Protecting the Future Electric Power Systems

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Direct Current (DC) grids are emerging electric power systems with remarkable potential benefits. The High-Voltage DC (HVDC) grid improves reliability and efficiency of bulk power transmission systems and also facilitates grid integration of large-scale renewable generation systems. The medium-voltage and low-voltage DC grids and the DC microgrid facilitate integration of distributed energy resources. However, unresolved protection issues have constrained utilization of DC grids. The existing protection systems (relays) do not fully protect DC grids against adverse effects of faults (short-circuits) and disturbances. The long-term objective of the proposed research program is to ensure secure operation of DC grids in the future electric power systems by developing high-speed, reliable, robust, and selective protection strategies. In the short-term, the proposed research program will address the main protection issues of the HVDC grid and the DC microgrid, as explained below.1) HVDC Grid Protection Currently there is no commercially available technology for fault protection of transmission lines in the meshed HVDC grid. A protection strategy will be developed to enable timely and reliable fault detection and location (identification of the faulted line) in the HVDC grid. The proposed protection strategy will be applicable to HVDC grids with different configurations, grounding types, and converter technologies. In addition, a wide-area System Protection Scheme (SPS) will be developed to protect integrity of the HVDC grid by detecting and counteracting line overloading conditions that can lead to cascading outages. 2) DC Microgrid Protection The existing protection strategies do not meet the speed and reliability requirements for DC microgrid applications. The proposed research program will develop a protection strategy for high-speed and reliable fault protection of DC microgrid feeders. Besides, a SPS will be developed to protect integrity of the DC microgrid against voltage collapse. The SPS will be capable of taking timely remedial actions to counteract the disturbances that can lead to voltage collapse, under both grid-connected and islanded operation modes. The proposed research program will advance the state-of-the-art in protection of the HVDC grid and the DC microgrid, and thereby:1) lead to development and commercialization of the first relays to protect these DC grid against faults and system-wide disturbances;2) facilitate long-distance transmission of bulk power with higher reliability and efficiency, in large countries including Canada; 3) improve dynamics and stability of the modernized power grid by preventing widespread catastrophic failures, e.g., the blackout of 2003 in Canada and USA; and 4) increase penetration of renewable energy systems into Canadian distribution systems.