ABSTRACT
The protective relays can be regulating, controlling, alarming, restoring, synchronizing, load shedding, out of step, rate of pressure rise, inadvertent energization, temperature, vibration sensing, relays specific for ground fault protection, etc. The indicator contactor switch indicates operation of the relay and is hand reset. A differential protection operates on the principle that the current entering a zone of protection is equal to the current leaving that zone of protection. This current balance does not hold if there is a fault within the protected zone. It is noteworthy that the overlapping of the differential zones of protection is achieved by proper location of the current transformers, and constructing a zone of protection so that one zone overlaps the other and no area is left unprotected. Variable percentage relays are used for generator protection and are less likely to have nuisance tripping.
