VACUUM CIRCUIT VACUUM CIRCUIT BREAKERBREAKER

WHAT IS A CIRCUIT WHAT IS A CIRCUIT BREAKERBREAKER A circuit breaker is an A circuit breaker is an

equipment that equipment that breaks a circuit either breaks a circuit either manually or manually or automatically under automatically under all conditions at no all conditions at no load, full load or load, full load or short circuit. short circuit.

VACUUM CIRCUIT VACUUM CIRCUIT BREAKERSBREAKERS A Vacuum circuit breaker A Vacuum circuit breaker

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

CONSTRUCTION OF CONSTRUCTION OF VCBVCB

The main parts of a The main parts of a typicaltypical

VCB are-VCB are- Fixed contactFixed contact Moving contactMoving contact Arc shieldArc shield

Which are mountedWhich are mounted

inside a vacuuminside a vacuum

chamber.chamber.

CONSTRUCTION OF CONSTRUCTION OF VCBVCB The fixed contact is a permanent contact The fixed contact is a permanent contact

provided in the VCB between the insulator provided in the VCB between the insulator support and pole terminal.support and pole terminal.

The moving support is provided between The moving support is provided between the insulator and metallic bellow.the insulator and metallic bellow.

The movable member is connected to the The movable member is connected to the control mechanism by stainless steel control mechanism by stainless steel bellows.bellows.

This enables the permanent sealing of the This enables the permanent sealing of the vacuum chamber so as to eliminate the vacuum chamber so as to eliminate the possibility of leak.possibility of leak.

CONSTRUCTION OF CONSTRUCTION OF VCBVCB A glass vessel or ceramic A glass vessel or ceramic

vessel is used as the vessel is used as the outer insulating body.outer insulating body.

The arc shield prevents The arc shield prevents the deterioration of the the deterioration of the internal dielectric internal dielectric strength by preventing strength by preventing metallic vapors falling on metallic vapors falling on the inside surface of the the inside surface of the outer insulating cover.outer insulating cover.

PRINCIPLE OF PRINCIPLE OF OPERATION OPERATION Two contacts called Two contacts called

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

PRINCIPLE OF PRINCIPLE OF OPERATION OPERATION

When the contacts of the breaker are When the contacts of the breaker are opened in vacuum (10-7 to 10 -5 torr), opened in vacuum (10-7 to 10 -5 torr), an arc is produced between the an arc is produced between the contacts by the ionization of metal contacts by the ionization of metal vapors of contacts. vapors of contacts.

The arc is quickly extinguished The arc is quickly extinguished because the metallic vapors, electrons because the metallic vapors, electrons and ions produced during arc and ions produced during arc condense quickly on the surfaces of condense quickly on the surfaces of the circuit breaker contacts, resulting the circuit breaker contacts, resulting in quick recovery of dielectric strength. in quick recovery of dielectric strength.

WORKINGWORKING

The circuit breaker are essential as isolator cannot be The circuit breaker are essential as isolator cannot be used to open a circuit under normal conditions as it used to open a circuit under normal conditions as it has no provision to quench arc that is produced after has no provision to quench arc that is produced after opening the line. It has to perform following function-opening the line. It has to perform following function- Full load current is to be carried continuouslyFull load current is to be carried continuously Opening and closing the circuit on no loadOpening and closing the circuit on no load Making and breaking the normal operating Making and breaking the normal operating

currentcurrent Making and breaking the fault currents of Making and breaking the fault currents of

magnitude up to which it is designed for. magnitude up to which it is designed for.

WORKINGWORKING

Arc extinction is the main process of a Arc extinction is the main process of a circuit breaker. We know that circuit circuit breaker. We know that circuit breakers work under the instructions breakers work under the instructions from relay. from relay.

When the trip coils from relay energize, When the trip coils from relay energize, circuit breaker identifies fault occurred circuit breaker identifies fault occurred and hence the contacts are pulled and hence the contacts are pulled apart. A high intensity current flows apart. A high intensity current flows through the contacts of the circuit through the contacts of the circuit breaker before they are opened by the breaker before they are opened by the system. system.

WORKINGWORKING

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

ADVANTAGES OF VCBADVANTAGES OF VCB

They are compact, reliable and They are compact, reliable and have longer life.have longer life.

There are no fire hazards.There are no fire hazards. They can interrupt any fault They can interrupt any fault

current. current. The outstanding feature of a The outstanding feature of a

VCB is that it can break any VCB is that it can break any heavy heavy fault fault current perfectly just before the current perfectly just before the contacts reach the definite contacts reach the definite open position.open position.

ADVANTAGES OF VCBADVANTAGES OF VCB

Low inertia and Low inertia and hence require hence require smaller power for smaller power for control operation.control operation.

No noise is produced No noise is produced while operating.while operating.

Require less power Require less power for control for control operation.operation.

It has higher It has higher dielectric strength.dielectric strength.

CONCLUSIONCONCLUSION

Thus, a circuit breaker is equipment that Thus, a circuit breaker is equipment that breaks a circuit either manually or breaks a circuit either manually or automatically under all conditions at no automatically under all conditions at no load, full load or short circuit.load, full load or short circuit.

Hence, we can say that Vacuum circuit Hence, we can say that Vacuum circuit breaker is really the most reliable one with breaker is really the most reliable one with low cost, no fire hazards, no gas low cost, no fire hazards, no gas generation, low arc energy, little generation, low arc energy, little maintenance and low inertia. So this is the maintenance and low inertia. So this is the most widely used circuit breaker used for most widely used circuit breaker used for high voltage transmission.high voltage transmission.

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