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Hydropower Flows Here
Direct current line still hot after 40 years
5/26/2010 12:00 AM
When you help build a region, you help build your nation.
That's what President John F. Kennedy said in a letter to the Bonneville Power Administration on its 25th anniversary. It was 1962. An obscure band called The Beatles was preparing to release its first album, and Congress had just authorized BPA's two-year direct current test program. Both acts were to have major consequences.
We know what happened to the Beatles. Less familiar is the story of direct current technology and the notable contribution BPA's test center made to transmission systems worldwide. It ultimately led to the first and longest ultra-high-voltage DC line in the nation. This month marks the 40th anniversary of the energization of this line.
The DC line came to life May 21, 1970, as the backbone of the Pacific Northwest-Pacific Southwest Intertie. The Celilo Converter Station, the northern genesis of the DC line, was dedicated Aug. 25, 1970.
"It seems like yesterday," reflected Fred Johnson, former vice president of Transmission Field Services. The northern terminal of the intertie is named after Johnson, who came to work at BPA in 1965. "Many men and women struggled long days and definitely long nights to reach that commissioning date. We toiled and struggled together, each of us bringing our professionalism, dedication and teamwork to create something that none of us could have done on our own."
For 40 years, the intertie has joined two regions – the Pacific Northwest and Californian/Pacific Southwest. It is a near perfect example of mutualism, like the give and take of flowers and bees. Only this relationship did not evolve naturally.
Pacific Northwest-Pacific Southwest Intertie.
"This was one of BPA's – and the nation's – greatest engineering feats," said Brian Silverstein, Transmission Services vice president. "It took technological breakthroughs and political triumphs, and ultimately paved the way for future long-distance interties around the world."
The largest in the nation
The intertie is the largest single electricity transmission link in the United States. Hundreds of millions of pounds of conductor make up four extra-high voltage transmission lines that link the BPA power grid to California utilities. Three 500-kilovolt alternating-current lines extend from John Day Dam to various points in northern California.
The colossal DC line spans 846 miles across 4,200 towers from Celilo near The Dalles, Ore., to the Sylmar Converter Station in Los Angeles. Celilo and Sylmar convert alternating current into direct current and send it on its way (more efficiently than AC) to the other station where it is converted back into AC.
It only takes two conductors versus three for AC. Accordingly, DC towers carry less weight and cost less. But first, pulsating alternating current must be changed to the steady one-directional flow of direct current at converter stations. While the conversion process requires expensive equipment at each terminal, power losses on DC transmission are lower for distances of 400 miles or more, so more power is delivered.
Technological advances by BPA engineers helped make a long-distance direct current line feasible. The largest mercury arc converters in the world were developed and installed at Celilo and Sylmar. New computer techniques were developed to integrate the DC link with the parallel 500-kV AC system. This was the first time a high-voltage DC line was embedded in an AC network.
Sharing (and saving) resources
Thanks to the intertie, electricity consumers on the West Coast enjoy a unique power-sharing arrangement that takes advantage of seasonal weather differences.
In spring and early summer, Northwest rivers usually provide more water for power generation than the region needs. At the same time, temperatures – and air-conditioning needs – in the Southwest climb. That is when the DC intertie sends power south. (It is offered in the region first and only sent south if it is surplus to regional needs.) The revenues from sales of this surplus help keep Northwest rates lower.
At other times, such as in winter and at night, California power plants generate more electricity than local consumers need. When temperatures in the Northwest are low and heating needs rise, the power flows north.
The Pacific Northwest Consumer Power Preference Act of 1964 concerned Northwest governors that the Intertie would not siphon Northwest power. The Preference Act required that BPA sell firm energy first to electric utilities in the Northwest and that only power surplus to Northwest needs would be offered for sale outside the region.
Because the two regions can back each other up, thanks to the intertie, less power has been generated at fossil-fuel power plants. And the regions do not have to build expensive power plants to meet peaking needs: plants that would be idled much of the time. Fish benefit from the intertie too. Money that southwestern utilities pay for power from BPA helps finance fish and wildlife restoration projects in the Columbia River Basin.
Since its original construction, modernizations have more than doubled DC intertie's capacity to 3,100 megawatts. Improvements made to the DC line should keep it humming for at least another 20 years.
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