Egypt Engineering Consultant Electrical

Practice session

A digital overcurrent protection relay on a 22 kV feeder is programmed with the standard IEC 60255 normal inverse time curve: t = [0.14 / ((I / Is)^0.02 - 1)] × TMS. The relay has a current pickup setting (Is) of 800 A and a Time Multiplier Setting (TMS) of 0.20. During a three-phase busbar fault, a prospective fault current of 4,000 A flows through the feeder. What is the calculated operating time (t) of the relay?

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