Pacific DC Intertie

The Pacific DC Intertie (also called Path 65) is an electric power transmission line that transmits electricity from the Pacific Northwest to the Los Angeles area using high voltage direct current (HVDC). The line capacity is 3,100 megawatts, which is enough to serve two to three million Los Angeles households and represents almost half of the Los Angeles Department of Water and Power (LADWP) electrical system's peak capacity.
The intertie originates near the Columbia River at the Celilo Converter Station of Bonneville Power Administration's grid outside The Dalles, Oregon and is connected to the Sylmar Converter Station north of Los Angeles, which is owned by five utility companies and managed by LADWP. The Intertie can transmit power in either direction, but power flows mostly from north to south.
The section of the line in Oregon is owned and operated by Bonneville Power Administration, while the line in Nevada and California is owned and operated by Los Angeles Department of Water and Power.
The transition is at the Oregon–Nevada border, at .
This is one of two HVDC lines serving Los Angeles; the other is Path 27.
Overview.
The idea of sending hydroelectric power to Southern California had been proposed as early as the 1930s, but was opposed and scrapped. By 1961, US president John F. Kennedy authorized a large public works project, using new high voltage direct current technology from Sweden. The project was undertaken as a close collaboration between General Electric of the US and ASEA of Sweden. Private California power companies had opposed the project but their technical objections were rebutted by Uno Lamm of ASEA at an IEEE meeting in New York in 1963. When completed in 1970 the combined AC and DC transmission system was estimated to save consumers in Los Angeles approximately US$600,000 per day by use of cheaper electric power from dams on the Columbia River.
One advantage of direct current over AC is that DC current penetrates the entire conductor as opposed to AC current which only penetrates to the skin depth. For the same conductor size the effective resistance is greater with AC than DC, hence more power is lost as heat. In general the total costs for HVDC are less than an AC line if the line length is over 500–600 miles, and with advances in conversion technology this distance has been reduced considerably. A DC line is also ideal for connecting two AC systems that are not synchronized with each another. HVDC lines can help stabilize a power grid against cascading blackouts, since power flow through the line is controllable.
The Pacific Intertie takes advantage of differing power demand patterns between the northwestern and southwestern US. During winter, the northern region operates electrical heating devices while the southern portion uses relatively little electricity. In summer, the north uses little electricity while the south reaches peak demand due to air conditioning usage. Any time the Intertie demand lessens, the excess is distributed elsewhere on the western power grid (states west of the Great Plains, including Colorado and New Mexico).
Components.
The Pacific Intertie consists of:
History.
The first phase of the scheme, completed in May 1970, used only mercury-arc valves in the converters. The valves were series connected in three six-pulse valve bridges for each pole. The blocking voltage of the valves was 133 kV with a maximum current of 1,800 amperes, for a transmission rating of 1,440 MW with a symmetrical voltage of 400 kV with respect to earth.
Each converter station housed six mercury arc valves groups, consisting each of seven valves, for a total of 42 valves in each converter.
The valves had a width of , a height of and a length of and weighed . Each valve contained mercury, with a weight of .