Open Loop Testing in Substations
Open loop testing is a critical step in the commissioning and maintenance of protection systems in substations.
It’s designed to ensure that protection relays function correctly - without actually operating circuit breakers.
During this test, we simulate inputs (like current and voltage) to the relay, verifying that it detects conditions like overcurrent or differential faults, and that the internal logic and timers respond appropriately. However, the trip signal is observed only it doesn’t energize the breaker. That’s why we call it an “open loop.”
Why it is important?
Open loop testing helps validate:
Relay configuration and settings
Protection logic and coordination
Reliable operation before involving any real-world breaker tripping.
It’s a safe and controlled way to test protection systems, reduce risk during commissioning, and catch configuration issues early.