Adaptive over current relay coordination algorithm for changing short circuit fault levels

Fault levels are continuously changing in the electric networks due to change in the network impendences and configurations. These changes causes maloperation of the over current relays. An over current relay coordination algorithm is proposed in this paper, which utilizes adaptive fuzzy technique to select the optimal relay settings. This is achieved in two phases. In phase-1 of proposed algorithm, the relay settings are obtained for all possible network topologies. In phase-2 of proposed algorithm, the network topology is identified by sensing the circuit breaker status. Line impendence change is estimated by measuring the change in the power flow on a series compensated line. Therefore phase-2 is an online process. Based on the prevailing network configuration and fault level, the corresponding optimized relay settings are selected using adaptive fuzzy technique. Then these settings are communicated to the over current relays in the network for coordinated operation of over current relays.