Recent and Ongoing Wide-Area Planning Efforts United States Wind Speed m/s >10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 <4.0 Existing Transmission HVdc HVac Voltage 345-499 kV 500-699 kV 700-799 kV 800-1,000 kV figure 4. U.S. wind resources and the existing extra-high-voltage grid. (Source: NREL). Juan de Fuca Cable West Coast Cable Western Alberta Transmission Line Eastern Alberta Transmission Line Zephyr Transwest Express Centennial West The U.S. grid is planned, regulated, and operated by a wide range of entities. While the advent of RTOs and recent FERC orders have sought to lessen this, great hurdles remain for planning and siting long-distance transmission that would enable vast amounts of renewables to be tapped. Aside from regulatory and siting challenges, technical challenges of siting high-voltage dc (HVdc) in relatively weak parts of the grid also exist. Traditional HVdc (current source-converter) projects suffer from the potential need for additional fast-acting reactive support or additional inertial support that add costs and complexity. Voltage Labrador Island Transmission Link Bipole III Champlain Power Express Lake Erie Clean Power Connector Roc Green Line k Isl and DATC 4 Grain Belt Express Plai ns an d DATC 2 Atlantic Wind Connection Ea ster n Southern Cross figure 5. The proposed HVdc projects in North America. DATC: Duke Energy & American Transmission Company 90 ieee power & energy magazine november/december 2017