The development of direct current (DC) transmission dates back to the 1930’s and has been a proven technology since the first major installations in 1954. Over the last 40 years, HVDC projects have demonstrated significant electrical, economic, and environmental advantages when transporting power across long distance. HVDC transmission is used primarily to connect energy resources in remote portions of the country to consumers in more heavily populated areas. Among those direct current lines is the Pacific DC Intertie, which has been in operation for over 30 years. Operating at ±500 kilovolts, the line is capable of transmitting up to 3,100 MW of power. In terms of operating voltage and capacity, the Pacific Intertie is similar to the Clean Line transmission line projects that will operate at ±600 kilovolts and deliver up to 3,500 MW of power.
Today, there are more than 20 HVDC transmission facilities in the United States and more than 35 across the North American electric grid as indicated in the map below.