What is an Oil circuit breaker?
During abnormal conditions, the circuit breaker contacts are separated from each other and the arc is produced between the fixed and moving contacts. Due to arc production between the contacts, heat is produced.
The oil circuit breaker uses insulating oil as a dielectric or insulating medium for arc extinction purposes. the oil circuit breaker consists of fixed and moving contacts that are enclosed inside the metal or porcelain encloser. The metal or porcelain encloser is filled with insulating oil.
The insulating oil is used for arc extinction and insulating purpose also. The Fixed and moving contacts of the circuit breaker are opened under insulating oil and arc produced between the contacts. Due to arc production between the contacts, heat is produced.
This arc heat evaporated the insulating oil and produced gases like hydrogen at high pressures. these hydrogen gases have high heat conductivity. the hydrogen gas cools down the arc and the arc will be extinguished.
Oil circuit breakers are divided into two categories
Construction of Oil circuit breaker
The oil circuit breaker consists of current-carrying fixed contacts, moving contacts and metal or porcelain enclosers. The oil circuit breaker uses insulating transformer oil. The fixed and moving contacts are enclosed inside the metal or porcelain encloser which is filled with insulating transformer oil. The oil performs both functions, as an arc extinguishing purpose and also as an insulating live part of breaker from the earth.
In a metal encloser or vessel, Air is filled at the top of the oil. This air works as a cushion that controls the displaced oil on the formation of various gases around the arc and also absorbs the mechanical shock produced due to the upward movement of oil.
The oil circuit breaker's metal encloser is tightly bolted to secure the breaker from heavy vibrations produced due to the interruption of heavy fault current. the oil circuit breaker consists gas outlet that is fitted at top of the metal cover for the removal of gases which is produced due to the arc extinction.
Working Oil circuit Breaker
During the normal operating conditions, the circuit breaker's fixed and moving contacts are remains in closed condition and normal current flow through the circuit breaker contacts.
This arc heat evaporates the surrounding oil and converts it to a volume of hydrogen gas at high pressure. the hydrogen gas occupies a volume about one thousand times that of the oil decomposed. The oil is pushed away from the arc and expands the hydrogen gas bubble surrounding the arc.
The arc extinction in the oil circuit breaker is carried by two processes.
1. The hydrogen gas has high heat conductivity so its cool down the arc. The hydrogen gas bubble adds a de-ionisation medium between the contacts.
2. The hydrogen gas set up turbulence in the oil and oil forces between the contacts. This oil removes the arcing products from the arc path.
By the above two processes, the arc will be extinguished and fault current interrupted.
Advantages of oil circuit breaker
1. Oil circuit breakers have high-speed operations.
2. Oil circuit breaker has better insulating properties than air.
3. The oil circuit breaker has the best cooling properties.
4. When the arc is formed, it decomposes oil into gases that have good cooling properties.
5. In an oil circuit breaker oil has good dielectric strength.
6. The oil circuit breaker has a low cost.
7. In an oil circuit breaker, oil is easily available.
8. The oil circuit breaker has a wide range of breaking capabilities.
9. In an oil circuit breaker, oil acts as an insulator and permit a smaller distance between the current-carrying parts and the earth.
Disadvantages of oil circuit breaker
1. In the oil circuit breaker, oil is inflammable and there is the risk of fire.
2. In the oil circuit breaker oil forms an explosive mixture with the atmospheric air.
3. The arcing products like carbon remain in oil so oil quality deteriorated after successive operations. so periodic checking of oil required and also replacement of oil required after some operations.
4. Oil circuit breaker required more maintenance.
5. In an oil circuit breaker, Oil absorbs moisture so the dielectric strength of oil is reduced.
6. In an oil circuit breaker, oil leakage problems were observed.
Applications of Oil circuit breaker
1. The oil circuit breaker is used in small and medium voltage substations for the protection of distribution lines.
2. The oil circuit breaker is also used in Power stations, power grids and transmission and distribution system voltage range up to 220kv.