Under Voltage Trip

When a dead generator or generator with low voltage is mistakenly included in the bus bar it may lead to a short circuit and cause a blackout.

To avoid such an emergency, an Undervoltage trip mechanism is fitted to all generator breakers and some main feeder circuit breakers that trip the breaker when a severe voltage dip occurs.

An undervoltage relay is used for this purpose which is either of magnetic or electronic type. The under-voltage relays are usually slugged to allow a time delay which prevents spurious tripping during transient voltage dips (typically 15%) caused by large motor starting currents.