Describe over current relay with time-current characteristic.

Describe over current relay with time-current characteristic.
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1 Answer

Answer :

Over current relay with time-current characteristics:- 1. Definite time over current relay: Operating time is constant, the relays operates after a predetermined time when the current exceeds the pickup value irrespective of the current magnitude. 2. Instantaneous over current relay: The relay operates instantly when current exceeds pick-up value. No intentional time delay. 3. Inverse time over current relay: The operating time depends on magnitude of operating current as shown in the figure. Higher the magnitude of current, lower is the operating time. The characteristic can be very inverse or extremely inverse as shown in the figure. 4. Inverse definite minimum time overcurrent (I.D.M.T.) relay: Inverse time characteristics at lower value of fault current and definite time characteristics at higher values of fault current.

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