Microgrid Protection Simulation and Testing using a Relay-Secondary Injection Device Testbed

This paper provides a comprehensive approach to addressing the challenges of protection settings due to the increasing penetration of renewable energy sources (RESs), specifically distributed generation (DG), into the power grid. The integration of DG introduces a bidirectional power flow that can affect the coordination of protection relays in the event of faults. Directional overcurrent relays (DOCRs) are used to protect transmission lines. The study is conducted on the IEEE 14-bus system, which includes a 50 MW wind farm as a DG source. DIgSILENT PowerFactory is employed to model the fault currents in the microgrid (MG) and conduct a protection coordination study. A test bench is developed to test the overcurrent functions of DOCRs. A secondary injection device is connected to the SEL-351A relays to ensure the relays operate within the calculated tripping times. The IEC 61850 Generic Object-Oriented Substation Events (GOOSE) communication protocol is implemented to enhance coordination between DOCRs and to improve the overall reliability of the protection scheme. The simulation results indicate that the proposed protection system can handle bidirectional power flow, prevent unnecessary tripping during fault conditions, and enhance the reliability of the protection scheme in the presence of RESs. This paper contributes DOCR simulation, testing, and advanced communication protocols to address the challenges associated with integrating renewable energy sources, particularly in MG systems. This comprehensive strategy reflects the complexity of modern power systems with various energy sources and bidirectional power flows.