Ministry Of Higher Education And Scientific Research University Of Anbar Department Of Electrical Engineering

Ministry Of Higher Education And Scientific Research University Of Anbar Department Of Electrical Engineering

Designing and assembling of a laboratory panel to simulate The overhead insulators Senior Project Report Submitted to the Department of Electrical Engineering in Partial Fulfillment of the Requirements for the Bachelor Degree of Science in Electrical Engineering

By 1-Ahmed Radi Hassan 2-Fatima Magdi Attia 3-Mustafa Othman Hameed

Supervised by Yasir A.AhmeD

List of Contents Subject

page

List of Contents

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Chapter One: General introduction 1.1 Introduction

1

1.2 Aim of work 1.3 Outline of thesis

2 2

Chapter Two: Overhead Insulators 2.1 Introduction

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2.2 Material 2.3 Types of Electrical Insulator 2.4 Potential Distribution over Suspension Insulator String 2.5 String Efficiency

4 8 12 13

Chapter Three: Result and Calculation 3.1 Introduction

16

3.2 Equivalent Circuit

18

3.3 Result 3.4 Conclusions 3.5 Experiment

20 22 23

References

27

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‫اعوذ باهلل السميع العليم من الشيطان الرجيم‬

‫(يرفع هللا الذين آمنوا منكم‬ ‫والذين أوتوا العلم درجات‬ ‫وهللا بما تعملون خبير)‬ ‫المجادلة ‪11‬‬

Acknowledgements Thanks to Allah for his bless we could complete our research. My supervisor , Yasir A.Ahmed, thank you for given us opportunity to complete my thesis your continuous passion and desire to guide us throughout the year in this Final Year project are highly appreciated. Lastly, a special thanks to all our family members, especially father and mother for their encouragement and support which had given us. Not forgotten our brothers and sisters, your sacrifice and love had given us strength to finish up the Final Year Project successfully.

Thank you

Abstract Insulators are used in overhead transmission lines to achieve two purposes: the first is to carry the electrical conductors. This requires a mechanical force to ensure this and the second for the purpose of securing a safe electrical insulation between the electrical conductors and the high pressure towers. The design and selection of the required insulators require special calculations after the completion of the electrical circuit equivalent to the required insulation and then the way to improve the efficiency of these insulators. In this work, a training board was designed for the students of the Department of Electrical Engineering to train them to complete the electrical circuit equivalent to the insulators and study their properties and measuring voltages on each part of it and calculate efficiency in any way. This will help the students to stand up to all these procedures in practice. A practical experiment has been developed for laboratory testing

‫تستعمل العوازل في خطوط الضغط العالي لتحقيق غرضين هما االول حمل الموصالت‬ ‫الكهربائية وهذا يتطلب قوة ميكانيكية تكفل ذلك والثاني لغرض تامين عزل كهربائي آمن بين‬ ‫ ان تصميم واختيار العوازل الالزمة تتطلب‬.‫الموصالت الكهربائية وابراج الضغط العالي‬ ‫حسابات خاصة بعد انجاز الدائرة الكهربائية المكافئة للعازل المطلوب ومن ثم طريق تحسين‬ ‫ في هذا العمل تم تصميم وتجميع لوحة تدريبية لطلبة قسم الهندسة الكهربائية‬.‫كفاءة هذه العوازل‬ ‫لتدريبهم على انجاز الدائرة الكهربائية المكافئة للعوازل ودراسة خواصها وقياس الفولتيات على‬ ‫ وهذا مم سيساعد الطلبة على للوقوف‬. ‫كل جزء من اجزاءها وحساب الكفاءة عند اي طريقة‬ ‫ كما تم اعداد تجربة عملية لغرض اجراء التجربة مختبريا‬.‫عمليا على جميع هذه االجراءات‬

