation Factors using the "Lumen Method". This method is fully outlined in CIBSE ‘code for interior lighting’. A quick ‘rule of thumb’ check method is presented here; this should not be used without consulting the full procedures. The illumination level for an empty room can be calculated using the following formula: N=ExA. F x n x MF x UF In which the symbols have the following meanings E = Average Illuminance on working plane(lux). N = Number of Luminaires. A = Area of working plane (m²). F = Initial bare lamp luminous flux (lumens). N = Number of lamps per luminaire. MF = Maintenance Factor. UF = Utilisation Factor for the working plane. The utilization factor is not only dependant on the characteristics of the luminaire itself, but also on the geometry of a room, and the reflectivity of its walls, ceiling, and floor. So the designer is able to make allowance for this utilization factor tables are produced which for a particular luminaire, give utilization factors across a range of wall, ceiling and floor cavity reflectance’s and a range of room indices. The room index is a number calculated from the dimensions of a room and is characteristic of the room’s geometry. The room index of a particular rectangular room is twice its plan area, divided by its wall area, and is calculated by the formula shown below.

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Room Index K = L.W . hm (L+W) Where: hm = The mounting height of the luminaires above the working plane (m) L

= Length of room (m)

W = Width of room (m) An Example of a Lumen Method Calculation. Consider a room 10m x 12m, with a ceiling height of 3.25m. The room has ceiling, wall and floor reflectance’s of 0.50, 0.30, and 0.20 respectively. It is proposed to install 3 x 36w Cat 3 recessed luminaires in the room mounted flush with the ceiling surface. (The utilisation factor table for the luminaire is shown below.) How many luminaires would be required to achieve an illumination level of 400 lux, at desk top height of 0.85m? i)

Calculate the room index. L = 10m, W = 12m, hm = (3.25 - 0.85) = 2.4m K = LxW = 10x12 hm (L + W) 2.4 x (10+12) K = 2.27

ii)

Calculate the effective ceiling and floor cavity reflectance’s. The ceiling has no cavity depth therefore its reflectance is 0.5. For the floor cavity we need to calculate its effective reflectance. a) Calculate Raf the average area weighted reflectance of the floor cavity.

Raf = (0.2x120) + 2(0.3x8.5) +2(0.3x10.2) 120+8.5+8.5+10.2+10.2 = 0.22 b) calculate floor cavity index.

CIf = K x hm = 2.27 X 2.4 = 6.41 h 0.8

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c) calculate effective floor cavity index.

approx. REf = Cif x Raf Raf + 2(1- Raf ) = 6.41 x 0.22 1 + 2(1-0.22) = 0.196 iii)

Obtain the Utilization Factor (UF) Utilization factors for a room index of 2.27 are not published in a standard CIBSE format utilization factor table. Within the room index range of 0.75 to 5.00 it is acceptable to use the utilization factor for the closest published room index, which in this case is RI = 2.50 On the Utilization factor table, we find a UF of 0.60 at the intersection of the RI = 2.5 column, and the effective Reflectance’s = 0.50, 0.30, 0.20 row.

iv)

Calculate the number of luminaires required. E = 400lux A = 10mx12m = 120m² F = 3450 lumens for a 36w T8 n = 3 lamps MF = Say 0.8 UF = 0.60 Number of fittings required:N = 400 x 120 3450 x 3 x 0.8 x 0.60 N = 9.66 (say 10 luminaires). Perhaps two rows of five luminaires.

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Checking the Spacing to Height Ratio, we find this layout would not provide an acceptably uniform distribution. The maximum spacing being 5m, and the mounting height 2.4m, the SHR would be: SHR = 5 = 2.08 2.4 Which exceeds the SHR MAX of 1.96. The designer now could now opt for an alternative luminaire, or a different layout using the original luminaire. As ten luminaires will not form a regular array other than 2 x 5, the designer may consider using twelve (3 x 4) or nine (3 x 3), luminaires, bearing in mind that as a consequence of changing the number of luminaires the illumination level would rise or fall. Considering the twelve luminaire option:

The maximum spacings would be 3.33m, in the axial, and 3.00m in the transverse direction, and the height, as before, 2.4m, giving SHRs of: In the axial direction: SHRax = 3.33 = 1.39 2.4 And in the transverse direction: SHRtr = 3.00 = 1.25 2.4 This time both SHRax and SHRtr are within the SHR MAX limit of 1.96, and therefore acceptable.

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To finish the designer must check that the geometric mean spacing to height ratio, lies within the range of the UF table used. Standard UF tables are valid over an SHR range of 0.5 either side of SHR NOM, in this case 1.75  0.5 (i.e. 1.25  2.25) The geometric mean spacing to height ratio is determined using the formula: ‘(SHRax x SHRtr) In this case: ‘( 1.39 x 1.25) = 1.32 1.32 lies inside the target range, and is therefore acceptable. Point to point method In cases where a luminaire approximates to a point source, (i.e. if its largest dimension is less than one fifth of the distance from it to the point being illuminated.) then the inverse square law may be applied to calculate the direct illumination on a plane normal to the luminaire. The illumination level would be calculated using the formula: E = I.Cos ³ h² In which: E = Illuminance (Lux) I = Intensity, in the particular direction (candelas), this may be taken from the polar curve. h = Vertical distance between the luminaire and plane (in metres). Example Consider a typical 400w SON high bay luminaire, mounted at a height (h) of 10m, what illumination level would be expected at a spot on the floor below at say 15° from the vertical. From the Polar Curve at 15° from the vertical we read an intensity of say 600cd/1000 lm, (600 candelas per thousand lumens).

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The light output of the lamp is 52500 lm, (52.5 thousand lumens), the intensity (I) at 15° would be: 600 x 52.5 = 31500 cd. And the illuminance (E) would be: 31500 x Cosy 15° 10² = 31500 x 0.901 100 = 283.8 lux

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CHAPTER - 7 WIRING CONCEPTS


SWITCH
TYPES OF CONNECTION
SITE EQUIPMENTS
DB CONNECTION (DISTRIBUTION BOX)
TYPES OF DB
SWITCH BOX
HOUSE WIRING PLAN
FLEMING’S LEFT HAND RULE
FARADAY’S LAW

SWITCH In electrical engineering, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another. The most familiar form of switch is a manually operated Electromechanical device with one or more sets of electrical contacts, which are connected to external circuits. Each set of contacts can be in one of two states: either "closed" meaning the contacts are touching and electricity can flow between them, or "open", meaning the contacts are separated and the switch is non conducting. The mechanism actuating the transition between these two states (open or closed) can be either a "toggle" (flip switch for continuous "on" or "off") or "momentary" (push-for "on" or push-for "off") type. A switch may be directly manipulated by a human as a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit, such as a light switch. Automatically operated switches can be used to control the motions of machines, for example, to indicate that a garage door has reached its full open position or that a machine tool is in a position to accept another work piece. Switches may be operated by process variables such as pressure, temperature, flow, current, voltage, and force,

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acting as sensors in a process and used to automatically control a system. For example, a thermostat is a temperature-operated switch used to control a heating process. A switch that is operated by another electrical circuit is called a relay. Large switches may be remotely operated by a motor drive mechanism. Some switches are used to isolate electric power from a system, providing a visible point of isolation that can be padlocked if necessary to prevent accidental operation of a machine during maintenance, or to prevent electric shock. An ideal switch would have no voltage drop when closed, and would have no limits on voltage or current rating. It would have zero rise time and fall time during state changes, and would change state without "bouncing" between on and off positions. Practical switches fall short of this ideal; they have resistance, limits on the current and voltage they can handle, finite switching time, etc. The ideal switch is often used in circuit analysis as it greatly simplifies the system of equations to be solved, but this can lead to a less accurate solution. Theoretical treatment of the effects of non-ideal properties is required in the design of large networks of switches, as for example used in telephone exchanges DESIGN The switches may be single or multiple, designed for indoor or outdoor use. Optional extras may include dimmer-controls, environmental protection, and weather and security protection. In the case of light switches, the circuit to be switched is within 10% of 230 volts at 5A 6A or 10A for all European and most of South American, African and Asian countries, whereas Japan, North America and Liberia use a supply between 100 and 127 volts with maximum circuit currents of up to 15 or 20 amperes so the overall power per circuit is similar. In the UK, putting normal 13A BS1363 sockets on a lighting circuit is frowned upon (though not explicitly prohibited), but 2A or 5A BS546 outlets are often put on lighting circuits to allow control of free-standing lamps from the room's light switches. In the U.S., this is very common in mobile homes. It is common in American site-built housing for living rooms and bedrooms to have a switched receptacle for a floor or table lamp.

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Internal operation

Internal operation of a toggle switch, explained A switch is most vulnerable when the contacts are opening or closing. As the switch is closed, the resistance of the switch changes from nearly infinite to nearly zero. At infinite resistance, no current flows and no power is dissipated. At zero resistance, there is no voltage drop and no power is dissipated. When the switch changes state however, there is a brief instant of partial contact when resistance is neither zero nor infinite and power is dissipated. During that transition the contacts heat up. If the heating is excessive, the contacts can be damaged or even weld themselves closed. The switch is designed to make the transition as swiftly as possible. This is achieved by the initial operation of the switch lever mechanism storing potential energy, usually as stress in a spring. When sufficient energy is stored, the mechanism in the switch "breaks over" driving the contacts through the transition from open to close, or close to open, without further input by the switch operator. This quick-break action of the switch is essential to a long life for the switch contacts, as disclosed in Holmes' 1884 patent. While the contacts are separating, the energy stored in the inductance of the circuit is dissipated as an arc within the switch, prolonging the transition and worsening the heating effect on the contacts. Switches are commonly rated by the current they are designed to break, under specified voltage and power factor conditions, as this is the most stringent constraint. The arc that results when the switch operates erodes the switch contacts. A switch therefore has a finite life, often rated at a given number of cycles of

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disconnection at a specified current. Operation outside its specified capacity will shorten the switch life very drastically. To combat contact corrosion a switch is usually designed to have a wipe action so that the contacts are cleaned. Large switches may be designed with a supplemental contact that closes and opens before the main contact, protecting the main current-carrying contacts from wear due to arcing. The contact area of the switch is constructed of materials that resist corrosion and arcing. Many higher current switch designs rely on the separation arc to assist in dispersing contact corrosion. A switch designed for high current/high voltage use may become unreliable if operated at very low currents and low voltages because the contact corrosion builds up excessively without an arc to disperse it. There are two kinds of "sparks" which may be seen during switch operation. On closure, a few sparks like those from a flint-and-steel may appear as a tiny bit of metal is heated to incandescence, melted, and thrown off. On opening, a bluish arc may occur with a detectable "electrical" (ozone) smell; afterwards the contacts may be seen to be darkened and pitted. Damaged contacts have higher resistance, rendering them more vulnerable to further damage and causing a cycle in which the contacts soon fail completely. To make a switch safe, durable, and reliable, it must be designed so that the contacts are held firmly together under positive force when the switch is closed. It should be designed so that regardless of how the person operating the switch manipulates it, the contacts always close or open quickly. The spring that stores the energy necessary for the snap action of the switch mechanism, in many small switch designs is made of a beryllium copper alloy, that is hardened to form a spring as part of the fabrication of the contact. The same part often also forms the body of the contact itself, and is thus the current path. Abusing the switch mechanism to hold the contacts in a transition state, or severely overloading the switch, will heat and thus anneal the spring, reducing or eliminating the "snap action" of the switch, leading to slower transitions, more energy dissipated in the switch, and progressive failure.

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TWO LAMP CONTROLLED BY ONE SWITCH

TWO LAMP CONTROLLED BY TWO SWITCH

SERIES CONNECTION

STAIRCASE WIRING

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GODOWN WIRING

LAMP CONTROLLED BY INDIVIDUAL SWITCHES

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CONDUIT PARTS

LIGHTING ACCESSORIES

ANGLE BATTEN

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BATTEN HOLDER

PENDANT HOLDER

CEILING ROSE

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MODULAR SWITCH

PUSH BUTTON SWITCHES

SITE EQUIPMENTS

DB CONNECTION

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SPDB

TPNDB

TPNDB

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VDB

SWITCH BOX

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SWITCH BOX

SWITCH BOX

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HOUSE WIRING PLAN

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As, m numbers of series connected in parallel equivalent internal resistance of that series and parallel battery is nr/m. Fleming Left Hand Rule Whenever a current carrying conductor comes under a magnetic field, there will be a force acting on the conductor and on the other hand, if a conductor is forcefully brought under a magnetic field there will be an induced current in that conductor. In both of the phenomenon there is an relation between magnetic field, electric current and force. This relation directionally determined by Fleming Left Hand rule and Fleming Right Hand rule respectively. 'Directionally' means these rules do not show the magnitude but show the direction of any of the three parameters (magnetic field, electric current, force) if the direction of other two are known. Fleming Left Hand rule is mainly applicable for electric motor and Fleming Right Hand rule is mainly applicable for electric generator. In late 19th century, John Ambrose Fleming introduced these both rules and as per his name the rules are well known as Fleming left and right hand rule.

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It is found that whenever a current carrying conductor is placed inside a magnetic field, a force acts on the conductor, in a direction, perpendicular perpen both to the direction of the electric current and the magnetic field. In the figure it shown that a portion of a conductor of length L placed vertically in a uniform horizontal magnetic field of strength strength H, produced by two magnetic poles N and S. If i is the electric current flowing through this conductor, the magnitude of the force acts on the conductor is, F = BiL

F = Bil Hold out your left hand with forefinger, second finger and thumb at right angle to one another. If the fore finger represents the direction of the field and the second finger that of the current, then thumb gives the direction of the force. While electric current flows through a conductor one magnetic field is induced around it. This can be imagined by considering numbers of closed magnetic lines of force around the conductor. The direction of magnetic lines

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of force can be determined by Maxwell's corkscrew rule or right-hand grip rule. As per these rules the direction of the magnetic lines of force (or flux lines) is clockwise if the current is flowing away from the viewer that is if the direction of current through the conductor is inward from the reference plane as shown in the figure. Now if a horizontal magnetic field is applied externally to the conductor, these two magnetic fields i.e. field around the conductor due to current through it and the externally applied field will interact each other. We observe in the picture, the magnetic lines of force of external magnetic field are form N to S pole that is from left to right. The magnetic lines of force of external magnetic field and magnetic lines of force due to current in the conductor are in same direction, above the conductor and they are in opposite direction below the conductor. Hence there will be larger numbers of co-directional magnetic lines of force above the conductor than that of below the conductor. Consequently, there will be a larger concentration of magnetic lines of force in a small space above the conductor. As magnetic lines of force are no longer straight lines, they are under tension like stretched rubber bands. As a result there will be a force which tends to move the conductor from more concentrated magnetic field to less concentrated magnetic field that is from present position to downwards. Now if you observe the direction of current, force and magnetic field in the above explanation, you will find that the directions are according to Fleming left hand rule.

Interaction of magnetic fields and current-carrying conductors

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Fleming Right Hand Rule

As per Faraday's law of electromagnetic induction, whenever a conductor moves inside a magnetic field, there will be an induced current in it. If this conductor is forcefully moved inside the magnetic field, there will be a relation between the direction of applied force, magnetic field and the electric current. This relation among these three directions is determined by by Fleming Right Hand Rule. This rule states "Hold out the right hand with the first finger, second finger and thumb at right angles to each other. If forefinger represents the direction of the line of force, the thumb points in the direction of motion or applied force, then second finger points in the direction of the induced current. Electrical conductivity Electrical conductivity is a basic property of material. Due to this property one material can conduct electricity. Some materials are good conductor of electricity that means electric current can pass through them very easily; again some materials do not allow electric current to flow through them. The material through which current passes easily, called good conductor of electricity in other words, the electrical conductivity of these materials is high. On the other hand the materials do not allow the electrical current to flow through them are called electrical insulators. There are some materials whose electrical conductivity is not as high as conductor and also not as poor as insulator, they have an intermediate conductivity and these type of materials are known as semiconductors. As per Ohm's law current through a conductor is proportional to applied voltage across the conductor provided other all condition of conductor remains same.

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But other conditions of the conductor including temperature vary, the current through it also varies for fixed applied voltage. If the cross section of the conductor is increased, the current through the conductor increases as it gets wider free path to flow. Hence current through the conductor is directly proportional to its cross - sectional area. If length of the conductor increases, the potential stress per unit length or voltage gradient along the conductor is decreased as a result current through it reduces. Hence current through the conductor is inversely proportional to its cross - sectional area. Now, if current through the conductor is I, applied voltage across it V, length and cross - sectional area of the conductor are l and a respectively, then,

Where, σ is a constant. This sigma (σ) is known as electrical conductivity of a material with which the conductor is made of. Depending upon the value of conductivity, different currents flow through different conductors, for same dimensions and applied voltage. That means for certain applied voltage, how much current will flow through a particular conductor depends upon the electrical conductivity of the material by which the conductor is made of. It is considered that temperature is fixed. Faradays Law

In 1831, Micheal Faraday formulated two laws on the bases of experiments. These laws are called Faraday's laws of electromagnetic induction. FIRST LAW First Law of Faraday's Electromagnetic Induction state that whenever a conductor are placed in a varying magnetic field emf are induced which is called induced emf, if the conductor circuit are closed current are also induced which is called induced current. Or

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Whenever a conductor is rotated in magnetic field emf is induced which are induced emf. SECOND LAW Second Law of Faraday's Electromagnetic Induction state that the induced emf is equal to the rate of change of flux linkages (flux linkages is the product of turns, n of the coil and the flux associated with it). FARADAY'S LAW'S EXPLANATION Let Initial flux linkages = Nφ1 Final flux linkages = Nφ2 Change in flux linkages= Nφ2 – Nφ1 = N((φ2-φ1) If (φ2-φ1) = φ Then change in flux linkages = Nφ Rate of change of flux linkages = Nφ/t wb/sec Taking derivative of right hand side we get Rate of change of flux linkages = Ndφ/dt wb/sec Rut according to Faraday's laws of electromagnetic induction, the rate of change of flux linkages equal to the induced emf, hence we can write = Ndφ/dt volt Generally Faraday's laws is written as e = -Ndφ/dt volt Where negative sign represents the direction of the induced current in the conductor will be such that the magnetic field produced by it will oppose the verb because producing it.

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INDUCED EMF Whenever a conductor is placed in a varying magnetic field, EMF is induced in the conductor and this EMF is called induced EMF. Induced EMF is of two types INDUCED EMF I.

Dynamically induced EMF When the conductor is in motion and the field is in stationary so the EMF is induced in the conductor, this type of EMF is called dynamically induced EMF.

II.

Statically induced EMF When the conductor is in stationary and the field is changing (varying) then in this case EMF is also induced in the conductor, which is called statically induced EMF.

Statically induced EMF is of two types 1. Self induced EMF Self-induced EMF is that EMF which is induced in the conductor by changing in its own. When current is changing the magnetic field is also changing around the coil and hence Faraday law is applied here and EMF are induced in the coil to it self which called self induced EMF.

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CHAPTER - 8 TRANSFORMERS


WORKING PRINCIPLE
TRANSFORMER CONNECTION
TYPES OF TRANSFORMERS
LOSSES IN TRANSFORMER

Transformer – Working Principle A transformer can be defined as a static device which helps in the transformation of electric power in one circuit to electric power of the same frequency in another circuit. The voltage can be raised or lowered in a circuit, but with a proportional increase or decrease in the current ratings. The main principle of operation of a transformer is mutual inductance between two circuits which is linked by a common magnetic flux. A basic transformer consists of two coils that are electrically separate and inductive, but are magnetically linked through a path of reluctance. The working principle of the transformer can be understood from the figure below.

Transformer Working

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As shown above the transformer has primary and secondary windings. The core laminations are joined in the form of strips in between the strips you can see that there are some narrow gaps right through the cross-section of the core. These staggered joints are said to be ‘imbricated’. Both the coils have high mutual inductance. A mutual electro-motive force is induced in the transformer from the alternating flux that is set up in the laminated core, due to the coil that is connected to a source of alternating voltage. Most of the alternating flux developed by this coil is linked with the other coil and thus produces the mutual induced electro-motive force. The so produced electro-motive force can be explained with the help of Faraday’s laws of Electromagnetic Induction as e = M*dI/dt If the second coil circuit is closed, a current flows in it and thus electrical energy is transferred magnetically from the first to the second coil. The alternating current supply is given to the first coil and hence it can be called as the primary winding. The energy is drawn out from the second coil and thus can be called as the secondary winding. In short, a transformer carries the operations shown below: 1) 2) 3) 4)

Transfer of electric power from one circuit to another. Transfer of electric power without any change in frequency. Transfer with the principle of electromagnetic induction. The two electrical circuits are linked by mutual induction.

Transformer Construction For the simple construction of a transformer, you must need two coils having mutual inductance and a laminated steel core. The two coils are insulated from each other and from the steel core. The device will also need some suitable container for the assembled core and windings, a medium with which the core and its windings from its container can be insulated. In order to insulate and to bring out the terminals of the winding from the tank, apt bushings that are made from either porcelain or capacitor type must be used. In all transformers that are used commercially, the core is made out of transformer sheet steel laminations assembled to provide a continuous magnetic path with minimum of air-gap included. The steel should have high permeability and low hysteresis loss. For this to happen, the steel should be made of high silicon content and must also be heat treated. By effectively laminating the core, the eddy-current losses can be reduced. The lamination can be done with the help of a light coat of core plate varnish or

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lay an oxide layer on the surface. For a frequency of 50 Hertz, the thickness of the lamination varies from 0.35mm to 0.5mm for a frequency of 25 Hertz. Types of Transformers The types of transformers differ in the manner in which the primary and secondary coils are provided around the laminated steel core. According to the design, transformers can be classified into two: 1. Core- Type Transformer In core-type transformer, the windings are given to a considerable part of the core. The coils used for this transformer are form-wound and are of cylindrical type. Such a type of transformer can be applicable for small sized and large sized transformers. In the small sized type, the core will be rectangular in shape and the coils used are cylindrical. The figure below shows the large sized type. You can see that the round or cylindrical coils are wound in such a way as to fit over a cruciform core section. In the case of circular cylindrical coils, they have a fair advantage of having good mechanical strength. The cylindrical coils will have different layers and each layer will be insulated from the other with the help of materials like paper, cloth, micarta board and so on. The general arrangement of the core-type transformer with respect to the core is shown below. Both low-voltage (LV) and high voltage (HV) windings are shown.

Core Type Transformer Cruciform Section

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The low voltage windings are placed nearer to the core as it is the easiest to insulate. The effective core area of the transformer can be reduced with the use of laminations and insulation. 2. Shell-Type Transformer In shell-type transformers the core surrounds a considerable portion of the windings. The comparison is shown in the figure below.

