A practical guide to how protective relays detect faults, trip circuit breakers, coordinate protection zones, and improve power system reliability. Core idea: Protective relays monitor electrical quantities and command protective devices to isolate faults or abnormal. 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. Eng, IEEE Life Fellow IEEE/IAS/I&CPSD Protection & Coordination WG Chair Jacobs Canada. Recognized under 2(f) and 12 (B) of UGC ACT 1956 (Affiliated to JNTUH, Hyderabad, Approved by AICTE - Accredited by NBA & NAAC – 'A' Grade - ISO 9001:2015 Certified) Maisammaguda, Dhulapally (Post Via.