Researchers from 3M, working with ORNL, are developing a promising replacement conductor for conventional power lines that addresses the problem of power outages caused by sagging lines. Lines sag under the heat of high current loads. The replacement conductor also avoids the high cost and environmentally harmful effects of building new towers.
"3M's new composite-core conductor can increase the current-carrying capacity of a transmission line at minimal cost and environmental impact," said John Stovall, technical leader in ORNL's Engineering Science and Technology Division. "Its advantage is using existing structures to increase transmission capacity without the cost of a new transmission line."
The design uses 3M Nextel 650 ceramic fibers, embedded in an aluminum matrix, to make a composite wire that does not stretch as much when heated. An enhancement in the new cables is the addition of zirconium, which makes the aluminum more resistant to deformation at higher temperatures. The aluminum matrix also helps prevent rust in the cable. 3M is working with Nexans and Wire Rope Industries to manufacture the conductor.
"The new conductor's ability to handle greater temperatures will allow more current to be transmitted," Stovall said.
ORNL researchers will test 3M's small, medium and large diameter conductor cables successively in a field experiment at ORNL. The tests will evaluate the overall performance of the conductors to verify predictions of computer models by looking at sag and tension data, such as stress/strain curve and breaking point, and by testing various conductor accessories that attach the conductor to the towers.
The 3M conductor and line accessories by Alcoa Fujikora and Preformed Line Products are being tested for thermocycling, or high current situations, at ORNL. In Fargo, N.D., the conductor and its accessories are being tested for resistance in high winds and ice on a transmission line owned by Western Area Power Administration, while corrosion tests are being performed by Hawaii Electric Co. ORNL is monitoring the performance of the conductor at the Fargo site as well as other future utility sites.
In addition, the National Electric Energy Testing, Research and Applications Center in Atlanta is testing all of the components in their laboratories.
"As far as I know, there is not a conventional conductor that has been tested as thoroughly," said Tom Rizy of the Engineering Science and Technology Division.
Each test will run from five to six months. The researchers hope to put each conductor through 500 cycles of simulated thermocycling--taking it to peak load and then returning it to normal load-- the equivalent of 30 years of peak loads.
The Power Line Conductor Accelerated Testing or PCAT facility will be a closed loop of approximately 2,400 feet of composite core conductor. A 2MW direct current power supply fed by a transformer will provide current for the site. The Tennessee Valley Authority is helping to design the line structure at PCAT and install poles, hardware and other accessories at the test site.
"If the tests show that the new conductor performs well, it could mean that electric utilities will take greater interest in replacing their lines with new cables," Stovall said. "It also could provide one possible answer to the growing energy demand and transmission bottlenecks."
Others involved in the project from ORNL are Roger Kisner, Larry Phillips and Randall Wetherington of Engineering Science and Technology Division. The project is funded by the Department of Energy and through a cooperative research and development agreement with 3M. TVA donated the PCAT line design and the Electric Power Research Institute's Power Electronics Applications Center, a local research and development company, donated the load equipment to test the refurbished power supply that came from UT-Tullahoma's Space Institute.
ORNL is a Department of Energy multiprogram research facility managed by UT-Battelle.
Written by Jodi Lockaby
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