The coils are form-wound but are multi layer disc type usually wound in the form of pancakes. Paper is used to insulate the different layers of the multilayer discs. The whole winding consists of discs stacked with insulation spaces between the coils. These insulation spaces form the horizontal cooling and insulating ducts. Such a transformer may have the shape of a simple rectangle or may also have a distributed form. Both designs are shown in the figure below:

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A strong rigid mechanical bracing must be given to the cores and coils of the transformers. This will help in minimizing the movement of the device and also prevents the device from getting any insulation damage. A transformer with good bracing will not produce any humming noise during its working and will also reduce vibration. A special housing platform must be provided for transformers. Usually, the device is placed in tightly-fitted sheet-metal tanks filled with special insulating oil. This oil is needed to circulate through the device and cool the coils. It is also responsible for providing the additional insulation for the device when it is left in the air. There may be cases when the smooth tank surface will not be able to provide the needed cooling area. In such cases, the sides of the tank are corrugated or assembled with radiators on the sides of the device. The oil used for cooling purpose must be absolutely free from alkalis, sulphur and

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most importantly moisture. Even a small amount of moistures in the oil will cause a significant change in the insulating property of the device, as it lessens the dielectric strength of the oil to a great extent. Mathematically speaking, the presence of about 8 parts of water in 1 million reduces the insulating quality of the oil to a value that is not considered standard for use. Thus, the tanks are protected by sealing them air-tight in smaller units. When large transformers are used, the air tight method is practically difficult to implement. In such cases, chambers are provided for the oil to expand and contract as its temperature increases and decreases. These breathers form a barrier and resist the atmospheric moisture from contact with oil. Special care must also be taken to avoid sledging. Sledging occurs when oil decomposes due to over exposure to oxygen during heating. It results in the formation of large deposits of dark and heavy matter that clogs the cooling ducts in the transformer. The quality, durability and handling of these insulating materials decide the life of the transformer. All the transformer leads are brought out of their cases through suitable bushings. There are many designs of these, their size and construction depending on the voltage of the leads. Porcelain bushings may be used to insulate the leads, for transformers that are used in moderate voltages. Oil-filled or capacitive-type bushings are used for high voltage transformers. The selection between the core and shell type is made by comparing the cost because similar characteristics can be obtained from both types. Most manufacturers prefer to use shell-type transformers for high-voltage applications or for multi-winding design. When compared to a core type, the shell type has a longer mean length of coil turn. Other parameters that are compared for the selection of transformer type are voltage rating, kilo-volt ampere rating, weight, insulation stress, heat distribution and so on. Three Phase Transformer It is found that generation, transmission and distribution of electrical power are more economical in three phase system than single phase system. For three phase system three single phase transformers are required. Three phase transformation can be done in two ways, by using single three phase transformer or by using a bank of three single phase transformers. Both are having some advantages over other. Single 3 phase transformer costs around 15% less than bank of three single phase transformers. Again former occupies less space than later. For very big transformer, it is impossible to transport large three phase transformer to the site and it is easier to transport three single phase transformers which is erected separately to form a three phase unit. Another advantage of using bank of three single phase

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transformers is that, if one unit of the bank becomes out of order, then the bank can be run as open delta. Connection of Three Phase Transformer A Verity of connection of three phase transformer are possible on each side of both a single 3 phase transformer or a bank of three single phase transformers. Marking or labeling the different terminals of transformer. Terminals of each phase of HV side should be labeled as capital letters, A, B, C, and those of LV side should be labeled as small letters, a, b, c. Terminal polarities are indicated by suffixes 1 & 2. Suffix 1’s indicate similar polarity ends and so do 2’s. Star Star Transformer

Star Star Transformer is formed in a 3 phase transformer by connecting one terminal of each phase of individual side, together. The common terminal is indicated by suffix 1 in the figure below. If terminal with suffix 1 in both primary and secondary are used as common terminal, voltages of primary and secondary are in same phase. That is why this connection is called zero degree connection or 0o - connection. If the terminals with suffix 1 are connected together in HV side as common point and the terminals with suffix 2 in LV side are connected together as common point, the voltages in primary and secondary will be in opposite phase. Hence, Star Star Transformer connection is called 180o - Connection, of three phase transformer. Delta Detla Transformer

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In delta delta transformer, 1 suffixed terminals of each phase primary winding will be connected with 2 suffixed terminal of next phase primary winding. If primary is HV side, then A1 will be connected to B2, B1 will be connected to C2 and C1 will be connected to A2. Similarly in LV side 1 suffixed terminals of each phase winding will be connected with 2 suffixed terminals of next phase winding. That means, a1 will be connected to b2, b1 will be connected to c2 and c1 will be connected to a2. If transformer leads are taken out from primary and secondary 2 suffixed terminals of the winding, then there will be no phase difference between similar line voltages in primary and secondary. This delta delta transformer connection is zero degree connection or 0o - Connection. But in LV side of transformer, if, a2 is connected to b1, b2 is connected to c1 and c2 is connected to a1. The secondary leads of transformer are taken out from 2 suffixed terminals of LV windings, and then similar line voltages in primary and secondary will be in phase opposition. This connection is called 180o - Connection, of three phase transformer. Star Delta Transformer Here in star delta transformer, star connection in HV side is formed by connecting all the 1 suffixed terminals together as common point and transformer primary leads are taken out from 2 suffixed terminals of primary windings.

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The delta connection in LV side is formed by connecting 1 suffixed terminals of each phase LV winding with 2 suffixed terminal of next phase LV winding. More clearly, a1 is connected to b2, b1 is connected to c2 and c1 is connected to a2. The secondary (here it considered as LV) leads are taken out from 2 suffixed ends of the secondary windings of transformer. The transformer connection diagram is shown in the figure beside. It is seen from the figure that the sum of the voltages in delta side is zero. This is a must as otherwise closed delta would mean a short circuit. It is also observed from the phasor diagram that, phase to neutral voltage (equivalent star basis) on the delta side lags by − 30o to the phase to neutral voltage on the star side; this is also the phase relationship between the respective line to line voltages. This star delta transformer connection is therefore known as − 30o - Connection. Star – Delta + 30o connection is also possible by connecting secondary terminals in following sequence. a2 is connected to b1, b2 is connected to c1 and c2 is connected to a1. The secondary leads of transformer are taken out from 2 suffixed terminals of LV windings,

Delta Star Transformer

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Delta star transformer connection of three phase transformer is similar to star – delta connection. If anyone interchanges HV side and LV side of star – delta transformer in diagram, it simply becomes delta – star connected 3 phase transformer. That means all small letters of star delta connection should be replaced by capital letters and all small letters by capital in delta star transformer connection. THE BASICS OF DRY TYPE TRANSFORMERS Transformers change voltages from one level to another. Most commonly, that change involves very high power line transmission voltages (500 kV) being reduced to the much lower levels used in heavy industry (as much as 30 kV) and households (120-240 V). Dry type, or air-cooled, transformers accomplish this function so safely and efficiently that they are commonly used for indoor applications where other transformer types are considered too risky. Electric Service Company (ELSCO) is the leading manufacturer of and repair facility for dry type transformers. HOW DRY TYPE TRANSFORMERS WORK A dry type transformer, like all transformers, uses basic physical principles of electricity and magnetic coupling to produce any desired voltage level: 1. When a fluctuating electric current flows through a wire, it generates a fluctuating magnetic field or "magnetic flux" all around it. 2. When a magnetic field fluctuates around a piece of wire, it generates an electric current in the wire. So, if a second wire is placed next to the first charged wire, within that fluctuating magnetic flux field, electric current is induced to flow in the second wire. Thus, electricity is “passed” from the first wire to the second without the two wires actually touching. In all transformers, including dry type transformers, the first wire, or primary coil winding, is connected to an alternating current (AC) voltage source while wrapped around a magnetic core, producing a fluctuating current in the wire coil. That fluctuating current magnetizes the core. The second wire coil, or secondary winding, is wrapped around another part of the core. The fluctuating magnetic field in the core induces a current in the secondary coil. The relative number of turns each winding makes around the core determines how much voltage is produced in the secondary. Most commonly, transformers step voltage down from high to low; but turns ratios can also be arranged to step up voltage if necessary, for instance, to allow 240-V foreign appliances to work in the US where the voltage supplied is 120 V.

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Basic Transformer Core Layout This electromechanical linkage in a transformer makes it possible for the same megavoltage source, like a dam, wind farm, or coal-powered generator, to supply power for both a high-demand steel mill and a low-demand kitchen toaster. The particular application will determine what size equipment is needed and which kind – a dry type transformer or some other technology. ELSCO can provide products, service and information covering many different transformer types, all of which contain copper windings, the most efficient coil wire material. Note that while power sources are rated in kilovolts (kV) -- the potential difference measured between two electrical points -- transformers are rated in kilovolt-amperes, or kVA -- the product of current and voltage, signifying the actual, or apparent, power consumed by an electrical load, that is, the energy required to actually run a device. Electric Service Company supplies dry type transformers from 500 kVA – the power necessary to run a school or small industrial building -- to 5000 kVA, enough for a power plant. PRACTICAL DRY TYPE TRANSFORMER CONSIDERATIONS But whatever specific transformer equipment is needed, major limiting factors to consider include heat, maintenance, and safety. Dry type transformers are especially valued for their stellar performance via these three important factors. An intrinsic byproduct of the transformation process is heat, specifically, the “I2R” (I=Current, R=Resistance) heating that occurs when current runs through a conductive wire. Heat breaks down transformer composition materials and insulation, resulting in less efficiency and shorter service life. Transformer heat is best controlled by the oil used in oil filled transformers, which conducts the heat away from the heat-producing parts while protecting other internal transformer workings. That is why these transformers are used in the highest voltage applications like high-voltage transmission. But with proper sizing and placement, as well as fans when appropriate, dry type transformers, which cool by air ventilation, provide excellent, low-heat service in tight enclosures and indoor situations where oil leakage could

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cause a fire or significant environmental hazard. Clearly, a system without these threats offers enhanced safety for indoor applications. A dry type transformer will typically incorporate a design with greater internal clearances to allow for better heat dissipation. No fireproofing, oil catch basins or venting of toxic gasses are required, and the transformer can be close to the load, minimizing secondary line losses. But a dry type transformer also reduces maintenance with no need to replace transformer oil while avoiding the contaminant and composition checks necessary for proper oil insulation and cooling.

INDOOR TYPE TRANSFORMER

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INDOOR TYPE TRANSFORMER

OIL TYPE TRANSFORMER

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CAST RESIN TRANSFORMER

UNITISED SUBSTATION

Losses In Transformer As the electrical transformer is a static device, mechanical loss in transformer normally does not come into picture. We generally consider

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only electrical losses in transformer. Loss in any machine is broadly defined as difference between input power and output power. When input power is supplied to the primary of transformer, some portion of that power is used to compensate core losses in transformer i.e. Hysteresis loss in transformer and Eddy Current loss in transformer core and some portion of the input power is lost as I2R loss and dissipated as heat in the primary and secondary winding, as because these windings have some internal resistance in them. The first one is called core loss or iron loss in transformer and later is known as ohmic loss or copper loss in transformer. Another loss occurs in transformer, known as Stray Loss, due to Stray fluxes link with the mechanical structure and winding conductors. Copper loss in transformer Copper loss is I2R loss, in primary side it is I12R1 and in secondary side it is I22R2 loss, where I1 & I2 are primary & secondary current of transformer and R1 & R2 are resistances of primary & secondary winding. As the both primary & secondary currents depend upon load of transformer, so copper loss in transformer vary with load. Core losses in transformer Hysteresis loss and eddy current loss, both depend upon magnetic properties of the materials used to construct the core of transformer and its design. So these losses in transformer are fixed and do not depend upon the load current. So core losses in transformer which is alternatively known as iron loss in transformer and can be considered as constant for all range of load. Hysteresis loss in transformer Hysteresis loss in transformer can be explained in different ways. We will discuss two of them, one is physical explanation other is mathematical explanation. Physical explanation of Hysteresis loss The magnetic core of transformer is made of ′Cold Rolled Grain Oriented Silicon Steel′. Steel is very good ferromagnetic material. This kind of materials are very sensitive to be magnetized. That means whenever magnetic flux passes through, it will behave like magnet. Ferromagnetic substances have numbers of domains in their structure. Domain are very small region in the material structure, where all the dipoles are paralleled to same direction. In other words, the domains are like small small permanent magnet situated randomly in the structure of substance. These domains are arranged inside the material structure in such a random manner, that net

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resultant magnetic field of the said material is zero. Whenever external magnetic field or mmf is is applied to that substance, these randomly directed domains are arranged themselves in parallel to the axis of applied mmf. After removing this external mmf, maximum numbers of domains again come to random positions, but some few of them still remain in their changed position. Because of these unchanged domains the substance becomes slightly magnetized permanently. This magnetism is called " Spontaneous Magnetism". To neutralize this magnetism some opposite mmf is required to be applied. The magneto motive force or mmf applied in the transformer core is alternating. For every cycle, due to this domain reversal there will be extra work done. For this reason, there will be a consumption of electrical energy which is known as Hysteresis loss of transformer. Eddy Current loss In transformer we supply alternating current in the primary, this alternating current produces alternating magnetizing flux in the core and as this flux links with secondary winding there will be induced voltage in secondary, resulting current to flow through the load connected with it. Some of the alternating fluxes of transformer may also link with other conducting parts like steel core or iron body of transformer etc. As alternating flux links with these parts of transformer, there would be a locally induced emf. Due to these emfs there would be currents which will circulate locally at those parts of the transformer. These circulating current will not contribute in output of the transformer and dissipated as heat. This type of energy loss is called eddy current loss of transformer. This was a broad and simple explanation of eddy current loss. The detail explanation of this loss is not in the scope of discussion in that chapter. Maximum Demand:  Maximum demand (often referred to as MD) is the largest current normally carried by circuits, switches and protective devices. It does not include the levels of current flowing under overload or short circuit conditions. 

Assessment of maximum demand is sometimes straightforward. For example, the maximum demand of a 240 V single-phase 8 kW shower heater can be calculated by dividing the power (8 kW) by the voltage (240 V) to give a current of 33.3 A. This calculation assumes a power factor of unity, which is a reasonable assumption for such a purely resistive load.



There are times, however, when assessment of maximum demand is less obvious. For example, if a ring circuit feeds fifteen 13 A sockets, the maximum demand clearly should not be 15 x 13 = 195 A, if only because the circuit protection will not be rated at more than 32 A. Some 13 A

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sockets may feed table lamps with 60 W lamps fitted, whilst others may feed 3 kW washing machines; others again may not be loaded at all. 

Lighting circuits pose a special problem when determining MD. Each lamp-holder must be assumed to carry the current required by the connected load, subject to a minimum loading of 100 W per lamp holder (a demand of 0.42 A per lamp holder at 240 V). Discharge lamps are particularly difficult to assess, and current cannot be calculated simply by dividing lamp power by supply voltage. The reasons for this are: 1) Control gear losses result in additional current, 2) the power factor is usually less than unity so current is greater, and 3) Chokes and other control gear usually distort the waveform of the current so that it contains harmonics which are additional to the fundamental supply current.



So long as the power factor of a discharge lighting circuit is not less than 0.85, the current demand for the circuit can be calculated from:



current (A) = (lamp power (W) x 1.8) / supply voltage (V)



For example, the steady state current demand of a 240 V circuit supplying ten 65 W fluorescent lamps would be: I = 10X65X1.8A / 240 = 4.88A



Switches for circuits feeding discharge lamps must be rated at twice the current they are required to carry, unless they have been specially constructed to withstand the severe arcing resulting from the switching of such inductive and capacitive loads.

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CHAPTER - 9 SWITCH GEAR & PROTECTION
GENERAL
FUSES
SWITCH FUSE UNIT (SFU)
CIRCUIT BREAKER (CB)
OIL CIRCUIT BREAKER (OCB)
AIR CIRCUIT BREAKER (ACB)
SF6 CIRCUIT BREAKER (SF6 CB)
VACCUM CIRCUIT BREAKER (VCB)
MINIATURE CIRCUIT BREAKER (MCB)
MOLDED CASE CIRCUIT BREAKER (MCCB)
EARTH LEAKAGE CIRCUIT BREAKER (ELCB)
INSTRUMENT TRANSFORMERS
LOW VOLTAGE SWITCH GEAR A switchgear or electrical switchgear is a generic term which includes all the switching devices associated with mainly power system protection. It also includes all devices associated with control, metering and regulating of electrical power system. Assembly of such devices in a logical manner forms a switch gear. This is very basic definition of switchgear. Switchgear and Protection

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We all familiar with low voltage switches and re-wirable fuses in our home. The switch is used to manually open and close the electrical circuit in our home and electrical fuse is used to protect our household electrical circuit from over current and short circuit faults. In same way every electrical circuit including high voltage electrical power system needs switching and protective devices. But in high voltage and extra high voltage system, this switching and protective scheme becomes complicated one for high fault current interruption in safe and secure way. In addition to that from commercial point of view every electrical power system needs measuring, control and regulating arrangement. Collectively the whole system is called Switchgear and Protection of power system. The electrical switchgear have been developing in various forms. Switchgear protection plays a vital role in modern power system network, right from generation through transmission to distribution end. The current interruption device or switching device is called circuit breaker in Switchgear protection system. The circuit breaker can be operated manually as when required and it is also operated during over current and short circuit or any other faults in the system by sensing the abnormality of system. The circuit breaker senses the faulty condition of system through protection relay and this relay is again actuated by faulty signal normally comes from current transformer or voltage transformer.

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What is Fuses  A fuse is a device that protects a circuit from an over current condition only. It has a fusible link directly heated and destroyed by the current passing through it. A fuse contains a current- carrying element sized so that the heat generated by the flow of normal current through it does not cause it to melt the element; however, when an over current or short-circuit current flows through the fuse, the fusible link will melt and open the circuit. 

A device that protects a circuit by fusing opens its current-responsive element when an over-current passes through it. An over-current is either due to an overload or a short circuit condition.



The Underwriter Laboratories (UL) classifies fuses by letters e.g. class CC, T, K, G, J, L, R, and so forth. The class letter may designate interrupting rating, physical dimensions, and degree of current limitation.



As per NEC and ANSI/IEEE standard 242 [2] – A current limiting fuse is a fuse that will interrupt all available currents above its threshold current and below its maximum interrupting rating, limit the clearing time at rated voltage to an interval equal to or less than the first major or symmetrical loop duration, and limit peak let-through current to a value less than the peak that would be possible with the fuse replaced by a solid conductor of the same impedance.

Fuse Construction:  The typical fuse consists of an element which is surrounded by filler and enclosed by the fuse body. The element is welded or soldered to the fuse contacts (blades or ferrules).

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The element is a calibrated conductor. Its configuration, mass and the materials employed are selected to achieve the desired electrical and thermal characteristics.



The element provides the current path through the fuse. It generates heat at a rate dependent on its resistance and the load current.



The heat generated by the element is absorbed by the filler and passed through the fuse body to the surrounding air. The filler material, such as quartz sand, provides effective heat transfer and allows for the small element cross-section typical in modern fuses.



The effective heat transfer allows the fuse to carry harmless overloads .The small element cross section melts quickly under short-circuit conditions. The filler also aids fuse performance by absorbing arc energy when the fuse clears an overload or short circuit.



When a sustained overload occurs, the element will generate heat at a faster rate than the heat can be passed to the filler. If the overload persists, the element will reach its melting point and open. Increasing the applied current will heat the element faster and cause the fuse to open sooner. Thus, fuses have an inverse time current characteristic: that is, the greater the over current, the less time required for the fuse to open the circuit.



This characteristic is desirable because it parallels the characteristics of conductors, motors, transformers, and other electrical apparatus. These components can carry low-level overloads for relatively long periods without damage. However, under high-current conditions, damage can occur quickly. Because of its inverse time current characteristic, a properly applied fuse can provide effective protection over a broad current range, from low-level overloads to high-level short circuits.

Commonly used terms for Fuse  I2t (Ampere Square second): A measure of the thermal energy associated with current flow.I2t is equal to (I RMS) 2 X t, where is the duration of current flow in seconds. A measure of thermal energy associated with current flow. It can be expressed as melting I2t, arcing I2t or the sum of them as Clearing I2t. Clearing I2t is the total I2t passed by a fuse as the fuse clears a fault, with t being equal to the time elapsed from the initiation of the fault to the instant the fault has been cleared. Melting I2t is the minimum I2t required to melt the fuse element 

Interrupting Rating (Abbreviated I.R.)Same as breaking capacity or short circuit rating. The maximum current a fuse can safely interrupt at

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rated voltage. Some special purpose fuses may also have a “Minimum Interrupting Rating”. This defines the minimum current that a fuse can safely interrupt. Safe operation requires that the fuse remain intact. Interrupting ratings may vary with fuse design and range from 35 amperes AC for some 250V metric size (5 x 20mm) fuses up to 200,000 amperes AC for the 600V industrial fuses (for example, ATDR series). 

Clearing I2t: The total I2t passed by a fuse as the fuse clears a fault, with being equal to the time elapsed from the initiation of the fault to the instant the fault has been cleared.



Melting I2t: The minimum I2t required melting the fuse element.



Ampere Rating: The continuous current carrying capability of a fuse under defined laboratory conditions. The ampere rating is marked on each fuse.



Available Fault Current: The maximum short-circuit current that can flow in an unprotected circuit.



Coordination: The use of over current protective devices that will isolate only that portion of an electrical system that has been overloaded or faulted.



Current limiting Range: currents a fuse will clear in less than ½ cycles, thus limiting the actual magnitude of current flow.



Element: A calibrated conductor inside a fuse that melts when subjected to excessive current. The element is enclosed by the fuse body and may be surrounded by an arc quenching medium such as silica sand. The element is sometimes referred to as a link.



Fast acting Fuse: This is a fuse with no intentional time-delay designed into the overload range. It is sometimes referred to as a “single-element fuse” or “non-delay fuse.”



Fault Current: Short-circuit current that flows partially or entirely outside the intended normal load current path of a circuit component. Values may be from hundreds to many thousands of amperes.

1. Ferrule: copper mounting terminals of fuses with amp ratings up to 60 amperes. The cylindrical terminals at each end of a fuse fit into fuse clips. 

Current limiting Fuse: A fuse that meets the following three conditions:

1. 1. interrupts all available over currents within its interrupt rating.

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1. 2. Within its current limiting range, limits the clearing time at rated voltage to an interval equal to, or less than, the first major or symmetrical current loop duration. 1. 3. Limits peak let-through current to a value less than the available peak current. The maximum level of fault current that the fuse has been tested to safely interrupt. 

Arcing time The amount of time from the instant the fuse link has melted until the over current is interrupted, or cleared.



Clearing time The total time between the beginning of the over current and the final opening of the circuit at rated voltage by an over current protective device. Clearing time is the total of the melting time and the arcing time.



Fast acting fuse A fuse which opens on overload and short circuits very quickly. This type of fuse is not designed to withstand temporary overload currents associated with some electrical loads. UL listed or recognized fast acting fuses would typically open within 5 seconds maximum when subjected to 200% to 250% of its rated current.IEC has two categories of fast acting fuses:

1. F= quick acting, opens 10x rated current within 0.001 seconds to 0.01 seconds 1. FF = very quick acting, opens 10x rated current in less than 0.001 seconds 

Overload Can be classified as an over current which exceeds the normal full load current of a circuit by 2 to 5 times its magnitude and stays within the normal current path.



Resistive load An electrical load which is characterized by not drawing any significant inrush current. When a resistive load is energized, the current rises instantly to its steady state value, without first rising to a higher value.



RMS Current The R.M.S. (root mean square) value of any periodic current is equal to the value of the direct current which,flowing through a resistance, produces the same heating effect in the resistance as the periodic current does.



Short circuit An over current that leaves the normal current path and greatly exceeds the normal full load current of the circuit by a factor of tens, hundreds, or thousands times.

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Time delay fuse A fuse with a built-in time delay that allows temporary and harmless inrush currents to pass without operating, but is so designed to open on sustained overloads and short circuits. UL listed or recognized time delay fuses typically open in 2 minutes maximum when subjected to 200% to 250% of rated current. IEC has two categories of time delay fuses:

1. T= time lag, opens 10x rated current within 0.01 seconds to 0.1 seconds 1. TT = long time lag, opens 10x rated current within 0.1 seconds to 1 second 

Voltage rating A maximum open circuit voltage in which a fuse can be used, yet safely interrupt an over current. Exceeding the Voltage rating of a fuse impairs its ability to clear an overload or short circuit safely.



Over current A condition which exists in an electrical circuit when the normal load current is exceeded. Over currents take on two separate characteristics-overloads and short circuits.



Threshold Current: The magnitude of symmetrical RMS available current at the threshold of the current-limiting range, where the fuse becomes current-limiting when tested to the industry standard.



Threshold ratio: A threshold ratio is a relationship of threshold current to a fuse’s continuous current rating.

Threshold Ratio = Fuse Threshold Current / Fuse Continuous Current. Maximum threshold ratio for various types of fuses:



Fuse Class

Ratio

CLASS RK5

65

CLASS RK1

30

CLASS J

30

CLASS CC

30

CLASS L

30 (601-1200 Amps)

CLASS L

35(1201-2000 Amps)

CLASS L

40 (2001-4000 Amps)

A current limiting fuse may be current limiting or may not be current limiting. The current limiting characteristic depends on the threshold ratio and available fault current.

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Let’s consider an example of 1500 kVA radial service feeding a fusible switchboard with 2000 amps class L fuses. As per ANSI C 57 [3] standard, a typical impedance value for this size of a transformer is 5.75%; this value is a key factor in calculating the short circuit current.



All utility’s network provides a specific fault current at a specific location which depends on various factors, e.g.; cable lengths, cable size, X/R ratio and etc. If we ignore this limitation and assume that there is an unlimited fault current available from a utility, then let’s calculate short circuit current from a 1500 kVA transformer at 480 volts



The formula to calculate short circuit current (Isc)



ISC = (KVA X 10,000) / (1.732 X VOLT X %Z).



ISC = 1500 X 10,000 / 1.732 X 480 X 5.75



ISC = 31378.65 Amp.

Type of Fuse:  A fuse unit essentially consists of a metal fuse element or link, a set of contacts between which it is fixed and a body to support and isolate them. Many types of fuses also have some means for extinguishing the arc which appears when the fuse element melts. In general, there are two categories of fuses. 1) Low voltage fuses. 2) High voltage fuses. 

