Optimal relay coordination has important effects on the stability, security, and reliability of a network. Hence, in this article, a method for optimal coordination of distance (D) and directional overcurrent (DOC) relays is presented. Taking into account the pickup current of the overcurrent relays as an optimization variable, in addition to the time setting multiplier (TSM) and the various characteristics of these relays, optimum and suitable settings for overcurrent and distance relays are obtained. The grey wolf optimizer algorithm has been used as an optimization tool to find optimum settings. The performance of this method has been investigated in 8-bus and 39-bus systems and compared with traditional GA and PSO algorithms. The results show that in the proposed method the operating times of the relays and the time interval between operating times of main and backup relays with respect to the coordination time interval have decreased.
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