Theory and Procedure of the Experiment - 7



It operates when the load current exceeds the preset value. The value of preset current above which the relay operates is known as pick-up current. This scheme is known as over current protection of an element of power system. The induction disc type construction is commonly used. The operation of induction disc relay is based on electromagnetic induction principle. So this can be used only on a.c. circuits and not on d.c. circuits.


  1. Switch ON the power supply.
  2. Switch ON the MCB ON/OFF switch.
  3. Press the start button S1. Now start LED glows.
  4. Change the current value using current adjustment knob provided on the left side of the Relay setup module.
  5. After setting the fault current then press the stop button S2 and also press the reset button of the stop clock to make the displayed time to zero.
  6. Now press the start button S1. The stop clock starts counting and when relay trips, it stops counting. During the interval the disc in the relay will rotate.
  7. When the relay coil trips, the disc returns to the normal (original) position. Note down the relay current from the Relay-current meter and trip time from the stop clock.
  8. Repeat the above procedure from step 5 for various fault currents.