Development of a New Combined Method for Optimal Protection Coordination of Directional Overcurrent Relays

Distributed generation (DG) sources in distribution networks lead to restructuration of network from typical radial arrangement to a interconnected or grid one. The presence of DG sources could generate changes in protection of distribution networks and in the case of grid networks, fault in the network could cause current flowing in both directions. In the present paper, the objective is to optimally coordinate directional over current relays (DOCRs) in grid distribution networks with DG sources. In order to coordinate DOCRs, time adjustment as well as current adjustment of DOCRs are needed. Consequently, optimization of performance time as well as adjustment values of relays is done. The results obtained from suggested protection coordination design with DOCRs were compared with the results of typical method which is based on common adjustment of directional relays. The design is applied on a standard IEEE30 distribution network with some distributed generation resources. The results suggest that in the case of using DOCRs and objective function for performance time optimization, the relays show significant decrease in terms of operation time and adjustment values.