Distributed generations (DGs) are widely connected to the electrical power grid to mitigate the overall system losses. Each DG contains a number of parallel units. The uncertainty due to planned or forced outage of the DG units changes the generation capacity, leading to overcurrent relays (OCRs) miscoordination in the distribution network. In this paper, new multiple optimal setting groups (SGs) are determined for OCRs that would satisfy protection coordination under various DGs capacity. In the first step, the proposed hybrid method uses k-means to classify different capacities of DGs into some clusters, whose number is equal to the number of SGs. The short-circuit current changes in each cluster; accordingly the OCRs coordination problems is modeled as an interval linear programming in the second stage, and optimal settings are determined for each setting group. The recommended technique is applied to the distribution section of the IEEE 14-bus system with two synchronous DGs. The outputs of the simulations and analysis have been done in PowerFactory and MATLAB software, respectively, indicate optimal coordination of relays for all DGs’ generation levels.

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