Low Voltage in Relay Protection Tester

Testing low-voltage relays involves connecting the relay to a protection tester, simulating voltage conditions, and verifying that the relay trips correctly under under-voltage or abnormal voltage scenarios.

Preparation and Safety

Before testing, ensure the circuit is de-energized and isolated. Wear appropriate PPE such as insulated gloves, safety glasses, and use insulated tools. Verify that the relay model, rating, and settings match the design specifications. Inspect for loose wiring, overheating, or physical damage. Ensure the relay protection tester is properly calibrated and grounded .

Wiring the Relay Protection Tester

1. Identify the voltage output terminals on the tester (commonly yellow, green, red, and black).
2. Connect the relay coil terminals to the corresponding color-coded outputs on the tester. For example, the black coil connects to the black jack.
3. Use a multimeter to confirm that all connections are correct and secure .

Performing the Low-Voltage Test

1. Power on the tester and select the appropriate test type (manual or automatic).
2. Set the voltage amplitude and step length according to the relay's rated voltage.
3. Apply normal voltage first to ensure the relay does not trip under standard conditions.
4. Gradually reduce the voltage below the under-voltage setting. Observe the relay and record the trip time when it activates.
5. Optionally, increase the voltage above the over-voltage setting to verify proper operation in over-voltage conditions.
6. Restore the voltage to normal and check the auto-reset function if applicable .

Monitoring and Recording

• Use the tester to inject voltage signals and monitor the relay's response.
• Record the pickup voltage (the voltage at which the relay begins to operate) and the trip time.
• Compare the results with the relay's specifications to ensure compliance .

Additional Functional Checks

• Simulate phase loss or imbalance by removing voltage from one phase and confirm the relay detects the fault.
• Perform step or ramp tests to progressively increase or decrease voltage and verify consistent relay operation.
• Ensure the relay coordinates correctly with other protective devices in the system . By following these steps, you can accurately test low-voltage relays, ensuring they respond correctly to under-voltage conditions and maintain reliable protection for the electrical system.