Navid Ghoaffarzadeh - Associated Professor, Electrical Engineering Department, Faculty of technical and Engineering, Imam Khomeini International University, Qazvin, Iran
Mostafa Dodangeh - Visiting Assistant Professor, Electrical Engineering Department, Faculty of technical and Engineering, Imam Khomeini International University, Qazvin, Iran

The introduction of distributed generation (DG) in the distribution system paved the way to the microgrids concept as a solution to the increased demand for energy. Microgrids can operate while grid connected or act as a standalone network in case of the main grid outage. However, this changeable conditions and configurations of microgrids: Grid-connected and Islanded modes significantly affect the short circuit levels. In this paper, a protection coordination algorithm that relies on the capability of using optimum characteristic curves of digital inverse overcurrent relays in solar microgrid. The main objective is to obtain the optimal setting for the conventional relay setting parameters: time multiplier setting (TDS) and pick up current (Ip) along with (A) and (B) as variable setting to be chosen optimally while considering both modes of operation of the microgrid. The optimal coordination problem is formulated as a constrained non-linear programming problem and optimized using Central Force optimization algorithm. The proposed approach is tested on the IEEE ۳۰-bus meshed distribution system equipped with solar resources. The main advantages of this paper shows that utilizing user-defined characteristic curves for DOCRs achieves notable reduction in total relays’ operating time over the conventional characteristic which makes the proposed protection method as an attractive option for microgrids with dual configuration.

Central Force optimization algorithm, Directional Overcurrent Relays, Optimal Protection Coordination, Relay Characteristics Selection, Solar Microgrids