What is a protective relay?

Answer: Protective relay is an electrical device which is designed to initiate isolation of a part of an electrical installations or to operate an alarm signal in the event of an abnormal condition or a fault.

The main function of a protective relay is to detect the fault and send signal to circuit breaker to isolate the faulty part from healthy system. Some advanced protective relay also detects the location of faults.
Relays operate to trip the power circuit breaker to disconnect the faulty section.

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Protective relays, also called protection relays, prevent unnecessary trips, isolate faults, protect motors and breakers, and provide system information.

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