Oil Circuit Breaker (ocb) – Types, Construction, Working and Applications ocb – Oil Circuit Breaker – Construction and Working Principle

Oil Circuit Breaker (OCB) – Types, Construction, Working and Applications
OCB – Oil Circuit Breaker – Construction and Working Principle
Circuit breakers are protection devices that protect circuits and equipment during fault conditions. They use different kinds of dielectric mediums to break the circuit safely. For instance, insulating oil is used as a dielectric medium inside the oil circuit breakers due to its excellent arc quenching properties. It is one of the oldest high voltage circuit breakers still being used.

What is Oil Circuit Breaker (OCB)?
An Oil circuit breaker aka OCB is a type of circuit breaker that uses insulating oil as a dielectric medium to quench the arc and break the circuit safely. The oil used is insulating oil used usually transformer oil that has better dielectric strength than air. The heat produced by the arc vaporizes the oil, producing a hydrogen gas bubble surrounding the arc. The pressure of the oil compresses the gas bubble increasing its dielectric strength which extinguishes the arc during the zero-crossing.

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Working Principle of OCB
When a fault condition occurs, the current-carrying contacts are separated inside the insulating oil. As the contacts separate, the high voltage difference between the contacts ionizes the medium surrounding it and an arc is struck. The immense heat generated by arc vaporizes the oil surrounding the contacts. The oil is decomposed into mostly hydrogen gas including a small amount of methane, ethylene, and acetylene. The decomposed gases form a gas bubble surrounding the contacts.

The hydrogen gas breaks into atomic form releasing immense heat that increases the temperature of the arc. Consequently, the oil vaporization increases. The volume of the gas produced is 1000 times larger than the oil decomposed. Due to high temperatures, the volume of the gas bubble rapidly increases. The surrounding oil inside an enclosed container puts a lot of pressure on the gas bubble. Due to compression, the ionized medium surrounding the contacts starts to de-ionize. As the pressure keeps increasing due to the heat of arc, the medium rapidly de-ionizes that increases the dielectric strength of the medium. The arc is quenched at the next current zero-crossing.
Besides that, the cooling effect of the oil and the gas bubbles also helps in arc quenching