Usually isolating switches are provided in series with fuses where it is necessary to permit fuses to be replaced or rewired with safety.



In absence of such isolation means, the fuses must be so shielded as to protect the user against accidental contact with the live metal when the fuse is being inserted or removed.

LOW VOLTAGE FUSES  Low voltage fuses can be further divided into two classes namely 1) Semi-enclosed or Rewire able type. 2) Totally enclosed or Cartridge type. (1) Re Wire able Fuse: 

The most commonly used fuse in ‘house wiring’ and small current circuit is the semi-enclosed or rewire able fuse. (also sometime known as KITKAT type fuse). It consist of a porcelain base carrying the fixed contacts to which the incoming and outgoing live or phase wires are connected

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and a porcelain fuse carrier holding the fuse element, consisting of one or more strands of fuse wire, stretched between its terminals.



The fuse carrier is a separate part and can be taken out or inserted in the base without risk, even without opening the main switch. If fuse holder or carrier gets damaged during use, it may be replaced without replacing the complete unit.



The fuse wire may be of lead, tinned copper, aluminum or an alloy of tin lead.



The actual fusing current will be about twice the rated current. When two or more fuse wire are used, the wires should be kept apart and a de rating factor of 0.7 to 0.8 should be employed to arrive at the total fuse rating.



The specification for re wire able fuses are covered by IS: 2086-1963. Standard ratings are 6, 16, 32, 63, and 100A.



A fuse wire of any rating not exceeding the rating of the fuse may be used in it that is a 80 A fuse wire can be used in a 100 A fuse, but not in the 63 A fuse. On occurrence of a fault, the fuse element blows off and the circuit is interrupted. The fuse carrier is pulled out, the blown out fuse element is replaced by new one and the supply can is resorted by reinserting the fuse carrier in the base.



Though such fuses have the advantage of easy removal or replacement without any danger of coming into the contact with a lie part and negligible replacement cost but suffers from following disadvantages: 1) 2) 3) 4) 5) 6)

Unreliable Operations. Lack of Discrimination. Small time lag. Low rupturing capacity. No current limiting feature. Slow speed of operations.

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(2) Totally Enclosed Or Cartridges Type Fuse: 

The fuse element is enclosed in a totally enclosed container and is provided with metal contacts on both sides. These fuses are further classified as 1) D-type. 2) Link type.



Link type cartridges are again of two type’s viz. Knife blade or bolted type.

A) D- Type Cartridges Fuses 

It is a non interchangeable fuse comprising s fuse base, adapter ring, cartridge and a fuse cap. The cartridge is pushed in the fuse cap and the cap is screwed on the fuse base. On complete screwing the cartridge tip touches the conductor and circuit between the two terminals is completed through the fuse link. The standard ratings are 6, 16, 32, and 63 amperes.



The breaking or rupturing capacity is of the order of 4k A for 2 and 4 ampere fuses the 16k A for 63 A fuses.



D-type cartridge fuse have none of the drawbacks of the re wire able fuses. Their operation is reliable. Coordination and discrimination to a reasonable extent and achieved with them.

B) Link type Cartridge or High Rupturing Capacity (HRC) 

Where large numbers of concentrations of powers are concerned, as in the modern distribution system, it is essential that fuses should have a definite known breaking capacity and also this breaking capacity should have a high value. High rupturing capacity cartridge fuse, commonly called HRC cartridge fuses, have been designed and developed after intensive research by manufactures and supply engineers in his direction.

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The usual fusing factor for the link fuses is 1.45. the fuses for special applications may have as low as a fusing factor as 1.2.



The specification for medium voltage HRC link fuses are covered under IS: 2202-1962.

(A) Knife Blade Type HRC Fuse: 

It can be replaced on a live circuit at no load with the help of a special insulated fuse puller.

(B) Bolted Type HRC Link Fuse:



it has two conducting plates on either ends. These are bolted on the plates of the fuse base. Such a fuse needs an additional switch so that the fuse can be taken out without getting a shock.



Preferred ratings of HRC fuses are 2, 4, 6, 10, 16, 25, 30, 50, 63, 80, 100, 125, 160, 200, 250, 320, 400, 500, 630,800, 1000 and 1,250 amperes.

SFU

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SFU

Definition of Circuit Breaker: Electrical Circuit Breaker is a switching device which can be operated manually as well as automatically for controlling and protection of electrical power system respectively. As the modern power system deals with huge currents, the special attention should be given during designing of circuit breaker to safe interruption of arc produced during the operation of circuit breaker. This was the basic definition of circuit breaker. Introduction to Circuit Breaker The modern power system deals with huge power network and huge numbers of associated electrical equipment. During short circuit fault or any other types of electrical fault these equipment as well as the power network suffer a high stress of fault current in them which may damage the equipment and networks permanently. For saving these equipments and the power networks the fault current should be cleared from the system as quickly as possible. Again after the fault is cleared, the system must come to its normal working condition as soon as possible for supplying reliable quality power to the receiving ends. In addition to that for proper controlling of power system, different switching operations are required to be performed. So for timely disconnecting and reconnecting different parts of power system network for protection and control, there must be some special type of switching devices which can be operated safely under huge current carrying condition. During interruption of huge current, there would be large arcing in between switching contacts, so care should be taken to quench these arcs in safe manner. The circuit breaker is the special device which does all the required switching operations during current carrying condition. This was the basic introduction to circuit breaker.

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Working Principle of Circuit Breaker The circuit breaker mainly consists of fixed contacts and moving contacts. In normal "on" condition of circuit breaker, these two contacts are physically connected to each other due to applied mechanical pressure on the moving contacts. There is an arrangement stored potential energy in the operating mechanism of circuit breaker which is realized if switching signal given to the breaker. The potential energy can be stored in the circuit breaker by different ways like by deforming metal spring, by compressed air, or by hydrolic pressure. But whatever the source of potential energy, it must be released during operation. Release of potential energy makes sliding of the moving contact at extremely fast manner. All circuit breaker have operating coils (tripping coils and close coil), whenever these coils are energized by switching pulse, the plunger inside them displaced. This operating coil plunger is typically attached to the operating mechanism of circuit breaker, as a result the mechanically stored potential energy in the breaker mechanism is released in forms of kinetic energy, which makes the moving contact to move as these moving contacts mechanically attached through a gear lever arrangement with the operating mechanism. After a cycle of operation of circuit breaker the total stored energy is released and hence the potential energy again stored in the operating mechanism of circuit breaker by means of spring charging motor or air compressor or by any other means. Till now we have discussed about mechanical working principle of circuit breaker. But there are electrical characteristics of a circuit breaker which also should be considered in this discussion of operation of circuit breaker. What is arc? During opening of current carrying contacts in a circuit breaker the medium in between opening contacts become highly ionized through which the interrupting current gets low resistive path and continues to flow through this path even the contacts are physically separated. During the flowing of current from one contact to other the path becomes so heated that it glows. This is called arc Arc in Circuit Breaker Whenever, on load current contacts of circuit breaker open there is an arc in circuit breaker, established between the separating contacts. As long as this arc is sustained in between the contacts the current through the circuit breaker will not be interrupted finally as because arc is itself a conductive path of electricity.

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For total interruption of current the circuit breaker it is essential to quench the arc as quick as possible. The main designing criteria of a circuit breaker is to provide appropriate technology of arc quenching in circuit breaker to fulfill quick and safe current interruption. So before going through different arc quenching techniques employed in circuit breaker, we should try to understand "e; what is arc"e; and basic theory of arc in circuit breaker, let’s discuss. Thermal Ionization of gas There are numbers of free electrons and ions present in a gas at room temperature due to ultraviolet rays, cosmic rays and radioactivity of the earth. These free electrons and ions are so few in number that they are insufficient to sustain conduction of electricity. The gas molecules move randomly at room temperature. It is found an air molecule at a temperature of 300oK (Room temperature) moves randomly with an approximate average velocity of 500 meters/second and collides other molecules at a rate of 1010 times/second. These randomly moving molecules collide with each other in very frequent manner but the kinetic energy of the molecules is not sufficient to extract an electron from atoms of the molecules. If the temperature is increased the air will be heated up and consequently the velocity on the molecules increased. Higher velocity means higher impact during intermolecular collision. During this situation some of the molecules are disassociated in to atoms. If temperature of the air is further increased many atoms are deprived of valence electrons and make the gas ionized. Then this ionized gas can conduct electricity because of sufficient free electrons. This condition of any gas or air is called plasma. This phenomenon is called thermal ionization of gas. Oil Circuit Breaker Mineral oil has better insulating property than air. In oil circuit breaker the fixed contact and moving contact are immerged inside the insulating oil. Whenever there is a separation of current carrying contacts in the oil, the arc is initialized at the moment of separation of contacts, and due to this arc the oil is vaporized and decomposed in mostly hydrogen gas and ultimately creates a hydrogen bubble around the arc. This highly compressed gas bubble around the arc prevents re-striking of the arc after current reaches zero crossing of the cycle. The Oil Circuit Breaker is the one of the oldest type of circuit breakers.

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Operation of Oil Circuit Breaker The operation of oil circuit breaker is quite simple let’s have a discussion. When the current carrying contacts in the oil are separated an arc is established in between the separated contacts. Actually, when separation of contacts has just started, distance between the current contacts is small as a result the voltage gradient between contacts becomes high. This high voltage gradient between the contacts ionized the oil and consequently initiates arcing between the contacts. This arc will produce a large amount of heat in surrounding oil and vaporizes the oil and decomposes the oil in mostly hydrogen and a small amount of methane, ethylene and acetylene. The hydrogen gas cannot remain in molecular form and its is broken into its atomic form releasing lot of heat. The arc temperature may reach up to 5000oK. Due to this high temperature the gas is liberated surround the arc very rapidly and forms an excessively fast growing gas bubble around the arc. It is found that the mixture of gases occupies a volume about one thousand times that of the oil decomposed. From this figure we can assume how fast the gas bubble around the arc will grow in size. If this growing gas bubble around the arc is compressed by any means then rate of de – ionization process of ionized gaseous media in between the contacts will accelerate which rapidly increase the dielectric strength between the contacts and consequently the arc will be quenched at zero crossing of the current cycle. This is the basic operation of oil circuit breaker. In addition to that cooling effect of hydrogen gas surround the arc path also helps, the quick arc quenching in oil circuit breaker. Arc quenching in bulk oil circuit breaker

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AIR CIRCUIT BREAKER This type of circuit breakers, is those kind of circuit breaker which operates in air at atmospheric pressure. After development of oil breaker, the medium voltage air circuit breaker (ACB) is replaced completely by oil circuit breaker in different countries. But in countries like France and Italy, ACBs are still preferable choice up to voltage 15 KV. It is also good choice to avoid the risk of oil fire, in case of oil circuit breaker. In America ACBs were exclusively used for the system up to 15 KV until the development of new vacuum and SF6 circuit breakers. Working principle of Air Circuit Breaker

The working principle of this breaker is rather different from those in any other types of circuit breakers. The main aim of all kind of circuit breaker is to prevent the reestablishment of arcing after current zero by creating a situation where in the contact gap will withstand the system recovery voltage. The air circuit breaker does the same but in different manner. For interrupting arc it creates an arc voltage in excess of the supply voltage. Arc voltage is defined as the minimum voltage required maintaining the arc. This circuit breaker increases the arc voltage by mainly three different ways. It may increase the arc voltage by cooling the arc plasma. As the temperature of arc plasma is decreased, the mobility of the particle in arc plasma is reduced; hence more voltage gradient is required to maintain the arc. It may increase the arc voltage by lengthening the arc path. As the length of arc path is increased, the resistance of the path is increased, and hence to maintain the same arc current more voltage is required to be applied across the arc path. That means arc voltage is increased. Splitting up the arc into a number of series arcs also increases the arc voltage. Types of ACB There are mainly two types of ACB are available. 1) Plain air circuit breaker 2) Air blast Circuit Breaker. Operation of ACB The first objective is usually achieved by forcing the arc into contact with as large an area as possible of insulating material. Every air circuit breaker is fitted with a chamber surrounding the contact. This chamber is called 'arc chute'. The arc is driven into it. If inside of the arc chute is suitably shaped, and if the arc can be made conform to the shape, the arc chute wall will help to achieve cooling. This type of arc chute should be made from some kind of

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refractory material. High temperature plastics reinforced with glass fiber and ceramics are preferable materials for making arc chute. The second objective that is lengthening the arc path, is achieved concurrently with fist objective. If the inner walls of the arc chute is shaped in such a way that the arc is not only forced into close proximity with it but also driven into a serpentine channel projected on the arc chute wall. The lengthening of the arc path increases the arc resistance. The third technique is achieved by using metal arc slitter inside the arc chute. The main arc chute is divided into numbers of small compartments by using metallic separation plates. These metallic separation plates are actually the arc splitters and each of the small compartments behaves as individual mini arc chute. In this system the initial arc is split into a number of series arcs, each of which will have its won mini arc chute. So each of the split arcs has its won cooling and lengthening effect due to its won mini arc chute and hence individual split arc voltage becomes high. These collectively, make the over all arc voltage, much higher than the system voltage. This was working principle of air circuit breaker now we will discuss in details the operation of ACB in practice. The air circuit breaker, operated within the voltage level 1KV, does not require any arc control device. Mainly for heavy fault current on low voltages (low voltage level above 1 KV) ABCs with appropriate arc control device, are good choice. These breakers normally have two pairs of contacts. The main pair of contacts carries the current at normal load and these contacts are made of copper. The additional pair is the arcing contact and is made of carbon. When circuit breaker is being opened, the main contacts open first and during opening of main contacts the arcing contacts are still in touch with each other. As the current gets, a parallel low resistive path through the arcing contact during opening of main contacts, there will not be any arcing in the main contact. The arcing is only initiated when finally the arcing contacts are separated. The each of the arc contacts is fitted with an arc runner which helps, the arc discharge to move upward due to both thermal and electromagnetic effects as shown in the figure. As the arc is driven upward it enters in the arc chute, consisting of splitters. The arc in chute will become colder, lengthen and split hence arc voltage becomes much larger than system voltage at the time of operation of air circuit breaker, and therefore the arc is quenched finally during the current zero.

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Although this type of circuit breakers has become obsolete for medium voltage application, but they are still preferable choice for high current rating in low voltage application.

ACB

SF6 Circuit Breaker A circuit breaker in which the current carrying contacts operate in Sulphur Hexafluoride or SF6 gas is known as an SF6 Circuit Breaker. SF6 has excellent insulating property. SF6 has high electro-negativity. That means it has high affinity of absorbing free electron. Whenever a free electron collides with the SF6 gas molecule, it is absorbed by that gas molecule and forms a negative ion.

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These negative ions obviously much heavier than a free electron and therefore over all mobility of the charged particle in the SF6 gas is much less as compared other common gases. We know that mobility of charged particle is majorly responsible for conducting current through a gas.

Hence, for heavier and less mobile charged particles in SF6 gas, it acquires very high dielectric strength. Not only the gas has a good dielectric strength but also it has the unique property of fast recombination after the source energizing the spark is removed. The gas has also very good heat transfer property. Due to its low gaseous viscosity (because of less molecular mobility) SF6 gas can efficiently transfer heat by convection. So due to its high dielectric strength and high cooling effect SF6 gas is approximately 100 times more effective arc quenching media than air. Due to these unique properties of this gas SF6 Circuit Breaker is used in complete range of medium voltage and high voltage electrical power system. These circuit breakers are available for the voltage ranges from 33KV to 800KV and even more. Disadvantages of SF6 CB The SF6 gas is identified as a greenhouse gas, safety regulation are being introduced in many countries in order to prevent its release into atmosphere. Puffer type design of SF6 CB needs a high mechanical energy which is almost five times greater than that of oil circuit breaker.

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Types of SF6 Circuit Breaker There are mainly three types of SF6 CB depending upon the voltage level of application 1) Single Interrupter SF6 CB applied for up to 245KV(220KV) system 2) Two Interrupter SF6 CB applied for up to 420KV(400KV) system 3) Four Interrupter SF6 CB applied for up to 800KV(715KV) system Working of SF6 Circuit Breaker

The working of SF6 CB of first generation was quite simple it is some extent similar to air blast circuit breaker. Here SF6 gas was compressed and stored in a high pressure reservoir. During operation of SF6 circuit breaker this highly compressed gas is released through the arc and collected to relatively low pressure reservoir and then it pumped back to the high pressure reservoir for reutilize. The working of SF6 circuit breaker is little bit different in moder time. Innovation of puffer type design makes operation of SF6 CB much easier. In buffer type design, the arc energy is utilized to develop pressure in the arcing chamber for arc quenching.

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Here the breaker is filled with SF6 gas at rated pressure. There are two fixed contact fitted with a specific contact gap. A sliding cylinder bridges these to fixed contacts. The cylinder can axially slide upward and downward along the contacts. There is one stationary piston inside the cylinder which is fixed with other stationary parts of the SF6 circuit breaker, in such a way that it can not change its position during the movement of the cylinder. As the piston is fixed and cylinder is movable or sliding, the internal volume of the cylinder changes when the cylinder slides. During opening of the breaker the cylinder moves downwards against position of the fixed piston hence the volume inside the cylinder is reduced which produces compressed SF6 gas inside the cylinder. The cylinder has numbers of side vents which were blocked by upper fixed contact body during closed position. As the cylinder move further downwards, these vent openings cross the upper fixed contact, and become unblocked and then compressed SF6 gas inside the cylinder will come out through this vents in high speed towards the arc and passes through the axial hole of the both fixed contacts. The arc is quenched during this flow of SF6 gas. During closing of the SF6 circuit breaker, the sliding cylinder moves upwards and as the position of piston remains at fixed height, the volume of the cylinder increases which introduces low pressure inside the cylinder compared to the surrounding. Due to this pressure difference SF6 gas from surrounding will try to enter in the cylinder. The higher pressure gas will come through the axial hole of both fixed contact and enters into cylinder via vent and during this flow; the gas will quench the arc. VACUUM CIRCUIT BREAKER A vacuum circuit breaker is such kind of circuit breaker where the arc quenching takes place in vacuum. The technology is suitable for mainly medium voltage application. For higher voltage Vacuum technology has been developed but not commercially viable. The operation of opening and closing of current carrying contacts and associated arc interruption take place in a vacuum chamber in the breaker which is called vacuum interrupter. The vacuum interrupter consists of a steel arc chamber in the centre symmetrically arranged ceramic insulators. The vacuum pressure inside a vacuum interrupter is normally maintained at 10 - 6 bar. The material used for current carrying contacts plays an important role in the performance of the vacuum circuit breaker. CuCr is the most ideal material to make VCB contacts. Vacuum interrupter technology was first introduced in the year of 1960. But still it is a developing technology. As time goes on, the size of the vacuum interrupter is being reducing from its early 1960’s size due to different technical developments in this field of engineering. The contact

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geometry is also improving with time, from butt contact of early days it gradually changes to spiral shape, cup shape and axial magnetic field contact. The vacuum circuit breaker is today recognized as most reliable current interruption technology for medium voltage system. It requires minimum maintenance compared to other circuit breaker technologies. Advantages of vacuum circuit breaker or VCB Service life of Vacuum Circuit Breaker is much longer than other types of circuit breakers. There is no chance of fire hazard as oil circuit breaker. It is much environment friendly than SF6 Circuit breaker. Beside of that contraction of VCB is much user friendly. Replacement of Vacuum Interrupter (VI) is much convenient. Operation of Vacuum Circuit Breaker The main aim of any circuit breaker is to quench arc during current zero crossing, by establishing high dielectric strength in between the contacts so that reestablishment of arc after current zero becomes impossible. The dielectric strength of vacuum is eight times greater than that of air and four times greater than that of SF6 gas. This high dielectric strength makes it possible to quench a vacuum arc within very small contact gap. For short contact gap, low contact mass and no compression of medium the drive energy required in vacuum circuit breaker is minimum. When two face to face contact areas are just being separated to each other, they do not be separated instantly, contact area on the contact face is being reduced and ultimately comes to a point and then they are finally de-touched. Although this happens in a fraction of micro second but it is the fact. At this instant of de-touching of contacts in a vacuum, the current through the contacts concentrated on that last contact point on the contact surface and makes a hot spot. As it is vacuum, the metal on the contact surface is easily vaporized due to that hot spot and create a conducting media for arc path. Then the arc will be initiated and continued until the next current zero.

At current zero this vacuum arc is extinguished and the conducting metal vapor is re-condensed on the contact surface. At this point, the contacts are already separated hence there is no question of re-vaporization of contact surface, for next cycle of current. That means, the arc cannot be

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reestablished again. In this way vacuum circuit breaker prevents the reestablishment of arc by producing high dielectric strength in the contact gap after current zero. There are two types of arc shapes. For interrupting current up to 10kA, the arc remains diffused and the form of vapour discharge and cover the entire contact surface. Above 10kA the diffused arc is constricted considerably by its own magnetic field and it contracts. The phenomenon gives rise over heating of contact at its center. In order to prevent this, the design of the contacts should be such that the arc does not remain stationary but keeps travelling by its own magnetic field. Specially designed contact shape of vacuum circuit breaker make the constricted stationary arc travel along the surface of the contacts, thereby causing minimum and uniform contact erosion. MCB Nowadays we use more commonly Miniature Circuit Breaker or MCB in low voltage electrical network instead of fuse. The MCB has some advantages compared to fuse. 1) It automatically switches off the electrical circuit during abnormal condition of the network means in over load condition as well as faulty condition. The fuse does not sense but Miniature Circuit Breaker does it in more reliable way. MCB is much more sensitive to over current than fuse. 2) Another advantage is, as the switch operating knob comes at its off position during tripping, the faulty zone of the electrical circuit can easily be identified. But in case of fuse, fuse wire should be checked by opening fuse grip or cutout from fuse base, for confirming the blow of fuse wire. 3) Quick restoration of supply cannot be possible in case of fuse as because fuses have to be rewired or replaced for restoring the supply. But in the case of MCB, quick restoration is possible by just switching on operation. 4) Handling MCB is more electrically safe than fuse. Because of to many advantages of MCB over fuse units, in modern low voltage electrical network, Miniature Circuit Breaker is mostly used instead of backdated fuse unit. Only one disadvantage of MCB over fuse is that this system is more costlier than fuse unit system.

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Miniature Circuit Breaker

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Miniature Circuit Breaker Working Principle

There are two arrangement of operation of miniature circuit breaker. One due to thermal effect of over current and other due to electromagnetic effect of over current. The thermal operation of miniature circuit breaker is achieved with a bimetallic strip whenever continuous over current flows through MCB; the bimetallic strip is heated and deflects by bending. This deflection of bimetallic strip releases mechanical latch. As this mechanical latch is attached with operating mechanism, it causes to open the miniature circuit breaker contacts. But during short circuit condition, sudden rising of electric current, causes electromechanical displacement of plunger associated with tripping coil or solenoid of MCB. The plunger strikes the trip lever causing immediate release of latch mechanism consequently open the circuit breaker contacts. This was a simple explanation of miniature circuit breaker working principle.

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Molded Case Circuit Breaker. The main difference between the two is their capacity with the MCB rated under 100 amps with an interrupting rating of under 18,000 amps. Consequently, their trip characteristics may not be adjusted since they basically cater to low circuits. On the other hand, an MCCB comes with an adjustable trip characteristic for the higher models. Usually, this type of circuit breaker would provide amps as high as 2,500 or as low as 10 depending on what is necessary. Their interrupting rating can be around 10,000 amps to 200,000 amps. Judging from their power capacities, the MCB is mainly used for low-energy requirements like home wiring or small electronic circuits. On the other hand, the MCCB is more suited in providing energy for high-power equipment. Although an MCCB has a higher capacity than an MCB, both are classified under low voltage circuit breakers and should, therefore, respond to standards set by the IEC 947. For convenience’s sake, some MCCB units have electrical motor operators which means that they can be tripped using only a remote control. For industrial or commercial use, they may be utilized as standby power that runs on an automatic transfer switch. Both are installed in special niches on the wall that would make it easy to install or uninstall without interrupting the whole system or damaging the switchgear. Both are specially made to handle direct current and are usually laid out in tiers for space efficiency. Circuit breakers are usually reset after they have been “tripped.” Both MCB and MCCB are highly durable and could last for years depending on the manufacturer. When choosing between using an MCB and an MCCB, it is important to consider the amount of power that would be coursing through the device. As mentioned above, MCCB is more suited for higher energy because of its better capacity. Of course, when it comes to home use, the MCB is usually the circuit breaker of choice. For heavier power requirements that go beyond the 2,500 amps ceiling of the MCCB, medium or high-voltage circuit breakers would be the next best possible choices. Circuit breakers are installed in any structure that requires power for safety reasons. They are made to ensure that fire hazards or electrical problems would not occur in a home by cutting of electricity flow. This is usually done when the system experiences a “short circuit” or an “overload.”

