Effect of distributed generation capacity on the coordination of protection system of distribution network

Conventional power distribution system is radial in nature, characterized by a single source feeding a network of downstream feeders. Protection scheme for distribution system, primarily consisting of fuses and reclosures and, in some cases, relays, has traditionally been designed assuming the system to be radial. In last year extra attention applied in use of distributed generator units in distribution networks. The integration of distributed sources into existing networks brings up several technical, economical and regulatory questions. The connection of distributed generators (DG) to distribution networks also influences the performance of the networks and the impact depends on the number, location and size of injected DG. The presence of distributed generators in the distribution network can cause the mis-coordination of the protection system. In order to overcome this problem, one can change the relay setting based on the number and location of DGs in the network. In this paper, another approach is selected in which, the capacity of DG at each node is determined in such a way, that the mis-coordination does not happen. The proposed method is explained in two cases. In the first case, just one DG at each node is considered, but in the second case existence of two or more DGs in separate nodes is taken into account. The simulation result are presented and discussed in a typical distribution network.