Novel Combined Coordination of Distance and Overcurrent Relay for a Radial Distribution System

This paper proposes a novel scheme for the combined coordination of distance relay (DR) and overcurrent relay (OCR), for the protection of a distribution network, as combined coordination of DR and OCRs can give superior protection. In this proposed scheme, all types of distribution network faults are detected and isolated with a suitable optimal coordination time interval (CTI). The proposed method is tested on IEEE 6-Bus radial distribution system (RDS). The fault analysis results show the current, voltage and impedance waveforms. New operating characteristics is experimented for DR, and parameters are analyzed with respect to a trip signal, resulting in a suitable range of CTI. The results indicate that the proposed combined relay coordination scheme is capable of providing reliable time margin between DR and OCRs.