Optimum Coordination of Directional Overcurrent Relay in presence of Distributed Generation Using Genetic Algorithm

Distributed generation (DG) is commonly used to supply the local loads. The penetration of distributed generation leads to violating the relay coordination in the distribution network. The interconnection of DG affects miscoordination of distribution system protection, because of the generator ability to contribute large fault currents to the fault point. The impact of DG on relay coordination affect the operating time of relay. The CTI associated with primary and backup relay pairs is getting violated due to changes in fault current level. Thus, coordination between primary and backup relays fails in the presence of distributed Generation. Hence, the interconnection of DG in the distribution system causes an adverse impact on protection coordination. Relay coordination problem has many constraints due to coordination criteria. Heuristic based optimization techniques are used to solve the optimization problems. These techniques have a drawback of converging to the values that may not be optimum due to the wide range of design variables and difficulty in getting an initial feasible solution with a short range of design variables. This paper presents a new algorithm to overcome the problem of the initial feasible solution in determining the optimum settings of OCRs. In this context, the optimization problem is formulated as constrained non- linear optimization problem and is determining using Genetic Algorithm (GA). This algorithm is tested on two different networks that found suitable to give satisfactory results.