Chapter One General Introduction 1.1 Introduction An electrical insulator is a material whose internal electric charges do not flow freely, and therefore make it nearly impossible to conduct an electric current under the influence of an electric field. This contrasts with other materials, semiconductors and conductors, which conduct electric current more easily. The property that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or conductors.A perfect insulator does not exist, because even insulators contain small numbers of mobile charges (charge carriers) which can carry current. In addition, all insulators become electrically conductive when a sufficiently large voltage is applied that the electric field tears electrons away from the atoms. This is known as the breakdown voltage of an insulator. Some materials such as glass, paper and Teflon, which have high resistivity, are very good electrical insulators. A much larger class of materials, even though they may have lower bulk resistivity, are still good enough to prevent significant current from flowing at normally used voltages, and thus are employed as insulation for electrical wiring and cables Examples include rubber-like polymers and most plastics. Insulators are used in electrical equipment to support and separate electrical conductors without allowing current through themselves. An insulating material used in bulk to wrap electrical cables or other equipment is called insulation. The term insulator is also used more specifically to refer to insulating supports used to attach electric power distribution or transmission lines to utility poles and transmission towers. They support the weight of the suspended wires without allowing the current to flow through the tower to ground .Insulator strings are widely used in power systems for the dual task of mechanically supporting and electrically isolating the live phase conductors from the support tower. This is due to their high mechanical strength, easy installation and operation, and low cost. The number of units of an insulator string depends on several factors such as operation voltage, mechanical strength, sea level (of alignment), lightning strength, and contamination level of the environment. Due to the coupling capacitance between disc insulators and conductors around them, the

1

potential distribution of insulator string is uneven greatly. The voltage and electric field on the insulators near wires is three to five times greater than others, which may easily lead to corona, insulators’ surface deterioration and even flashover. And these problems will seriously affect the operation safety of transmission lines. So the calculation of the electric field and voltage distribution in and around high voltage insulators is a very important factor in the design of the insulators. Furthermore, the knowledge of the electric field is useful for the detection of defects in insulators.The overhead line conductors should be supported on the poles or towers in such a way that currents from conductors do not flow to earth through supports i.e., line conductors must be properly insulated from supports .This is achieved by securing line conductors to supports with the help of insulators. [1][2][3] The insulators provide necessary insulation between line conductors and supports and thus prevent any leakage current from conductors to earth. *The function of the insulators are: 1- Insulate the conductors from each other and from the towers under highest voltage and under bad air estimate circumstance 2-Carry the conductors under the bad estimate mechanical stresses

1.2 Aim Of Work The main aim of the project included at several points: 1. Designing a laboratory panel to use in electrical power lab, for it doesn't exist in the university laboratories. 2. Training the students on this device to simulate the electrical insulator 1.3 Outline Of Thesis Our project included a number of chapters and each of the separation contains a number of concepts. Chapter One: it contains a general introduction of the insulators as well as it ensures the basic objective of the project and an Outline of thesis Chapter two: one of the most important chapters dealing with the topics of basic insulation and illusions are substances that insulators and the importance of every kind made of them by article made of them, as well as the general classification Insulation Insulation according to where they are used. Turning this chapter to how the distribution of voltages on insulators and efficient manner and methods of calculating happen improve time through this chapter shows that it is possible

2

representation insulators for power transmission lines in the form of capacitors to facilitate study. Chapter three: Contains the contents and details of each part in the laboratory board. Experimenting a practical experience to calculate the efficiency of the insulators and compare them with the actual values in the case of the presence and non-use of the guard ring insulator

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Chapter Two Overhead Insulators 2.1 Introduction Insulator strings are widely used in power systems for the dual task of mechanically supporting and electrically isolating the live phase conductors from the support tower. This is due to their high mechanical strength, easy installation and operation, and low cost. The number of units of an insulator string depends on several factors such as operation voltage, mechanical strength, sea level (of alignment), lightning strength, and contamination level of the environment. [7] Due to the coupling capacitance between disc insulators and conductors around them, the potential distribution of insulator string is uneven greatly. The voltage and electric field on the insulators near wires is three to five times greater than others, which may easily lead to corona, insulators’ surface deterioration and even flashover. And these problems will seriously affect the operation safety of transmission lines. So the calculation of the electric field and voltage distribution in and around high voltage insulators is a very important factor in the design of the insulators. Furthermore, the knowledge of the electric field is useful for the detection of defects in insulators. [1]

