Circuit Breakers

‫قواطع الجهد المنخفض‬

‫قواطع الجهد المنخفض‬

‫ مقدمة عن القواطع‬‫ أنواع القواطع‬‫ تركيب القاطع‬‫‪-‬قراءة بيانات القواطع‬

‫ مقدمة عن القواطع‬‫و يعرف القاطع ‪ Circuit breaker‬على أنه أداة فصل ووصل للدائرة‬ ‫الكهربائية‪ ،‬يقع بين المصدر الكهربائي‪(Source‬وبين الحمال‪ Loads‬المغذاة‬ ‫من هذا المصدر‪.‬‬ ‫وتتحرك الجزاء الميكانيكية فيه إما يدويا)‪ (Manual‬أو كهربائيا)‪(Electrical‬‬ ‫لتعمل بدورها على فصل التيار الكهربائي عن مركز الحمال مهما كانت سواء‬ ‫محركات أو دوائر إضاءة أو تغذية لوحات كهربائية أو دوائر مراقبة و تحكم ‪...‬إلخ‪.‬‬ ‫ويمكن تشغيل القاطع يدويا أو كهربائيا أو ذاتيا بأشكال وطرق وتوصيلت‬ ‫مختلفة‪ ،‬وقد يكون مزودا بعناصر حماية الدوائر الكهربائية )‪Fuses Or‬‬ ‫‪ (Relays‬الكافية لحماية تلك الدائرة المستخدم فيها‪،‬وتكون وظيفته إيصال التيار‬ ‫الكهربائي إلى الدارة الكهربائية حالة أنه يراد إيصاله ويقوم بفضل التيار‬ ‫الكهربائي‪ -‬في حالة أنه يراد فصله ‪.‬‬ ‫أما الفصل الذاتي )‪ (Automatic‬فيقوم به القاطع في حالة حدوث دائرة‬ ‫قصر‪ SC‬أو خطأ))‪ Fault‬أو زيادة الحمل أو التيار أو في حالة هبوط الجهد أو‬ ‫زيادته غير ذلك من إشارات يتلقاها من النواع المختلفة من ال ‪(Relays).‬‬

‫ أنواع القواطع‬‫القواطع الكهربية المنمنمة‬ ‫)‪(Miniature circuit breaker‬‬ ‫ لحماية دوائر التوزيع النهائية وحيث يكون القاطع أقرب ما‬‫يكون للحمال‪.‬‬ ‫ تقوم القواطع المنمنة بحماية الحمال ودوائر التوزيع وكذلك‬‫الحد من الجهادات الحرارية والميكانيكية التي تنشأ من تيار‬ ‫القصر‪.‬‬ ‫ تعتمد طريقة عمل القواطع المنمنمة علي وجود مشغل‬‫مغناطيسي يقوم بتحريك القطب المتحرك في القاطع بسرعة‬ ‫عالية جدا تؤدي إلي تولد جهد قوسي في مرحلة مبكرة مما‬ ‫يحد من قيمة تيار القصر‪.‬‬ ‫‪ -‬يبدأ تيار الحماية من ‪ 0.5‬الي ‪ 125‬أمبير‪.‬‬

Definitions Main CB’s Partes -Main Circuit Pos. 6-5-4

-Operating Mechanism Pos. 10-11

-Arc Chamber Pos. 7

-Protection Release Pos. 2-9

Thermal-Magnetic Principle

Main Current & Arc Current Limiting Path

______________

Main (line) Current Path

----------------

Arc Current Limiting Path

Thermal Principle (Overload Protection) • The thermal part of the circuit breaker utilizes a bimetallic strip electrically in series with the circuit. The heat generated by the current during an overload deforms the bimetallic strip and trips the circuit breaker.

Example: Overload occurs when the vacuum is obstructed and the power cord gets overheated.

NOTE: The thermal part of the circuit breaker is temperature sensitive and can be adversely affected by changes in ambient temperature (MCB calibrated at 40° C (104° F) ).

