Optimal relay coordination suitable for grid-connected and islanded operational modes of microgrid

Microgrids are the localized grids which consists of number of distributed generators (DGs) with the distribution system. Introduction of DGs into distribution system cause changes in the fault current levels & directions, thus results in inaccurate operation of the existing protection system. Fault currents in the system also varies significantly following the transition of grid-connected and islanded operational modes of microgrid. Procuring a coordinated protection system which operates accurately in DGs integrated scenario is still a challenging aspect for the planners. In this paper, protection system has been proposed which is suitable for both grid-connected and islanded operational modes of microgrid. Differential evolution (DE) algorithm has been used for achieving the proper coordination of directional overcurrent relays (DOCR) in the distribution systems. IEEE-9-bus distribution system integrated with four DGs have been analysed in this paper. Discrete plug setting (PS) and time multiplier setting (TMS) has been obtained which are feasible for numerical relays. Obtained optimized relay settings provide efficient and accurate operation of relays with minimum operating time.