Time variation of industrial system short-circuit currents and induction motor contributions

CALCULATIONS of the approximate variation with time of industrial power system short-circuit currents were made for a discussion of the circuit-breaker application procedure proposed in an AIEE paper.1 The results of the calculations indicate that induction motor loads produce contributions to short-circuit currents that do not decay rapidly in every case and perhaps should not be ignored even when present simplified application calculating procedures permit it.2 In this paper, the method used to determine the approximate short-circuit current time variation is described, and the behavior of induction motors which produce short-circuit current contributions that do not decay rapidly is discussed.