Optimal coordination of directional overcurrent relays in power systems using Symbiotic Organism Search Optimisation technique

The modern power system networks are very complex and often consist of multiloop structures with increased penetration of renewable energy sources-based distributed generations. Directional overcurrent relays (DORs) are the key protection devices in such networks and their coordination has a profound impact on the overall protection of networks. Optimisation of DOR settings is an important concern in protection coordination in power systems. In this study, optimisation of DOR settings, namely time dial setting and pickup current (I-p) setting is achieved by adopting symbiotic organism search technique which is a recently proposed proficient optimiser imitating biological give and take policy while searching for an optimum. Computational ability of the technique to coordinate DORs is validated in IEEE 6-bus and WSCC 9-bus test systems. Results show that the new technique causes for notable reduction in relays' operating time, with maintaining reliable coordination margin for each primary/backup relay pair, in comparison with other techniques. Also, computation time to find optimum solution is less using the new method.