1. VACUUM CIRCUIT BREAKER

2. WHAT IS A CIRCUIT BREAKER A circuit breaker is an equipment that breaks a circuit either manually or automatically under all conditions at no load, full load or short circuit. A circuit breaker is an equipment that breaks a circuit either manually or automatically under all conditions at no load, full load or short circuit.

3. VACUUM CIRCUIT BREAKERS A Vacuum circuit breaker is a circuit breaker in which vacuum is used to extinct the arc. VCB have excellent interruption and dielectric recovery characteristics, and can interrupt the high frequency currents which result from arc instability, superimposed on the line frequency current. A Vacuum circuit breaker is a circuit breaker in which vacuum is used to extinct the arc. VCB have excellent interruption and dielectric recovery characteristics, and can interrupt the high frequency currents which result from arc instability, superimposed on the line frequency current.

4. CONSTRUCTION OF VCB The main parts of a typical VCB are- Fixed contact Fixed contact Moving contact Moving contact Arc shield Arc shield Which are mounted inside a vacuum chamber.

5. CONSTRUCTION OF VCB The fixed contact is a permanent contact provided in the VCB between the insulator support and pole terminal. The fixed contact is a permanent contact provided in the VCB between the insulator support and pole terminal. The moving support is provided between the insulator and metallic bellow. The moving support is provided between the insulator and metallic bellow. The movable member is connected to the control mechanism by stainless steel bellows. The movable member is connected to the control mechanism by stainless steel bellows. This enables the permanent sealing of the vacuum chamber so as to eliminate the possibility of leak. This enables the permanent sealing of the vacuum chamber so as to eliminate the possibility of leak.

6. CONSTRUCTION OF VCB A glass vessel or ceramic vessel is used as the outer insulating body. A glass vessel or ceramic vessel is used as the outer insulating body. The arc shield prevents the deterioration of the internal dielectric strength by preventing metallic vapors falling on the inside surface of the outer insulating cover. The arc shield prevents the deterioration of the internal dielectric strength by preventing metallic vapors falling on the inside surface of the outer insulating cover.

7. PRINCIPLE OF OPERATION Two contacts called electrode remains closed under normal operating conditions. When fault occurs on any part of the system, the trip coil of the circuit breaker gets energized and contacts are separated. Two contacts called electrode remains closed under normal operating conditions. When fault occurs on any part of the system, the trip coil of the circuit breaker gets energized and contacts are separated.

8. PRINCIPLE OF OPERATION When the contacts of the breaker are opened in vacuum (10-7 to 10 -5 torr), an arc is produced between the contacts by the ionization of metal vapors of contacts. When the contacts of the breaker are opened in vacuum (10-7 to 10 -5 torr), an arc is produced between the contacts by the ionization of metal vapors of contacts. The arc is quickly extinguished because the metallic vapors, electrons and ions produced during arc condense quickly on the surfaces of the circuit breaker contacts, resulting in quick recovery of dielectric strength. The arc is quickly extinguished because the metallic vapors, electrons and ions produced during arc condense quickly on the surfaces of the circuit breaker contacts, resulting in quick recovery of dielectric strength.

9. WORKING The circuit breaker are essential as isolator cannot be used to open a circuit under normal conditions as it has no provision to quench arc that is produced after opening the line. It has to perform following function- Full load current is to be carried continuously Full load current is to be carried continuously Opening and closing the circuit on no load Opening and closing the circuit on no load Making and breaking the normal operating current Making and breaking the normal operating current Making and breaking the fault currents of magnitude up to which it is designed for. Making and breaking the fault currents of magnitude up to which it is designed for.

10. WORKING Arc extinction is the main process of a circuit breaker. We know that circuit breakers work under the instructions from relay. Arc extinction is the main process of a circuit breaker. We know that circuit breakers work under the instructions from relay. When the trip coils from relay energize, circuit breaker identifies fault occurred and hence the contacts are pulled apart. A high intensity current flows through the contacts of the circuit breaker before they are opened by the system. When the trip coils from relay energize, circuit breaker identifies fault occurred and hence the contacts are pulled apart. A high intensity current flows through the contacts of the circuit breaker before they are opened by the system.

11. WORKING VCBs are capable of interrupting currents with a very high (di/dt), typically in the range of 150 - 1000A/μs and consequently the high-frequency current may be interrupted during one of the high frequency excursions through zero. This is known as virtual current chopping. VCBs are capable of interrupting currents with a very high (di/dt), typically in the range of 150 - 1000A/μs and consequently the high-frequency current may be interrupted during one of the high frequency excursions through zero. This is known as virtual current chopping.

12. ADVANTAGES OF VCB They are compact, reliable and have longer life. They are compact, reliable and have longer life. There are no fire hazards. There are no fire hazards. They can interrupt any fault current. They can interrupt any fault current. The outstanding feature of a VCB is that it can break any heavy fault current perfectly just before the contacts reach the definite open position. The outstanding feature of a VCB is that it can break any heavy fault current perfectly just before the contacts reach the definite open position.

13. ADVANTAGES OF VCB Low inertia and hence require smaller power for control operation. Low inertia and hence require smaller power for control operation. No noise is produced while operating. No noise is produced while operating. Require less power for control operation. Require less power for control operation. It has higher dielectric strength. It has higher dielectric strength.

14. CONCLUSION Thus, a circuit breaker is equipment that breaks a circuit either manually or automatically under all conditions at no load, full load or short circuit. Thus, a circuit breaker is equipment that breaks a circuit either manually or automatically under all conditions at no load, full load or short circuit. Hence, we can say that Vacuum circuit breaker is really the most reliable one with low cost, no fire hazards, no gas generation, low arc energy, little maintenance and low inertia. So this is the most widely used circuit breaker used for high voltage transmission. Hence, we can say that Vacuum circuit breaker is really the most reliable one with low cost, no fire hazards, no gas generation, low arc energy, little maintenance and low inertia. So this is the most widely used circuit breaker used for high voltage transmission.

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