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For this reason, an MCB or MCCB should both be installed by professionals. This would minimize the chance of problems throughout use. At the same time, choosing the right MCB or MCCB brand to install in a building is necessary as some brands are actually better than others. Ideally, the location of circuit breakers should provide easy access and known to all the individuals residing in a building.

Summary: 1) An MCB has less than 100 amps while an MCCB goes as high as 2,500 amps. 2) The interrupting rating for an MCB is 18,000 amps up to 200,000 amps for an MCCB. 3) MCBs are mostly installed for home use while an MCCB is generally utilized for commercial or industrial purposes. 4) Both are low-voltage circuit breakers created to respond to IEC 947 standards. 5) Some MCCB units are specially made to respond to remote control signals usually as standby power. 6) Circuit breakers are installed for safety reasons. 7) The location of circuit breakers in every structure should be known to the people who reside in it.

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MCCB

Working Principle of ELCB and RCB: 

An Earth Leakage Circuit Breaker (ELCB) is a device used to directly detect currents leaking to earth from an installation and cut the power and mainly used in TT earthing systems.



There are two types of ELCBs, 1) Voltage Earth Leakage Circuit Breaker (voltage-ELCB) 2) Current Earth Leakage Current Earth Leakage Circuit Breaker (Current-ELCB).



Voltage-ELCBs were first introduced about sixty years ago and CurrentELCB was first introduced about forty years ago. For many years, the voltage operated ELCB and the differential current operated ELCB were both referred to as ELCBs because it was a simpler name to remember. But the use of a common name for two different devices gave rise to considerable confusion in the electrical industry. If the wrong type was used on an installation, the level of protection given could be substantially less than that intended. To ignore this confusion, IEC decided to apply the term Residual Current Device (RCD) to differential current operated ELCBs. Residual current refers to any current over and above the load current.

Voltage Base ELCB. 

Voltage-ELCB is a voltage operated circuit breaker. The device will function when the Current passes through the ELCB. Voltage-ELCB contains relay Coil which it being connected to the metallic load body at one end and it is connected to ground wire at the other end.

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If the voltage of the Equipment body is rise (by touching Phase to metal Part or Failure of Insulation of Equipment) which could cause the difference between earth and load body voltage, the danger of electric shock will occur. This voltage difference will produce an electric current from the load metallic body passes the relay loop and to earth. When voltage on the equipment metallic body rose to the danger level which exceed to 50Volt, the flowing current through relay loop could move the relay contact by disconnecting the supply current to avoid from any danger electric shock.



The ELCB detects fault currents from live to the earth (ground) wire within the installation it protects. If sufficient voltage appears across the ELCB’s sense coil, it will switch off the power, and remain off until manually reset. A voltage-sensing ELCB does not sense fault currents from live to any other earthed body.



These ELCBs monitored the voltage on the earth wire, and disconnected the supply if the earth wire voltage was over 50 volts.



These devices are no longer used due to its drawbacks like if the fault is between live and a circuit earth, they will disconnect the supply. However, if the fault is between live and some other earth (such as a person or a metal water pipe), they will NOT disconnect, as the voltage on the circuit earth will not change. Even if the fault is between live and a circuit earth, parallel earth paths created via gas or water pipes can result in the ELCB being bypassed. Most of the fault current will flow via the gas or water pipes, since a single earth stake will inevitably have a much higher impedance than hundreds of meters of metal service pipes buried in the ground.

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The way to identify an ELCB is by looking for green or green and yellow earth wires entering the device. They rely on voltage returning to the trip via the earth wire during a fault and afford only limited protection to the installation and no personal protection at all. You should use plug in 30mA RCD’s for any appliances and extension leads that may be used outside as a minimum. Advantages



ELCBs have one advantage over RCDs: they are less sensitive to fault conditions, and therefore have fewer nuisance trips.



While voltage and current on the earth line is usually fault current from a live wire, this is not always the case, thus there are situations in which an ELCB can nuisance trip.



When an installation has two connections to earth, a nearby high current lightning strike will cause a voltage gradient in the soil, presenting the ELCB sense coil with enough voltage to cause it to trip.



If the installation’s earth rod is placed close to the earth rod of a neighboring building, a high earth leakage current in the other building can raise the local ground potential and cause a voltage difference across the two earths, again tripping the ELCB.



If there is an accumulated or burden of currents caused by items with lowered insulation resistance due to older equipment, or with heating elements, or rain conditions can cause the insulation resistance to lower due to moisture tracking. If there is a some mA who is equal to ELCB rating than ELCB may give nuisance Tripping.



If either of the earth wires become disconnected from the ELCB, it will no longer trip or the installation will often no longer be properly earthed.

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Some ELCBs do not respond to rectified fault current. This issue is common for ELCBs and RCDs, but ELCBs are on average much older than RCB so an old ELCB is more likely to have some uncommon fault current waveform that it will not respond to.



Voltage-operated ELCB are the requirement for a second connection, and the possibility that any additional connection to earth on the protected system can disable the detector.



Nuisance tripping especially during thunderstorms.

Disadvantages: 

They do not detect faults that don’t pass current through the CPC to the earth rod.



They do not allow a single building system to be easily split into multiple sections with independent fault protection, because earthing systems are usually use common earth Rod.



They may be tripped by external voltages from something connected to the earthing system such as metal pipes, a TN-S earth or a TN-C-S combined neutral and earth.



As electrically leaky appliances such as some water heaters, washing machines and cookers may cause the ELCB to trip.



ELCBs introduce additional resistance and an additional point of failure into the earthing system.

Can we assume whether Our Electrical System is protected against Earth Protection or not by only Pressing ELCB Test Switch? 

Checking the health of the ELCB is simple and you can do it easily by pressing TEST Push Button Switch of ELCB. The test push-button will test whether the ELCB unit is working properly or not. Can we assume that If ELCB is Trip after Pressing TEST Switch of ELCB than your system is protected against earth protection? Then you are wrong.



The test facility provided on the home ELCB will only confirm the health of the ELCB unit, but that test does not confirm that the ELCB will trip when an electric shock hazard does occur. It is a really sad fact that all the while this misunderstanding has left many homes totally unprotected from the risk of electric shocks.



This brings us or alarming us to think over second basic requirement for earth protection. The second requirement for the proper operation of a home shock protection system is electrical grounding.

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We can assume that the ELCB is the brain for the shock protection, and the grounding as the backbone. Therefore, without a functional grounding (Proper Earthing of Electrical System) there is totally no protection against electrical shocks in your house even if You have installed ELCB and its TEST switch show proper result. Looking after the ELCB alone is not enough. The electrical Earthing system must also be in good working order for the shock protection system to work. In addition to routine inspections that should be done by the qualified electrician, this grounding should preferably be inspected regularly at shorter intervals by the homeowner and need to pour Water in Earthing Pit at Regular interval of Time to minimize Earth Resistance.

Current-operated ELCB (RCB):  Current-operated ELCBs are generally known as Residual-current devices (RCD). These also protect against earth leakage. Both circuit conductors (supply and return) are run through a sensing coil; any imbalance of the currents means the magnetic field does not perfectly cancel. The device detects the imbalance and trips the contact. 

When the term ELCB is used it usually means a voltage-operated device. Similar devices that are current operated are called residual-current devices. However, some companies use the term ELCB to distinguish high sensitivity current operated 3 phase devices that trip in the milliamp range from traditional 3 phase ground fault devices that operate at much higher currents.

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Typical RCB circuit:



The supply coil, the neutral coil and the search coil all wound on a common transformer core.



On a healthy circuit the same current passes through the phase coil, the load and return back through the neutral coil. Both the phase and the neutral coils are wound in such a way that they will produce an opposing magnetic flux. With the same current passing through both coils, their magnetic effect will cancel out under a healthy circuit condition.



In a situation when there is fault or a leakage to earth in the load circuit, or anywhere between the load circuit and the output connection of the RCB circuit, the current returning through the neutral coil has been reduced. Then the magnetic flux inside the transformer core is not balanced anymore. The total sum of the opposing magnetic flux is no longer zero. This net remaining flux is what we call a residual flux.



The periodically changing residual flux inside the transformer core crosses path with the winding of the search coil. This action produces an electromotive force (e.m.f.) across the search coil. An electromotive force is actually an alternating voltage. The induced voltage across the search coil produces a current inside the wiring of the trip circuit. It is this current that operates the trip coil of the circuit breaker. Since the trip current is driven by the residual magnetic flux (the resulting flux, the net effect between both fluxes) between the phase and the neutral coils, it is called the residual current devise.



With a circuit breaker incorporated as part of the circuit, the assembled system is called residual current circuit breaker (RCCB) or residual current devise (RCD). The incoming current has to pass through the circuit breaker first before going to the phase coil. The return neutral

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path passes through the second circuit breaker pole. During tripping when a fault is detected, both the phase and neutral connection is isolated. 

RCD sensitivity is expressed as the rated residual operating current, noted I∆n. Preferred values have been defined by the IEC, thus making it possible to divide RCDs into three groups according to their I∆n value.



High sensitivity (HS): 6- 10- 30 mA (for direct-contact / life injury protection)



Standard IEC 60755 (General requirements for residual current operated protective devices) defines three types of RCD depending on the characteristics of the fault current.



Type AC: RCD for which tripping is ensured for residual sinusoidal alternating currents

Sensitivity of RCB:  

Medium sensitivity (MS): 100- 300- 500- 1000 mA (for fire protection) Low sensitivity (LS): 3- 10- 30 A (typically for protection of machine)

Type of RCB: Type A: RCD for which tripping is ensured  for residual sinusoidal alternating currents  for residual pulsating direct currents  For residual pulsating direct currents superimposed by a smooth direct current of 0.006 A, with or without phase-angle control, independent of the polarity. Type B: RCD for which tripping is ensured 

as for type A



for residual sinusoidal currents up to 1000 Hz



for residual sinusoidal currents superposed by a pure direct current



for pulsating direct currents superposed by a pure direct current



for residual currents which may result from rectifying circuits   

three pulse star connection or six pulse bridge connection two pulse bridge connection line-to-line with or without phase-angle monitoring, independently of the polarity There are two groups of devices:

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Break time of RCB: 1. G (general use) for instantaneous RCDs (i.e. without a time delay) • •

Minimum break time: immediate Maximum break time: 200 ms for 1x I∆n, 150 ms for 2x I∆n, and 40 ms for 5x I∆n

2. S (selective) or T (time delayed) for RCDs with a short time delay (typically used in circuits containing surge suppressors) • •

Minimum break time: 130 ms for 1x I∆n, 60 ms for 2x I∆n, and 50 ms for 5x I∆n Maximum break time: 500 ms for 1x I∆n, 200 ms for 2x I∆n, and 150 ms for 5x I∆n.

Instrument transformers Instrument transformers means current transformer & voltage transformer used in electrical power system for stepping down currents and voltages of the system for metering and protection purpose. Actually relays and meters used for protection and metering, are not designed for high currents and voltages. High currents or voltages of electrical power system can not be directly fed to relays and meters. CT steps down rated system current to 1 Amp or 5 Amp similarly voltage transformer steps down system voltages to 110V. The relays and meters are generally designed for 1 Amp, 5 Amp and 110V. Definition of current transformer (CT) A CT is an instrument transformer in which the secondary current is substantially proportional to primary current and differs in phase from it by ideally zero degree. CT Accuracy Class or Current Transformer Class A CT is similar to a electrical power transformer to some extent, but there are some difference in construction and operation principle. For metering and indication purpose, accuracy of ratio, between primary and secondary currents are essential within normal working range. Normally accuracy of current transformer required up to 125% of rated current; as because allowable system current must be below 125% of rated current. Rather it is desirable the CT core to be saturated after this limit since the unnecessary electrical stresses due to system over current can be prevented from the metering instrument connected to the secondary of the CT as secondary current does not go above a desired limit even primary current of the CT rises to a very high value than its ratings. So accuracy within working range

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is main criteria of a CT used for metering purpose. The degree of accuracy of a Metering CT is expressed by CT Accuracy Class or simply Current Transformer Class or CT Class.

But in the case of protection, the CT may not have the accuracy level as good as metering CT although it is desired not to be saturated during high fault current passes through primary. So core of protection CT is so designed that it would not be saturated for long range of currents. If saturation of the core comes at lower level of primary current the proper reflection of primary current will not come to secondary, hence relays connected to the secondary may not function properly and protection system losses its reliability. Suppose you have one CT with current ratio 400/1A and its protection core is situated at 500A. If the primary current of the CT becomes 1000A the secondary current will still be 1.25A as because the secondary current will not increase after 1.25A because of saturation. If actuating current of the relay connected the secondary circuit of the CT is 1.5A, it will not be operated at all even fault level of the power circuit is 1000A. The degree of accuracy of a Protection CT may not be as fine as Metering CT but it is also expressed by CT Accuracy Class or simply Current Transformer Class or CT Class as in the case of Metering Current Transformer but in little bit different manner.

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Theory of Current Transformer or CT A CT functions with the same basic working principle of electrical power transformer, as we discussed earlier, but here is some difference. If a electrical power transformer or other general purpose transformer, primary current varies with load or secondary current. In case of CT, primary current is the system current and this primary current or system current transforms to the CT secondary, hence secondary current or burden current depends upon primary current of the current transformer. In a power transformer, if load is disconnected, there will be only magnetizing current flows in the primary. The primary of the power transformer takes current from the source proportional to the load connected with secondary. But in case of CT, the primary is connected in series with power line. So current through its primary is nothing but the current flows through that power line. The primary current of the CT, hence does not depend upon whether the load or burden is connected to the secondary or not or what is the impedance value of burden. Generally CT has very few turns in primary where as secondary turns are large in number. Say Np is number of turns in CT primary and Ip is the current through primary. Hence the primary AT is equal to NpIp AT.

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If number of turns in secondary and secondary current in that current transformer are Ns and Is respectively then Secondary AT is equal to NsIs AT. In an ideal CT the primary AT is exactly is equal in magnitude to secondary AT. So from the above statement it is clear that if a CT has one turn in primary and 400 turns in secondary winding, if it has 400 A current in primary then it will have 1A in secondary burden. Thus the turn ratio of the CT is 400/1A. Error in Current Transformer or CT But in an actual CT, errors with which we are connected can best be considered through a study of phasor diagram for a CT,

Is - Secondary Current Es - Secondary induced emf Ip - primary Current Ep - primary induced emf KT - turns ratio = numbers of secondary turns/number of primary turns Io - Excitation Current Im - magnetizing component of Io Iw - core loss component of Io Φm - main flux. Let us take flux as reference. EMF Es and Ep lags behind the flux by 90o. The magnitude of the passers Es and Ep are proportional to secondary and primary turns. The excitation current Io which is made up of two

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components Im and Iw. The secondary current Io lags behind the secondary induced emf Es by an angle Φ s. The secondary current is now transferred to the primary side by reversing Is and multiplied by the turns ratio KT. The total current flows through the primary Ip is then vector sum of KT Is and Io. The Current Error or Ratio Error in Current Transformer or CT From above passer diagram it is clear that primary current Ip is not exactly equal to the secondary current multiplied by turn’s ratio, i.e. KTIs. This difference is due to the primary current is contributed by the core excitation current. The error in current transformer introduced due to this difference is called current error of CT or sometimes Ratio Error in Current Transformer.

Phase Error or Phase Angle Error in Current Transformer

For a ideal CT the angle between the primary and reversed secondary current vector is zero. But for an actual CT there is always a difference in phase between two due to the fact that primary current has to supply the component of the exiting current. The angle between the above two phases in termed as Phase Angle Error in Current Transformer or CT. Here in the pharos diagram it is β the phase angle error is usually expressed in minutes. Cause of error in current transformer The total primary current is not actually transformed in CT. One part of the primary current is consumed for core excitation and remaining is actually transformers with turns ratio of CT so there is error in current transformer

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means there are both Ratio Error in Current Transformer as well as a Phase Angle Error in Current Transformer. How to reduce error in current transformer It is desirable to reduce these errors, for better performance. For achieving minimum error in current transformer, one can follow the following, 1) Using a core of high permeability and low hysteresis loss magnetic materials. 2) Keeping the rated burden to the nearer value of the actual burden. 3) Ensuring minimum length of flux path and increasing cross – sectional area of the core, minimizing joint of the core. 4) Lowering the secondary internal impedance. Low Voltage Switchgear or LV Switchgear Generally electrical switchgear rated up to 1 KV is termed as low voltage switchgear. The term LV Switchgear includes low voltage circuit breakers, switches, off load electrical isolators, HRC fuses, earth leakage circuit breaker, miniature circuit breakers (MCB) and molded case circuit breakers (MCCB) etc i.e. all the accessories required to protect the LV system.

Low Voltage Switchgear The most common use of LV switchgear is in LV Distribution Board. This system has the following parts 1) Incomer The incomer feeds incoming electrical power to the incomer bus. The switch gear used in the incomer should have a main switching device. The switch gear devices attached with incomer should be capable of withstanding abnormal current for a short specific duration in order to allow downstream

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devices to operate. But it also be cable of interrupting maximum value of the fault current generated in the system. It must have interlocking arrangement with downstream devices. Generally Air Circuit Breakers are preferably used as interrupting device. Low voltage air circuit breaker is preferable for this purpose because of the following features i) Simplicity ii) Efficient performance iii) High normal current rating up to 600 A iv) High fault withstanding capacity upto 63 Ka Although Air Circuit Breakers have long tripping time, big size, high cost but still they are most suitable for low voltage switchgear for the above mentioned features. 2) Sub - Incomer Next downstream part of the LV Distribution board is sub - incomer. These sub - incomers draw power from main incomer bus and feed this power to feeder bus. The devices installed as parts of a sub - incomer should have the following features i) ii)

Ability to achieve economy without sacrificing protection and safety Need for relatively less number of inter - locking since it cover limited are of network.

ACBs and switch fuse units are generally used as sub - incomers along with molted case circuit breakers (MCCB). 3) Feeders Different feeders are connected to the feeder bus to feeds different loads like, motor loads, lighting loads, industrial machinery loads, air conditioner loads, transformer cooling system loads etc. All feeders are primarily protected by switch fuse unit and in addition to that, depending upon the types of load connected to the feeders, the different switchgear devices are chosen for different feeders. Let's discuss in details a) Motor feeder Motor feeder should be protected against over load, short circuit, over current up to locked rotor condition and single phasing. b) Industrial Machinery load feeder Feeder connected industrial machinery load like oven, electroplating bath etc are commonly protected by MCCBs and switch fuse units

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c) Lighting load feeder This is protected similar to industrial machinery load but additional earth leakage current protection is provided in this case to reduce any damage to life and property that could be caused by harmful leakages of electric current and fire. In LV switchgear system, electrical appliances are protected against short circuit and over load conditions by electrical fuses or electrical circuit breaker. However, the human operator is not adequately protected against the faults occurs inside the appliances. The problem can be overcome by using earth leakage circuit breaker. This operates on low leakage current. The earth leakage circuit breaker can detect leakage current as low as 100 mA and is capable of disconnecting the appliance in less than 100 msec.

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A typical diagram of low voltage switchgear is shown above. Here the main incomer comes from LV side of an electrical transformer. This incomer through an electrical isolator as well as an MCCB (not shown in the figure) feeds the incomer bus. Two sub-incomers are connected to the incomer bus these sub incomers are protected by means of either switch fuse unit or Air Circuit Breaker. These switches are so interlocked along with bus section switch or bus coupler that only one incomer switch can be put on if bus section switch is in on position and both sub incomer switches can be put on only if bus section switch is at off position. This arrangement is fruitful for preventing any mismatch of phase sequence between the subs incomers. The different load feeders are connected to any of the both sections of the feeder bus. Here motor feeder is protected by thermal overload device along with conventional switch fuse unit. Heater feeder is protected only by conventional switch fuse unit. The domestic lighting and AC loads are separately protected by miniature circuit breaker along with common conventional switch fuse unit. This is most basic and simple scheme for low voltage switchgear or LV distribution board. For star delta stater, the motor connection must have 6 cables from control panel and 6 terminals at induction (U1,U2,V1,V2,W1,W3). To wiring the motor connection for star delta starter, the important thing that we must fully understand is about the basic of STAR DELTA MAGIC TRIANGLE. For detail about star delta stater please read my last post about it. From this triangle diagram, we can determine the correct phase, cable termination for right terminal and the rotation. As we know, the star delta stater is so tricky if we not fully understand the concept and their method. This time i want share my technique when perform wiring task and connected to the star delta stater for induction motor. Don`t worry, it simple and easy if we understand the basic concepts. I explains detail step by step how to do it : D

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CHAPTER - 10 GENERATORS AND INVERTERS


DIESEL GENERATION
BATTERY
INVERTOR DIESEL GENERATOR A diesel generator is the combination of a diesel engine with an electric generator (often an alternator) to generate electrical energy. Diesel generating sets are used in places without connection to the power grid, as emergency power-supply if the grid fails, as well as for more complex applications such as peak-lopping, grid support and export to the power grid. Sizing of diesel generators is critical to avoid low-load or a shortage of power and is complicated by modern electronics, specifically non-linear loads. Diesel generator set The packaged combination of a diesel engine, a generator and various ancillary devices (such as base, canopy, sound attenuation, control systems, circuit breakers, jacket water heaters and starting system) is referred to as a "generating set" or a "genset" for short. Set sizes range from 8 to 30 kW (also 8 to 30 kVA single phase) for homes, small shops and offices with the larger industrial generators from 8 kW (11 kVA) up to 2,000 kW (2,500 kVA three phase) used for large office complexes, factories. A 2,000 kW set can be housed in a 40 ft (12 m) ISO container with fuel tank, controls, power distribution equipment and all other equipment needed to operate as a standalone power station or as a standby backup to grid power. These units, referred to as power modules are gen sets on large triple axel trailers weighing 85,000 pounds (38,555 kg) or more. A combination of these modules are used for small power stations and these may use from one to 20 units per power section and these sections can be combined to involve hundreds of power modules. In these larger sizes the power module (engine and generator) are brought to site on trailers separately and are connected together with large cables and a control cable to form a complete synchronized power plant. Diesel generators, sometimes as small as 200 kW (250 kVA) are widely used not only for emergency power, but also many have a secondary function of

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feeding power to utility grids either during peak periods, or periods when there is a shortage of large power generators. Ships often also employ diesel generators, sometimes not only to provide auxiliary power for lights, fans, winches etc., but also indirectly for main propulsion. With electric propulsion the generators can be placed in a convenient position, to allow more cargo to be carried. Electric drives for ships were developed prior to World War I. Electric drives were specified in many warships built during World War II because manufacturing capacity for large reduction gears was in short supply, compared to capacity for manufacture of electrical equipment.[1] Such a diesel-electric arrangement is also used in some very large land vehicles such as railroad locomotives.

Generator size Generating sets are selected based on the electrical load they are intended to supply, the electrical loads total characteristics kWe, kVA, var and harmonic content including starting currents (normally from motors) and non-linear loads. The expected duty, for example, emergency, prime or continuous power as well as environmental conditions such as altitude, temperature and emissions regulations must be taken into account as well. Most of the larger generator set manufacturers offer software that will perform the complicated sizing calculations by simply inputting site conditions and connected electrical load characteristics.

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BATTERY In modern era electrical energy is normally converted from mechanical energy, solar energy, and chemical energy etc. A battery is such a device which converts chemical energy to electrical energy. The first battery was developed by Alessandro Volta in the year of 1800. In the year 1836, John Frederic Daniell, a British chemist developed Daniell cell as an improved version of voltaic cell. From that time to till date battery is most popular source of electricity in many daily life applications. In our daily life we generally use two types of batteries one is which use and through type means it can be used once before it totally discharged. Another type of batteries is rechargeable that means it can be reused multiple time by recharging it externally. The former is called primary battery and latter is called secondary battery. The battery can be found in different sizes. A battery may be as small as a shirt button or may be such big in size that a total room is required to install a battery bank. For this variation of sizes the battery is used anywhere from small wrist watch to large ship.