2.2 Material Insulators used for high-voltage power transmission are made from glass, porcelain or composite polymer materials. Porcelain insulators are made from clay, quartz or alumina and feldspar, and are covered with a smooth glaze to shed water. Insulators made from porcelain rich in alumina are used where high mechanical strength is a criterion. Porcelain has a dielectric strength of about 4–10 kV/mm.[1] Glass has a higher dielectric strength, but it attracts condensation and the thick irregular shapes needed for insulators are difficult to cast without internal strains.[2] Some insulator manufacturers stopped making glass insulators in the late 1960s, switching to ceramic materials. Recently, some electric utilities have begun converting to polymer composite materials for some types of

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insulators. These are typically composed of a central rod made of fibre reinforced plastic and an outer weather shed made of silicone rubber or ethylene propylene diene monomer rubber (EPDM). Composite insulators are less costly, lighter in weight, and have excellent hydrophobic capability. This combination makes them ideal for service in polluted areas. However, these materials do not yet have the long-term proven service life of glass and porcelain. [13] 2.2.1 Properties of Insulating Material The materials generally used for insulating purpose is called insulating material. For successful utilization, this material should have some specific properties as listed below [12] 1. It must be mechanically strong enough to carry tension and weight of conductors. 2. It must have very high dielectric strength to withstand the voltage stresses in High Voltage system. 3. It must possesses high Insulation Resistance to prevent leakage current to the earth. 4. The insulating material must be free from unwanted impurities. 5. It should not be porous. 6. There must not be any entrance on the surface of electrical insulator so that the moisture or gases can enter in it. 7. There physical as well as electrical properties must be less effected by 8. changing temperature.[4][10] 2.2.2 Sections insulators for the material, which makes them 2.2.2.1 Porcelain Insulator

Fig (2.1) Porcelain Insulator porcelain in most commonly used material for overhead insulator in present days. The porcelain is aluminum silicate. The aluminum silicate is mixed with plastic kaolin, feldspar and quartz to obtain final hard and 5

glazed porcelain insulator material. The surface of the insulator should be glazed enough so that water should not be traced on it. Porcelain also should be free from porosity since porosity is the main cause of deterioration of its dielectric property. It must also be free from any impurity and air bubble inside the material which may affect the insulator properties. [6] Table (2.2) Properties of Porcelain Insulator Property Value(Approximate) Dielectric Straight

60 KV / cm

Compressive Strength

70,000 Kg / cm2

Tensile Strength

500 Kg / cm2

2.2.2.2 Glass Insulator Now day's glass insulator has become popular in transmission and distribution system. Annealed tough glass is used for insulating purpose. Glass insulator has numbers of advantages over conventional porcelain insulator. [3]

Fig (2.2) Glass Insulator Advantages Of Glass Insulator 1. It has very high dielectric strength compared to porcelain. Its resistivity is also very high. 2. It has low coefficient of thermal expansion. 3. It has higher tensile strength compared to porcelain insulator. 6

4. As it is transparent in nature theis not heated up in sunlight as porcelain. 5. The impurities and air bubble can be easily detected inside the glass insulator body because of its transparency. 6. Glass has very long service life as because mechanical and electrical properties of glass do not be affected by ageing. 8. After all, glass is cheaper than porcelain. Disadvantages of Glass Insulator 1. Moisture can easily condensed on glass surface and hence air dust will be deposited on the wed glass surface which will provide path to the leakage current of the system. 2. For higher voltage glass can not be cast in irregular shapes since due to irregular cooling internal cooling internal strains are caused. Table (2.2) Properties of Glass Insulator Property

Value(Approximate)

