Working of circuit breaker

Working of circuit breaker

The fixed and moving contacts,which are called electrodes, exist in a normal circuit breaker.The medium in which these contacts are placed could either be oil or air. When the power is operating normally,these contacts will remain closed and will not open automatically until a faulty condition occurs in the system.Whenever a fault occurs in the system, these contacts can be opened either manually or automatically or  by using a remote control. During a faulty condition, due to energization of trip coils of the circuit breaker,the moving contact is pulled apart, which opens the circuit and an arc is formed between these contacts. The schematic diagram of the circuit breaker normal and fault conditions is shown in below figure.

An arc develops between the fixed and moving contacts ,when a fault occurs in the power system. The fault current in the power system will continue to flow until this arc is extinguished or stopped. Therefore, the formation of the arc not only delays the interruption of faulty current, but also generates huge amounts of heat , which might cause damage to the power system or the circuit breaker itself. Hence, it is necessary to extinguish the arc developed in a short interval of time, so that the magnitude of heat generated will not exceed a maximum value.