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Battery Symbol We often see this symbol in many diagrams electrical and electronics network. This is the most popularly used symbol of battery. The bigger lines represent positive terminal of the cells and smaller lines represent negative terminal of the cells connected in the battery. We are often confused about the terms, battery cell and battery. We generally refer a battery as a single electrochemical cell. But literally battery does not mean that. Battery means a number of electrochemical cells connected together to meet up certain voltage and current level. Although there may single cell battery but literally battery and cell are different. History of Battery

Parthian Battery In the year of 1936 during middle of summer an ancient tomb was discovered during construction of a new railway line near Bagdad city in Iraq. The relics found in that tomb were about 2000 years old. Among these relics there were some clay jars or vessels which were sealed at the top with pitch. An iron rod, surrounded by a cylindrical tube made of wrapped copper sheet was projected from this sealed top. When these pots were filled with an acidic liquid, they produced a potential difference of around 2 volts between the iron and copper. These clay jars were suspected to be 2000 years old battery cells.

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Luigi Galvani experiment frog’s legs In 1786, Luigi Galvani, an Italian anatomist and physiologist, was surprised to see that when he touched a dead frog’s leg by two different metals the muscles of the legs contract. He could not understand the actual reason of that otherwise he would be known as the first inventor of battery cell. He thought the reaction might be due to a property of the tissues.

Voltaic Pile After that, Alessandro Volta realized that same phenomenon could be occurred by using cardboard soaked in salt water instead of frog's leg. He sandwiched a copper disc and a zinc disc with a piece of cardboard soaked in salt water in between them and found a potential difference between the copper and zinc. After that in 1800 he developed the first Voltaic Pile (battery) constructed of alternating copper and zinc discs with pieces of cardboard soaked in brine between them. This system could produce measurable electrical current. Alessandro Volta's voltaic pile was considered as first "wet battery cell" History of battery began.

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Daniell Cell The main problem of Voltaic pile was that it could not deliver current for long time. This problem was solved by a British inventor John F. Daniell in 1836, he invented more developed version of battery cell which is known as Daniell cell. Here in this cell one zinc rod is immersed in zinc sulfate in one container and one copper rod is immersed in copper (II) sulfate in another container. The solutions of these two containers are bridged by a U shaped salt bridge. A Daniell cell could produce 1.1 volt and this type of battery last much longer than Voltaic pile. In 1839, fuel cell was planned by Sir William Robert Grove, a discoverer and man of science. He mixed hydrogen and oxygen within an electrolyte solution, and created electricity and water. The fuel cell, did not deliver enough electricity but it is helpful. Bunsen (1842) and Grove (1839) created enhancements to batteries that used liquid electrodes to supply electricity.

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Lead Acid Battery In the year of 1859, Gaston Plante first developed lead acid battery cell. This was the first form rechargeable secondary battery. Lead acid battery is still in use for many industrial purposes. It is still most popularly used as car battery. In 1866 the battery was again developed by a French engineer, Georges Leclanche. It is a carbon-zinc wet cell battery which known as Leclanche cell. Crushed manganese dioxide mixed with a bit of carbon forms positive electrode and a zinc rod is used as negative electrode. Ammonium chloride solution is used as liquid electrolyte. After some years Georges Leclanche himself improved his own design by replacing liquid ammonium chloride solution by the ammonium chloride. This was the invention of first dry cell. In 1901 Thomas Alva Edison discovered the alkaline accumulator. Thomas Edison's basic cell had iron as the anode material (-) and nickel oxide as the cathode material (+). This was a portion of endless history of battery. Working principle of battery For understanding properly the basic principle of battery, we first should have some basic concept of electrolyte and electrons affinity. Actually when two dissimilar metals or metallic compounds are immersed in an electrolyte, there will be a potential difference produced between these metals or metallic compounds. It is found that when some specific compounds are added to water, they are dissolved and produce negative and positive ions. This type of compound is called electrolyte. The popular examples of electrolyte are almost all kind of salts, acids, and bases etc.

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The energy released during accepting an electron by a neutral atom is known as electron affinity. As the atomic structure for different materials are different, the electron affinity of different materials will differ. If two different kinds of metals or metallic compounds are immersed in same electrolyte solution, one of them will gain electrons and other will release electrons. Which metal (or metallic compound) will gain electrons and which will lose it depends upon the electron affinities of these metals or metallic compounds. The metal with low electron affinity will gain electrons from the negative ion of the electrolyte solution. On other hand metal with high electron affinity will release electrons and these electrons come out to the electrolyte solution and are being added to positive ions of the solution. In this way one of these metals or compound gains electrons and another one losses electrons. As a result there will be a difference in electron concentration between these two metals. This difference of electron concentration causes a potential difference developed between the metals. This potential difference or emf can be utilized as a source of voltage in any electronics or electrical circuits. This is what most general and basic principle of battery. All the battery cells are based on this only basic principle. Let’s discuss one by one. As we said earlier Alessandro Volta developed the first battery cell and this cell is popularly known as simple voltaic cell. This type of simple cell can be created very easily. Take one container and fill it with diluted sulfuric acid as electrolyte. Now immerse zinc and one copper rod in the solution and connect them externally by an electric load. Now your simple voltaic cell is completed. Current will start flowing through the external load. Zinc in dilute sulfuric acid give up electrons as below: Zn → Zn + + + 2e These Zn + + ions pass into electrolyte and their concentration is very high near the zinc electrode. As a result of the above oxidation reaction, zinc electrode is left negatively charged and hence it acts as cathode. The dilute sulfuric acid and water disassociate into hydronium ions as given below: H2SO4 + 2H2O → 2H3O+ + SO4 - Due to high concentration of Zn + + ions near the cathode, the H3O+ ions are repelled towards the copper electrode and get discharged by removing electrons from the copper atoms. The following reaction takes place at the anode: 2H3O+ + 2e - → 2H2O + H2

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As a result of the reduction reaction taking place at copper electrode, copper is left positively charged and hence it cats as anode. Denial Battery Cell: Denial cell consists of a copper vessel containing copper sulfate solution. The copper vessel itself acts as the positive electrode. A porous pot containing dilute sulfuric acid is placed in the copper vessel. An amalgamated zinc rod dipping inside the sulfuric acid acts as negative electrode. When the circuit is completed, dilute sulfuric acid in porous pot reacts with zinc so as to liberate hydrogen gas. The reaction takes place as below: Zn + H2SO4 → ZnSO4 + H2 The formation of ZnSO4 in porous pot does not affect the working of the cell, until crystals of ZnSO4 are deposited. The hydrogen gas passes through the porous pot and reacts with CuSO4 solution as below: H2 + CuSO4 → H2SO4 + Cu Copper so formed gets deposited on the copper vessel.

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INVERTER An inverter is an electric apparatus that changes direct current (DC) to alternating current (AC). It is not the same thing as an alternator, which converts mechanical energy (e.g. movement) into alternating current. Direct current is created by devices such as batteries and solar panels. When connected, an inverter allows these devices to provide electric power for small household devices. The inverter does this through a complex process of electrical adjustment. From this process, AC electric power is produced. This form of electricity can be used to power an electric light, a microwave oven, or some other electric machine. An inverter usually also increases the voltage. In order to increase the voltage, the current must be decreased, so an inverter will use a lot of current on the DC side when only a small amount is being used on the AC side. Inverters are made in many different sizes. They can be as small as 150 watts, or as large as 1 megawatt (1 million watts).

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CHAPTER - 11 MOTOR STARTER


STAR – DELTA CONNECTION
WORKING PRINCIPLE OF STAR – DELTA STARTER.
D O L STARTERS
WORKING OF D O L STARTERS STAR DELTA CONNECTION Star delta magic triangle

When we refer to this diagram, We can see correct terminal for the winding for each phase :*CAUTION: Please refer to the name plate of motor to confirm the winding numbering (U1,U2,V1,V2,W1,W2 ) and the motor connection of winding. Why it very important?? Because each manufacturing have their own style for numbering and winding motor connection. Star Delta phase and terminals RED PHASE : U1 and W2 YELLOW PHASE : U2 and V1 BLUE PHASE : V2 and W1 So from this formula, we must wiring the motor follow the phase color code. See my example below:-

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We can refer the complete wiring for star delta starter diagram below. If you want change their rotation for clock-wise or anti clock-wise, you need change two of phase (RED or BLUE) at delta contactor. I share the technique how to change rotation in my next post. If you want motor rotation for clock-wise, the phase colors are RED, YELLOW, and BLUE. But if you want anti clock-wise rotation, the phase colors are BLUE, YELLOW, and RED. For star delta control wiring diagram, please refer to my post about star delta diagram control.

This is a starting method that reduces the starting current and starting torque. Star delta starter design normally consists of three contactors, an overload relay and a timer for setting the time in the star-position (starting position).

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For the star delta starter, a motor must be in delta connected during a normal run and the main purpose is to be able to use star delta starter. Star delta starter received the starting current is about 30 % of the starting current during direct on line start and the starting torque is reduced to about 25 % of the torque available at a D.O.L start. Star delta starter only works when the application is light loaded during the start. If the motor is too heavily loaded, there will not be enough torque to accelerate the motor up to speed before switching over to the delta position. Description of Star Delta Starter Operation

For star delta starter, the basic function is to enable the motor to start and the motor windings are configured in a star formation to the supply voltage. The voltage applied for star delta starter to the individual motor winding is therefore reduced by a factor of 1√3 = 0.58 this connection amounts to approximately 30% of the delta values. The starting current is reduced to one third of the direct starting current.

Due to the reduced starting torque, the star-delta-connection is suitable for drives with a high inertia mass but a resistance torque which is low or only

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increases with increased speed. It is preferably used for applications where the drive is only put under a load after run-up. After motor run-up, in most cases an automatic timing relay controls the switch-over from star to delta. The run-up using star connection should last until the motor has reached the approximate operational speed. so that after switching to delta, as little post acceleration as possible is required. Post-acceleration in delta connection will instigate high currents as seen with direct on-line starting.

The duration of start in star connection depends on the motor load. During delta connection, the full mains voltage is applied to the motor windings. To enable a switch-over from star to delta, the six ends of the motor winding are connected onto terminals. The contactors of a star-delta starter switch over the windings accordingly. Working Principal of Star-Delta Starter: 

This is the reduced voltage starting method. Voltage reduction during star-delta starting is achieved by physically reconfiguring the motor windings as illustrated in the figure below. During starting the motor windings are connected in star configuration and this reduces the voltage across each winding 3. This also reduces the torque by a factor of three. After a period of time the winding are reconfigured as delta and the motor runs normally.

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Star/Delta starters are probably the most common reduced voltage starters. They are used in an attempt to reduce the start current applied to the motor during start as a means of reducing the disturbances and interference on the electrical supply.



Traditionally in many supply regions, there has been a requirement to fit a reduced voltage starter on all motors greater than 5HP (4KW). The Star/Delta (or Wye/Delta) starter is one of the lowest cost electromechanical reduced voltage starters that can be applied.



The Star/Delta starter is manufactured from three contactors, a timer and a thermal overload. The contactors are smaller than the single contactor used in a Direct on Line starter as they are controlling winding currents only. The currents through the winding are 1/root 3 (58%) of the current in the line.



There are two contactors that are close during run, often referred to as the main contractor and the delta contactor. These are AC3 rated at 58% of the current rating of the motor. The third contactor is the star contactor and that only carries star current while the motor is connected in star. The current in star is one third of the current in delta, so this contactor can be AC3 rated at one third (33%) of the motor rating.

Star-delta Starter Consists following units: 1) Contactors (Main, star and delta contactors) 3 No’s (For Open State Starter) or 4 No’s (Close Transient Starter). 2) Time relay (pull-in delayed) 1 No. 3) Three-pole thermal over current release 1No. 4) Fuse elements or automatic cut-outs for the main circuit 3 Nos. 5) Fuse element or automatic cut-out for the control circuit 1No. Power Circuit of Star Delta Starter: 

The main circuit breaker serves as the main power supply switch that supplies electricity to the power circuit.



The main contactor connects the reference source voltage R, Y, B to the primary terminal of the motor U1, V1, W1.



In operation, the Main Contactor (KM3) and the Star Contactor (KM1) are closed initially, and then after a period of time, the star contactor is opened, and then the delta contactor (KM2) is closed. The control of the contactors is by the timer (K1T) built into the starter. The Star and Delta

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are electrically interlocked and preferably mechanically interlocked as well. In effect, there are four states:



The star contactor serves to initially short the secondary terminal of the motor U2, V2, W2 for the start sequence during the initial run of the motor from standstill. This provides one third of DOL current to the motor, thus reducing the high inrush current inherent with large capacity motors at startup.



Controlling the interchanging star connection and delta connection of an AC induction motor is achieved by means of a star delta or wye delta control circuit. The control circuit consists of push button switches, auxiliary contacts and a timer.

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Control Circuit of Star--Delta Starter (Open Transition):



The ON push button starts the circuit by initially energizing Star Contactor Coil (KM1) of star circuit and Timer Coil (KT) circuit.



When Star Contactor Coil (KM1) energized, Star Main and Auxiliary contactor change its position from NO to NC.



When Star Auxiliary Contactor (1) (which is placed on Main Contactor coil circuit )became NO to NC it’s complete The Circuit of Main contactor Coil (KM3) so Main Contactor Coil energized and Main Contactor’s Main and Auxiliary Contactor Change its Position from NO To NC. This sequence happens in a friction of time.



After pushing the ON push button switch, the auxiliary contact of the main contactor coil (2) which is connected in parallel across the ON push button will become NO to NC, thereby providing a latch to hold the main

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contactor coil activated which eventually maintains the control circuit active even after releasing the ON push button switch. 

When Star Main Contactor (KM1) close its connect Motor connects on STAR and it’s connected in STAR until Time Delay Auxiliary contact KT (3) become NC to NO.



Once the time delay is reached its specified Time, the timer’s auxiliary contacts (KT)(3) in Star Coil circuit will change its position from NC to NO and at the Same Time Auxiliary contactor (KT) in Delta Coil Circuit(4) change its Position from NO To NC so Delta coil energized and Delta Main Contactor becomes NO To NC. Now Motor terminal connection change from star to delta connection.



A normally close auxiliary contact from both star and delta contactors (5&6)are also placed opposite of both star and delta contactor coils, these interlock contacts serves as safety switches to prevent simultaneous activation of both star and delta contactor coils, so that one cannot be activated without the other deactivated first. Thus, the delta contactor coil cannot be active when the star contactor coil is active, and similarly, the star contactor coil cannot also be active while the delta contactor coil is active.



The control circuit above also provides two interrupting contacts to shutdown the motor. The OFF push button switch break the control circuit and the motor when necessary. The thermal overload contact is a protective device which automatically opens the STOP Control circuit in case when motor overload current is detected by the thermal overload relay, this is to prevent burning of the motor in case of excessive load beyond the rated capacity of the motor is detected by the thermal overload relay.



At some point during starting it is necessary to change from a star connected winding to a delta connected winding. Power and control circuits can be arranged to this in one of two ways – open transition or closed transition.

What is Open or Closed Transition Starting (1) Open Transition Starters. •

Discuss mention above is called open transition switching because there is an open state between the star state and the delta state.

•

In open transition the power is disconnected from the motor while the winding are reconfigured via external switching.

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•

When a motor is driven by the supply, either at full speed or at part speed, there is a rotating magnetic field in the stator. This field is rotating at line frequency. The flux from the stator field induces a current in the rotor and this in turn results in a rotor magnetic field.



When the motor is disconnected from the supply (open transition) there is a spinning rotor within the stator and the rotor has a magnetic field. Due to the low impedance of the rotor circuit, the time constant is quite long and the action of the spinning rotor field within the stator is that of a generator which generates voltage at a frequency determined by the speed of the rotor. When the motor is reconnected to the supply, it is reclosing onto an unsynchronized generator and this result in a very high current and torque transient. The magnitude of the transient is dependent on the phase relationship between the generated voltage and the line voltage at the point of closure can be much higher than DOL current and torque and can result in electrical and mechanical damage.



Open transition starting is the easiest to implement in terms or cost and circuitry and if the timing of the changeover is good, this method can work well. In practice though it is difficult to set the necessary timing to operate correctly and disconnection/reconnection of the supply can cause significant voltage/current transients.

In Open transition there are Four states: 1. OFF State: All Contactors are open. 2. Star State: The Main [KM3] and the Star [KM1] contactors are closed and the delta [KM2] contactor is open. The motor is connected in star and will produce one third of DOL torque at one third of DOL current. 3. Open State: This type of operation is called open transition switching because there is an open state between the star state and the delta state. The Main contractor is closed and the Delta and Star contactors are open. There is voltage on one end of the motor windings, but the other end is open so no current can flow. The motor has a spinning rotor and behaves like a generator. 4. Delta State: The Main and the Delta contactors are closed. The Star contactor is open. The motor is connected to full line voltage and full power and torque are available.

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(2) •

•

•

Closed Transition Star/Delta Starter. There is a technique to reduce the magnitude of the switching transients. This requires the use of a fourth contactor and a set of three resistors. The resistors must be sized such that considerable current is able to flow in the motor windings while they are in circuit. The auxiliary contactor and resistors are connected across the delta contactor. In operation, just before the star contactor opens, the auxiliary contactor closes resulting in current flow via the resistors into the star connection. Once the star contactor opens, current is able to flow round through the motor windings to the supply via the resistors. These resistors are then shorted by the delta contactor. If the resistance of the resistors is too high, they will not swamp the voltage generated by the motor and will serve no purpose. In closed transition the power is maintained to the motor at all time. This is achieved by introducing resistors to take up the current flow during the winding changeover. A fourth contractor is required to place the resistor in circuit before opening the star contactor and then removing the resistors once the delta contactor is closed. These resistors need to be sized to carry the motor current. In addition to requiring more switching devices, the control circuit is more complicated due to the need to carry out resistor switching

In Close transition there are Four states: 1. OFF State. All Contactors are open 2. Star State. The Main [KM3] and the Star [KM1] contactors are closed and the delta [KM2] contactor is open. The motor is connected in star and will produce one third of DOL torque at one third of DOL current. 3. Star Transition State. The motor is connected in star and the resistors are connected across the delta contactor via the aux [KM4] contactor. 4. Closed Transition State. The Main [KM3] contactor is closed and the Delta [KM2] and Star [KM1] contactors are open. Current flows through the motor windings and the transition resistors via KM4. 5. Delta State. The Main and the Delta contactors are closed. The transition resistors are shorted out. The Star contactor is open. The motor is connected to full line voltage and full power and torque.

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Wiring Diagram of DOL Starter:

Working of DOL Starter: 

The main heart of DOL starter is Relay Coil. Normally it gets one phase constant from incoming supply Voltage (A1).when Coil gets second Phase relay coil energizes and Magnet of Contactor produce electromagnetic field and due to this Plunger of Contactor will move and Main Contactor of starter will closed and Auxiliary will change its position NO become NC and NC become (shown Red Line in Diagram) .

Pushing Start Button: 

When We Push the start Button Relay Coil will get second phase from Supply Phase-Main contactor(5)-Auxiliary Contact(53)-Start button-Stop

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button-96-95-To Relay Coil (A2).Now Coil energizes and Magnetic field produce by Magnet and Plunger of Contactor move. Main Contactor closes and Motor gets supply at the same time Auxiliary contact become (53-54) from NO to NC . 

Release Start Button:



Relay coil gets supply even though we release Start button. When We release Start Push Button Relay Coil gets Supply phase from Main contactor (5)-Auxiliary contactor (53) – Auxiliary contactor (54)-Stop Button-96-95-Relay coil (shown Red / Blue Lines in Diagram).



In Overload Condition of Mo

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CHAPTER - 12 CABLES AND BUS BAR
CABLES
XLPE CABLE
PVC CABLE
PILC CABLE
CABLE GLANDS
BUS BAR CABLES A cable is two or more wires running side by side and bonded, twisted, or braided together to form a single assembly. The term originally referred to a nautical line of specific length where multiple ropes, each laid clockwise, are then laid together anti-clockwise and shackled to produce a strong thick line, resistant to water absorption, that was used to anchor large ships. In mechanics, cables, otherwise known as wire ropes, are used for lifting, hauling, and towing or conveying force through tension. In electrical engineering cables are used to carry electric currents. An optical cable contains one or more optical fibers in a protective jacket that supports the fibers. Electrical wiring in general refers to insulated conductors used to carry electricity, and associated devices. This article describes general aspects of electrical wiring as used to provide power in buildings and structures, commonly referred to as building wiring. This article is intended to describe common features of electrical wiring that may apply worldwide. For information regarding specific national electrical codes, refer to the articles mentioned in the next section. Separate articles cover long-distance electric power transmission and electric power distribution.

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Electrical cables [edit]

Electrical cable cross section Electrical cable is an assembly consisting of one or more conductors with their own insulations and optional screens, individual covering(s), assembly protection and protective covering(s). Electrical cables may be made more flexible by stranding the wires. wires. In this process, smaller individual wires are twisted or braided together to produce larger wires that are more flexible than solid wires of similar size. Bunching small wires before concentric stranding adds the most flexibility. Copper wires in a cable may be bare, or they may be plated with a thin layer of another metal, most often tin but sometimes gold, silver or some other material. Tin, gold, and silver are much less prone to oxidation than copper, which may lengthen wire life, and makes soldering easier. Tinning is also used to provide lubrication between strands. Tinning was used to help removal of rubber insulation. insulation. Tight lays during stranding makes the cable extensible (CBA – as in telephone handset cords). Cables can be securely fastened and organized, such as by using trunking, cable trays, cable ties or cable lacing. Continuous-flex or flexible cables used in moving applications within cable carriers can be secured using strain relief devices or cable ties. At high frequencies, current tends to run along the surface surface of the conductor. This is known as the skin effect. effect Cables and electromagnetic fields

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Coaxial cable.

Twisted pair cabling Any current-carrying carrying conductor, including a cable, radiates an electromagnetic field. Likewise, any conductor or cable will pick up energy from any existing electromagnetic field around it. These effects are often undesirable, in the first case amounting to unwanted transmission of energy which may adversely affect nearby equipment or other other parts of the same piece of equipment; and in the second case, unwanted pickup of noise which may mask the desired signal being carried by the cable, or, if the cable is carrying power supply or control voltages, pollute them to such an extent as to cause equipment malfunction. The first solution to these problems is to keep cable lengths in buildings build short, since pick up and transmission are essentially proportional to the length of the cable. The second solution is to route cables away from trouble. Beyond this, there are particular cable designs that minimize electromagnetic pickup and transmission. transmission. Three of the principal design techniques are shielding, shielding coaxial geometry, and twisted-pair geometry. Shielding makes use of the electrical principle of the Faraday cage. cage The cable is encased for its entire length in foil or wire mesh. All wires running inside this shielding layer will be to a large extent decoupled from external electric fields, particularly if the shield is connected to a point of constant voltage, such as earth. Simple Simple shielding of this type is not greatly effective against low-frequency frequency magnetic fields, however - such as magnetic "hum" from a nearby power transformer. transformer. A grounded shield on cables operating at 2.5 kV or more gathers leakage current and capacitive current, protecting people from electric shock and equalizing stress on the cable insulation. Coaxial design helps to further reduce low-frequency low frequency magnetic transmission and pickup. In this design the foil or mesh shield has a circular cross section and the inner conductor is exactly at its center. This causes the voltages induced by a magnetic field between the shield and the core conductor to consist of two nearly equal magnitudes which cancel can each other. A twisted pair has two wires of a cable twisted around each other. This can be demonstrated by putting one end of a pair of wires in a hand drill and turning while maintaining moderate tension on the line. Where the interfering signal has a wavelength that is long compared to the pitch of the twisted pair, alternate lengths of wires develop opposing voltages, tending to cancel the effect of the interference.

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Fire protection [edit] In building construction, electrical cable jacket material is a potential source of fuel for fires. To limit the spread of fire along cable jacketing, one may use cable coating materials or one may use cables with jacketing that is inherently fire retardant. The plastic covering on some metal clad cables may be stripped off at installation to reduce the fuel source for fires. Inorganic coatings and boxes around cables safeguard the adjacent areas from the fire threat associated with unprotected cable jacketing. However, this fire protection also traps heat generated from conductor losses, so the protection must be thin. There are two methods of providing fire protection to a cable: 1. Insulation material is deliberately added with fire retardant materials 2. The copper conductor itself is covered with mineral insulation (MICC cables) Earthed System: 

Earlier the generators and transformers were of small capacities and hence the fault current was less. The star point was solidly grounded. This is called earthed system.



In Three phases earthed system, phase to earth voltage is 1.732 times less than phase to phase voltage. Therefore voltage stress on cable to armor is 1.732 times less than voltage stress between conductors to conductor.