Magnetic Principle (Short Circuit Protection)

• The magnetic part of the circuit breaker consists of an electromagnetic coil and an armature device that opens the movable contact quickly to protect the circuit whenever the current (short circuit current) exceeds a predetermined value. This happens because the current in the coil generates sufficient magnetic flux to attract the armature. Reset is manual and rapid. Example: Short circuit occurs when the hot wire and neutral/ground accidentally come together.

Trip-Characteristics & Applications

Section A Overload

Y

Time

Z

X

V

W U

Current

Section B Short Circuit

Time

Trip-Characteristics & Applications

Z

Section A Overload

Y

Current

Section A- Overload •

This section reflects the protection behavior of the circuit breaker when an overload occurs. Usually the overload increases its value above the rated current slowly. –The left line shows when the MCB does not trip. –The right line is the opposite, the MCB must trip! –The middle black line indicates the “ideal” trip curve. Due to manufacturing tolerances and surrounding influences, the MCB can only be calibrated “around” this line.

Section B Short Circuit

Time

Trip-Characteristics & Applications X V U W

Current

Section B - Short Circuit •

This section reflects the protection behavior of the circuit breaker in the case of an inrush current or a short circuit. –Inrush current occurs when the load is turned on and off (the inrush of a regular motor is approximately 6x the rated current). It is VERY important to know the inrush current when selecting the proper circuit breaker. The time of an inrush is usually between 100-500ms. If the correct circuit breaker is selected it will be insensitive to the inrush current (see points “X” & “W”). The circuit breaker will trip if the current exceeds 16XRC in 100ms (see point “V”).

Section B Short Circuit

Time

Section B - Short Circuit - Continued

X V U W

Current

–Short Circuit Current is the current which occurs in the case of a hot wire and ground/neutral coming together.

This current is usually very high (between 300A - 2000A) and the circuit breaker will trip within milliseconds. Note: If the MCB has a rated current of 10A, it will trip in 7ms, if the short circuit current is 400A (see point “U”).

TIME

The B-Trip Characteristic

CURRENT

•

Applications –Business equipment, wiring protection, lighting, appliances, control circuits, some motors and some electronic circuits • Available current –0.3A-60/63A

The C-Trip Characteristic

•

Applications –Low inrush, 3-4x rated current, motors, lighting, wiring protection, appliances, business equipment, control circuits • Available current –0.3A-60/63A

The D-Trip Characteristic

•

Applications –High inrush, 10-16x rated current, motors, transformers, power supplies, heaters, reactive loads • Available current –0.3A-60/63A

The E-Trip Characteristic

•

Application –High efficiency motors, which have very high inrush, 12x rated current • Available current –0.3-60/63A

The G-Trip Characteristic

•

Applications –General industrial, including motors, some transformers, solenoids, control circuits, lighting, wiring • Available current –0.3-60/63A

The Z-Trip Characteristic

•

Applications –Semiconductors, components with low surge current and short circuit withstand capabilities • Available current –0.3-50A

Summary of Applications/Trip Curve Selection Guide

Summary of Applications/Trip Curve Selection Guide

(Continue

.

Style

• (1 pole, B-Trip characteristic, UL Type, 16 A).

MA Three Phase Adjustable Trip Miniature Circuit Breaker

UL508 listed

CAN/CSA-C22.2 No. 14 certified C

MA Three Phase Adjustable Trip Miniature Circuit Breaker

The MA was designed to handle the high inrush loads of 3 phase transformers, power supplies, motors, etc. •

General Specifications –Complies with various national and international standards e.g. UL, CSA, VDE, IEC, CE –DIN Rail mountable –Adjustable thermal trip allows finalization of initial designs before procurement of the load equipment is complete –Voltage rating: 480Y/277 V AC –Rated current from 0.16A - 40A –3 poles • Accessories available (same as V-EA MCB) –Auxiliary Switch –Shunt Trip –Undervoltage Trip

Circuit Breaker Accessories Accessories can be factory or field mounted on V-EA miniature circuit breakers and MA motor protection switches for enhanced control and monitoring capabilities. Field mounting kits include all necessary parts and instructions. Accessories can be gang mounted on a single breaker (the Auxiliary Switch in the outside position). The mounting arrangement links the internal latch-pins for the tripping mechanisms, ensuring simultaneous trips. Handles are linked to simplify manual resetting.

