Circuit Breaker Control:

As we have elaborate, circuit breakers might be remotely operated. Within order to operate the breakers from a remote location, there have to be an electrical control circuit incorporated.  Below Figure displays a simple control circuit for a remotely-operated breaker.

Control power is supplied through an AC source and then rectified to DC.  The main elements of a simple control circuit are:  the rectifier unit, the closing relay, the auxiliary contacts, the closing coil, the tripping coil, and the circuit breaker control switch.

Figure: Simple Circuit Breaker Control Circuit - Breaker Open

For close the remotely-operated circuit breaker, turn the circuit breaker control switch to the close position.  This gives a complete path by the CR (closing relay) and energizes the closing relay.  A closing relay shuts an auxiliary contact that energizes the CC (closing coil), that, within turn shuts the circuit breaker, as display in Figure. The breaker latches in the closed position. At one the breaker is shut, the "b" contact related along with the closing relay opens, de-energizing the closing relay and, thereby, the closing coil.  While the breaker closes, the "a" contact also closes, that enables the trip circuit for manual or automatic trips of the breaker. A circuit breaker control switch might now be released and will automatically return to the neutral position.

For open the circuit breaker you have to turn the circuit breaker control switch to the trip position.   This action energizes the TC (trip coil), that acts directly on the circuit breaker to release the latching mechanism which contains the circuit breaker closed.

While the latching mechanism is released, a circuit breaker will open and opening the "a" contact for the tripping coil and de-energizing the tripping coil.  In addition, while the circuit breaker opens, the "b" contact will close, thus setting up the circuit breaker to be remotely closed by using the closing relay, while desired.  The circuit breaker control switch might now be released.

Figure: Simple Circuit Breaker Control Circuit - Breaker Closed

As you could see from Figure, the circuit breaker control circuit could be designed so in which any one of a number of protective characterized might be incorporated. The three most generally-used automatic trips characterized for a circuit breaker are overcurrent (as discussed previously), undervoltage, and underfrequency. If any one of the conditions exists although the circuit breaker is closed, it will close its related contact and energize the tripping coil that, in turn, will trip the circuit breaker.