February 1, 2009

HTS Cables Speed up the Electric Superhighway

Angela Neville, JD

Cryogenic Features

One of the most unusual features of the HTS cables is that their cores have to be maintained at cryogenic temperatures. As a result of this requirement, the HTS cable’s design had to be specially adapted to include a cryogenic refrigeration system.

"All known superconductor materials exist in either a superconducting or non-superconducting state," McCall said. "To achieve superconductivity, the materials must operate below a certain critical temperature, below a certain critical current, and below a certain critical magnetic field. The magnetic field is not an issue in cable applications. The current criterion is met through basic cable design. The cryogenic refrigeration system is required to meet the temperature requirement. The liquid nitrogen coolant flows between the layers of HTS wire in the cable to cool them to about –200C (–328F) and to provide dielectric insulation between the center conductor layer and the outer layers of the cable."

HTS cables consist of concentric layers of HTS wire and a dielectric material providing electrical insulation compatible with cryogenic temperatures, he explained. This is referred to as a coaxial "cold-dielectric" design. The cable system was designed, manufactured, and installed by Nexans, a worldwide leader in the cable industry. Figure 2 illustrates Nexans’ HTS cable design used at Long Island Power Authority (LIPA).

2. The big chill. Flowing between the layers of HTS wires in the cable, the liquid nitrogen coolant cools them to about –200C. The cables use a liquid nitrogen refrigeration system provided by Air Liquide. Courtesy: Nexans