By R. Vijay Krishna. CONTENTS INTRODUCTION WORKING PRINCIPLE OF C.B TYPES OF CIRCUIT BREAKERS ...
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Transcript of By R. Vijay Krishna. CONTENTS INTRODUCTION WORKING PRINCIPLE OF C.B TYPES OF CIRCUIT BREAKERS ...
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ByR. Vijay Krishna
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CONTENTS
INTRODUCTIONWORKING PRINCIPLE OF C.BTYPES OF CIRCUIT BREAKERSSF6 CIRCUIT BREAKER
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INTRODUCTION
A circuit breaker is an equipment designed to protect an electrical apparatus from damage caused by overload or short circuit.
Unlike a fuse, a circuit breaker can be reset (either manually or automatically) to resume normal operation.
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WORKING PRINCIPLE OF CIRCUIT BREAKER
The basic circuit breaker consists of a simple switch, connected to either a bimetallic strip or an electromagnet.
The electricity magnetizes the electromagnet When the current jumps to unsafe levels, the electromagnet is strong enough to pull down a metal lever connected to the switch linkage.
The entire linkage shifts, tilting the moving contact away from the stationary contact to break the circuit. The electricity shuts off.
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TYPES OF CIRCUIT BREAKERS
OIL CIRCUIT BREAKERS
AIR CIRCUIT BREAKERS
VACUUM CIRCUIT BREAKERS
SF6 CIRCUIT BREAKERS
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SF6 CIRCUIT BREAKER
SF6 has excellent insulating strengthWhen a free electron collides neutral gas
molecule a negative ion is formed and the electron is absorbed by neutral gas molecule
SF6 + e SF6-
Negative ions formed are relatively higher compared to free electrons
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FEATURES OF SF6
SF6 possess high dielectric strength
SF6 has property of fast recombination after source energizing spark is removed.
SF6 has excellent heat transfer properties because its high molecular weight together with its low gaseous viscosity enabling it to transfer heat by convection.
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CONSTRUCTION OF SF6 CIRCUIT BREAKER
SF6 circuit breaker consists of
Interrupter unit
Gas system
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INTERRUPTER UNIT
Consists of fixed contacts with set of current carrying fingers and an arcing probe.
Fingers make contact with the moving contact when the breaker is in close position.
The contacts are surrounded by interrupting nozzles and a blast shield
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The moving contact is in the form of hollow nozzle sliding in a second set of spring loaded fingers.
As soon as the moving contact is with drawn from the fixed finger contacts an arc is drawn between the moving nozzle and the arcing probe.
As the contacts move further apart, the arc is extended and attenuated and finally extinguished by the gas flow from high pressure to low pressure.
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GAS SYSTEMPerfect sealing to prevent leakage of gas
as it is maintained at high pressure.
Low and high pressure system are fitted
with low pressure alarms which gives
warning the moment gas pressure drops
below certain value.
If danger limit is reached the safety
devices immobilize the breaker.
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ADVANTAGES OF SF6 C.B.
Current chopping is minimized at low
pressure and low velocity.
Eliminates moisture problem.
Gives noiseless operation.
No carbon particle is formed during arcing.
Atmospheric conditions does not affect
Circuit breaker performance.
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