Optimal Protection Relay Placement in Microgrids

This paper proposes an optimal relay placement approach for microgrids. The proposed approach considers both grid-connected and islanded microgrid modes. The algorithm separately calculates the System Average Interruption Frequency Index (SAIFI) of a microgrid in each operating mode. Then, two weighting factors corresponding to different operating modes are used to calculate the overall SAIFI of the microgrid. The objective is to find the optimal relay locations such that the microgrid overall SAIFI is minimized. The power electronics interfaces associated with distributed energy resources may be classified as grid following or grid forming. As opposed to grid-following distributed energy resources (DERs) such as typical solar inverters, grid-forming inverters are able to control the microgrid voltage and frequency at the point of their interconnection. Therefore, these DERs can facilitate the formation of sub-islands in the microgrid when the protective relays isolate a portion of the microgrid. If there is at least one grid-forming DER available in a sub-island, that sub-island can continue supplying its local load. The exchange market algorithm (EMA) is used for optimizing functions. The effectiveness of the proposed optimal relay placement approach is verified using an 18-bus microgrid and IEEE 123-bus test system.