How to test Over Current Relay with Three phase Secondary Injection test set

Over-current relays protect power system equipment from damage caused by overloads or short circuits. It is very important to test these relays periodically to ensure their reliability and performance. One of the most popular methods is by using a three-phase secondary injection test set.

Three-phase secondary injection test sets are essentially a set of current and voltage sources that simulate the electrical power system to which the relay is connected. By injecting three-phase currents and voltages into the relay's inputs, the device being tested can be monitored for its performance based on the expected response to the simulated faults.

First Visual Checks

• Check the cables for damage and that they are connected correctly,

• Inspect physical connection as per approved drawings.

• Remove the relay from the case and check for tightness and that all shorting terminals are making proper contact

• Check the tightness of the connection on the relay case

• Check the ferrules

• Check that all the test and setting switches operate properly and all are labeled. Properly by device number and individual function.

The next step is to properly connect the test set to the over-current relay under test. Verification of the connections and proper operation of the test set is very important. Then, it is necessary to configure the test set to match the exact settings of the over-current relay to be tested.

Once all the preparations are complete, the actual testing process can begin. Start with low-level current and voltage injection gradually increasing it up to the maximum values. Observe the relay's trip status as the level of current and voltage is increased and verify that the trip time and current level match the expected results based on the test set configuration and the proper relay settings.

If the relay does not respond as expected, further analysis is required to determine the root cause of the issue. It is important to note, that some over-current relays perform different functions, such as directional and time delay functions. These tests require additional testing procedures beyond the basic current relay testing.