When the circuit breaker with a circuit breaking current, the movable, stationary arcing contacts separate. With the downward movement of the rod movable contact, an arc extinguishing chamber sequentially drawn human oil bag in contact with the oil, the oil evaporation, high pressure oil is decomposed to form a bubble, at a pressure difference, the high-pressure oil through the center of the arc extinguishing plate continuous vertical upward circular arc blow, the arc is cooled and extinguished.

Oil circuit breaker is self-interrupter, the interrupter ability and arc current size. The larger the arc current, the arc energy is larger, the higher the oil pressure generated, the more intense the blown arc, the stronger the arc extinguishing capability. Arc current, the arc extinguishing weak, medium current zero arc gap dielectric strength tends to complex small shake, there will be over-voltage capacitive current breaking.

Increasing the oil capacity of a small current circuit breaker arc, in less modern oil circuit breakers, oil pressure piston means is provided. Static contact pressure oil built with piston seat, when separation of the contacts, the spring force pushing the piston down, the oil pressure below the piston people arc gap can eliminate the "vacuum" phenomenon, rapid increase in the dielectric strength of the arc gap, there conducive to extinguish small current arc.

The circuit breaker also uses counterflow principle, using drop-conductive rod. I.e., downward movement of the opening lever conductive, high temperature and pressure generated by the arc spray oil upwardly, the rapid discharge of the charged particles of the arc up the arc track, the arc is conducive to rapid recovery of the dielectric strength of the gap. Conductive rod moves downward pull down the arc, the arc roots is in contact with a lower cold oil, and can reduce the temperature of the arc contacts, thermal free weakened. While downward movement, always a part of the cold oil squeezed upwardly interrupter forming an additional blowing machine oil, it is extremely beneficial to the small current arc extinguishing.

Less oil chamber less oil circuit breaker at rated breaking capacity, after breaking a two arc extinguishing chamber on the oil carbonization darkened, the dielectric strength of the oil will be reduced. Therefore, oil breaker is not suitable for frequent operation.