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It is a circuit breaker in which the heat generated by the high current in the medium between the contacts is sufficient to ionize the medium. Which medium is used in the circuit breaker?

It is a circuit breaker in which the heat generated by the high current in the medium between the contacts is sufficient to ionize the medium. Which medium is used in the circuit breaker? Correct Answer oil or air

Arc in a circuit breaker:

  • The heat generated by the high current in between the contact of circuit breakers is sufficient to ionize the medium which is also known as an arc. 
  • To extinguish this arc, circuit breakers generally use oil or air as their arc quenching medium. 

Oil Circuit Breaker :

  1. Insulating oil is used as the arc extinguishing medium.
  2. As the contacts are opened in oil, when the arc strikes, the surrounding oil is evaporated as hydrogen gas.
  3. The hydrogen gas bubble will surround the arc region. Hydrogen gas, due to its high thermal conductivity, cools the arc and also deionizes the medium. 
  4. Also, the gas causes turbulence in the surrounding oil and all the arcing products are pushed away from the arc.

Air Circuit Breaker :

  1. High-pressure air-blast is used as arc extinguishing medium.
  2. The arc and the arching products are swept into the atmosphere, which rapidly increases the dielectric strength of the medium. As a result, the restriking of the arc is prevented.
  3. The arc is extinguished consequently and the flow of current is completely interrupted. 

SF6 Circuit Breaker :

  1. SF6 is used as the arc extinguishing medium.
  2. When the circuit contacts are opened, a high-pressure SF6 gas flows through the chamber as the arc strikes.
  3. Free electrons produced during the arcing are quickly absorbed by the SF6 gas resulting in immobile negative ions.
  4. As the arc loses its conducting electrons, the insulating strength of the surrounding medium is quickly increased and the arc completely extinguishes.

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