A study on power-flow and short-circuit algorithms capable of analyzing the effect of load current on fault current using the bus impedance matrix

Abstract

In short-circuit studies, load makes difficult to determine fault current that flows in positive-, negative-, and zero-sequence networks. Therefore, it is often ignored because the magnitude of load current is much less than that of fault current that flows from generators when a fault occurs. As distributed generation (DG) resources such as photovoltaic systems, wind farms, and non-linear generators based on power electronics have being deployed into power system networks, load current that flows from them may affect a magnitude of fault current. Thus, the objective of this study is to develop a short-circuit algorithm that analyzes the effect of load current on fault current. For this purpose, using the bus impedance matrix and the iterative current compensation method presented in [1], this study initially develops a power-flow analysis algorithm that iterates to calculate current to be injected and determines voltage. Then, the proposed short-circuit algorithm uses as input data the results of power-flow calculation. To verify the algorithms developed in MATLAB, a distribution system with a DG resource is presented in a case study. Then, this study (a) calculates the power flow of the distribution system, (b) generates a single line-to-ground fault, and (c) changes the capacity of load, the capacity of a DG resource, and the location of a fault. Finally, it examines the effect of load and DG on a magnitude of fault current.