Abstract:

The advent 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 strategy that relies on the capability of using user-defined characteristic curves of digital inverse overcurrent relays in microgrid utilizing fault current limiter (FCL) at point of common coupling. The main objective is to obtain the optimal setting for FCL, and 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 solved using Matlab optimization toolbox through the built-in function fmincon solver. The proposed approach is tested on the IEEE 30-bus meshed distribution system equipped with DG units. The outcome of this study shows that user-defined characteristic curves for DOCRs achieves notable reduction in total relays’ operating time over the conventional characteristic.<

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