Per press release (edited) and supercables website. A $9 million dollar 200 meters (660 feet) long second-generation high temperature superconducting (HTS) cable was energized on Sept 18 near Columbus, Ohio. The cable is used to efficiently deliver electric power to approximately 8,600 homes and businesses in suburban Columbus through American Electric Power's (AEP) Bixby substation in Groveport, Ohio.
Superconducting cables, operating at extremely low temperatures, eliminate virtually all resistance to the flow of electric current. One Triax HTS cable can carry as much current as 18 large copper cables, with much less energy loss. Although called high-temperature, this HTS system operates at temperatures just below the boiling point of liquid nitrogen (-321 degrees Fahrenheit).
As shown in the illustration, the Triax design places the three phase conductors (red) concentrically around a common central core. The three superconducting phases separated by a thin, 15 kV-class, electrical insulation material (yellow), Cryoflex™. Thus there is only one cooling pipe (dark grey), and the voltage that the dielectric has to withstand is the full phase to phase voltage. The advantage to the design is that it is ultra-compact, and uses the least amount of superconductor.
The compact design gives low impedance, low loss and reduced materials cost. It uses half the quantity of superconducting material needed and reduces the cold surface area, which reduces the critical cooling requirements. Earlier designs required a separate cable for each phase. The more compact Triax design reduces by half the quantity of HTS wire needed. It also reduces the cold surface area, and with it the critical cooling requirements. Both of these innovations lower the cost of HTS systems.
Designed in a joint venture of Southwire and nkt cables, a European cable manufacturer, this second-generation cable design can carry up to 3,000 amps of power, approximately three times more current than other superconducting projects now energized or under construction.
Because HTS cables can carry more current at a lower voltage over short or long distances, large power transformers can be located farther away from urban centers, allowing urban planners to free up valuable real estate for development or green space. HTS technology also enables greater interconnectivity between electrical substations, creating redundancies that increase the reliability of the electrical grid.
Superconducting cables are one solution to the challenging task of providing sufficient electric power to densely populated areas. In an increasing number of cities, there is little room underground to bury cable. The cost of building new tunnels or ducts, including the cost of acquiring the rights-of-way, to lay additional cable is prohibitive - representing up to 75 percent of a cable project. With their higher capacity, superconducting cables have the potential to multiply the supply of electricity to an area using the existing infrastructure footprint.
Despite these advantages, high temperature superconducting cable systems are still expensive. The U.S. Department of Energy provided partial funding through its Superconductivity Partnership with Industry program to help make the Columbus project possible.
The Columbus project is the first demonstration of the new Triax HTS cable design, which dramatically reduces the cost of superconducting systems and brings the technology one step closer to commercial viability. The system was developed by Southwire Company and its partners, American Electric Power (NYSE: AEP), Praxair (NYSE: PX), American Superconductor (NASDAQ: AMSC) and the U.S. Department of Energy's Oak Ridge National Laboratory (ORNL).
For more information on the new HTS cable design and the Bixby substation demonstration project, visit www.supercables.com.
American Superconductor, Westborough, Mass., is the world's principal vendor of high temperature superconductor wire and large rotating superconductor machinery. www.amsuper.com.