Where in unearthed system, (if system neutral is not grounded) phase to ground voltage can be equal to phase to phase voltage. In such case the insulation level of conductor to armor should be equal to insulation level of conductor to conductor.



In an earthed cable, the three phase of cable are earthed to a ground. Each of the phases of system is grounded to earth. Examples: 1.9/3.3 KV, 3.8/6.6 KV system

Unearthed System: 

Today generators of 500MVA capacities are used and therefore the fault level has increased. In case of an earth fault, heavy current flows into the fault and this lead to damage of generators and transformers. To reduce the fault current, the star point is connected to earth through a resistance. If an earth fault occurs on one phase, the voltage of the faulty

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phase with respect to earth appears across the resistance. Therefore, the voltage of the other two healthy phases with respect to earth rises by 1.7 times. If the insulation of these phases is not designed for these increased voltages, they may develop earth fault. This is called unearthed system. 

In an unearth system, the phases are not grounded to earth .As a result of which there are chances of getting shock by personnel who are operating it. Examples : 6.6/6.6 KV, 3.3/3.3 KV system.



Unearthed cable has more insulation strength as compared to earthed cable. When fault occur phase to ground voltage is √3 time the normal phase to ground voltage. So if we used earthed cable in unearthed System, It may be chances of insulation puncture. So unearthed cable are used. Such type of cable is used in 6.6 KV systems where resistance type earthing is used.

3.5 CORE XLPE CABLE

SINGLE CORE XLPE CABLE

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3 CORE XLPE CABLE

3 CORE XLPE CABLE

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INTERNAL PARTS OF XLPE

4 CORE XLPE CABLE

XLPE Cross-linked polyethylene, commonly abbreviated PEX or XLPE, is a form of polyethylene with cross-links. It is formed into tubing, and is used predominantly in building services pipe work systems, hydronic radiant heating and cooling systems, domestic water piping, and insulation for high tension (high voltage) electrical cables. It is also used for natural gas and offshore oil applications, chemical transportation, and transportation of sewage and slurries.

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In the 21st century, PEX has become a viable alternative to polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC) or copper tubing for use as residential water pipes. PEX tubing ranges in size from imperial sizes of 1/4-inch to 4-inch, but 1/2-inch, 3/4-inch, and 1-inch are by far the most widely used.[1] Metric PEX is normally available in 16 mm, 20 mm, 25 mm, 32 mm, 40 mm, 50 mm and 63 mm sizes. Properties Almost all PEX is made from high density polyethylene (HDPE). PEX contains cross-linked bonds in the polymer structure, changing the thermoplastic to athermoset. Cross-linking is accomplished during or after the extrusion of the tubing. The required degree of cross-linking, according to ASTM Standard F 876-93, is between 65 and 89%. A higher degree of cross-linking could result in brittleness and stress cracking of the material. The high-temperature properties of the polymer are improved. Adequate strength to 120–150 °C is maintained by reducing the tendency to flow. Chemical resistance is enhanced by resisting dissolution. Low temperature properties are improved. Impact and tensile strength, scratch resistance, and resistance to brittle fracture are enhanced. PEX- or XLPE-insulated cables have a rated maximum conductor temperature of 90 °C and an emergency rating up to 140 °C, depending on the standard used. They have a conductor short-circuit rating of 250 °C. XLPE has excellent dielectric properties, making it useful for medium voltage - 10 to 50 kV AC, and high voltage cables - up to 380 kV AC-voltage, and several hundred kV DC. Numerous modifications in the basic polymer structure can be made to maximize productivity during the manufacturing process. For medium voltage applications, reactivity can be boosted significantly. This results in higher line speeds in cases where limitations in either the curing or cooling processes within the continuous vulcanization (CV) tubes used to cross-link the insulation. PEX insulations can be modified to limit the amount of byproduct gases generated during the cross-linking process. This is particularly useful for high voltage cable and extra-high voltage cable applications, where degassing requirements can significantly lengthen cable manufacturing time. Benefits Benefits of using PEX in plumbing include: •

Flexibility. PEX has become a contender for use in residential water plumbing because of its flexibility.[7] It can bend into a wide-radius turn if space permits, or accommodate turns by using elbow joints. In

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addition, it can handle short-radius turns, sometimes supported with a metal brace; in contrast, PVC, CPVC and copper all require elbow joints. A single length of PEX pipe cannot handle a sharp 90-degree turn, however, so in those situations, it is necessary to connect two PEX pipes with a 90-degree PEX elbow joint. •

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Direct routing of pipes. PEX can run straight from a distribution point to an outlet fixture without cutting or splicing the pipe. This reduces the need for potentially weak and costly joints and reduces the drop in pressure due to turbulence induced at transitions. Since PEX is flexible, it is often possible to install a supply line directly from the water source to an appliance using just one connection at each end.[2] Greater water pressure at fixtures. Since PEX pipes typically have fewer sharp turns, there is greater water pressure at the sinks and showers and toilets where it is needed. Less materials cost. Cost of materials is approximately 25% of alternatives. One account suggested that the price of copper had quadrupled from 2002 to 2006. Easier installation. Installing PEX is much less labor intensive than copper pipes, since there is no need to use torches to solder pipes together, or to use glue to attach pipes to fittings.[8] One home inspector wrote that "Once you've worked with PEX, you'll never go back to that other stinky glue stuff."[10] Builders putting in radiant heating systems found that PEX pipes "made installation easy and operation problemfree". PEX connections can be made by pushing together two matching parts using a compression fitting, or by using an adjustable wrench or a special crimping tool Generally, fewer connections and fittings are needed in a PEX installation. Reliable. It neither corrodes nor develops so-called "pinhole" leaks. No fire risk during installation. Copper piping required soldering using torches, and there was a risk of flame and heat causing a fire; but with PEX there is virtually no danger from fire. However, there was an unfortunate counter-incident in 2011 in which authorities suspect that six firefighters were injured when a fire melted the plastic PEX pipes, causing water to soak into ceiling insulation, adding greater weight, which caused the ceiling to collapse; but the PEX tubing was not blamed as the cause of the fire. [11] Overall PEX piping is much safer to install.

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•

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Acceptance by plumbers. There are routinely advertisements for plumbers specifically seeking ones with PEX experience. Ability to merge new PEX with existing copper and PVC systems. Manufacturers make fittings allowing installers to join a copper pipe on one end with a PEX line at the other,[2] as well as have options to reduce or expand the diameter of the pipes. Longevity. The advantageous properties of PEX also make it a candidate for progressive replacement of metal and thermoplastic pipes, especially in long-life applications, because the expected lifetime of PEX pipes reaches 50 years. However, the longest warranty offered by any PEX producer is 25 years. Suitable for hot and cold pipes. A convenient arrangement is to use color-coding to lessen the possibility of confusion.[10] Typically, red PEX tubing is used for hot water while blue PEX tubing is used for cold water.[3] Less likely to burst from freezing. The general position is that PEX plastic materials are slower to burst than copper or PVC pipes, but that they will burst eventually since freezing causes water to expand.[12] One account suggested that PEX water-filled pipes, frozen over time, will swell and tear; in contrast, copper pipe "rips" and PVC "shatters".[13] Home expert Steve Maxwell suggested in 2007 that PEX water-filled pipes could endure "five or six freeze-thaw cycles without splitting" while copper would split apart promptly on the first freeze.[14] In new unheated seasonal homes, it is still recommended to drain pipes during an unheated cold season or take other measures to prevent pipes from bursting because of the cold. In new construction, it is recommended that all water pipes be sloped slightly to permit drainage, if necessary.[14] No corrosion. Copper and iron pipes can experience corrosion leaks but PEX does not have these problems. Environmental benefits. One account suggested that PEX used in radiant heating was better for the environment than a copper choice, although it noted that the pipes were based on petroleum products. Pipe insulation possible. Conventional foam wrap insulation materials can be added to PEX piping to keep hot water hot, and cold water cold, and prevent freezing, if necessary.[15]

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Drawbacks •

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Degradation from sunlight. PEX tubing cannot be used in applications exposed to sunlight, as it degrades fairly rapidly.[16] Prior to installation it must be stored away from sunlight, and needs to be shielded from daylight after installation. Leaving it exposed to direct sunlight for as little as 30 days may result in premature failure of the tubing due to embrittlement. Perforation by insects. PEX tubing is vulnerable to being perforated by the mouthparts of plant-feeding insects; in particular, the Western conifer seed bug (Leptoglossus occidental is) is known to sometimes pierce through PEX tubing, resulting in leakage. Problems with yellow brass fittings. There have been some claimed PEX systems failures in the U.S., Canada and Europe resulting in several pending class action lawsuits. The failures are claimed to be a result of the brass fittings used in the PEX system. Generally, builders and manufacturers have learned from these experiences and have found the best materials for use in fittings used to connect pipe with connectors, valves and other fittings. But there were problems reported with a specific type of brass fitting used in connection with installations in Nevada that caused a negative interaction between its mineralrich hard water[18] and so-called "yellow brass" fittings.[6] Zinc in the fittings leached into the pipe material in a chemical reaction known as dezincification, causing some leaks or blockages.[18] A solution was to replace the yellow brass fittings, which had 30% zinc, with red brass fittings, which had 5% to 10% zinc. It led California building authorities to insist on fittings made from "red brass" which typically has a lower zinc content, and is unlikely to cause problems in the future since problems with these specific fittings have become known. Initial adjustment to a new plumbing system. There were a few reported problems in the early stages as plumbers and homeowners learned to adjust to the new fittings, and when connections were poorly or improperly made, but home inspectors have generally not noticed any problems with PEX since 2000.[19] Can't use adhesives for pipe insulation. One source suggested that pipe insulation, applied to PEX using certain adhesives, could have a detrimental effect causing the pipe to age prematurely; however, other insulating materials can be used, such as conventional foam wrap insulation, without negative effects.

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•

Fittings somewhat more expensive. Generally, PEX fittings, particularly the do-it-yourself compression ones, are more expensive than copper ones, although there is no soldering required.[2] Due to the flexibility of PEX, it generally requires fewer fittings, which tends to offset the higher cost per fitting. Potential problems for PEX radiant heating with iron-based components. If PEX tubing is used in a radiant heating system that has ferrous radiators or other parts, meaning they are made out of iron or its alloys, then there is the possibility of rust developing over time; if this is the case, then one solution is to have an "oxygen barrier" in these systems to prevent rust from developing. However, in new installations PEX pipes and iron-based components are not intermixed.

Possible health effects. There was controversy in California during the 2000s about health concerns. Several groups blocked adoption of PEX for concerns about chemicals getting into the water, either from chemicals outside the pipes, or from chemicals inside the pipes such as methyl tertiary butyl ether and tertiary butyl alcohol. These concerns delayed statewide adoption of PEX for almost a decade. After substantial "back-and-forth legal wrangling", which was described as a "judicial rollercoaster", the disputing groups came to a consensus, and California permitted use of PEX in all occupancies. An environmental impact report and subsequent studies determined there were no causes for concerns about public health from use of PEX piping. PVC •

Poly (vinyl chloride), commonly abbreviated PVC, is the third-most widely produced plastic, after polyethylene and polypropylene. PVC is used in construction because it is more effective than traditional materials such as copper, iron or wood in pipe and profile applications. It can be made softer and more flexible by the addition of plasticizers, the most widely used being phthalates. In this form, it is also used in clothing and upholstery, electrical cable insulation, inflatable products and many applications in which it replaces rubber.[5 Mechanical properties PVC has high hardness and mechanical properties. The mechanical properties enhance with the molecular weight increasing, but decrease with the temperature increasing. The mechanical properties of rigid PVC (uPVC) is very good, the elastic modulus can reach to 1500-3,000 MPa. The soft PVC (Flexible PVC) elastic is 1.5-15 MPa. However, elongation at break is up

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to 200% -450%. PVC friction is ordinary, the static friction factor is 0.4-0.5, the dynamic friction factor is 0.23.[17] Thermal properties The heat stability of PVC is very poor, when the temperature reaches 140 °C PVC starts to decompose. Its melting temperature is 160 °C. The linear expansion coefficient of the PVC is small and has flame retardancy, the oxidation index is up to 45 or more. Therefore, the addition of a heat stabilizer during the process is necessary in order to ensure the product's properties. Electrical properties PVC is a polymer with good insulation properties but because of its higher polar nature the electrical insulating property is inferior to non polar polymers such as polyethylene and polypropylene. As the dielectric constant, dielectric loss tangent value and volume resistivity are high; the corona resistance is not very good; it is generally suitable for medium or low voltage and low frequency insulation materials. Electric cables PVC is commonly used as the insulation on electrical cables; PVC used for this purpose needs to be plasticized. In a fire, PVC-coated wires can form hydrogen chloride fumes; the chlorine serves to scavenge free radicals and is the source of the material's fire retardance. While HCl fumes can also pose a health hazard in their own right, HCl dissolves in moisture and breaks down onto surfaces, particularly in areas where the air is cool enough to breathe, and is not available for inhalation.[23] Frequently in applications where smoke is a major hazard (notably in tunnels and communal areas) PVC-free cable insulation is preferred, such as low smoke zero halogen (LSZH) insulation. Any metal parts must not be mixed together during the raw material stage, as it may lead to EMI

PVC CABLE

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PILC CABLE

PILC CABLE

Cable Glands 

A device designed to permit the entry of cable in to electrical equipment which provide sealing, retention and earthing, bonding, grounding, insulation, strain relief or combination of all these.



Gland should maintain overall integrity of enclosure in to which it is to be fitted.

Gland Selection 

Gland should be selected on following Points 1. 2. 3. 4. 5.

Type of Cable Gland Size Entry Type/Thread Specification of application Ingress Protection required. Material

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Type of Cable: 

Unarmored: Unarmored Cable will require outer seal within Gland to not only Provide ingress protection but also degree of retention.



Armored: Gland that required clamping mechanism to terminate the armored both mechanically and electrically.



The Gland will usually be required to provide ingress protection by sealing outer sheath and retention by clamping amour.

Type of Glands: 1. 2. 3. 4. 5. 6.

Brass Indoor Type Gland Brass Outdoor Type Gland Brass Straitening Unarmored Cable Gland Brass Weather Proof Gland PG Threaded Gland: Industrial Type Gland

1) Brass Indoor Type Gland 

This Gland is quite handy in use with various types of cable whether plastic, rubberized, metal or any other.



Application: Dry indoor, for use with all type of SWA cables, plastic or rubber sheathed cable.



Brass indoor gland suitable for single wire armored, plastic or rubber sheathed cable. Recommended to use with shroud for additional ingress protection.



Cable Type: Steel Wire Amour.



Amour Clamping: Two Part Amour Lock.

2) Brass Outdoor Type Gland 

This come in stunning high quality material for use in outdoor or indoor application with various types of cables sheathed or unsheathed.

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Brass indoor and outdoor gland popularly used with single wire armored.



Plastic or rubber sheathed cable. Terminates and secure cable armoring and outer seal grips sheath of cable thus ensuring mechanical strength and earth continuity.



CW brass glands are also supplied with integral earth facilities.



Recommended to use PVC shroud for additional ingress protection

Application: a) Outdoor or indoor, for use with all type of SWA cables, plastic or rubber sheathed cable. b) Most suitable for SWA, plastic of rubber (Elastomeric) sheathed cables. c) Used in dry indoor conditions. d) No loose parts and easy to install. e) Save times & money. 

Gland size: 20 mm to 75 mm (S & L)



Accessories : Earth Tag, PVC Shroud, Neo prime Rubber & LSF Rubber, PVC Washer, Brass Lock Nut.



Cable Type: Wire Braid Armor.



Armor Clamping: Three Parts (With Lock Nut).

(3) Brass Straitening Unarmored Cable Gland 

Nickel plated or natural brass A2 type cable glands are used with variety of unarmored or rubber sheathed cables.



Brass indoor and outdoor cable gland suitable for all types of unarmored cables, plastic or rubber sheathed cables.

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Application: 1. For use with unarmored elastomeric and plastic insulated cables. 2. Indoor & Outdoor whenever it is required to provide sealing on cable outer sheath.



Size : Metric – 20mm to 75mm (S/L)



Accessories: Earth Tag, PVC Shroud, Neo prime Rubber & LSF Rubber, PVC Washer, Brass Lock Nut.



Cable Type : Unarmored

4) Brass Weather Proof Gland 

Unlike other types of cable glands, This type cable gland is used precisely with single armored various types of swa cables whether plastic or rubber sheathed ones. this type cable gland is known for its uninterrupted services once the gland is fixed to the desired wires and wire components.



Suitable for SWA or rubber sheathed cables.



Outer seal grips bedding layer of cable for use in most climatic conditions.



Weather proof and water proof.



Design has separate armor lock rings. Can be supplied with integral earth facility.



Gland size: 20 mm to 75 mm (S & L)

Application :

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1. Outdoor or indoor, for use with single armored, all type of SWA cable, plastic or rubber sheathed cable. 2. E1W Gland is Weatherproof & Waterproof Cable Gland 

Cable Type : Steel Wire Armour



Armour Clamping: Three Part Armour Lock



Sealing Technique: Compression & Displacement Type



Sealing Area(s): Inner & Outer Sheath

5) PG Threaded Gland: 

Nickel chrome plated PG threaded cable gland is a custom made threaded gland to meet the needs from the meet industries. Apart from the round headed PG threaded cable gland, we also offer hexagonal gland or any other like spherical rectangular or any other dimensional PG threaded cable gland as per the specification of the customer.

6) Industrial Cable Gland: 



Brass gland suitable for wire braid armored, plastic or rubber sheathed cable. Terminates and secure cable armoring and outer seal grips sheath of cable thus ensuring mechanical strength and earth continuity. Recommended to use PVC shroud for additional ingress protection



Cable Type: Wire Braid Armour



Armour Clamping : Three Part (With Lock Nut)



Sealing Technique: Compression Type.

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Brass gland suitable for steel tape armored, plastic or rubber sheathed cables. Terminates and secure cable armoring and outer seal grips sheath of cable thus ensuring mechanical strength and earth continuity.



Recommended to use PVC shroud for additional ingress protection



Cable Type : Steel Tape Armour



Armour Clamping : Three Part (With Lock Nut)



Sealing Technique: Compression Type.

CABLE GLAND

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GLANDED CABLE

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

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BUSBAR In electrical power distribution, a busbar (also spelled bus bar, or sometimes incorrectly as buss bar or busbar, with the term bus being a contraction of the Latin omnibus - meaning for all) is a strip or bar of copper, brass or aluminum that conducts electricity within a switch board, distribution board, substation, battery bank or other electrical apparatus. Its main purpose is to conduct electricity, not to function as a structural member. The cross-sectional size of the busbar determines the maximum amount of current that can be safely carried. Busbars can have a cross-sectional area of as little as 10 mm2 but electrical substations may use metal tubes of 50 mm in diameter (20 cm2) or more as busbars. An aluminum smelter will have very large busbars used to carry tens of thousands of amperes to the electrochemical cells that produce aluminium from molten salts. Design and placement Busbars are typically either flat strips or hollow tubes as these shapes allow heat to dissipate more efficiently due to their high surface area to cross-sectional area ratio. The skin effect makes 50–60 Hz AC busbars more than about 8 mm (1/3 in) thickness inefficient, so hollow or flat shapes are prevalent in higher current applications. A hollow section has higher stiffness than a solid rod of equivalent current-carrying capacity, which allows a greater span between busbar supports in outdoor switchyards.

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A busbar may either be supported on insulators, or else insulation may completely surround it. Busbars are protected from accidental contact either by a metal earthed enclosure or by elevation out of normal reach. Power Neutral busbars may also be insulated. Earth (safety grounding) busbars are typically bare and bolted directly onto any metal chassis of their enclosure. Busbars may be enclosed in a metal housing, in the form of bus duct or busway, segregated-phase bus, or isolated-phase bus. Busbars may be connected to each other and to electrical apparatus by bolted, clamp, or welded connections. Often joints between high-current bus sections have matching surfaces that are silver-plated to reduce the contact resistance. At extra-high voltages (more than 300 kV) in outdoor buses, corona around the connections becomes a source of radio-frequency interference and power loss, so connection fittings designed for these voltages are used. Busbars are typically contained inside switchgear, panel boards, or busway. Distribution boards split the electrical supply into separate circuits at one location. Busways, or bus ducts, are long busbars with a protective cover. Rather than branching the main supply at one location, they allow new circuits to branch off any where along the route of the busway.

COPPER BUSBAR

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CABLE CONNECTED TO BUSBAR

BUSBAR TRUNKING

STEEL CASE BUSBAR TRUNKING

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CHAPTER - 13 POWER FACTOR IMPROVEMENT


AUTOMATIC POWER FACTOR CORRECTION
APFC PANEL AUTOMATIC POWER FACTOR CORRECTION What is Power Factor 

Power Factor Definition: Power factor is the ratio between the KW and the KVA drawn by an electrical load where the KW is the actual load power and the KVA is the apparent load power. It is a measure of how effectively the current is being converted into useful work output and more particularly is a good indicator of the effect of the load current on the efficiency of the supply system.



All current flow causes losses both in the supply and distribution system. A load with a power factor of 1.0 results in the most efficient loading of the supply. A load with a power factor of, say, 0.8, results in much higher losses in the supply system and a higher bill for the consumer. A comparatively small improvement in power factor can bring about a significant reduction in losses since losses are proportional to the square of the current.



When the power factor is less than one the ‘missing’ power is known as reactive power which unfortunately is necessary to provide a magnetizing field required by motors and other inductive loads to perform their desired functions. Reactive power can also be interpreted as wattles, magnetizing or wasted power and it represents an extra burden on the electricity supply system and on the consumer’s bill.



A poor power factor is usually the result of a significant phase difference between the voltage and current at the load terminals, or it can be due to a high harmonic content or a distorted current waveform.



A poor power factor is generally the result of an inductive load such as an induction motor, a power transformer, and ballast in a luminary, a welding set or an induction furnace. A distorted current waveform can be the result of a rectifier, an inverter, a variable speed drive, a switched mode power supply, discharge lighting or other electronic loads.

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A poor power factor due to inductive loads can be improved by the addition of power factor correction equipment, but a poor power factor due to a distorted current waveform requires a change in equipment Design or the addition of harmonic filters.



Some inverters are quoted as having a power factor of better than 0.95 when, in reality, the true power factor is between 0.5 and 0.75. The figure of 0.95 is based on the cosine of the angle between the voltage and current but does not take into account that the current waveform is discontinuous and therefore contributes to increased losses.



An inductive load requires a magnetic field to operate and in creating such a magnetic field causes the current to be out of phase with the voltage (the current lags the voltage). Power factor correction is the process of compensating for the lagging current by creating a leading current by connecting capacitors to the supply.



P.F (Cos Ǿ) = K.W / KVA Or



P.F (Cos Ǿ) = True Power / Apparent Power.



KW is Working Power (also called Actual Power or Active Power or Real Power).



It is the power that actually powers the equipment and performs useful work.



KVAR is Reactive Power.



It is the power that magnetic equipment (transformer, motor and relay) needs to produce the magnetizing flux.



KVA is Apparent Power.



It is the “vectorial summation” of KVAR and KW.

Displacement Power Factor Correction. An induction motor draws current from the supply that is made up of resistive components and inductive components. The resistive components are: 1) Load current. 2) Loss current. 3) And the inductive components are: 4) Leakage reactance. 5) Magnetizing current.

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The current due to the leakage reactance is dependent on the total current drawn by the motor, but the magnetizing current is independent of the load on the motor. The magnetizing current will typically be between 20% and 60% of the rated full load current of the motor. The magnetizing current is the current that establishes the flux in the iron and is very necessary if the motor is going to operate. The magnetizing current does not actually contribute to the actual work output of the motor. It is the catalyst that allows the motor to work properly. The magnetizing current and the leakage reactance can be considered passenger components of current that will not affect the power drawn by the motor, but will contribute to the power dissipated in the supply and distribution system.



Take for example a motor with a current draw of 100 Amps and a power factor of 0.75 The resistive component of the current is 75 Amps and this is what the KWh meter measures. The higher current will result in an increase in the distribution losses of (100 x 100) /(75 x 75) = 1.777 or a 78% increase in the supply losses.



In the interest of reducing the losses in the distribution system, power factor correction is added to neutralize a portion of the magnetizing current of the motor. Typically, the corrected power factor will be 0.92 – 0.95



Power factor correction is achieved by the addition of capacitors in parallel with the connected motor circuits and can be applied at the starter, or applied at the switchboard or distribution panel. The resulting capacitive current is leading current and is used to cancel the lagging inductive current flowing from the supply.

