Electronic Circuit Breaker
Electronic Circuit Breaker
Electronic Circuit Breaker
CONTENTS
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2. 3.
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5. 6.
Working of Circuit Breaker. Principle of Circuit Breaker. Arc Interruption. Classification of Circuit Breaker. Operating Mechanism. Selection of Circuit Breaker.
ARC INTERRUPTION
An arc is struck when contacts are separated The current is thus able to continue Thus the main duty of a C.B.is distinguish the arc with in the shortest possible time. The arc provides the low resistance path to the current and the current in the circuit remain uninterrupted.
High Resistance Interruption. Current Zero Interruption. In high resistance its resistance is increased so as to reduce the current to a value insufficient to maintain the arc .The arc resistance can be increased by cooling, lengthening, constraning and splitting the arc. This method is not suitable for a large-current interruption, This can be employed for low power ac and dc circuit breakers.
Current Zero Interruption is applicable only in case of ac circuit breakers . The current is not interrupted at any pt. other than the zero current instant, otherwise a high transient voltage will occur across the contact gap.
5.
Oil Circuit Breaker. Air blast Circuit Breaker. SF6 Circuit Breaker. Air - Break Circuit Breaker. Vacuum Circuit Breaker.
It has good dielectric strength and excellent arc quenching property. It is an electronegative gas,i.e. it has high affinity for electrons. The SF6 gas has also excellent heat transfer property.
4. Its thermal time constant is about 1000 times shorter than that of air. 5. It decomposes to SF4,SF2,S2,F2,S and F at temp. of the order of 1000 degree Celsius. After arc extinction, the products of decomposition recombine in short time, with in about 1 microsecond.
Disadvantages :-1. 2. 3.
It is condensate at low temperature. The temperature at which SF6 changes to liquid depends on the pressure. SF6 breakers are equipped with thermostatically controlled heaters wherever such low ambient temperatures are encountered.
OPERATING MECHANISM
For opening and closing the circuit breaker, one of the following mechanism is employed.
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2. 3.
END
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