What is Minimum Oil Circuit Breaker (MOCB) ?

These types of circuit breakers only use oil as the interrupting medium and not as insulating material in all chambers.These types of breakers are widely used in transmission and distribution networks, but have a known sensitivity to transient recovery voltages (TRV) and are prone to re-strikes during the switching of capacitor banks.The operation of a minimum oil circuit breaker is similar to that of the bulk oil circuit breaker, as the arc is contained within the arc chamber. This results in a pressurized bubble of vaporized hydrogen around the arc. This pressure is released by an orifice when contact separation distance is reached. This results in the rapid cooling of the area between arcing contacts and fast deionisation at current zero. This in turn gives rise to transient recovery voltages over the contacts aiming to reinstate the current flow. This can result in a restrike and an unsuccessful interruption. This effect can further be complicated with the switching of capacitor loads and out-of-phase currents, but can be addressed by pressurizing the device with dry nitrogen.

36 KV MOCB