Optimal Coordination of Overcurrent Directional and Distance Relays in Meshed Networks Using Genetic Algorithm

Protection of transmission lines is essential to ensure a correct operation of power systems. In this paper a pilot protection scheme, known as permissive overreaching transfer trip, is used. This structure combine two different protection relays: directional overcurrent relay, a backup protection for phase-earth faults, and distance relay for phase-phase faults. An intelligent method was developed to the optimal coordination of protection relays in meshed networks like transmission networks. The proposed method employs the genetic algorithm as optimization procedure that considers network characteristics (maximum load current and minimum fault current) and adjustment parameters of overcurrent and distance relays. Two testing networks, one of 8-bus and other of 39-bus, were used to evaluate the proposed method that obtained feasible and good solutions for the coordination problem.