Pacific DC Intertie
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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 is 48.7% of the Los Angeles Department of Water and Power (LADWP) electrical system's peak capacity.[1]
The intertie originates near the Columbia River at the Celilo Converter Station on Bonneville Power Administration's (BPA) grid outside The Dalles, Oregon and is connected exclusively to the Sylmar Converter Station north of Los Angeles, which is owned by five utility companies and managed by LADWP. The Intertie is capable of transmitting power in either direction, but power on the Intertie flows mostly from north to south.
The idea of shipping hydroelectric power to Southern California had been proposed as early as the 1930s, but was opposed and scrapped. By 1961, U.S. 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 U.S. and ASEA of Sweden. Private California power companies opposed the project but their technical objections were rebutted by Uno Lamm of ASEA at the 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 U.S. $600,000 per day by use of electric power from projects on the Columbia River.
The Pacific Intertie takes advantage of differing power demand patterns between the northwestern and southwestern U.S. 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 powergrid (states west of the Great Plains, including Colorado and New Mexico).[2]
The Pacific Intertie consists of:
- The Celilo Converter Station which converts three phase 60 Hz AC at 235 to 525 kV to 500 kV DC.
- The grounding system at Celilo consists of 1,067 cast iron anodes buried in a two foot trench of petroleum coke, which behaves as an electrode, arranged in a ring of 3,255 meters (2.02 mi) circumference at Rice Flats (near Rice, Oregon), which is 10.6 km (6.6 mi) SSE of Celilo. It is connected to the converter station by two aerial cables.
- A 1,362 kilometer (846 mile) overhead transmission line consisting of two uninsulated conductors 1,171 mm2 containing a steel wire core for strength.
- The Sylmar Converter Station which converts DC to AC (a process also called inverting) and phase-synchronized with the L.A. power grid.
- The Sylmar grounding system is 24 silicon-iron alloy electrodes submerged in the Pacific Ocean suspended in concrete enclosures about one meter above the ocean floor. The grounding array is 48 km (30 mi) from the converter station.
- The wires have a capacity of 2 gigawatts in bipolar mode and 1.55 gigawatts with earth return.[3]
Originally only mercury arc rectifiers were used as static inverter valves. 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 rate of 1,440 megawatts with a symmetrical voltage of 400 kV against earth. The line is the DC part of a system of four 500 kV lines that connect the Pacific Northwest with the Southwest; the AC part is Path 15. This is one of two HVDC lines serving Los Angeles, the other is the Intermountain.
- In 1972, after the Sylmar earthquake, the static inverter station in Sylmar had to be reconstructed after damage to the largest part.
- In 1982, the power rating of the mercury arc valve rectifiers was raised by various improvements to 1,600 megawatts.
- In 1984, the transmission voltage was pushed to 500 kV and the transmission power was increased to 2,000 megawatts by adding two six-pulse thyristor valve groups to each pole.
- In 1989, a further increase of the transmission power took place by a parallel switched thyristor static inverter in Celilo and Sylmar.
- In 2004, Sylmar East station was upgraded from 1,100 MW to 3,100 MW (rededicated as the Sylmar Converter Station in 2005). The controls and older converters, including the mercury arc valves, were completely replaced by a single pair of 3,100 MW 12-pulse converters built by ABB. In parallel with this project, the six-pulse mercury arc valves at the Celilo Converter Station were replaced with Siemens light-triggered thyristors (MARP replacement).
[edit] See also
[edit] References
- ^ Sharon Bernstein and Amanda Covarrubias, Times Staff Writers (September 10, 2006). Heat Wave Caught DWP Unprepared. L.A. Times online. Retrieved on 2006-09-11.
- ^ Prabha Kundur, Powertech Labs Inc. (October 3, 2003). Power System Security in the New Industry Environment: Challenges and Solutions (powerpoint) 17. IEEE. Retrieved on 2006-09-11.
- ^ The Pacific Intertie Scheme. Bonneville Power Administration (2000-11-3). Retrieved on 2006-09-10.
[edit] External links
More on the ABB website on Pacific HVDC Intertie:
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