A practical guide to how protective relays detect faults, trip circuit breakers, coordinate protection zones, and improve power system reliability. For example, unselective protection operation during a medium voltage network fault will cause an outage for an unnecessarily large number of consumers. Types of Protective Relays: Protective relays are categorized by their mechanism (electromagnetic, static, mechanical) and function. Protective Relays - Technical Seminar Nov 2016 - Copyright: IEEE 2 Abstract: Protective relays and devices have been developed over 100 years ago to provide “lastline”of defense for the electrical systems. It initiates the operation of circuit breakers to isolate the affected section. This prevents damage to equipment, reduces downtime, and safeguards.