Using short-circuit currents to perform a protective device coordination study

Abstract

The article provides a brief background on the fundamentals of short-circuit analysis. Following that background is a discussion of how various types of phase overcurrent protective devices respond to the short-circuit current waveform. Based on this discussion, the short-circuit currents which are necessary to perform a protective device coordination study are specified. A comparison of the two types of short-circuit studies follows, based on the complex impedance network representation of the power system. The results of the comparison are then used to present recommendations for how the results of a computer-aided study to compute short-circuit current duties can be applied to determine the short-circuit currents necessary to select the settings of phase overcurrent protective devices. Finally, a sample industrial power system is provided to clarify the recommendations.