Last Wednesday, American Superconductor officially commissioned the world's first high-temperature superconductor power-transmission cable system to be used in a commercial power grid. The system, part of the Long Island Power Authority's grid, consists of three cables operating at 138 kilovolts. It was energized in April 2008 and has the ability to power 300,000 homes when operating at full capacity.
Superconductors can supply lots of energy quickly, efficiently, and unobtrusively. They conduct 150 times the electricity of similarly sized copper wires. But because of technological difficulties, the commercial development of superconductor power-cable systems has been slow. The first-generation cables now operating successfully on Long Island are costly, mainly because the wires are coated with silver. Testing has just begun on a second-generation cable coated with copper, which cuts four-fifths of the cost.
I'm cautiously optimistic. This article is a bit misleading however - the cable length is only 2000ft (610m)
http://www.amsc.com/ (page includes high-res photos)
I have no idea what the economics are. How much power is spent liquefying the liquid nitrogen? How much does the insulation cost?
The economics are pretty good. The power saved outweighs the refrigeration costs. A buried 138kv cable of over 3 miles has to have an insulator pumped (and cooled) through it anyways. Liquid nitrogen is probably cheaper. The price per kilo-ampere of a superconducting cable is approaching that of bare copper. Not least because the price of bare copper is climbing as demand from developing countries is rising. And then there's the physical size factor. The cable's a lot smaller so you don't need to dig and maintain as many holes throughout a city. Don't underestimate the costs of that.
It isn't quite EPS conduit, but still pretty cool1 eh?
1 Pun entirely intended. ;]