Dielectric Straight

140 KV / cm

Compressive Strength

10,000 Kg / cm2

Tensile Strength

35,000 Kg / cm2

2.2.2.3 Polymer Insulator

Fig (2.3) Polymer Insulator 7

In a polymer insulator has two parts, one is glass fiber reinforced epoxy resin rod shaped core and other is silicone rubber or EPDM (Ethylene Propylene Diane Monomer) made weather sheds. Rod shaped core is covered by weather sheds. Weather sheds protect the insulator core from outside environment. As it is made of two parts, core and weather sheds, polymer insulator is also called composite insulator. The rod shaped core is fixed with Hop dip galvanized cast steel made end fittings in both sides. [6] Advantages of Polymer Insulator 1. It is very light weight compared to porcelain and glass insulator. 2. As the composite insulator is flexible the chance of breakage becomes minimum. 3. Because of lighter in weight and smaller in size, this insulator has lower installation cost. 4. It has higher tensile strength compared to porcelain insulator. 5. Its performance is better particularly in polluted areas. 6. Due to lighter weight polymer insulator imposes less load to the supporting structure. 7. Less cleaning is required due to hydrophobic nature of the insulator. Disadvantages of Polymer Insulator. 1. Moisture may enter in the core if there is any unwanted gap between core and weather sheds. This may cause electrical failure of the insulator. 2. Over crimping in end fittings may result to cracks in the core which leads to mechanical failure of polymer insulator.

2.3 Types of Electrical Insulator The successful operation of an overhead line depends to a considerable extent upon the proper selection of insulators. There are several types of insulators but the most commonly used are pin type, suspension type, Strain insulator and shackle insulator. 2.3.1 Pin Type Insulators The part section of a pin type insulator is shown in Fig (2.4) as the Name suggests, the pin type insulator is secured to the cross-arm on the pole. There is a groove on the upper end of the insulator for housing the conductor. The conductor passes through this groove and is bound by the annealed wire of the same material as the conductor See Fig (2.4) Pin type insulators are used for transmission and distribution of electric power at voltages up to 33 kV. Beyond operating voltage of 33 kV, the

8

pin type insulators become too bulky and hence uneconomical as in fig (2.5)

Fig (2.4) Pin type insulators

Fig (2.5) Pin type insulators

2.3.2. Suspension Insulator. The cost of pin type insulator increases rapidly as the working voltage is increased. Therefore, this type of insulator is not economical beyond 33 kV. For high voltages (>33 kV), it is a usual practice to use suspension type insulators shown in Fig(2.6) They consist of a number of porcelain discs connected in series by metal links in the form of a string. The conductor is suspended at the bottom end of this string while the other end of the string is secured to the cross-arm of the tower. Each unit or disc is designed for low voltage, say 11 kV. The number of discs in series would obviously depend upon the working voltage. For instance, if the working voltage is 66 kV, then six discs in series will be provided on the string. [12][7] Advantages Of Suspension Insulator. 1. Suspension type insulators are cheaper than pin type insulators for voltages beyond 33 kV. 2. Each unit or disc of suspension type insulator is designed for low voltage, usually 11 kV.Depending upon the working voltage, the desired number of discs can be connected in series. 3. If anyone disc is damaged, the whole string does not become useless because the damaged disc can be replaced by the sound one. 4. The suspension arrangement provides greater flexibility to the line. The connection at the cross arm is such that insulator string is free to swing in any direction and can take up the position where mechanical stresses are minimum.

9

5. In case of increased demand on the transmission line, it is found more satisfactory to supply the greater demand by raising the line voltage than to provide another set of conductors. The additional insulation required for the raised voltage can be easily obtained in the suspension arrangement by adding the desired number of discs. 6. The suspension type insulators are generally used with steel towers. As the conductors run below the earthed cross-arm of the tower, therefore, this arrangement provides partial protection from lightning.[9]

Fig (2.6) Suspension insulators Table (2.3) Properties of Suspension insulators Rated System Voltage

Number of disc insulator used in suspension insulator string 3 4 8 14

33kv 66kv 132kv 220kv

2.3.3 Strain insulators When there is a dead end of the line or there is corner or sharp curve, the line is subjected to greater tension. In order to relieve the line of excessive tension, strain insulators are used. For low voltage lines (< 11 kV), shackle insulators are used as strain insulators. However, for high voltage transmission lines, strain insulator consists of an assembly of suspension insulators as shown in Fig(2.7) The discs of strain insulators are used in the vertical plane. When the tension in lines is exceedingly high, as at long river spans, two or more strings are used in parallel. [12]

