What is full form of OCB?OCB means Oil Circuit Breaker and oil is used as a arc quenching medium as well as insulating medium, but mineral oil is preferable. Oil has better insulating property than air.
The moving contact and fixed contact are immerged inside the insulating oil with a seal packed chamber. When the separation of the contacts take place, then the arc in circuit breaker is initialized at the moment of separation of contacts, and due to this arc in the oil vaporization occur and decomposed in hydrogen gas and finally creates a hydrogen bubble around the arc.
Due to this highly compressed gas bubble around and arc prevents re-striking of the arc after current reaches zero crossing of the cycle. It is the old type of circuit breakers.
Full form of OCB is Oil circuit breaker are further classified in to two types
- Bulk oil circuit breaker
- Minimum oil circuit breaker
Bulk Oil Circuit Breaker (BOCB)
In the BOCB, oil is used as a arc the quenching medium and it is also used as insulating medium in between earth parts of circuit breaker and current carrying contacts. It is same as transformer insulating oil is used.
The working principle of the BOCB says that when a current carrying contacts of CB which is immerse in the oil are separated, then an arc is generated between the separated contacts.
Due to this arc which will produce rapid growing gas bubble around the arc. The moving contacts move apart from the fixed contact of arc and as as result the resistance of the arc gets increased. Due to this increasing resistance the temperature become lower. Hence the reduced formations of gasses surround the arc.
When the current passes through zero crossing the arc quenching in the BOCB takes places. In the totally air tight If the vessel is totally air tight then the gas bubble remain enclosed inside the oil. The oil surround with high pressure on the bubble, due to which highly compressed gas around the arc.
If the pressure of oil is increased the de- ionization of the gas also increases, which results in arc quenching. The hydrogen gas is used as cooling medium in arc quenching in the oil circuit breaker.
- Its has good cooling property due to decomposition
- The oil absorb arc energy while decomposing
- Oil has high dielectric strength
- It acts like an insulator between earth and live parts.
- It will not permit high speed of interruption
- It takes long arcing time.
Minimum Oil Circuit Breaker
In this type oc CB oil is used as the interrupting medium. The minimum oil circuit breaker will place the interrupting unit in an insulating chamber at the live potential. But insulating material is available in interrupting chamber. It requires less amount of oil therefore it is called minimum oil circuit breaker.
- It is suitable for both automatic operation and manual.
- It requires less maintenance.
- It requires smaller space
- Oil deteriorates because of carbonization.
- The cost for breaking capacity in MVA is also less.
- There is a possibility of explosion and fire
- As it has a smaller quantity of oil, so carbonization increases.
- It is very difficult to remove gases from the space between the contacts.
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