Optimal Coordination of Overcurrent Relays Considering Generators Transient Currents
Short-circuit current in the power networks, consists of steady and transient states. In the conventional relay coordination method, the transient component of short-circuit current is ignored and the relays are coordinated via fixed currents. The transient component of short-circuit currents causes relays operate fast and thus miscoordinations appear between the main and backup pair relays. In this paper, a relay coordination method considering the transient component of short-circuit current is presented. Dynamic model of inverse time overcurrent relay is used to calculate operating time of relays. In the proposed method, both TSM and IP of relays are calculated considering coordination constraints. It is shown that when the IP is entered to the optimization problem, the objective function is reduced but miscoordinations between relays are increased because of the transient component of short-circuit current. Genetic optimization algorithm is used for relays coordination. The proposed coordination method is implemented on a radial and a meshed network, and the results are compared with the conventional method of coordination.