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, DC projects have shown to offer significant electrical, economic, and environmental advantages when transporting power across long distances, where there has been a veritable boom in the use of HVDC to tap energy resources in remote portions of the country and bring the energy 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, which will operate at ±600 kilovolts and deliver up to 3,500 MW of power.
Currently there are more than 20 HVDC transmission facilities in the United States and more than 35 across the North American grid as indicated in the map below.