5 May 2008 – The world’s first high temperature superconductor (HTS) power transmission cable in a commercial power grid was energised last week. The 138 kV system consists of three individual HTS power cable phases running in parallel and is operated by Long Island Power Authority in the United States.
The cable system, including six outdoor terminations for connection to LIPA’s grid, was designed, manufactured and installed by Nexans. The 2 000 foot long cable system is cryogenically cooled using a liquid nitrogen refrigeration system.
The US Department of Energy provided funding of US$27.5 million for the US$58.5 million project.
The cable system contains hair-thin, ribbon-shaped HTS wires that conduct 150 times the electricity of similar sized copper wires. This power density advantage enables transmission voltage HTS cables to utilise far less wire and yet 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 HTS cable system is capable of transmitting up to 574MW of electricity, enough to power 300,000 homes.
HTS cables conduct electricity with virtually no electrical losses, meaning more of the power generated at power plants gets to customers. Conventional power grids typically lose seven to 10 percent of power due to the inherent electrical resistance experienced with copper wires. The higher electrical efficiency of HTS cables provides a means to reduce carbon emissions while meeting the growing demand for electric power in the digital age.
Alternating current HTS power cables have inherently low impedance, which means they can draw power flow away from overtaxed conventional cables or overhead lines, thereby relieving network congestion. They can also be specially designed to have very low impedance (VLI) characteristics. When deployed in strategic locations, VLI superconductor cables 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.