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Relay Protection in Microgrids: Settings and Sensitivity in Presence of IBDERs

Modern power systems are passing through the most significant change after they are built. This change leads to the faster achievement of three key goals: decarbonization, digitalization, and decentralization. The emergence of an increasing number of distributed energy resources (DERs) supports this process. The microgrid, as a new concept of local connection of consumptions and DERs, enables the achievement of these goals but also brings many challenges posed to power system engineers. Since most modern DERs are entirely different in nature and operation from traditional synchronous and asynchronous machines, primarily because they are connected to the grid via power electronics devices, their contributions to fault current are also entirely different from conventional sources’ contributions. In addition, the microgrid transition from the grid-connected to islanded operation mode creates new circumstances that must be analyzed. In grid-connected operation mode, the most significant contribution to the fault current comes from the utility network, while in islanded, the complete fault current consists only of DER contributions. Short-circuit analysis and its impact on relay protection settings in microgrids with high penetration of DERs were performed on the most modern "Hardware-in-the-loop" setup, relay protection testing device, and commercial relays. The results of this analysis in both microgrid’s modes of operation are presented in the paper.