A New Index for Evaluating Distributed Generation Impacts on Overcurrent Relay Coordination

The presence of Distributed Generation (DG) resources in power system, versus economic benefits, can be cause a miss- coordination in operation of overcurrent relay. In this paper, a new index is proposed to determine the impact of DG installation on coordination constraints of overcurrent relay, independent of relay settings. In the presence of DG in network, the fault current passing through the backup and primary relays change in compare to the no presence of DG. According to this, the proposed index is defined as the difference between the rate of change of fault current passing through backup relay and the rate of change of fault current passing through primary relay, for each relay pairs. In the presence of DG, mathematically proven that the sign of the proposed index for each coordination constraints, indicates the increase or decrease of coordination time interval and the measure of proposed index indicates the reduction of coordination time interval. The proposed index for the coordination constraints of overcurrent relay of an 8-bus test system is determined at each DG location. The results have shown the correctness of proposed index to evaluate the impact of location and capacity of DG on the coordination constraints. Also, the locations and capacities of DG have been ranked base on proposed index.