Oil circuit breakers
in oil circuit breakers insulating oil is used as an arc quenching medium. The contacts are opened under oil and an arc is struck between them, heat of the arc evaporates the surrounding oil and produce hydrogen at high pressure. The oil is pushed away from the arc region and the gas bubble occupies adjacent portions of the contact. The arc extinction is facilitated mainly by two processes. Firstly the hydrogen gas has high heat conductivity and cools the arc, thus aiding the deionisation of the medium between the contacts. Secondly the gas sets up turbulence in the oil and forces it into the space between contacts thus eliminating the arcing products from the arc path resulting in arc extinction and interruption of current.
The advantages of using oil as an arc quenching medium are:
1. It absorbs the arc energy to decompose the oil into gases, which have excellent cooling properties.
2. It acts as an insulator and permits smaller clearance between live conductors and earthed
components.
The disadvantages of oil as an arc quenching medium are:
1. Its inflammable and there is risk of fire
2. It may form an explosive mixture with air.
3. The arcing products remain in the oil and it reduces the quality of oil after several operations.
This necessitates periodic checking and replacement of oil.
Written by John on October 10th, 2008 with
no comments.
Read more articles on circuit breakers and oil circuit breaker and Power System and Switchgear&Protection.