1. 1. Group Members Usman Rehman M. Saleem M. Zeeshan
2. 2. Content Introduction to Circuit breaker Basic Defination Of Circuit Breaker Working Principle of Circuit Breaker Types Of Circuit Breakers 1. Oil Circuit Breakers 2. Vacuum Circuit Breakers 3. Air Blast Circuit Breakers 4. SF6 Circuit Breakers 5. Miniature Circuit Breakers 6. Earth Leakage Circuit Breakers Precautions with CB CONCLUSION
3. 3. 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.
4. 4. Basic Defination Of Circuit Breaker : . A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow.
5. 5. 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. 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. When fault occurs on any part of the system, the trip coil of the circuit breaker get energized and contacts are separated.
6. 6. Breaker Components All breakers contain the same basic components: Stationary Main Line Contacts Moveable Mainline Contacts Arcing Contacts Auxiliary Contacts Arc Interrupting Device Closing Mechanism Opening Mechanism Control Mechanism Interlocks Frame Assembly
7. 7. Arc Phenomenon An arc is struck when contacts are separated. The current is thus able to continue. Thus the main duty of a circuit breaker is to distinguish the arc within the shortest possible time. The arc provides the low resistance path to the current and the current in the circuit remains uninterrupted.
8. 8. A breaker is designed to provide quick isolation of a component from a voltage source. Circuit Breaker selection process is based upon the use and type of Arc Control desired.
9. 9. Frequency Frequency selection is solely based on the application that the breaker will serve. Operating at the improper frequency could change the characteristics of how the breaker would operate. This is primary concern for breakers that rely upon inductive trip mechanisms. Breakers are generally designed for 50 and 60 Hz. Other models are available based of specific applications.
10. 10. Types Of Circuit Breakers Oil Circuit Breakers Vacuum Circuit Breakers Air Blast Circuit Breakers SF6 Circuit Breakers Miniature Circuit Breakers Earth Leakage Circuit Breakers
11. 11. OIL CIRCUIT BREAKER It is designed for 11kv-765kv. These are of two types BOCB (Bulk oil Circuit Breaker) MOCB (Minimum oil Circuit Breaker) The contacts are immersed in oil bath. Oil provides cooling by hydrogen created by arc. It acts as a good dielectric medium and quenches the arc.
12. 12. Advantages: Oil has good dielectric strength. Low cost. Oil is easily available. It has wide range of breaking capability. Disadvantages: Slower operation , takes about 20 cycles for arc quenching. It is highly inflammable , so high risk of fire. High maintenance cost.
13. 13. VACCUM CIRCUIT BREAKER It is designed for medium voltage range (3.3-33kv). This consists of vacuum of pressure (1*10-6) inside arc extinction chamber. The arc burns in metal vapour when the contacts are disconnected. At high voltage , its rate of dielectric strength recovery is very high. Due to vacuum arc extinction is very fast. The contacts loose metals gradually due to formation of metal vapours.
14. 14. Advantages: Free from arc and fire hazards. Low cost for maintenance & simpler mechanism. Low arcing time & high contact life. Silent and less vibrational operation. Due to vacuum contacts remain free from corrosion. No byproducts formed. Disadvantages: High initial cost due to creation of vacuum. Surface of contacts are depleted due to metal vapours. High cost & size required for high voltage breakers.
15. 15. AIR BLAST CIRCUIT BREAKERS This operates using high velocity blast of air which quenches the arc. It consists of blast valve , blast tube & contacts. Blast valve contains air at high pressure. Blast tube carries the air at high pressure & opens the moving contact attached to spring. There is no carbonization of surface as in VCB. Air should be kept clean & dry to operate it properly.
16. 16. Advantages: High speed operation as compared to OCB. Ability to withstand frequent switching. Facility for high speed enclosure. Less maintenance as compared to OCB. Disadvantages: Little moisture content prolongs arcing time. Pressure should be checked frequently for frequent operation. Risk of fire hazards due to over voltages. It cant be used for high voltage operation due to prolonged arc quenching.
17. 17. SF6 CIRCUIT BREAKERS It contains an arc interruption chamber containing SF6 gas. In closed position the contacts remain surrounded by SF6 gas at a pressure of 2.8 kg/cm2 . During opening high pressure SF6 gas at 14 kg/cm2 from its reservoir flows towards the chamber by valve mechanism. SF6 rapidly absorbs the free electrons in the arc path to form immobile negative ions to build up high dielectric strength. It also cools the arc and extinguishes it. After operation the valve is closed by the action of a set of springs. Absorbent materials are used to absorb the byproducts and moisture.
18. 18. Advantages: Very short arcing period due to superior arc quenching property of SF6 . Can interrupt much larger currents as compared to other breakers. No risk of fire. Low maintenance, light foundation. No over voltage problem. There are no carbon deposits. Disadvantages: SF6 breakers are costly due to high cost of SF6. SF6 gas has to be reconditioned after every operation of the breaker, additional equipment is required for this purpose.
