Testing Of AC Under Voltage Relay (27)

AC Under voltage relay is tested with secondary Voltage test set with electronic relay test set. . Isolate the Relay Voltage Measuring Elements & Trip/Alarm contact by inserting the Test Block MMLB01. If the test block available on the metering. . Connect correct polarity/rating of DC Voltage through Test Plug MMLB01 to Relay. Press the “Target Reset” button and check that all target LED lights up. . Set the time for instantaneous mode (all switches to the left). . Set the Under voltage trip level on the relay. . Apply 3-phase AC Voltage on phase A (terminals A1-B1), phase B (terminals A2-B2) and phase C (terminals A3-B3) and slowly vary the AC voltage and check that the relay trips within ±5% of voltage setting. . Set the Under Voltage trip level on the relay to the minimum. . Apply a voltage lower than the trip level on phase A (terminals A1-B1), phase B (terminals A2-B2) and phase C (terminals A3-B3). . Check that the time measured is less than 50ms. . Set the time delay element of the Relay for time delayed Trip. . Set the Under voltage trip level on the relay. . Apply a voltage lower than the trip level on phase A (terminal A1-B1). Phase B ( terminal A2-B2) and phase C (terminals A3-B3) . Check that the time measured is within ± 5% or 30ms (which ever is greater) than the expected value.