Verify that power system has sufficient redundant and back-up protection while relay is out of service for testing. Use test switches to isolate output contacts to prevent undesired tripping and alarms. Be aware of effect on other relays in. When a protection relay fails to operate during a real fault, the consequences can be severe — prolonged fault duration, equipment damage, and major production losses. The issue of relay not operating during fault is one of the most challenging topics for protection and maintenance engineers. Selectivity is a mandatory requirement for all protection, but the importance of it depends on the application. While this is bad, It's not a. Protective relays and devices have been developed over 100 years ago to provide “lastline”of defense for the electrical systems. However, relay malfunctions can occur, which can lead to incorrect.