11

Fig (2.7) Strain insulators Table (2.4) Properties of Strain insulators Rated System Voltage Number of disc insulator used in strain type tension insulator string 33kv 3 66kv 5 132kv 9 220kv 15

2.3.4 Shackle insulators In early days, the shackle insulators were used as strain insulators as in fig (2.8). But now a days, they are frequently used for low voltage distribution lines. Such insulators can be used either in a horizontal position or in a vertical position. They can be directly fixed to the pole with a bolt or to the cross arm. Fig (8.9) shows a shackle insulator fixed to the pole. The conductor in the groove is fixed with a soft binding wire. [1][5]

Fig 2.8 Strain insulators

11

2.4 Potential Distribution Over Suspension Insulator String. A string of suspension insulators consists of a number of porcelain discs connected in series through metallic links. Fig. 1.8(i) shows 3-disc string of suspension insulators. The porcelain portion of each disc is in between two metal links. Therefore, each disc forms a capacitor C as shown in Fig.1.8 (ii). This is known as mutual capacitance or self-capacitance. If there were mutual capacitance alone, then charging current would have been the same through all the discs and consequently voltage across each unit would have been the same i.e., V/3 as shown in Fig. 1.8 (ii). However, in actual practice, capacitance also exists between metal fitting of each disc and tower or earth. This is known as shunt capacitance C1. Due to shunt capacitance, charging current is not the same through all the discs of the string See Fig 2.9(iii). Therefore, voltage across each disc will be different. Obviously, the disc nearest to the line conductor will have the maximum* voltage. Thus referring to Fig.2.9 (iii), V3 will be much more than V2 or V1.

Fig (2.9) Potential Distribution The following points may be noted regarding the potential distribution over a string of suspension insulators: 1. The voltage impressed on a string of suspension insulators does not distribute itself uniformly across the individual discs due to the presence of shunt capacitance.

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2. The disc nearest to the conductor has maximum voltage across it. As we move towards the cross-arm, the voltage across each disc goes on decreasing. 3. The unit nearest to the conductor is under maximum electrical stress and is likely to be punctured. Therefore, means must be provided to equalise the potential across each unit. 4. If the voltage impressed across the string were d.c then voltage across each unit would be the same. It is because insulator capacitances are ineffective for d.c.

2.5 String Efficiency As stated above, the voltage applied across the string of suspension insulators is not uniformly distributed across various units or discs. The disc nearest to the conductor has much higher potential than the other discs. This unequal potential distribution is undesirable and is usually expressed in terms of string efficiency .The ratio of voltage across the whole string to the product of number of discs and the voltage across the disc nearest to the conductor is known as string efficiency i.e. String efficiency(𝜂) =

Voltage across the string 𝑛 × Voltage across disc nearest to conductor

where n = number of discs in the string. String efficiency is an important consideration since it decides the potential distribution along the string. The greater the string efficiency, the more uniform is the voltage distribution. Thus 100% string efficiency is an ideal case for which the voltage across each disc will be exactly the same. Although it is impossible to achieve 100% string efficiency, yet efforts should be made to improve it as close to this value as possible. 2.5.1 Methods Of Improving String Efficiency It has been seen above that potential distribution in a string of suspension insulators is not uniform. The maximum voltage appears across the insulator nearest to the line conductor and decreases progressively as the cross arm is approached. If the insulation of the highest stressed insulator (i.e. nearest to conductor) breaks down or flash over takes place, the breakdown of other units will take place in succession. This necessitates

13

to equalize the potential across the various units of the string i.e. to improve the string efficiency. 2.4.1.1 By using longer cross-arms. The value of string efficiency depends upon the value of K as in fig (1.9) i.e., ratio of shunt capacitance to mutual capacitance. The lesser the value of K, the greater is the string efficiency and more uniform is the voltage distribution. The value of K can be decreased by reducing the shunt capacitance. In order to reduce shunt capacitance, the distance of conductor from tower must be increased i.e., longer cross-arms should be used. However, limitations of cost and strength of tower do not allow the use of very long cross-arms. In practice, K = 0·1 is the limit that can be achieved by this method.