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Displacement Static Correction (Static Compensation).  As a large proportion of the inductive or lagging current on the supply is due to the magnetizing current of induction motors, it is easy to correct each individual motor by connecting the correction capacitors to the motor starters. 

With static correction, it is important that the capacitive current is less than the inductive magnetizing current of the induction motor. In many installations employing static power factor correction, the correction capacitors are connected directly in parallel with the motor windings.



When the motor is Off Line, the capacitors are also Off Line. When the motor is connected to the supply, the capacitors are also connected providing correction at all times that the motor is connected to the supply. This removes the requirement for any expensive power factor monitoring and control equipment.



In this situation, the capacitors remain connected to the motor terminals as the motor slows down. An induction motor, while connected to the supply, is driven by a rotating magnetic field in the stator which induces current into the rotor. When the motor is disconnected from the supply, there is for a period of time, a magnetic field associated with the rotor. As the motor decelerates, it generates voltage out its terminals at a frequency which is related to its speed.



The capacitors connected across the motor terminals, form a resonant circuit with the motor inductance. If the motor is critically corrected, (corrected to a power factor of 1.0) the inductive reactance equals the capacitive reactance at the line frequency and therefore the resonant frequency is equal to the line frequency. If the motor is over corrected, the resonant frequency will be below the line frequency. If the frequency of the voltage generated by the decelerating motor passes through the resonant frequency of the corrected motor, there will be high currents and voltages around the motor/capacitor circuit. This can result in severe damage to the capacitors and motor. It is imperative that motors are never over corrected or critically corrected when static correction is employed.



Static power factor correction should provide capacitive current equal to 80% of the magnetizing current, which is essentially the open shaft current of the motor.



The magnetizing current for induction motors can vary considerably. Typically, magnetizing currents for large two pole machines can be as low as 20% of the rated current of the motor while smaller low speed motors

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can have a magnetizing current as high as 60% of the rated full load current of the motor 

Where the open shaft current cannot be measured, and the magnetizing current is not quoted, an approximate level for the maximum correction that can be applied can be calculated from the half load characteristics of the motor. It is dangerous to base correction on the full load characteristics of the motor as in some cases, motors can exhibit a high leakage reactance and correction to 0.95 at full load will result in over correction under no load, or disconnected conditions.



Static correction is commonly applied by using on e contactor to control both the motor and the capacitors. It is better practice to use two contactors, one for the motor and one for the capacitors. Where one contactor is employed, it should be up sized for the capacitive load. The use of a second contactor eliminates the problems of resonance between the motor and the capacitors.

How Capacitors Work  Induction motors, transformers and many other electrical loads require magnetizing current (kvar) as well as actual power (kW). By representing these components of apparent power (kVA) as the sides of a right triangle, we can determine the apparent power from the right triangle rule: kVA2 = kW2 + kVAR2. 

To reduce the kva required for any given load, you must shorten the line that represents the kvar. This is precisely what capacitors do. By supplying kvar right at the load, the capacitors relieve the utility of the burden of carrying the extra kvar. This makes the utility transmission/ distribution system more efficient, reducing cost for the utility and their customers. The ratio of actual power to apparent power is usually expressed in percentage and is called power factor.

What Causes Low Power Factor?  Since power factor is defined as the ratio of KW to KVA, we see that low power factor results when KW is small in relation to KVA. Inductive loads. Inductive loads (which are sources of Reactive Power) include: 1. 2. 3. 4. 

Transformers Induction motor Induction generators (wind mill generators) High intensity discharge (HID) lighting

These inductive loads constitute a major portion of the power consumed in industrial complexes.

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Reactive power (KVAR) required by inductive loads increases the amount of apparent power (KVA) in your distribution system .This increase in reactive and apparent power results in a larger angle (measured between KW and KVA). Recall that, as increases, cosine (or power factor) decreases.

Why Should I Improve My Power Factor?  You want to improve your power factor for several different reasons. Some of the benefits of improving your power factor include: (1) Lower utility fees by: a) Reducing peak KW billing demand: 

Inductive loads, which require reactive power, caused your low power factor. This increase in required reactive power (KVAR) causes an increase in required apparent power (KVA), which is what the utility is supplying. So, a facility’s low power factor causes the utility to have to increase its generation and transmission capacity in order to handle this extra demand.



By lowering your power factor, you use less KVAR. This results in less KW, which equates to a dollar savings from the utility.

b) Eliminating the power factor penalty: 

Utilities usually charge customers an additional fee when their power factor is less than 0.95. (In fact, some utilities are not obligated to deliver electricity to their customer at any time the customer’s power factor falls below 0.85.) Thus, you can avoid this additional fee by increasing your power factor.

(2) Increased system capacity and reduced system losses in your electrical system 

By adding capacitors (KVAR generators) to the system, the power factor is improved and the KW capacity of the system is increased.



For example, a 1,000 KVA transformer with an 80% power factor provides 800 KW (600 KVAR) of power to the main bus.



By increasing the power factor to 90%, more KW can be supplied for the same amount of KVA.



1000 KVA = (900 KW)2 + (? KVAR)2



KVAR = 436

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The KW capacity of the system increases to 900 KW and the utility supplies only 436 KVAR.



Uncorrected power factor causes power system losses in your distribution system. By improving your power factor, these losses can be reduced. With the current rise in the cost of energy, increased facility efficiency is very desirable. And with lower system losses, you are also able to add additional load to your system.

(3) Increased voltage level in your electrical system and cooler, more efficient motors 

As mentioned above, uncorrected power factor causes power system losses in your distribution system. As power losses increase, you may experience voltage drops. Excessive voltage drops can cause overheating and premature failure of motors and other inductive equipment. So, by raising your power factor, you will minimize these voltage drops along feeder cables and avoid related problems. Your motors will run cooler and be more efficient, with a slight increase in capacity and starting torque.

Automatic Power Factor Correction (APFC) Panel Power Factor Improving: 1. Please check if required kVAr of capacitors are installed. 2. Check the type of capacitor installed is suitable for application or the capacitors are de rated. 3. Check if the capacitors are permanently ‘ON’. The Capacitor are not switched off 4. when the load is not working, under such condition the average power factor is found to be lower side. 5. Check whether all the capacitors are operated in APFC depending upon the load operation. 6. Check whether the APFC installed in the installation is working or not. Check the CT connection is taken from the main incomer side of transformer, after the fix compensation of transformer. 7. Check if the load demand in the system is increased. 8. Check if power transformer compensation is provided. Thumb Rule if HP is known.

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The compensation for motor should be calculated taking the details from the rating plate of motor Or



the capacitor should be rated for 1/3 of HP

Kvar Required For Transformer Compensation: Transformer  <= 315 kVA T.C  315kVA To 1000 kVA  >= 1000 kVA

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Required Kva = 5% of KVA = 6% of KVA = 8% of KVA

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

Where to connect capacitor:  Fix compensation should be provided to take care of power transformer. Power and distribution transformers, which work on the principle of electro-magnetic induction, consume reactive power for their own needs even when its secondary is not connected to any load. The power factor will be very low under such situation. To improve the power factor it is required to connect a fixed capacitor or capacitor bank at the LT side of the Transformer. For approximate kVAr of capacitors required

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If the installation is having various small loads with the mixture of large loads then the APFC should be recommended. Note that APFC should have minimum step rating of 10% as smaller step.



If loads are small then the capacitor should be connected parallel to load. The connection should be such that whenever the loads are switched on the capacitor also switches on along with the load.



Note that APFC panel can maintain the power factor on L.T side of transformer and it is necessary to provide fix compensation for Power transformer.



In case there is no transformer in the installation, then the C.T for sensing power factor should be provided at the incoming of main switch of the plant.

Calculation of required capacitor:  Suppose Actual P.F is 0.8, Required P.F is 0.98 and Total Load is 516KVA. 

Power factor = kwh / kvah



kW = kVA x Power Factor



= 516 x 0.8 = 412.8



Required capacitor = kW x Multiplying Factor



= (0.8 x 516) x Multiplying Factor



= 412.8 x 0.547 (See Table to find Value according to P.F 0.8 to P.F of 0.98)



= 225.80 kVar

Multiplying factor for calculating kVAr Target PF Testing of Capacitor at Site: Measurement of Voltage:  Check the voltage using multi meter at capacitor terminals. 

Please note that the current output of 440 volt capacitor connected to a system of 415 volt will be lesser than rated value.



Table no -1 & 2give you the resultant kVAr output of the capacitor due to variation in supply voltage.

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The kVAr of capacitor will not be same if voltage applied to the capacitor and frequency changes. The example given below shows how to calculate capacitor current from the measured value at site.

Example: 

1. Name plate details – 15kVAr, 3 phases, 440v, and 50Hz capacitor.



Measured voltage – 425v , Measured frequency – 48.5Hz



Kvar = (fM / fR) x (VM / VR)2 x kvar



Kvar = (48.5/50) x (425 / 440)2 x 15



= 13.57kVAr.



2. Name plate details – 15kVAr, 3 phases, 415v, and 50Hz capacitor.



Measured voltage – 425v, Measured frequency – 48.5Hz



Kvar = (fM / fR) x (VM / VR)2 x kVAr



Kvar = (48.5/50) x (425 / 415)2 x 15



= 15.26kVAr THREE PHASE 440V CAPACITOR kVAr 440V

Line current 440V

kVAr at 415V

Line Current at 415V

Measured capacitance Across two terminals with third terminal open. (Micro farad) 440V

5

6.56

4.45

6.188

41.10

7.5

9.84

6.67

9.28

61.66

10

13.12

8.90

12.38

82.21

12.5

16.4

11.12

15.47

102.76

15

19.68

13,34

18.56

123.31

20

26.24

17.79

24.75

164.42

25

32.80

22.24

30.94

205,52

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ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

THREE PHASE 415V CAPACITOR kVAr 415V

Line current 415V

kVAr at 440V

Line Current at 415V

Measured capacitance across two terminals with third terminal open. (Micro farad) 415V

5

6.55

5.62

7.38

46.21

7.5

10.43

8.43

11.06

69.31

10

13.91

11.24

14.75

92.41

12.5

17.39

14.05

18.44

116.51

15

20.87

16.86

22.13

138.62

20

27.82

22.48

29.50

184.82

25

34.78

38.10

36.88

231.03

Measurement of Current:  The capacitor current can be measured using Multi meter. 

Make a record of measurement data of individual phase and other parameter.



Check whether the current measured is within the limit value with respect to supply voltage & data given in the name plate of capacitor Refer formula for calculation



Formula for calculating rated current of capacitor with rated supply voltage and frequency.



l = kvar x 103 / ( 3 X V ) L L

Example: 

15kVAr, 3 phase, 440v, 50Hz capacitor.



l = kVAr x 103 / ( 3 X V ) L L



l = (15 x 1000) / (1.732 x 440) L



l = 19.68AMPs L



15kVAr, 3 phases, 415v, 50Hz capacitor

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l = kVAr x 103/ ( 3 X V ) L L



l = (15 x 1000) / (1.732 x 415) L



l = 20.87 Amps

Discharge of Capacitor: 

L.T power capacitors are provided with discharge resistor to discharge the capacitor which is limited to one min. The resistor are provided as per clause No-7.1 of IS 13340-1993.



Switch off the supply to the capacitor and wait for 1 minute and then short the terminals of capacitor to ensure that the capacitor is completely discharged.



This shorting of terminals ensures the safety while handling the capacitor



Discharge of capacitor also becomes necessary for the safety of meter used for capacitance measurement.

Termination and Mounting: 

Use suitable size lugs for connecting the cable to the terminals of capacitor.



Ensure that there is no loose connection: As loose connection may lead to failure of capacitor / insulation break down of cable.



Use proper tools for connection / tightening.



Ensure that the capacitor is mounted vertically.



The earthing of capacitor should be done before charging.



The applied voltage should not exceed more than 10%. Refer technical specification of capacitor.



The capacitor should be provided with the short circuit protection device as indicated in following Table

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KVAr

HRC Fuse

Cable Amps

5

12 Amps

12 Amps

7.5

25 Amps

25 Amps

10

32 Amps

32 Amps

12.5

32 Amps

32 Amps

15

50 Amps

50 Amps

20

50 Amps

50 Amps

25

63 Amps

63 Amps

50

125 Amps

125 Amps

75

200 Amps

200 Amps

100

200 Amps

250 Amps

Use of capacitor in APFC panel 

The capacitor should be provided with suitable designed inrush current limiting inductor coils or special capacitor duty contactors. Annexure d point no d-7.1 of IS 13340-1993



Once the capacitor is switched off it should not be switched on again within 60 seconds so that the capacitor is completely discharged. The switching time in the relay provided in the APFC panel should be set for 60 seconds for individual steps to discharge. Clause No-7.1 of IS 133401993



If the capacitor is switched manually or if you are switching capacitors connected in parallel with each other then “ON” delay timer (60sec) should be provided and in case of parallel operation once again point No 1 should be taken care. Clause No-7.1 of IS 13340-1993



The capacitor mounted in the panel should have min gap of 25-30 mm between the capacitor and 50 mm around the capacitor to the panel enclosure.

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In case of banking a min gap of 25mm between the phase to phase and 19mm between the phases to earth should be maintained. Ensure that the banking bus bar is rated for 1.8 times rated current of bank.



The panel should have provision for cross ventilation, the louver / fan can be provided in the care Annexure d point No d-3.1 IS 13340-1993



For use of reactor and filter in the panel fan should be provided for cooling.



Short circuit protection device (HRC fuse / MCCB) should not exceed 1.8 x rated current of capacitor.

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CHAPTER - 14 EARTHING
NECESSITY OF EQUIPMENT EARTHING
PLATE EARTHING
PIPE EARTHING EARTHING Equipment Earthing is a connection done through a metal link between the body of any electrical appliance, or neutral point, as the case may be, to the deeper ground soil. The metal link is normally of MS flat, CI flat, GI wire which should be penetrated to the ground earth grid. Equipment Earthing based on IS:3043-1987 Standard •

Classification of Electrical Equipment IS: 9409-1980

•

Important Rules for Safety and Earthing practice is based on IE Rules 1956

•

Guide on effects of current passing through Human body – IS:84371997

•

Protection of Buildings and Structures from Lightning – IS:2309-1969

•

Earth: The conductive mass of the earth, whose Electric Potential at any point is conventionally assumed and taken as ZERO.

•

Earth Electrode: A Conductor or group of Conductors in Intimate contact with and providing as electrical connection to earth.

•

Earth Electrode Resistance: The resistance of an earth electrode to the general mass of earth.

•

Earthing Conductor: A protective conductor connecting the main earthing terminal to an earth electrode or other means of earthing.

•

Equipotential Bonding: Electrical connection putting various exposed conductive parts and extraneous conductive parts at a substantially equal potential.

•

Example:

Inter

connect

protective

conductor,

conductors and risers of AC/HV Systems if any.

244

earth

continuity

ELECTRICAL DESIGNING --------------------------------------------------------------------------------------------------------------------------------•

Potential Gradient: The Potential Difference per unit length measured in the direction in which it is max.

•

Touch Voltage: The P.D. between a grounded metallic structure and a point on the earth’s surface separated by a horizontal reach of one Metre.

•

Step Voltage: The P.D. between two points on the earth’s surface separated by a distance one pace (Step) assumed to be one Metre.

•

Earth

grid:

A

System

of

grounding

electrodes

consisting

of

Interconnected Connectors buried in the earth to provide a common ground fro electrical devices and metallic structures. •

Earth mat: A grounding system formed by a grid of horizontally buried conductors - Serves to dissipate the earth fault current to earth and also as an equipotential bonding conductor system.

Necessity of Equipment Earthing Protection a) Safety of personnel b) Safety of Equipment Prevent or at least minimize damage to equipment as a result of flow of heavy currents. c) Improvement of the reliability of the Power System. Classification of Earthing The earthing is broadly divided as a) System earthing (Connection between part of plant in an operating system like L V neutral of a power Transformer winding) and earth. b) Equipment earthing (Safety grounding) Connecting bodies of equipment (like motor body, Transformer tank, Switch gear box, operating rods of air break switches, LV breaker body, HV breaker body, Feeder breaker bodies etc) to earth. Permissible values of earth resistance a) Power stations - 0.5 ohms b) EHT Stations - 1.0 ohms c) 33KV SS - 2 ohms

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ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

d) DTR Structures - 5 ohms e) Tower foot resistance - 10 ohms What is the Basics for arriving at permissible earth resistances As per IE rules One has to have a definite base for that As per IE rules one has to keep touch potential less than

a)

Recommended safe value 523 volts

b)

Ifault = maximum current in fault conditions,

c)

Maximum fault current is 100 KVA the current in 100 KVA is about 100 A; where percentage impedance is 4%

d)

For a Substation of 100 KVA Transformer

0.26 ohms being quite low, Quality work is to be done during construction, to obtain such a value of earthing system, and the expenditure for that will be very high. Hence the electrical inspectors are insisting about 1.0 ohms. This seems justifying for the urban areas This value may be 2ohms in case of Rural areas, which is recommended by most of the authorities. e)

The earth electrode resistance value also carries importance in view of full protection by lightning arrestors against lightning. The earth electrode resistance value in that case is given by the formula

Flash over voltage of 11KV = 75 KV

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ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

Lightning Arrestor Displacement = 40 KA.

TYPE OF EARTHING Plate Type Earthing In this, cast Iron plate of size 600 mm X 600 mm X 6.3 mm thick plate is being used as earth plate. This is being connected with Hot dip GI main earth strip of size 50mm X 6mm thick X 2.5 meter long by means of nut, bolts & washers of required size. The main earth strip is connected with hot dip GI strip of size 40mm X 3mm of required length as per the site location up to the equipment earth / neutral connection. The earth plate is back filled & covered with earthing material (mixture of charcoal & salt) by 150mm from all six sides. The remaining pit is back filled with excavated earth. Along with earth plate, rigid PVC pipe of 2.5 meter long is also provided in the earth pit for watering purpose for to keep the earthing resistance within specific limit. Pipe Type Earthing In this Hot dip GI pipe of size 40mm dia X 2.5 meter is being used for equipment earthing. This pipe is perforated at each interval of 100mm and is tapered at lower end. A clamped is welded with this pipe at 100mm below the top for making connection with hot dip GI strip of size 40mm X 3mm of required length as per the site location up to the equipment earth / neutral connection. On its open end funnel is being fitted for watering purpose. The earth pipe is placed inside 2700 mm depth pit. A 600mm dia “farma“ of GI sheet or Cement pipe in two halves is are placed around the pipe. Then the angular space between this “farma” and earth pipe is back filled with alternate layer of 300mm height with salt and charcoal. The remaining space outside “farma” will be backfilled by excavated earth. The “farma” is gradually lifted up as the backfilling up progresses. Thus the pit is being filled up to the 300mm below the ground level. This remaining portion is covered by constructing a small chamber of brick so that top open end of pipe and connection with main earth pipe will be accessible for attending when necessary. The chamber is closed by wooden / stone cover. Water is poured into the pipe through its open end funnel to keep the earthing resistance within specific limit.

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ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

CHAPTER - 15 CCTV AND FIRE ALARM


EXTRA LOW VOLTAGE SYSTEMS
CCTV
FIRE ALARM SYSTEMS CCTV Closed-circuit television (CCTV) is the use of video cameras to transmit a signal to a specific place, on a limited set of monitors. It differs from broadcast television in that the signal is not openly transmitted, though it may employ point to point (P2P), point to multipoint, or mesh wireless links. Though almost all video cameras fit this definition, the term is most often applied to those used for surveillance in areas that may need monitoring such as banks, casinos, airports, military installations, and convenience stores. Video telephony is seldom called "CCTV" but the use of video in distance education, where it is an important tool, is often so called. In industrial plants, CCTV equipment may be used to observe parts of a process from a central control room, for example when the environment is not suitable for humans. CCTV systems may operate continuously or only as required to monitor a particular event. A more advanced form of CCTV, utilizing digital video recorders (DVRs), provides recording for possibly many years, with a variety of quality and performance options and extra features (such as motion-detection and email alerts). More recently, decentralized IPbased CCTV cameras, some equipped with megapixel sensors, support recording directly to network-attached storage devices, or internal flash for completely stand-alone operation. Surveillance of the public using CCTV is particularly common in many areas around the world including the United Kingdom, where there are reportedly more cameras per person than in any other country in the world.[3] There and elsewhere, its increasing use has triggered a debate about security versus privacy CAMERA Video camera A couple of CS-mount lenses for surveillance cameras. The left one is designed to be hidden behind a wall.

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ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

Video cameras are either analogue or digital, which means that they work on the basis of sending analogue or digital signals to a storage device such as a video tape recorder or desktop computer or laptop computer. Analogue Can record straight to a video tape recorder which are able to record analogue signals as pictures. If the analogue signals are recorded to tape, then the tape must run at a very slow speed in order to operate continuously. This is because in order to allow a three hour tape to run for 24 hours, it must be set to run on a time lapse basis which is usually about four frames a second. In one second, the camera scene can change dramatically. A person for example can have walked a distance of 1 meter, and therefore if the distance is divided into four parts, i.e. four frames or "snapshots" in time, then each frame invariably looks like a blur, unless the subject keeps relatively still. Analogue signals can also be converted into a digital signal to enable the recordings to be stored on a PC as digital recordings. In that case the analogue video camera must be plugged directly into a video capture card in the computer, and the card then converts the analogue signal to digital. These cards are relatively cheap, but inevitably the resulting digital signals are compressed 5:1 (MPEG compression) in order for the video recordings to be saved on a continuous basis. Another way to store recordings on a non-analogue media is through the use of a digital video recorder (DVR). Such a device is similar in functionality to a PC with a capture card and appropriate video recording software. Unlike PCs, most DVRs designed for CCTV purposes are embedded devices that require less maintenance and simpler setup than a PC-based solution, for a medium to large number of analogue cameras. Some DVRs also allow digital broadcasting of the video signal, thus acting like a network camera. If a device does allow broadcasting of the video, but does not record it, then it's called a video server. These devices effectively turn any analogue camera (or any analogue video signal) into a network TV. Digital

249

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

These cameras do not require a video capture card because they work using a digital signal which can be saved directly to a computer. The signal is compressed 5:1, but DVD quality can be achieved with more compression (MPEG-2 is standard for DVD-video, and has a higher compression ratio than 5:1, with a slightly lower video quality than 5:1 at best, and is adjustable for the amount of space to be taken up versus the quality of picture needed or desired). The highest picture quality of DVD is only slightly lower than the quality of basic 5:1-compression DV. Saving uncompressed digital recordings takes up an enormous amount of hard drive space, and a few hours of uncompressed video could quickly fill up a hard drive. Holiday uncompressed recordings may look fine but one could not run uncompressed quality recordings on a continuous basis. Motion detection is therefore sometimes used as a work around solution to record in uncompressed quality. However, in any situation where standard-definition video cameras are used, the quality is going to be poor because the maximum pixel resolution of the image chips in most of these devices is 320,000 pixels (analogue quality is measured in TV lines but the results are the same); they generally capture horizontal and vertical fields of lines and blend them together to make a single frame; the maximum frame rate is normally 30 frames per second. That said, multi-megapixel IP-CCTV cameras are coming on the market. Still quite expensive, but they can capture video images at resolutions of 1, 2, 3, 5 and even up to 11 Mpix. Unlike with analogue cameras, details such as number plates are easily readable. At 11 Mpix, forensic quality images are made where each hand on a person can be distinguished. Because of the much higher resolutions available with these types of cameras, they can be set up to cover a wide area where normally several analogue cameras would have been needed.

