Effects of fault type and pre-fault load flow on optimal coordination of directional overcurrent protections

Abstract

• This paper is on optimal coordination of directional overcurrent protections (OC-DOCP). • Effects of fault type and pre-fault load flow on OC-DOCP are analyzed. • Changes in optimal settings can be considerably greater than changes in short-circuit currents. • Changes in objective functions can be considerably lower than changes in short-circuit currents. This short article shows an analysis of the effects of fault type and pre-fault load flow on the optimal coordination of directional overcurrent protections. A well-known case from the literature is taken as an example, because this case has been previously solved considering only three-phase faults and only one pre-fault load flow. The fault type and the pre-fault load flow have an influence on the results of short-circuit currents and, consequently, on the results of the optimal coordination of directional overcurrent protections. It is shown herein that the effects of pre-fault load flow and single-line-to-ground faults can be important on the results of optimal coordination. For the analyzed cases, the percentage changes in the optimal results of time delay settings can be considerably greater than the percentage changes in short-circuit currents. On the other hand, the percentage changes in optimal results of objective functions can be considerably lower than the percentage changes in short-circuit currents for the analyzed cases.