A Framework for Optimal Operation of Overcurrent Relays in Microgrids Using a Modified Tripping Formulation

This paper presents a method which is capable of satisfying the optimal protection coordination of relays in Microgrids (MGs) in both islanded and grid-connected modes. While the tripping times are minimized, the requirement of having multiple setting groups for relays is alleviated. Non-linear constrained programming is formulated in firefly algorithm (FA) and static penalties are considered for constraints handling. The goal is to obtain the optimal coordination between the directional overcurrent relays (OCRs). The formulation includes a framework to satisfy coordination constraints for both connectivity modes of MG operation and yield the least tripping times, while maintaining an appropriate time interval between the primary and the backup relays. A 9-bus IEEE test system is simulated as the MG in DIgSILENT software and the achieved results are compared with a similar study where the genetic algorithm has been applied for optimization. The comparative results verify the capability of the current method and its superiority.