Short-circuit currents to perform a protective device coordination study

There are two types of short-circuit studies of interest to the power engineer. The results of the first type are used to select the withstand and interrupting capabilities of switchgear; whereas, the results of the second type are used to properly select the settings of overcurrent protective devices. Oftentimes, the engineer is in possession of commercial software for the first type of short-circuit study. Thus, a natural question is whether its output can also be applied to the second type. The purpose of this paper is to address this question, in accordance with Chapter 4 of the IEEE Red Book, by comparing the two types of short-circuit studies. The basis for the comparison is the complex impedance network method. A sample industrial power system is used to clarify the findings.