Multi-characteristic overcurrent relay of feeder protection for minimum tripping times and self-protection

Abstract

The main goal of this study is to propose new characteristics to an REF 615 model (overcurrent and earth fault relay) that is used for feeder protection in an actual radial system of an Egyptian Substation. When studying fault current, both light and heavy loads as well as fault locations are considered based on the radial nature of the network. The proposed algorithm relies on simultaneously activating the three settings of REF 615 OC relay, with the three settings being set on the respective normal inverse (NI), very inverse (VI) and definite time (DMT) curves. The relay’s operating area is divided into two areas. The VI curve functions as a backup for NI in the first area, whereas the NI curve functions as a backup for VI in the second area. The novelty of this study is the proposed model’s ability to handle relay failure through its self-protection, which increases the network’s protection level and minimizes the relay operating time by about 41.07% for rapid response to a fault. The presence of self-backup protection can minimize the coordination time interval between the main protection and backup protection (CTI) by about 77.98%. The ETAP software is used to investigate the actual radial system and in the analysis of the protection coordination.