Long Island Power Authority (LIPA) and American Superconductor Corp have commenced operation of the world’s first high temperature superconductor (HTS) power transmission cable system in a commercial power grid. The 138 kV system, which consists of three individual HTS power cable phases running in parallel, was energised on April 2 and is operating successfully in LIPA’s Holbrook transmission right of way. The cable system, including six outdoor terminations for connection to LIPA’s grid, was designed, manufactured and installed by Nexan and utilises HTS wire produced by AMSC, which was also the prime contractor for the project. The 2000 foot long cable system is cryogenically cooled using a liquid nitrogen refrigeration system from Air Liquide.
The Department of Energy (DOE) previously funded $27.5 million of the $58.5 million total project cost, which advances the Department’s ongoing efforts, through the Office of Electricity Delivery and Energy Reliability, to modernize the Nation’s electricity delivery infrastructure.
The cable system contains hair-thin, ribbon-shaped HTS wires that conduct at 150 times the density of similar sized copper wires, an advantage that means transmission-voltage HTS cables can with far less wire conduct up to five times more power – in a smaller right of way – than traditional copper-based cables. When operated at full capacity, the new system is capable of transmitting up to 574 MW. HTS power cables are envisaged by the US DOE as a component of a modern electricity superhighway – one that is free of bottlenecks and can readily transmit power to customers from remote generation sites, such as wind farms.
Losses are also much lower. Conventional power grids typically lose seven to 10 percent of power transmitted. They can also be specially designed to have very low impedance (VLI) characteristics. When deployed in strategic locations, VLI superconductor cables, such as the one currently operating in LIPA’s power grid, can rapidly absorb additional power flows when conventional power grid components are damaged during electrical storms or other events. Because HTS cables are self-adjusting, they are expected to become core components of intelligent, more secure power networks.
LIPA is the third electric utility in the United States to have deployed an HTS cable system in its power grid. In the summer of 2006, National Grid and American Electric Power energised distribution voltage HTS power cable systems in Albany, New York and Columbus, Ohio, respectively. At nearly half a mile in length, LIPA’s HTS cable system is the longest of the three. It also is the first to operate at transmission voltages. After an initial operational period and following performance and economic reviews of the cable system, LIPA plans to retain the new superconductor cable as a permanent part of its grid.
In mid-2007, AMSC announced that it would lead the development of an extension of LIPA’s HTS cable system. The new cable will be powered by AMSC’s second generation (2G) HTS wire, branded as 344 superconductors. AMSC, who will again serve as the project’s prime contractor and wire supplier, has chosen Nexans as the cable manufacturer and Air Liquide as the provider of the cryogenics system. The DOE plans to provide up to $9 million in cost sharing for the $18 million project.
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