Fig (2.10) By using longer cross-arms. 2.5.1.2 By grading the insulators. In this method, insulators of different dimensions are so chosen that each has a different capacitance. The insulators are capacitance graded i.e. they are assembled in the string in such a way that the top unit has the minimum capacitance, increasing progressively as the bottom unit (i.e., nearest to conductor) is reached. Since voltage is inversely proportional to capacitance, this method tends to equalize the potential distribution across the units in the string. This method has the disadvantage that a large number of different-sized insulators are required. However, good results can be obtained by using standard insulators for most of the string and larger units for that near to the line conductor.[5]

14

2.5.1.3 By Using a Guard Ring. The potential across each unit in a string can be equalized by using a guard ring which is a metal ring electrically connected to the conductor and surrounding the bottom insulator as shown in the Fig (2.10) The guard ring introduces capacitance be.[9]

Fig.2.11. guard ring

15

Chapter three Result and Calculation 3.1 Introduction A laboratory lab was designed to train students on the specifications of insulators for power transmission lines, the painting was composed as follows 3.1.1 BOARD The board is made of aluminum material and has the appropriate measurements as shown below in the form

Fig (3.1) Board dimensions

16

The board contains many of the most important things 3.1.1.1 Capacitors This type of electronic component was used to represent the insulators as each disc of the insulators was represented by one capacitor .Three types of condoms were used in the project 3.1.1.1.1 Self Capacitors Represents the number of real disks for insulation it was selected with a scale of 100nf which is represented by the value of c as in figure (3.2) 3.1.1.1.2 Shunt Capacitors The capacitors formed by the earth represent 10% of the value of the main expansions .Which is equivalent to the value of c1 as in Fig (3.2) 3.1.1.1.3 Line Capacitors They are insulators that are bonded between the main insulator and the line which is worth 5% of the value of the self capacitors which represented by the symbol c2 and is as in Fig(3.2)

Fig (3.2) Types of capacitors use

17

3.1.1.2 Transformers We have used transformers to obtain different levels of voltages to determine their effect on insulation efficiency. Four transformers were used and their values were First Transformer (220V / 110V) Second transformer (220V / 33V) Third Transformer (220V / 380V) The fourth transformer (220V / 12V)

3.2 Equivalent Circuit

Fig (3.3) Equivalent Circuit 3.2.1 Ideal Circuit

Fig (3.4) Ideal Circuit 18

3.2.2 Shunt circuit

Fig (3.5) shunt circuit

3.2.3 Circuit With Guard Ring

Fig (3.6) Circuit with Guard Ring

19

3.3 Result When connecting the circuit to four discs of insulator we will observe actual measurements as well as laboratory measurements 3.3.1 Result With Out Guard Ring At first we connect the insulator without the guard isolator and calculate both actual and laboratory readings 3.3.1.1 Actual Measurements 𝑉1 = 21.3𝑣 𝑉2 = 23.5𝑣 𝑉3 = 28𝑣 𝑉4 = 35.25𝑣

Fig (3.6) Actual Circuit 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦

𝜂=

𝑡𝑜𝑡𝑎𝑙 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑎𝑐𝑟𝑜𝑠𝑠 𝑡ℎ𝑒 𝑠𝑡𝑟𝑖𝑛𝑔 × 100 𝑛 × 𝑤𝑜𝑟𝑘𝑖𝑛𝑔 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑎𝑐𝑟𝑜𝑠𝑠 𝑏𝑜𝑡𝑡𝑜𝑛 𝑢𝑛𝑖𝑡

