Restricted Earth Fault Protection Stability & Sensitivity Test.

This article is to guide the responsible persons in conducting Restricted Earth Fault Protection stability & sensitivity test. Testing restricted earth fault (REF) protection involves ensuring the stability and sensitivity of the relay to detect earth faults within its designated zone while minimizing the risk of maloperation.

Test Equipment: 1phase AC Generator kit, Clamp Meter and Phase Angle Meter.

Safety Precautions: The following Safety precautions shall be taken in consideration prior, during and after conducting the test measurements.

• Safety tagging shall be implemented.
• Isolate the Area by Safety Warning Tape.
• Keep a Safe Distance from the device being tested.
• Wear Appropriate Personal Protective Equipment(PPE) Prior to starting any testing activity.
• Implementation of Proper Grounding.

Restricted Earth Fault Protection Stability & Sensitivity Test.

ADDITIONAL SAFETY PRECAUTIONS BEFORE STARTING TEST:

1.) LOCKOUT RELAY should be isolated and ensure NO POSSIBLE tripping during the test
2.) Remove the neutral earthing resistor (NER) bypassing it to increase the current to facilitate measuring.
3.) Ensure that there is no saturation in any of the CT’s or any wrong circuit connection, or different CT ratios.
4.) REF is a high impedance protection and should be tested as a trip/no trip test with short durations of power supply switching ON to protect the relay from burning.
5.) Isolate the trip link for REF protection. Check the correct terminal connections.
6.) Check that all associated CT cores are having the same Knee point nearly.

1. Apply single phase voltage on each phase (Red, Yellow, and Blue) individually & N.

2. Holding the neutral CTn as a reference:
3. For Restricted Earth Fault Stability Test for R Phase.

4. For Restricted Earth Fault Sensitivity Test Swap 1 phase of CT Polarity.

5. Normalize the reversed CT.
6. Repeat the test for the other phases (Yellow, Blue)
7. Normalize the CT connections.
8. Normalize trip isolation links.

Following manufacturer specific testing procedures and adhering to industry standards and guidelines are crucial for conducting accurate REF protection testing. Qualified personnel with expertise in protective relaying should perform these tests.