Self-testing method for relay protection devices

Relay protection devices can perform self-tests to detect most internal faults, but periodic verification of inputs, outputs, and measuring accuracy is also recommended.

Understanding Relay Self-Tests

Modern digital relays, such as SEL relays, continuously monitor their internal components and diagnostics. Self-test diagnostics can detect approximately 85% of component failures, including hardware and software issues, and provide alerts if a fault is detected . These self-tests are designed to run automatically and continuously, ensuring the relay is operational without requiring a full system fault simulation.

Steps to Perform a Self-Test

1. Check Self-Test Status
   • Verify that the relay's self-test alarm is not asserted. This indicates that the internal diagnostics have not detected any faults .
   • For relays with SCADA or communication systems, ensure the self-test status is monitored remotely.
2. Verify Inputs and Outputs
   • Inject known current and voltage signals to confirm the relay's measuring accuracy.
   • Assert digital inputs and pulse output contacts to ensure proper operation of trip circuits and annunciations .
   • This step helps identify failures not detected by the self-test, such as wiring issues or contact malfunctions.
3. Review Relay Settings
   • While self-tests do not require re-verifying settings, ensure that the relay configuration matches the commissioning documentation.
   • Confirm that time-current curves, mho circles, or other characteristic settings remain unchanged.
4. Periodic Manual Testing
   • Even with self-tests, some components may not be fully covered. It is recommended to perform manual testing every 1–6 years depending on system criticality and relay type .
   • This includes secondary injection tests, asserting inputs, and pulsing outputs to verify the relay's functional performance.

Best Practices

• Always wear protective gear when performing tests, including insulated gloves and safety glasses .
• Use a relay test set or appropriate test equipment to simulate fault conditions safely.
• Document all test results and compare them with previous records to detect trends or degradation.
• Ensure compliance with relevant standards such as IEC 60255, IEEE C37.90, and any local regulatory requirements .

Limitations

• Self-tests do not detect all possible failures; approximately 15% of potential failures may go undetected .
• Some rare applications, such as installations without SCADA or communications, require more frequent manual testing to ensure reliability. By following these steps, you can effectively use the relay's self-test capabilities while supplementing them with periodic manual verification to maintain system reliability and safety.