Comparison of Over-current Relay Coordination by using fuzzy and genetic algorithm Methods

Abstract

The inverse definite minimum time relay has been used in the power distribution system in order to protect the system from power system faults.[1] These relays will function after a certain time delay when the current going through the relay exceeds a predefined set point. This time delay depends on the ratio of the fault current flowing through the relay with the set point current defined by the protection engineer [2]. The basic problem with these relays is that the relays will have a longer time delay for a less severe fault [3]. Another problem that these relays would face is when the impedance between the backup relay and the main relay is much smaller than the impedance between the fault and the main relay. In this paper, the possibility of using a fuzzy logic controller (FLC) is studied in order to determine the time delay of the over current relay. a new genetic algorithm (GA) method is presented to solve the optimization problem in coordination of over current and distance relays. The objective function (OF) is developed in a way that in addition to coordination of over current relays, the coordination of over current and distance relays is achieved. Various relay characteristics are considered for each over current relay and the best of them is selected by GA to fulfill optimal coordination. The proposed method is applied to a sample power network. Simulation results demonstrate that the method can obtain feasible and effective solutions and, it is a promising approach for optimal coordination in practical power networks.