Comprehensive Methodology for Relay Protection Coordination in Distribution Networks with Distributed Generation

The increasing penetration of distributed generation in distribution networks poses significant challenges for protection coordination due to bidirectional power flows, variable fault contributions, and transformer magnetizing inrush currents. This paper presents a microgrid model with IEC-type configuration developed in ETAP software, including synchronous machine-based sources, wind turbines, and realistic relay settings. Initial analysis demonstrated that conventional inverse time-current characteristics and nonstandard tripping curves could not ensure both sensitivity and selectivity, leading to miscoordination when transformer inrush currents were present. To address these limitations, a set of enhancements was introduced, including blocking functions against transformer inrush currents, the transition to definitetime characteristics, and the integration of voltage-supervised directional overcurrent protection. Autonomous automatic circuit reclosers were employed to avoid dependence on centralized communication-based schemes. Simulation results confirmed that the proposed approach improves protection reliability under grid-connected, islanded, and parallel modes of operation, while maintaining robust performance across a wide range of fault scenarios. The methodology simplifies implementation by eliminating complex communication infrastructures and provides a scalable framework for future power systems, including interconnected microgrids and data center infrastructures. These results demonstrate that high levels of protection dependability and selectivity can be achieved with practical, cost-effective solutions tailored to distributed generation networks.

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