Determination of overcurrent time delay using fuzzy logic relays

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 setpoint 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 impedence between the backup relay and the main relay is much smaller than the impedence 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 overcurrent relay.