High-Temperature Superconductor Technology Stepped Up

A new project planned by RWE and partners Nexans, the Karlsruhe Institute for Technology (KIT), and Jülich is poised to mark another milestone for high-temperature superconductor (HTS) cable technology, which transports electricity without losses when cooled down to about –200C (–392F). In January the firms announced they would kick off a project to replace a 1-kilometer (km, 3,280 feet) high-voltage cable connecting two transformer stations in the city of Essen, Germany, with a buried three-phase concentric 10-kV HTS cable made by Nexans, which is designed for a transmission capacity of 40 MW (Figure 5).

5. A freezing current. A 10-kV high-temperature superconductor cable made by Nexans will replace a 1-kilometer high-voltage cable in Essen, Germany. At temperatures of around –200C (–392F), with cooling provided by liquid nitrogen, the concentric superconducting cable is transformed into an almost perfect electrical conductor able to transport at least 100 times more electricity than copper. Despite the cooling jacket, the compact design of the superconductor means that it can transport five times the electricity as a similarly sized copper cable with much lower electrical losses. Courtesy: Nexans

HTS technology has seen sparse development since 2008, when the U.S. Department of Energy energized a 138-kV, 600-meter (1,968-foot) superconducting transmission power cable in a test installation for the Long Island Power Authority in New York. That cable was manufactured by Paris-based Nexans using wire produced by American Superconductor Corp. A handful of projects have been tested since then, including a 300-m cable with fault current limiting functionality installed under Manhattan. Known as Project Hydra, Con Edison and wire-maker Southwire plan to use that technology to connect two Con Edison substations in late 2014 with a 170-m-long cable.

Asked why superconductor technology development has been limited to smaller scales, Nexans said that though production processes have improved, “superconducting wires are only now available in sufficient lengths and quantities.” But “experts anticipate that these innovative cables will soon be in a position to compete with copper solutions in energy-intensive applications,” the company added.

One suitable use for the technology is in city networks. According to Nexans, the “AmpaCity” project, scheduled for operation in Essen by 2013, could “herald a whole new dimension in the restructuring of inner-city networks.” The project follows a study by KIT that found superconducting cables are the only “reasonable” alternative to high-voltage cables in city networks. Although copper medium-voltage cables could also be used in inner-city areas to transmit power, the cost efficiency of this solution would be cancelled out by the much higher ohmic loss, the study says.

After successful completion of a two-year field test, the project could make it possible to install 10-kV superconducting links in large sections of the Essen distribution network, Nexans claims. In addition to greater efficiency and lower operating and maintenance costs, a key benefit would be to reduce land use because numerous 110/10-kV transformer stations would no longer be needed.

Backed by the energy research arm of Germany’s Federal Ministry of Economics and Technology, total project costs are approximately €13.5 million ($17.7 million), including a government-funded €6 million ($7.9 million).

—Sonal Patel is POWER’s senior writer.

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