Protection Coordination in Grid Connected and Islanded Mode of Microgrid

Protection of modern power system is facing new challenges due to presence of distributed generation (DG). Any microgrid can operate in grid connected and islanded mode. Since short circuit level in both cases is different, separate protection scheme is required. In this paper, settings of numerical directional overcurrent relay are obtained separately for both modes. This is achieved by formulating a nonlinear optimization problem which is solved using three techniques. Further the scheme for online update of settings based on operating mode is also proposed. Primary and backup relays are coordinated using the optimal settings which confirm reliable protection of a grid under both topologies. MATLAB/SIMULINK platform is used for 9 bus test system designing and coding.