Its main purpose is to safeguard electrical equipment like transformers, generators, and transmission lines from damage due to abnormal conditions such as overloads, short circuits, or voltage imbalances. What controls it: Relay performance depends on the protected zone, CT/PT inputs, pickup settings, time delay, breaker clearing time, trip. Selectivity is a mandatory requirement for all protection, but the importance of it depends on the application. For example, unselective protection operation during a medium voltage network fault will cause an outage for an unnecessarily large number of consumers. While this is bad, It's not a. A protective relay is an intelligent electrical device designed to detect faults in power systems and initiate corrective actions such as tripping a circuit breaker. : 4 The first protective relays were electromagnetic. Protective relays and devices have been developed over 100 years ago to provide “last line” of defense for the electrical systems.
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