𝜂=

108 × 100% = 76.635% 4 × 35.25

3.3.1.2 Laboratory Measurements

𝜂

Fig (3.7) Laboratory Circuit 21

Voltages

values

𝑉1

21.62v

𝑽𝟐

23.54v

𝑽𝟑

27.83v

𝑉4

34.73 𝟏𝟎𝟖 × 𝟏𝟎𝟎% = 𝟕𝟕. 𝟕𝟒% 𝟒 × 𝟑𝟒. 𝟕𝟑

3.3.2 Result With Guard Ring After connecting the guard ring insulator, and calculate both actual and laboratory measurements. We will notice after connecting the insulator the guard that the efficiency will increase 3.3.2.1 Actual Measurements

𝑉1 = 34.3𝑣 𝑉2 = 21.2𝑣 𝑉3 = 21𝑣 𝑉4 = 31.5𝑣

Fig (3.8) Actual Circuit

𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦

𝜂=

𝑡𝑜𝑡𝑎𝑙 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑎𝑐𝑟𝑜𝑠𝑠 𝑡ℎ𝑒 𝑠𝑡𝑟𝑖𝑛𝑔 × 100 𝑛 × 𝑤𝑜𝑟𝑘𝑖𝑛𝑔 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑎𝑐𝑟𝑜𝑠𝑠 𝑏𝑜𝑡𝑡𝑜𝑛 𝑢𝑛𝑖𝑡

𝜂=

108 4 × 31

× 100% = 85.7%

3.3.1.2 Laboratory Measurements

𝜂

Fig (3.9) Laboratory circuit

21

Voltages

values

𝑉1

34.5v

𝑽𝟐

21.3v

𝑽𝟑

20.7v

𝑉4

31.85 𝟏𝟎𝟖 × 𝟏𝟎𝟎% = 𝟖𝟒. 𝟕% 𝟒 × 𝟑𝟏. 𝟖𝟓

3.4 Conclusions When experimenting and calculating laboratory values, we found a small difference between theoretical values and laboratory values where the value of laboratory efficiency (77.74%) and theoretical value (76.635%) after the use of the guard buffer was the laboratory values (84.7%) and the theoretical value (85.7% ) Through the results in both cases we observed increased efficiency when using the guard isolator and this is required

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3.5 Experiment

Voltage Distribution on the Insulators of Overhead Transmission Line Towers Object: the object of this experiment is to teach the student how to calculate the distribution of voltages on the insulators of overhead transmission line towers. Theory: The function of insulators is to support the conductor on towers or poles while keeping safe electrical insulations. Insulators are mechanically strong and electrically no conducting under worst weather conditions. Electrically each disk of suspension insulator can be represented as a capacitance. Under normal conditions, the string can be represented as a capacitance unites in series. The voltage across each similar disk will be uniform. But because of the presence of tower metal parts in the vicinity the voltage distribution becomes non uniform.

In general 𝑖 = 𝑗𝜔𝐶𝑉 This technique will be applied on (n) insulators as shown in the figure below

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Apply Kirchhoff law at point A 𝑖2 = 𝐼1 + 𝑖1 𝑗𝜔𝐶𝑉2 = 𝑗𝜔 𝐾𝐶𝑉1 + 𝑗𝜔𝐶𝑉1 𝑉2 = (1 + 𝐾) 𝑉1

……..(1)

Apply Kirchhoff law at point B 𝑖3 = 𝐼2 + 𝑖2 𝑉3 = (1 + 3𝐾 + 𝐾 2 ) 𝑉1

……..(2)

On the same way 𝑉4 = (1 + 6𝐾 + 5𝐾 2 + 𝐾 3 ) 𝑉1 This will be done until we reach the last one 𝑉𝑛 𝑉 = 𝑉1 + 𝑉2 + 𝑉3 + 𝑉4 + ⋯ … . . +𝑉𝑛 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦

𝜂=

𝑡𝑜𝑡𝑎𝑙 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑎𝑐𝑟𝑜𝑠𝑠 𝑡ℎ𝑒 𝑠𝑡𝑟𝑖𝑛𝑔 × 100 𝑛 × 𝑤𝑜𝑟𝑘𝑖𝑛𝑔 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑎𝑐𝑟𝑜𝑠𝑠 𝑏𝑜𝑡𝑡𝑜𝑛 𝑢𝑛𝑖𝑡

Procedure: 1- Measure the voltage across each capacitor by means of voltmeter without the effect of the tower material.