Remote Trip-Shunt Trip •

Coil actuated, the FA Shunt Trip allows electrical remote tripping of a breaker. It is trip-free and the housing and terminal specifications are the same as for V-EA miniature circuit breakers.

•

The Shunt Trip contains its own contacts which break the tripping power circuit when tripped. It is available with trip-coils in the most standard control voltages.

Undervoltage Trip Re-power your system under controlled conditions following a power loss or serious undervoltage. Altech UA Undervoltage Trips are coupled to the tripping latch pins of the VEA or MA to which they are attached, reliably producing trips at the drop-out voltage and preventing resetting when less than 85% line voltage is present. The Undervoltage Trip is provided with at least 6-inch pigtails of stranded fixture wire for hook-up to the V-EA or MA line terminals.

• Reset-Hold Voltage = 0.85 x Ve • Drop-Out Voltage = 0.35 to 0.7 x Ve

Auxiliary Switch

•

Altech H Auxiliary Switch is suitable for logic interrogation and for use as a two-circuit Form C contact. It can also function as an auxiliary switch for control circuits.

More Accessories

‫‪ -‬أنواع القواطع‬

‫القواطع الكهربية المقولبة‬ ‫)‪(Moulded case circuit breaker‬‬ ‫ تتكون هذة القواطع أساسا من وحدة متكاملة‬‫مغلقة داخل صندوق محكم مصنوع من مادة‬ ‫عازلة وأغلب هذة القواطع غيرقابلة بحيث ل‬ ‫يمكن صيانتها أو استبدال القاطع بأكملة في حالة‬ ‫إصايتة بأي عطل‪.‬‬ ‫‪ -‬يبدأ تيار الحماية من ‪ 100‬الي ‪ 3200‬أمبير‪.‬‬

‫‪ -‬أنواع القواطع‬

‫القواطع الكهربية الهوائية‬ ‫)‪(Air circuit breaker‬‬ ‫ تستخدم القواطع الكهربية الهوائية عادة للتيارات‬‫المقننة العالية وتستخدم في الشبكة الكهربية إما‬ ‫كقاطع عمومي أو كقواطع عمومية للفرعيات‪.‬‬ ‫‪ -‬هذة القواطع ذات سعات عالية من حيث التيار‪.‬‬

‫‪ -‬أنواع القواطع‬

‫أجزاء القواطع الكهربية المقولبة‬ ‫)‪(Moulded case circuit breaker‬‬ ‫‪.‬‬



Residual Current Circuit Breakers (RCCB)  ‫قاطع التسريب الرضي‬

Fault Current Circuit

Residual Current Circuit

‫‪ -‬أنواع القواطع‬

‫معايرة القواطع الكهربية‬

‫العيار‬ ‫المغناطيس‬ ‫ي‬

‫العيار‬ ‫الحراري‬

‫‪ -‬أنواع القواطع‬

‫طرازالقاطع‬

‫كيفية قراءة بيانات القواطع‬

‫الجهد‬ ‫المقنن‬ ‫أقصي تيار‬ ‫للقصر‬

CONVENTIONAL CIRCUIT BREAKERS 1- Automatic Switch The simplest circuit interruption device is the knife switch shown in Fig. By closing the switch against the action of a spring, energy is stored. By applying a small force on the latch, the stored energy is released and the contacts open within a short time.

2-Air-Break Circuit Breakers Air-circuit breakers cool the gases to naturally deionize them, causing arc interruption. The arc can be stretched. Its resistance can be increased by increasing its length. The increase in resistance is significant so that the current and voltage are brought into phase. If the phase difference between the system voltage and the short-circuit current is reduced, when the current is interrupted at its zero value, the recovery voltage is very low at that instant. The application of high-resistance interruption is limited to low- and medium-power ac circuit breakers. It is also used for low- and medium-power dc circuit breakers.

