Wednesday, October 19, 2016

Oil Circuit Breaker¦ Construction of Oil Circuit Breaker¦ Function of Oil Circuit Breaker¦


Oil circuit breaker is such type of circuit breaker which used oil as a dielectric or insulating medium for arc extinction. In oil circuit breaker the contacts of the breaker are made to separate within an insulating oil. When the fault occurs in the system the contacts of the circuit breaker are open under the insulating oil, and an arc is developed between them and the heat of the arc is evaporated in the surrounding oil.

In this I will going to show about oil circuit breaker.


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During the normal operating conditions, the contact of the oil circuit breaker is closed and carry the current. When the fault occurs in the system, the contacts of the breaker are moving apart, and an arc is struck between the contacts.


Due to this arc, a large amount of heat is liberated, and a very high temperature is reached which vaporizes the surrounding oil into gas. The gas, thus liberated surrounds the arc and its explosive growth around it displaces the oil violently. The arc is extinguished when the distance between the fixed and moving contact reaches a certain critical value, depends on the arc current and recovery voltage.

The oil circuit breaker is very reliable in operation, and it is very cheap. The most important feature of oil circuit breaker is that no special devices are used for controlling the arc caused by moving contact.


Oil circuit breaker is very easy in construction. It consists of current carrying contacts enclosed in a strong, weather-tight earth metal tank and the tank is filled with transformer oil.


The oil is both acts as an arc extinguishing medium and as an insulator between the live part and earth.



1. The oil has a high dielectric strength and provides insulation between the contact after the arc has been extinguished.
2. The oil used in circuit breaker provides a small clearance between the conductors and the earth components.
3. The hydrogen gas is formed in the tank which has a high diffusion rate and good cooling properties.




1. The oil used in oil circuit breaker is inflammable and hence, cause a fire hazard.
2. There is a risk of formation of explosive mixture with air.
3. Due to decomposition of oil in the arc, the carbon particles is generated which polluted the oil and hence the dielectric strength of the oil decreases.


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