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2- Measure the voltage across each capacitor by means of voltmeter take into account the effect of the tower material. 3- Measure the voltage across each capacitor by means of voltmeter take into account the effect of the tower material and guard ring. 4- Calculate the efficiency in each case. 5- Compare each practical result with the theoretical one. 6- Record the result in the table below. Voltages Ideal Presence of Presence of theoretical tower guard ring 𝑉1 𝑉2 𝑉3 𝑉4 𝑉5 𝑉6 Report and Discussion: 12345-

Calculate the string efficiency from the practical results. Calculate theoretically the voltage across each capacitor. Calculate theoretically the string efficiency. Compare between practical and theoretical efficiencies. Compare between the efficiencies with and without using guard ring.

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REFERENCES: [1]. V.k Mehta“PRINCIPLE OF POWER SYSTEM ”,Proceedings of Generation, Transmission and Distribution, Vol. 153, No. 3, pp. 343–349, May 2006. [2]. B. Wang, ZR. Peng, “A Finite Element Method for the Calculation of the Voltage Distribution along the 500kV Line Insulators”, Insulators and Surge Arresters, No.1, pp.13-15, 2003. [3]. V.T. Kontargyri, I.F. Gonos, I.A. Stathopulos, A.M. Michaelides, “Measurement and verification of the voltage distribution on high-voltage insulators”, Proceedings of the 12th Biennial IEEE Conference on Electromagnetic Field Computation (CEFC 2006), Maimi, FL, April, 2006. [4]. S. M. Al Dhalaan, and M. A. Elhirbawy, “Simulation of voltage distribution calculation methods over a string of suspension insulators”, 2003 IEEE PES Transmission and Distribution Conference and Exposition, Vol. 3, pp. 909-914, 2003. [5]. E. Izgi., A. Inan, and S. Ay, “The analysis and simulation of voltage distribution over string insulators using Matlab/Simulink”, Electric Power Components and Systems, Vol. 36, No. 2, pp. 109–123,2008. [6]. W. McAllister, “Electric fields and electrical insulation”, IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 9, No. 5, pp. 672-696, 2002. [7]. H. Wei, Y. Fan, W. Jingang, Y. Hao, C. Minyou, and Y. Degui, “Inverse application of charge simulation method in detecting faulty ceramic insulators and processing influence from tower”, IEEE Transactions on Magnetics, Vol. 42, No. 4, pp. 723-726, 2006. [8]. N. Morales, E. Asenj, and A. Valdenegro, “Field solution in polluted insulators with non-symmetric boundary conditions”, IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 8, No. 2, pp. 168-172, 2001. [9]. T. Zhao, and M. G. Comber, “Calculation of electric field and potential distribution along no ceramic insulators considering the effects of conductors and transmission towers”, IEEE Transactions on Power

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Delivery, Vol. 15, No. 1, pp. 313-318, 2000. [10]. Sh. M. Faisal, “Simulation of Electric Field Distribution on Ceramic Insulator Using Finite Element Method”, European Journal of Scientific Research, Vol.52, No.1, pp.5260, 2011. [11]. M. Ashouri, M. Mirzaie, and A. Gholami, “Calculation of Voltage Distribution along Porcelain Suspension Insulators Based on Finite Element Method”, Electric Power Components and Systems, Vol. 38, pp. 820-831, 2010. [12]. B. S. Reddy, N. A. Sultan, P. M. Monika, B. Pooja, O. Salma and K. V. Ravishankar, “Simulation of potential and electric field for high voltage ceramic disc insulators”, International Conference on Industrial and Information Systems (ICIIS) Indian Institute of Science, Bangalore, India, 2010, , 13. "Electrical Porcelain Insulators" (. Product spec sheet. Universal Clay Products, Ltd. Retrieved 2008-10-19.

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