The circuit breaker in which the vacuum is used as the arc extinguishing medium is called vacuum circuit breaker. There is a vacuum chamber inside which the circuit breaking operation then the arcing occurs.
Construction of Vacuum Circuit Breaker:
It is made up of a vacuum chamber-mounted arc shield, moving contact, and fixed contact. Stainless steel bellows link the moving member to the control mechanism. This makes it possible to permanently seal the vacuum chamber, eliminating the chance of an air leak.
The outside insulating body is made of glass or ceramic. 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.
How Vacuum Circuit Breaker works?
Working of VCB:
The moving contact disengages from the fixed contact when the breaker operates, creating an arc between the contacts. Arc formation results from the ionization of metal ions and is highly dependent on the contacts' material.
The metallic vapors, electrons, and ions generated by the arc are immediately diffused and absorbed by the surfaces of the moving and fixed parts and the shields, as a result the arc is quickly extinguished. Since the vacuum has very fast rate of recovery of dielectric strength, the arc extinction in a vacuum breaker occurs with a short contact separation.
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