Protective relays are special electrical devices used to detect faults in power systems and quickly disconnect faulty parts to prevent damage. These relays sense abnormal conditions like overcurrent, under-voltage, or short circuits and send a signal to circuit breakers to open the. Protective Relay Definition: A protective relay is an automatic device that senses abnormal conditions in electrical circuits and triggers actions to isolate faults. They don't just protect equipment; they ensure safety, prevent downtime, and save lives.