Overcurrent Relay Coordination in Distributed Networks under Various Topological Configurations

This study investigates the protection coordination of overcurrent relays (OCRs) in a distributed generation (DG) system under different operational scenarios. Two distinct cases are analyzed: (i) a DG-integrated distribution system operating in grid-connected mode, and (ii) the same system functioning in islanded mode. The proposed method is validated using the Canadian urban benchmark distribution network comprising nine buses. During fault conditions, the variation in fault current significantly affects the operating time of OCRs. Consequently, accurate relay setting is essential to minimize operating time and prevent maloperation. The protection scheme developed in this study is optimized based on these operational considerations. By selecting optimal time dial settings (TDS), coordination among relays is improved while reducing their operating time. A Genetic Algorithm (GA) is employed to determine the optimal TDS values and corresponding relay response times.