A protective relay is a relay device designed to trip a circuit breaker when a fault is detected. The first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as over-current, over-voltage, reverse power flow, over-frequency, and under-frequency.
Protection systems play a key role for the safe and reliable operation of today’s electrical power systems. Properly working protection devices help to maintain the safety of the system and safeguard assets from damage. Protective relays and recloser controls must be tested throughout their life cycle in order to ensure reliable operation from their initial development through to production and commissioning, to periodical maintenance during operation.