High-temperature superconducting (HTS) distribution and transmission line has been at the nearly there stage for almost a decade, but industry participants say the technology is now approaching wide commercial use. These proponents say the technology offers a potential solution for utilities seeking to expand distribution capacity in cramped urban settings. But its sensitive requirements could pose challenges for installers who will want to explore whatever training opportunities present themselves as products reach broad commercialization.

A superconductor is a conducting material that poses zero electrical resistance. Typically, this characteristic appears at extremely low temperatures—as low as –457°F in some cases. However, about 20 years ago, scientists discovered a new family of ceramic materials that could reach a superconducting state at as high as –321°F. Though this still may seem impossibly cold, it is a temperature that can be maintained through the use of chilled liquid nitrogen.

HTS technology already is in use in some medical equipment and sophisticated motors. The material offers advantages for electricity transmission and distribution, as it allows cable to carry high current at relatively low-voltage levels, according to David Lindsay, HTS cable systems business manager for Carrollton, Ga.-based Southwire, currently the only U.S. manufacturer of HTS cable. In a milestone test installation for Columbus, Ohio-based utility AEP, its Bixby station replaced a 138 kV copper line with a 15 kV HTS line in 2006.

“There have been a lot of demonstrations in the last decade,” said Jason Fredette, director of investor and media relations with Westborough, Mass.-based American Superconductor, manufacturer of the superconducting wire powering the Bixby station cable. “But last summer was the first time power was turned on [with HTS cable] in the U.S. grid. Utilities are beginning to feel comfortable regarding the technology.”

Two more grid-connected HTS demonstrations were announced this summer. The Long Island Power & Light Authority will be developing a transmission-voltage extension of a U.S. Department of Energy-funded project already underway, expected to be energized later this year. New York City’s Con Edison (ConEd) is installing HTS cable in a midtown Manhattan portion of its system as part of a U.S. Department of Homeland Security effort to develop “super grids” that are able to survive catastrophic events.

Market pressures boost interest

The momentum developing behind HTS installation is driven by less-expensive, second-generation wire design, and increasing pressure on utilities to increase transmission and distribution capacity. Many companies serving urban areas are facing major challenges meeting growing electricity demand because there simply is not space for new transformer facilities to handle added transmission-level supplies. Because of HTS cable’s added current capacity, transmission-to-distribution exchanges can occur outside the urban boundary.

“A lot of utilities are running into problems because they can’t expand their downtown substations. They’re landlocked,” Lindsay said. With HTS, on the other hand, “once you get into that downtown transformer, you don’t need all that high-voltage equipment.”

Additionally, distribution systems in some cities are facing similar space constraints, with maxed-out duct banks leaving little room for expanded electrical capacity. Replacing existing copper distribution cable with HTS material could expand capacity exponentially without need for new duct banks. This benefit also enables new grid designs, such as those ConEd will be testing, which use redundant connections to create greater operational security.

“What ConEd wants to do is to start connecting their substations, so if one substation goes down, the others can pick up the slack,” said Jim Maguire, American Superconductor’s vice president of superconducting projects. “They’re able to interconnect those substations with the wire we provide.”

Though HTS cable can be installed in standard duct bank, the process requires special expertise. First, a hollow, stainless steel tube, called a cryostat, is pulled into the bank. The cryostat acts as an insulating sleeve through which the cable is pulled. The cryostat is then flooded with liquid nitrogen to cool the cable, supplied by refrigeration equipment to which the assembly is attached. A single refrigeration station can handle runs up to two miles, Lindsay said, with longer runs requiring multiple systems.

Though much of this process would be familiar to some contractors, specialized training is required for splicing and terminating superconducting cable. Cable manufacturers now maintain control over these installations with proprietary techniques unique to their products, but broad adoption could stretch manufacturers’ installation resources, creating opportunities for qualified electrical contractors.

“As the market grows, that will become an issue,” Lindsay said. “And we think this is a market that will grow.”   EC