Hybrid GSA-SQP algorithm for optimal coordination of directional overcurrent relays

This study presents a hybrid gravitational search algorithm-sequential quadratic programming (GSA-SQP) algorithm based on the GSAand SQP to optimal coordination of directional overcurrent relays (DOCRs). The SQP routine is incorporated in GSA as a local search mechanism to improve the performance of the conventional GSA algorithm. The coordination between DOCRs is formulated as a non-linear and highly constrained optimisation problem in which two settings namely time dial setting and pick up current setting of each relay are considered as decision variables. The main objective is to minimise the sum of operating times of all the primary relays, which are expected to operate in order to clear the faults of their corresponding zones. Performance of this approach is studied and evaluated on three different test systems with 6, 24 and 38 relays. Simulation results show that the proposed approach provides effective and robust high-quality solution of the problem.