Optimal Protection Coordination of Dual-Setting Directional Overcurrent Relays Based on Three-point Coordination Strategy

The changes in operation modes of microgrids is one of the most crucial challenges for protection systems. Although communication-based and adaptive protection schemes have various advantages, because of their required infrastructures, much attention has been paid to the communication-free schemes. In the proposed protection scheme, the dual-setting relays are used, while the time settings, current settings, and curve breakpoints are simultaneously optimized. Moreover, only considering the coordination constraints for the single-point strategy (the maximum short circuit current) might adversely affect the protection coordination. This challenge is highlighted if different curve types or special characteristics, such as dual-setting characteristics, are used for the primary and back-up relays. The three-point strategy, including the faults at the nearest point, the far end of the protection zone of the primary relay, and the middle of the protection zone, is considered in this research. The coordination constraint violation does not occur in the proposed method because different current pairs are concerned with determining the feasible are of the optimization problem. The introduced method is applied to the distribution portion of the IEEE 30-bus test system. The power flow and short circuit analyses are performed in DIgSILENT, and the proposed optimization problem is solved using the Genetic algorithm in MATLAB environment. The comparison of the obtained results and other available methods illustrates the advantages of the proposed scheme.