19. 19. MINIATURE CIRCUIT BREAKER An MCB is an Electromagnetic Device which Operates and Disconnects the Circuit when the Current reaches a pre determined value. It is most modern substitute for conventional rewireable fuse with most accurate & efficient system in over-load & short circuit protection. In fact, it provides over-load protection & short circuits protection whereas FUSE offers short circuit protection only. An MCB will normally operate at 1.25 times it rated current i.e. 20 A. MCB operates at 25 A compared with 30 A for cartridge fuse or 40 A for rewireable type of fuse of the same rating.
20. 20. Also the MCB which has tripped due to over-load or short circuit can be readily identified as the dolly or toggle or operating knob automatically moves to the OFF position. PRINCIPLE OF OPERATION : MCB is a device which operates on the two metallic plates for the protection against over-load & short circuit. 1. Thermal for normal overload protection. 2. Magnetic for the short Circuit protection .
21. 21. The thermal operation is achieved by metallic strip, which defects when heated by any over current flowing through it . In doing so release the latch mechanism and causes the contacts to open. When short Circuit occurs, the rising energizes the solenoid operating plunger to strike the trip lever causing immediate release of the latch mechanism
22. 22. CLASSIFICATION OF MCBs: 1.L-Series MCB for Lighting Circuits:- Suitable for resistive Load installation with Low & Steady Currents like heaters , ovens, geysers, electric irons , etc. The L-Series MCBs are also used for protection of distribution equipment like wires, Cables, metering equipment etc. 2.G-Series MCB for Motor Circuits:- It is suitable for use in installation with high inrush current peaks which require closer over-load protection. These include inductive Loads such as motors, A.C. transformers , halogen fluorescent sodium vapor lamps , machine tools etc.
23. 23. APPLICATION OF MCB: They are required in homes, offices, shops distribution boards for protection of individual circuit & complete wiring system in that buildings through main circuits. Whatever be the application, these MCBs offer perfect over-load & circuit protection. ON OFF
24. 24. EARTH LEAKAGE CIRCUIT BREAKER : An Earth Leakage Circuit Breaker is a safety device used in electrical installations with high earth impedance to prevent Shock. Many electrical installations have a relatively high earth impedance. These may be due to use of local earth rod to dry ground conditions. These installations have a major problem if no ELCB is used. During live to earth fault current,two conditions occur. Because earth impedance is high,
25. 25. 1. Not enough current exist to trip a fuse or circuit breaker, so condition persists uncleared indefinitely . 2. The high impedance earth can not keep the voltage of all exposed CPC connected metalwork to safe voltage all such metalwork may rise to close to live conductor voltage. TYPES OF ELCB: I. Voltage Operated:- They Provide a major advance in safety for mains electrical supplies with inadequate earth impedance. II. Current Operated:- They Provide protection against earth leakage, through the details & method of operation are different.
26. 26. PRINCIPLE OF OPERATION: It is a current operated device designed to operate when a leakage current exceeds a pre-determined value. It essentially consist of an operating coil & a trip mechanism which operates contacts controlling the supply to the circuit concerned. Consider a single-phase circuit. The two supply wires i .e. phase & neutral are fed through separate winding of current transformer as shown in the fig: another winding controls the tripping mechanism.
27. 27. Ip = In Therefore, the fluxes linking the phase & neutral conductors are equal in magnitude & opposite in direction. Thus, no fluxes links with tripping. Winding. ADVANTAGES : They are less sensitive to fault conditions , therefore have less nuisance strips. They can be arranged to protect against cable damage only. And not strip on faults in down line installations.
28. 28. DISADVANTAGES: They do not detect faults that dont pass current through the CPC to the earth rod. They do not allow a single building system to be easily spilt into multiple sections with independent fault protection, because earthing system are usually bounded to pipe work. ELCBs introduce additional resistance & an additional point of failure into earthing systems.
29. 29. Precautions with Breakers Always completely de- energize any breaker before servicing it. Always check voltages between phases and between each phase and ground. Always ensure that the Control Power source has been removed prior to Racking In or Out any breaker. Always use a procedure when performing any type of inspection on a breaker.
30. 30. Breaker Precautions Precautions with Breakers Avoid touching contact surfaces with bare hands. Oil from your finger tips will damage the contact face. Avoid setting a breaker on its side or back. This could damage the Secondary Disconnects, Auxiliary Contacts, or any of the control modules. Some breakers are equipped with oil filled over current devices. This oil may leak out and damage the breaker.
31. 31. Precautions with Breakers Breaker Precautions Arc Chutes should be kept clean and generally free of defects.
32. 32. Ensure that the breaker charging mechanisms is completely discharged prior to breaker disassembly. Precautions with Breakers
33. 33. Precautions with Breakers Never override an interlock. A breaker in the TEST position is still as dangerous as a breaker that is racked in. Ensure the proper lubricant is used for the right breaker. There is a difference!
34. 34. For SF6 Breakers, ensure that O2 concentrations are kept less than 18%. This will ensure that there is not a sustained arc. Precautions with Breakers Breaker Precautions
35. 35. Precautions with Breakers Breaker Precautions For Vacuum Breakers, ensure that each interrupter has the proper vacuum IAW its associated tech manual.
36. 36. CONCLUSION: Therefore, we conclude that circuit breaker is the most essential part of the electrical networks as it protects every device from damage. It helps us to detect the fault and area affected by it. Nowadays vacuum and SF6 circuit breakers are widely used due to their reliable and fast operations.