250

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

Network IP cameras or network cameras are analogue or digital video cameras, plus an embedded video server having an IP address, capable of streaming the video (and sometimes, even audio). Because network cameras are embedded devices, and do not need to output an analogue signal, resolutions higher than CCTV analogue cameras are

251

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

possible. A typical analogue CCTV camera has a PAL (768×576 pixels) or NTSC (720×480 pixels), whereas network cameras may have VGA (640×480 pixels), SVGA (800×600 pixels) or quad-VGA (1280×960 pixels, also referred to as "megapixel") resolutions. An analogue or digital camera connected to a video server acts as a network camera, but the image size is restricted to that of the video standard of the camera. However, optics (lenses and image sensors), not video resolution, are the components that determine the image quality. Network cameras can be used for very cheap surveillance solutions (requiring one network camera, some Ethernet cabling, and one PC), or to replace entire CCTV installations (cameras become network cameras, tape recorders become DVRs, and CCTV monitors become computers with TFT screens and specialised software. Digital video manufacturers claim that turning CCTV installations into digital video installations is inherently better). There continues to be much debate over the merits and price-forperformance of Network cameras as compared to analog cameras. Many in the CCTV industry claim that many analog cameras can outperform network cameras at a lower price. Digital still cameras These cameras can be purchased in any high street shop and can take excellent pictures in most situations. The pixel resolution of the current models has easily reached 7 million pixels (7-mega pixels). Some point and shoot models like those produced by Canon or Nikon boast resolutions in excess of 10 million pixels. At these resolutions, and with high shutter speeds like 1/125th of a second, it is possible to take jpg pictures on a continuous or motion detection basis that will capture not only anyone running past the camera scene, but even the faces of those driving past. These cameras can be plugged into the USB port of any computer (most of them now have USB capability)and pictures can be taken of any camera scene. All that is necessary is for the camera to be mounted on a wall bracket and pointed in the desired direction. Modern digital still cameras can take 500 kb snapshots in the space of 1 second, and these snapshots are then automatically downloaded by the camera software straight to the computer for storage as timed and dated JPEG files. The images themselves don't need to stay on the computer for long. If the computer is connected to the Internet, then the images can

252

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

automatically be uploaded to any other computer anywhere in the world, as and when the pictures are taken. The user does not need to lift a finger except to simply plug the camera in and point it in the desired direction. The direction could just as easily be the street outside a house, or the entrance to a bank or underground station. Digital still cameras are now being made with in-built wireless connectivity, so that no USB cable is required; images are simply transmitted wirelessly through walls or ceilings to the computer. Types There are three main types of cameras. After reading the descriptions, click to look at pictures of these cameras. 1. Dome cameras - These are usually placed inside a dark dome, and can't be seen from outside, so the thief will not know whether the camera is pointing his way or not. These cameras may turn or may be fixed, but what is important is that when looking at it, no one can tell

2. Wall cameras - These are big visible cameras. They may be simple, or have a lot of options, such as a waterproof or bulletproof shell, infrared light, or zoom

3. Hidden cameras - These small and covert cameras are hidden inside other objects and are not easily detectable

253

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

Networking CCTV cameras The city of Chicago operates a networked video surveillance system which combines CCTV video feeds of government agencies with those of the private sector, installed in city buses, businesses, public schools, subway stations, housing projects etc. Even home owners are able to contribute footage. It is estimated to incorporate the video feeds of a total of 15,000 cameras. The system is used by Chicago's Office of Emergency Management in case of an emergency call: it detects the caller's location and instantly displays the real-time video feed of the nearest security camera to the operator, not requiring any user intervention. While the system is far too vast to allow complete real-time monitoring, it stores the video data for later usage in order to provide possible evidence in criminal cases.[53] London also has a network of CCTV systems that allows multiple authorities to view and control CCTV cameras in real time. The system allows authorities including the Metropolitan Police Service, Transport for London and a number of London boroughs to share CCTV images between them. It uses a network protocol called Television Network Protocol to allow access to many more cameras than each individual system owner could afford to run and maintain. The Glynn County Police Department uses a wireless mesh-networked system of portable battery-powered tripods for live megapixel video surveillance and central monitoring of tactical police situations. The systems can be used either on a stand-alone basis with secure communications to nearby police laptops, or within a larger mesh system with multiple tripods feeding video back to the command vehicle via wireless, and to police headquarters via 3G.

254

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

WALL MOUNTED

255

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

FIRE ALARM SYSTEM An automatic fire alarm system is designed to detect the unwanted presence of fire by monitoring environmental changes associated with combustion. In general, a fire alarm system is classified as either automatically actuated, manually actuated, or both. Automatic fire alarm systems are intended to notify the building occupants to evacuate in the event of a fire or other emergency, report the event to an off-premises location in order to summon emergency services, and to prepare the structure and associated systems to control the spread of fire and smoke.

A medium-sized control panel with touchpad for alarm and trouble silence and system reset is shown above. Referring to the installation manual, you can use the touchpad to program the system’s many options.

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ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

The modern fire alarm system is capable of detecting smoke and heat from a small flame, water flow in a sprinkler system or an activated pull station, and reporting this information to on-site personnel via dedicated phone line to any location in the world. Although a seemingly straightforward device from an installation standpoint, fire alarm work can be quite complex, especially when you consider the enormous moral and legal responsibilities involved. There have also been some recent updates to the technology over the last few years worth noting. Recent advances. The latest major development in the fire alarm system arena has been the introduction of the addressable head. Before these updates, in the event of an alarm, the alphanumeric display at the control panel indicated which zone was affected — something like “Fire Alarm — Zone 6, East Wing Third Floor.” With an addressable head system; however, the exact location is pinpointed. Moreover, the addressable head system has enhanced diagnostic capabilities. This is a great advantage because when a system goes down, time is of the essence in restoring fire protection to the building. To upgrade to addressable heads, it's not usually necessary to do a complete system replacement. Typically, installers must put in new heads, pull some extra wire, and insert new printed circuit cards into the existing control panel. Each new head possesses an address, which conveys its exact location. You may be asking yourself if this means a spare head has to be kept in inventory for each location. No, each initiating device has on its back a set of DIP switches by means of which you enter a binary number that comprises the address prior to installation. If replacement is necessary, use a small screwdriver to set the DIP switches on the new device. The option to upgrade with addressable heads or to completely replace a legacy system has to be carefully considered by building owners with the input of in-house electricians and outside consultants. For a large set of buildings, the expense to upgrade can be formidable. For example, besides addressable and non-addressable heads, there are high- and low-impedance initiating devices, 2- and 4-wire circuitry, and various operating protocols. These are reflected in the different states a control panel can be in as reported by the alphanumeric display. A system may also be power limited, or, less commonly, non-power limited. In addition to familiarizing yourself with the most recent technology trends as outlined above, it's also important for electrical contractors to realize how sensitive these devices are to certain design, installation, and operational issues — all of which can result in lost revenue, unplanned downtime, and

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ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

unhappy customers. Here's a good example. Say an expensive commercial building is all but finished; however, the fire alarm doesn't pass inspection, meaning the facility cannot legally be used. As a few rattled electricians work feverishly to get the bugs out of the system, the owners lose thousands of dollars every day. Another potentially problematic scenario might involve slightly creased conductors coming out of a conduit connector at the detector head base. Although this situation would pose no problem in ordinary power or telephone circuits, it could throw one of these systems into false alarm. Realizing that these types of unforeseen circumstances can throw a wrench into even the best conceived plans, it makes sense for contractors to review fundamental design, installation, and operational considerations for fire alarm systems to keep their skills sharp. Design considerations. Typically, a fire alarm system is made up of the following components: •

•

•

•

•

Initiating devices, capable of placing the system in the alarm state. These can be photoelectric smoke and heat detectors, ionization smoke detectors, heat detectors, in-duct smoke detectors, manually operated pull stations and sprinkler water flow sensors. Indicating appliances, whose purpose is to announce building occupants or at a remote location when the system enters the alarm state, such as horns, strobe lights, chimes, bells, or combination units. They are also available in weatherproof and hazardous location versions. A control panel, containing programming and operating electronics and user interface, is fed by standard branch-circuit wiring and contains replaceable circuit cards — one for each zone. This includes an alphanumeric display, showing the state of the system and providing troubleshooting information, and a touchpad so that onsite personnel can silence an alarm or trouble signal, reset the system following an event, and reprogram if necessary (Photo on page C10). Sealed batteries similar to emergency light batteries, but listed for fire alarm systems. These are usually 6V batteries wired in series to make up 24VDC for a power-limited system. The batteries can be contained in the control panel or in a separate enclosure. When AC power fails, the batteries take over with no interruption in fire protection. Of course, there is also a charger. Auxiliary devices, including remote annunciators with LEDs showing the state of the system, an alarm silence switch, and visual LED indication of

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the zone from which a fire alarm is initiated. Electromagnetic door holders (floor- or wall-mounted) are available. In case of alarm, the magnet is de-energized, allowing the door to swing shut. Later, it is reopened manually. Initiating devices are connected to the control panel by a 2- or 4-wire initiating device circuit. In the case of a power-limited system, 24VDC is applied to two wires going to a string of initiating devices, which are wired in parallel. Neither wire is grounded, nor are they isolated from EMT or other raceways, which are grounded through the connector at the control panel. Polarity is also critical. This voltage is used to power the solid-state circuitry within each detector. It's also used by the control panel to monitor the state (alarm or no alarm) of the initiating devices and zone wiring. A typical fire alarm system has numerous initiating devices divided among separate zones — each connected via an initiating device circuit to a central control panel. The control panel performs supervisory functions over the initiating devices, indicating appliances, all associated field wiring, telephone ties, and its own internal wiring and circuit cards. Installation tips. During initial setup, all zone wiring, initiating device, and indicating appliance installation should be completed before the telephone tie is hooked up, typically by means of a ribbon connector. This is so that the monitoring agency won't receive false alarms. The control panel should be located where it can be responded to as necessary either around the clock or during operating hours. This can be at building security headquarters, adjacent to a telephone switchboard or in a maintenance office - whichever location offers maximum coverage. It should also be positioned in a fairly central location because if the system goes into alarm, a person needs to be able to race to the location and verify fire status before the alarm is silenced. Operational issues. A fire alarm system operates in one of three (or more) states: normal, alarm, and trouble. The state is reported at all times on the alphanumeric display. If the system goes into alarm, the indicating appliances throughout the building go off. These could be very loud horns for some occupancies, or softer chimes in others, such as a nursing home. The control panel monitors the initiating device circuits at all times for shorts and open wiring by means of the applied DC voltage. The initiating devices are normally open. In the event of a fire they become conductive at close to zero ohms. How, then, is it possible for the control panel to

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differentiate between a non-alarm state and an open wiring fault? This is accomplished by means of an end-of-line resistor. A 4.7 kilohm (typically) resistor is placed across the line after the final device. When this resistance is seen by the control panel, normal status is maintained. If the resistance increases, it means that an open has developed, and the panel goes into the trouble state. A buzzer sounds to alert maintenance personnel but the much louder horns throughout the building do not go off. The alphanumeric display will read something like “Open Circuit in Zone Three.” The trouble alert can be silenced by pressing a touchpad location under the trouble alert LED. The control panel also monitors the functionality of its own wiring and zone cards, and trouble is reported in the display. A low-level voltage is applied to the indicating appliance circuits when the system is normal. This voltage is not sufficient to set off the horns, but it is monitored as part of the control panel's supervisory function. If current ceases to flow, the trouble alert buzzer sounds, and the display indicates the presence of an open circuit. Several troubleshooting techniques are appropriate when the system enters the trouble state. Initially, you can unhook a zone in the control panel (after disabling the system) and place an end-of-line resistor across the output terminals. This will simulate a zone in place and the actual field wiring (including devices) can be worked on while the rest of the system is operational. Another approach is to break the zone at the middle of the run and insert an end-of-line resistor. Using the “half-splitting” troubleshooting method, as discussed in “Maintenance Facts” on page 16 of the November issue, you can easily pinpoint a fault — either short or open. Another capability of the fire alarm system is to call out in case of alarm. Two dedicated phone lines are connected, and the system performs test calls periodically in accordance with programmed instructions. If either phone line won't connect, the system goes into the trouble state, so repairs can be made. The essence of a fire alarm system, as opposed to individual smoke detectors, even if they are wired to indicate in concert, is that it is supervised from a central location. The whole notion of supervision is critical. It does not mean that a person sits at the console and watches it at all times. What it means is that a supervisory voltage is applied to all circuitry, and current flow is monitored electronically to verify that equipment and wiring are intact.

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If the system goes into alarm and won't silence due to touchpad malfunction, for example, it can be disarmed after the zone is checked for fire by cutting off the power. First, unhook one side of the battery array, then unhook the black-white-green incoming power connector. If a fire alarm system is disabled, maintenance and security personnel should initiate fire patrols throughout the building. The telephone monitoring agency should be informed, and the insurance company contacted to verify that coverage is not voided. Sidebar: Regulatory Mandates At a Glance The following regulatory documents apply to the fire alarm system as opposed to individual smoke alarms of the residential type, even when they are AC powered and used for group operation. NFPA 101 Life Safety Code — denotes which occupancies are required to have fire alarm systems. NFPA 72 National Fire Alarm Code — lays out overall system design parameters, such as location and spacing of heads and pulls stations, testing and maintenance procedures, minimum performance requirements and operational protocols. NFPA 70 National Electric Code — Article 760 covers the equipment and wiring of the fire alarm system, both power to the control console and zone wiring to initiating devices and to annunciators, as well as any phone lines for automatic calling. Also included are other fire alarm functions, such as guard's tour, sprinkler water flow, sprinkler supervisory equipment, elevator capture and shutdown, door release, smoke doors and damper control, fire doors and fan shutdown — only where these functions are actually controlled by the fire alarm system. Article 725, Class 1, Class 2 and Class 3 Remote Control, Signaling and Power-Limited Circuits, covers wiring emanating from the control panel. Where these circuits are power-limited, alternative requirements take effect for minimum wire sizes, derating factors, over current protection, insulation requirements, and wiring methods and materials. Underwriters Laboratory or other inspecting agencies — List all components such as control panel, smoke detecting heads, horns, pull stations, and any other equipment.

261

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CHAPTER - 16 STANDARDS AND CHARTS ACRONYMS ac ACB ALF

Alternative Current Air Circuit Breaker Aluminium Conductor Steel Reinforced Accuracy Limit Factor

AMF

Auto Mains Failure

ACSR

AVR BDV BIS CBCT CEB CFL COS

MCB MCC MCCB

Main Switch Board

MTA

Maximum Torque Angle

MV

Medium Voltage

MVA

Mega Volt Ampere

NEC

National Electric Code Neutral Ground Resistor Neutral Grounding Transformer Oil Circuit Breaker

NGR NGT

DB dc

Direct Current

OTI

DCP

PCC

EHT

Dry Chemical Powder Dough Moulded Compound Direct Online Directorate of Radiation Safety Extra High Tension

EHV

Extra High Voltage

CT CTRC

DMC DOL DRS

OCB OCR

Over Current Relay

OH

Over Head

OLTC

PE

On Load Tap Changer Oil Temperature Indicator Power Control Centre Power Distribution Board Protective Earthing

PF

Power Factor

PL

Polarisation Index Programmable Logic Control Power &Motor Control Centre Potential Transfer Poly Vinyl Chloride Residential Current Circuit Breaker Restricted Earth Fault Radio Frequency Resistance Temperature Device

PDB

PLC

ELR FBA

Earth Leakage Circuit Breaker Earth Leakage Rely Factor Built Assembly

FDB

Fuse Distribution Board

RCCB

FRP FSD

Fibre Reinforced Plastic Fuse Switch Disconnector

REF RF

GCP

Generator Control Panel

RTD

ELCB

Low Tension Low Voltage Miniature Circuit Breaker Motor Control Centre Moulded Case Circuit Breaker

MSB

Central Power Research Institute Current Transformer Central Tariff Regulatory Commission Distribution Board

CPRI

262

Automatic Voltage Regulator Break Down Voltage Bureau of Indian Standards Core Balance Current Transformer Central Electricity Board Compact Flourescent Lamp Change Over Switch

LT LV

PMCC PT PVC

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

Switch Disconnector Fuse Specific Energy Consumption

GI

Galvanized Iron

SDF

GLS

Generator Lighting Service

SEC

HBC

High Breaking Capacity

SHF/S F6

Sulpher Hexa Flouride

HRC

High Rupturing Capacity

SMC

Sheet Moulded Compound

Inverse Definite Minimum Time Lag Indian Electricity Rules Ingress Protection Indian Standard Institution

SSB

Sub Switch Board

SWG TSM

Standard Wire Gauge Time Setting Multiplier

TOD

Time of Day

KV

Kilo Volt

TRC

KVA

Kilo Volt Ampere

UG

KVAR

Kilo Volt Ampere Reactive

UPS

KW KWH

Kilo Watt Kilo Watt Hour

USS VA

LA

Lightning Arrestor

VCB

LDB

Lighting Distribution Board

VVVF

OLR

Over Load Rely

WTI

LED

Light Emitting Diode

XLPE

IDMT IER IP ISI

263

Tariff Regulatory Commission Under Ground Uninterrupted Power Supply Unitised Sub Station Voltage Ampere Vacuum Circuit Breaker Variable Voltage Variable Frequency Winding Temperature Indicator Cross Linked Polyethylene

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

SYMBOLS

264

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265

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266

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267

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268

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269

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270

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271

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272

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273

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

CAPACITORS IN KVAR FOR REQUIRED POWER FACTOR CORRECTION Initial power factor

0.85

0.50 0.51 0.52 0.53 0.54 0.55 0.56 0.57 0.58 0.59 0.60 0.61 0.62 0.63 0.64 0.65 0.66 0.67 0.68 0.69 0.70 0.71 0.72 0.73 0.74 0.75 0.76 0.77 0.78 0.79 0.80 0.81 0.82 0.83 0.84 0.85 0.86 0.87 0.88 0.89 0.90 0.91 0.92 0.93 0.94 0.95 0.96 0.97 0.98 0.99

1.112 1.066 1.024 1.980 0.939 0.899 0.860 0.822 0.785 0.748 0.714 0.679 0.645 0.613 0.580 0.549 0.518 0.488 0.459 0.429 0.400 0.372 0.343 0316 0.289 0.262 0.235 0.209 0.183 0.156 1.130 0.104 0.178 0.052 0.026 -

274

Correction to 0.90 1.248 1.202 1.160 1.116 1.075 1.035 0.996 0.958 0.921 0.884 0.849 0.815 0.781 0.749 0.716 0.685 0.654 0.624 0.595 0.565 0.536 0.508 0.479 0.452 0.425 0.425 0.398 0.371 0.345 0.319 0.292 0.266 0.250 0.214 0.188 0.162 0.136 0.109 0.083 0.054 0.028 -

0.95

0.98

1.00

1.403 1.357 1.315 1.271 1.230 1.190 1.151 1.113 1.076 1.039 1.005 0.970 0.936 0.904 0.871 0.840 0.809 0.779 0.750 0.720 0.691 0.663 0.634 0.607 0.580 0.535 0.526 0.500 0.473 0.447 0.421 0.395 0.369 0.343 0.317 0.291 0.264 0.238 0.209 0.183 0.155 0.124 0.097 0.066 0.034 -

1.529 1.483 1.441 1.397 1.356 1.316 1.277 1.239 1.202 1.165 1.131 1.096 1.062 1.030 0.997 0.966 0.935 0.905 0.876 0.840 0.811 0.753 0.754 0.727 0.700 0.673 0.652 0.620 0.594 0.567 0.541 0.515 0.489 0.463 0.437 0.417 0.390 0.364 0.335 0.309 0.251 0.250 0.223 0.192 0.160 0.126 0.089 0.47 -

1.732 1.686 1.344 1.600 1.559 1.519 1.450 1.442 1.405 1.368 1.334 1.299 1.265 1.233 1.200 1.169 1.138 1.108 1.076 1.049 1.020 0.992 0.963 0.863 0.909 0.882 0.855 0.829 0.833 0.776 0.750 0.725 0.698 0.672 0.645 0.620 0.593 0.567 0.538 0.512 0.484 0.453 0.426 0.395 0.363 0.239 0.292 0.25 0.203 0.143

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

ELECTRICAL LAYOUT IN RESIDENTIAL BUILDINGS IS 6648 -1968 (REAFFIRMED 1997) 1. Energy meter shall be at such a place which is readily accessible to both consumer and supplier. 2. Energy meter shall not be installed below 1 meter from ground. 3. Isolating device shall be placed immediately after the energy meter and should be readily accessible to consumer. 4. Fuses or other protective devices shall have adequate breaking capacity. 5. Insulated conductors connected to live lines shall be red, yellow or blue color. Neutral shall be black. 6. All switches shall be on live lines and never on neutral. 7. Earthing conductors may be un-insulated. If insulated the covering shall be finished to show a green color. 8. After the main switch there shall be a Distribution board. 9. "there shall be separate circuits for power and lighting. 10. There shall be minimum two sub circuits for lighting. 11. Total load on a lighting sub circuit shall be 800 Watts. Number of points shall not Exceed 10. 12. Total load on a power sub circuit shall be 3000 Watts. There shall not be more than 2 outlets in a power sub circuit. 13. A switch shall be provided adjacent to normal entrance to any area for controlling the general lighting in that area. 14. Two way switching is recommended for halls and staircases. 15. Switches and bell pushes should be self i l l u m i n a t i ng where they are often operated in dark. 16. Local light fittings in kitchen should be so placed that all working surfaces are well illuminated. 17. In bedroom it is recommended that some lighting be controlled from the bed location.

275

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18. It is recommended to use ceiling lighting with the switch located outside for bathroom. 19. Waterproof light fitting shall only be used for outdoor lighting. 20.All socket outlets shall be three pin types. 21.Only 3 pin, 15A socket outlets shall be used in power circuits. 22.All socket outlets shall be controlled by a switch located adjacent to it. 23.(Drily shuttered type sockets shall be provided at location accessible to children. 24.For socket outlets of rating more than 16A double pole switch shall be provided. 25.No socket outlets shall be provided in bathroom at a height not less than 130cm. 26.All ceiling fans shall be provided with a switch beside its regulator. 27.Ceiling fan shall be hung not less than 2.75m above floor. 28.Flexible cords shall be used only in the following cases.

276

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CABLE CODE Constituent Aluminum Conductor

Code Letter A

XLPE insulation

2X

PVC insulation

Y

Steel round wire armored

W

Non –magnetic round wire armored

Wa

Steel strip armored

F

Non-magnetic strip armored

Fa

Double steel strip armored

FF

Double steel wire armored

WW

PVC outer sheath

Y

Note: for copper conductor no code letter. E.g.: AYFY –aluminum conductor PVC insulated Steel strip armored PVC insulated cable. CURRENT RATING OF AYFY CABLES (IS 1554 PART -1,1964 & IS 3961 PART –II ,1967) Corresponding current rating (A) Nominal area of conductor(mm2)

277

1.5

16

2.5

21

4

28

6

35

10

46

16

50

25

76

35

93

50

110

70

135

95

165

120

185

150

210

185

235

240

275

300

305

400

335

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

Note: (1) Derating Factors For single laying

- 0.9

For 2 Nos. of cable grouping

- 0.71

For 3 Nos. of cable grouping

- 0.62

For 4 Nos. of cable grouping

- 0.56

(2) Short circuit current carrying capacity of AYFY cables can be calculated from the formula. A

= 13.1 x Is x√t

Where A = Area of conductor in mm2 Is

= short circuit current - kA

t

= Duration of fault current in seconds

CURRENT RATING OF AYFY FEEDER CABLES Feeder rating in

Size in sq.mm

A

278

Feeder rating in

Size in sq.mm

A

16

4

150

150

25

6

160

185

32

10

200

240

40

16

250

400

50

25

320

2 x 185

63

35

400

2 x 240

80

50

500

2 x 400

100

70

630

3 x 400

120

95

800

4 x 400

125

120

ELECTRICAL DESIGNING ---------------------------------------------------------------------------------------------------------------------------------

VOLTAGE DROP & RESISTANCE OF AYFY CABLES Installation method (clipped direct)

Conductor cross sectional Areas

mm2 1.5 2.5 4 6 10 16 25 35 50 70 95 120 150 185 240 300 400 2 x 185 2 x 240 2 x 300 2 x 400 3 x 185 3 x 240 3 x 300 3 x 400 4 x 400

279

Single Phase Current Volt Drop/A Carrying /m Capacity A mV 16 21 29 28 18.2 35 12.1 46 7.3 60 4.5 76 2.9 92 2.1 110 1.6 135 1.1 165 0.79 185 0.65 210 0.53 235 0.45 275 0.36 305 0.31 335 0.26 423 495 549 603 620 726 805 884 -

Three Core Phase Current Volt Drop/ Carrying A/m Capacity A mV 19 25.1 25 15.8 32 10.5 43 6.3 58 3.9 74 2.5 90 1.8 115 1.3 135 0.93 165 0.68 190 0.54 215 0.45 250 .37 295 0.30 340 0.25 415 0.225 -

Backup Fuse

AC resistance at 200C

A 10 16 16 25 32 40 50 63 80 100 120 125 150 160 200 225 250 320 400 425 450 450 500 630 630 800

Ohm/km(app) 14.491 9.122 6.062 3.637 2.252 1.443 1.039 0.751 0.537 0.393 0.312 0.250 0.214 0.173 0.144 0.090 -

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280

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NOTES

281

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282

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283

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284

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285