METHODS FOR INCREASING ARC RESISTANCE The following methods increase the arc resistance: 1. Arc lengthening. The resistance is approximately proportional to the arc length. 2. Arc cooling. A decrease in temperature increases the voltage required to maintain ionization. Therefore, cooling effectively increases the resistance.

PLAIN BREAK TYPE The plain break type is the simplest type of air-break circuit breaker. The contacts are made in the shape of two horns, as illustrated in Fig. 19.4. The arc initially strikes across the shortest distance between the horns. Then it is driven steadily upward by the convection currents which are caused by heating the air during arcing. The arc extends between the horns. This results in lengthening and cooling of the arc. The arc interruption process is relatively slow. It limits the application of these circuit breakers to 500 V and lowpower circuits.

MAGNETIC BLOWOUT TYPE This type of circuit breaker extinguish the arc by means of a magnetic blast. It is limited to circuits up to 11 kV. The arc is subjected to the action of a magnetic field set up by coils connected in series with the circuit being interrupted (Fig.). These coils are called blowout coils because they help blow out the arc magnetically. The arc is magnetically blown into arc chutes where the arc is lengthened, cooled, and extinguished. The breaking action becomes more effective with heavy currents. This results in higher breaking capacities for these breakers. The arc chute is an efficient device for quenching the arc in air. It performs the following

interrelated functions: 1. It confines the arc within a restricted space. 2. It provides control of the movement of the arc to ensure extinction occurs within the device. 3. It cools the arc gases to ensure extinction by deionization.

ARC SPLITTER TYPE The blowouts in these breakers consist of steel inserts in the arcing chutes. These inserts are arranged so that the magnetic field induced in them by the current in the arc helps move the arc upward. The steel plates divide the arc into a number of short arcs in series. Figure illustrates an air-break arc splitter-type circuit breaker. APPLICATION In general, air-break circuit breakers are suitable for the control of power station auxiliaries and industrial plants. They combine a high degree of safety with minimum maintenance. They do not require any associated equipment such as compressors. Since they have no oil, they are recommended for locations where fire or explosion hazards are feared.

OIL CIRCUIT BREAKERS In oil circuit breakers, the arc energy is used to crack the oil molecules to generate hydrogen gas. The hydrogen is used to sweep, cool, and compress the arc plasma. This deionizes the arc plasma in a self-extinguishing process. Even if the breaker contacts are immersed in oil, arcing still occur during contact separation. The heat from the arc evaporates the surrounding oil and dissociates it into carbon and a substantial volume of gaseous hydrogen at high pressure. The heat conductivity of hydrogen is high, resulting in cooling of the arc and the contacts. This increases the ignition voltage and extinguishes the arc.

The cooling caused by the hydrogen (due to its high conductivity) is very effective. It increases the voltage required for reignition significantly (5 to 10 times higher than the reignition voltage required for air). Hydrogen is produced spontaneously in arcs under oil. Interruption of heavy short-circuit currents generates extremely high pressures which should be released safely or controlled properly. These high pressures are used to extinguish the arc which generated them.

Advantages of Oil As an arc extinguishing medium, oil has the following advantages: 1. Oil produces hydrogen during arcing. The hydrogen helps extinguish the arc. 2. The oil provides insulation for the live exposed contacts from the earthed portions of the container. 3. Oil provides insulation between the contacts after the arc has been extinguished. Disadvantages of Oil Circuit Breakers Oil has the following disadvantages when used as an arc extinguishing medium:

1. Oil is inflammable and may cause fire hazards. When a defective circuit breaker fails under pressure, it may cause an explosion. 2. The hydrogen generated during arcing, when combined with air, may form an explosive mixture. 3. During arcing, oil decomposes and becomes polluted by carbon particles which reduces its dielectric strength. Hence, it requires periodic maintenance and replacement.