PR 53 07
BONNEVILLE POWER ADMINISTRATION
FOR IMMEDIATE RELEASE
Tuesday, December 11, 2007
CONTACT: Doug Johnson (503) 230-5840
BPA uses aluminum shunts to increase power line capacity and save money
Portland, Ore. - The Bonneville Power Administration is using a new method that allows transmission lines to carry more electricity capacity while also meeting more stringent outage standards. Thanks to a nontraditional approach, BPA was able to increase the amperage on one of its major 230kV lines at far less cost than rebuilding and replacing existing equipment.
The new practice is an important industry achievement at a time when utilities and grid managers nationwide are working to use transmission resources even more efficiently to address growing electricity demands and avoid costly new line projects when possible, all the while maintaining grid reliability.
BPA installed aluminum shunts, which are strands of aluminum added to a transmission line that provide another path for current to travel through to relieve strain on key line components, on its 230kV power line to allow it to handle a peak capacity of 1,500 amps, up from an existing capacity of 1,070 amps. The shunts allowed BPA to take full advantage of the existing conductor, helping save money and time that would have been required had BPA elected to replace the line.
The modifications arose out of a need to accommodate the output from the Mint Farm natural gas-fired power plant in Longview, Wash., into the Northwest electricity grid, which will require more current to be pushed through the line.
"We are entering a period where we will need to find creative solutions like this one to ensure that we continue to provide reliable transmission of power to the region," said Vickie VanZandt, BPA's senior vice president of Transmission Services. "Challenges like complying with strict reliability standards and integrating new resources into our power grid continue to put upward pressure on BPA's costs associated with doing business."
When BPA realized conditions would require the additional amperage to be transmitted through the line, it originally considered completely rebuilding and replacing the existing conductor. Testing showed that the existing line could handle the increased temperature associated with the additional amperage. However, the conventional compression connectors, which join sections of conductor together, would age quickly and create the risk of short-term failure if the line temperature were increased from 212 degrees Farenheit to 347 degrees.
Using aluminum shunts on the line alleviated the problem. Shunting involves, among other things, wrapping preformed aluminum wires over sections of a power line adjacent to compression connectors. The shunt provides a parallel path for line current in addition to the path through the compression connector. The shunt conducts most of the current around the connector, so only a fraction of the current flows through the compression connector. Since the shunt reduces the amount of current traveling through the connector, the connector operates at a cooler temperature and is protected from premature aging and failure.
While many traditional "non-wires" solutions to reducing the strain on transmission systems focus on demand response or distributed generation projects, this non-traditional approach could hold promise in future applications.
"Any time we can modify an existing line and increase the capacity of our power grid in the process, it is a significant step in the right direction," said Brian Silverstein, BPA vice president of Planning and Asset Management. "Non-wires solution or not, this is a great example of using innovation to save money while avoiding new construction, ultimately benefiting electricity consumers in the Northwest."
BPA is a not-for-profit federal electric utility that markets more than a third of the electricity consumed in the Pacific Northwest. The power is produced at 31 federal dams and one nuclear plant in the Northwest and is sold to more than 140 Northwest utilities. BPA operates a high-voltage transmission grid comprising more than 15,000 miles of lines and associated substations in Washington, Oregon, Idaho and Montana.
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