Optimal coordination of directional overcurrent relays in complex distribution networks using sine cosine algorithm

The modern power distribution networks are very complex due to the growing integration of distributed generators in recent years. Optimal coordination of directional overcurrent relays (DOCRs) used for protection of such complex networks is a highly constrained and nonlinear optimization problem. In this paper, a new optimization algorithm called Sine Cosine Algorithm (SCA) is used first time to solve the optimal coordination problems of DOCRs. SCA is a recently proposed population-based algorithm used for solving highly nonlinear optimization problems. The cyclic pattern of sine and cosine function allows a solution to be re-positioned around another solution. This can guarantee exploitation of the space defined between solutions. The effectiveness of SCA in solving the optimal coordination problems of DOCRs is tested on different fault data generated on 3-bus, 8-bus, 15-bus and 30-bus test systems. The results clearly show that the effectiveness of the proposed algorithm is superior in reducing the overall operating time of primary relays compared to the recently published optimization algorithms for DOCRs coordination. Also, the proposed algorithm is robust in maintaining the coordination between primary and backup relay pairs. Compared to existing optimization algorithms, the proposed algorithm has reduced coordination interval time between primary and backup relay pairs.