Optimal Coordination of Dual-Setting Directional Overcurrent Relays in Microgrids

Microgrids are gaining popularity due to their improved reliability and resilience. However, their protection is challenging due to bidirectional current flow and varying fault current levels in different operating modes. This paper proposes the use of dual-setting directional overcurrent relays for microgrid protection. To demonstrate their effectiveness, a comparative analysis of dual-setting relays and conventional relays is conducted. The relay coordination problem is formulated as a nonlinear programming problem, and the settings of relays are optimally determined using genetic algorithm and an efficient hybrid optimization algorithm that combines the modified firefly algorithm and genetic algorithm to minimize the overall relay operating time for primary relays. The proposed scheme is implemented on the distribution section of the IEEE-14 bus system, demonstrating a reduction in total system operating time with dual-setting directional overcurrent relays.