Protection Coordination of Microgrids Using Dual Setting Directional Overcurrent Relays Based on Optimal Operating Characteristics and Curve Breakpoints

The change in network topology and operation modes of microgrids is one of the most crucial challenges for protection systems, which might lead to some coordination constraint violations.  Although communication-based and adaptive protection schemes have various advantages, because of their required hardware and software infrastructures, the communication-free schemes have received a great deal of attention. The cyber-attacks and failures in communication-based protection schemes highlight the advantages of communication-free systems. In this paper, the main contribution is to develop a new communication-free method using double setting directional overcurrent relays considering different operation modes and network topologies. There is a research gap in developing a method incorporating the optimal selection of relay characteristics and curve breakpoints for dual setting directional overcurrent relays. The proposed method tries to fill such a research gap by proposing a new method using the dual setting relays, while the time settings, current settings, types of relay curves, and curve breakpoints are simultaneously optimized. The microgrids are simulated in DIgSILENT environment, and power flow and short circuit analyses are performed to determine the required data and information for the proposed optimization problem. Thus, the proposed optimization problem for protection coordination of microgrids is solved using the Genetic Algorithm (GA) in MATLAB. Test results of applying the proposed method on the IEEE 8-bus and the distribution portion of the IEEE 30-bus test systems result in 12.42% and 9.56% improvement in the operating time of the protection system, respectively, that illustrate the advantages of the proposed method. Obtained results show that optimizing the curve types for dual setting directional overcurrent relays besides the optimal selection of curve breakpoints significantly improves the performance of the protection schemes using the dual setting characteristics in various operation modes and network topologies.