A Case History of Motor Current Contribution to an Industrial System Short Circuit

Oscillograph recordings made during a severe primary short circuit on an industrial power system include the total three-phase currents contributed by plant motors to the fault. An analysis of the recorded motor current contribution to estimate the initial magnitude and time variation is described as well as a calculation of the motor contribution using procedures of ANSI standard application guides. Results are presented for easy comparison of the values obtained from the oscillogram and the standard calculation.