Optimal Coordination of Dual Setting Directional Over Current Relays in Microgrid With Different Standard Relay Characteristics

In the presence of distributed generation (DG), the fault current through the relay in forward direction is higher as compared to reverse direction. Thus it is desirable to have dual setting directional over current relay (DOCR) which can operate for both forward and reverse direction of fault current with two independent relay settings. A comparative study of relay coordination problem is presented using conventional and dual setting DOCR having different standard relay characteristics, simple inverse (SI), very inverse (VI) and extremely inverse (EI) according to IEC-60255 std. In this article the relay coordination problem is formulated as a nonlinear programming (NLP) to minimize the total relay operating time and to obtain the optimal relay settings. The proposed protection scheme is applied on low voltage section (7-bus system) of IEEE-14 bus test system having 16 DOCR. The optimal relay settings are obtained by using genetic algorithm (GA) optimization technique in the environment of MATLAB.