On Feb. 6, 2009, Southwire Company and its partners marked the two-and-a-half year anniversary of an urban power distribution project using high-temperature superconductor—known as HTS Triax Superconducting Cable systems. The installation in Groveport, OH used approximately 200 m (600 ft) of Southwire’s HTS Triax Superconducting Cable to distribute electric power to 8,600 homes and businesses through American Electric Power’s Bixby substation. In addition to American Electric Power (AEP), project partners included American Superconductor, the U.S. Department of Energy's Oak Ridge National Laboratory, and Praxair.
“Using second-generation cable design and recent advances in cooling technology, the Bixby installation proves the reliability of HTS Triax Superconducting Cable systems in reducing the cost of high-efficiency power distribution in an urban setting,” says David Lindsay, Southwire Director of Engineering, Distribution Applications.
The system has experienced more than 75 transient events, including lightning strikes, during its 2.5 years of operation. Most of these events were through-faults—fault current that entered the Bixby station from the distribution circuits powered by the HTS Triax cable. No change in system temperature or pressure was recorded as a result of the events and the system has never been taken out of service as a result of these events.
The system has operated successfully since its installation in August 2006. Designed and built for a load rating of 3,000 A per phase, it performed at 90.5% of the design rating, reaching 2,715 A during peak loading in the summer months. “Our partnership with Southwire has allowed us to test advances in superconductivity and cooling design on our system with virtually no interruption to customers,” says Michael Heyeck, AEP Senior Vice President of Transmission.
HTS Triax cables add capacity to existing duct banks. One HTS Triax cable can carry as much current as 18 large copper cables. This is possible because HTS Triax cable operates at extremely low temperatures for power cable — 281 deg F (-196 degrees C) — and eliminates current flow resistance.
Large power transformers can be located further away from urban centers because HTS Triax cables carry very high currents at lower distribution voltages. Additionally, valuable real estate for development and green space is freed up.
Reduced critical cooling requirements, combined with newly commercialized cryogenic cooling technology, reduces cost and maintenance. HTS Triax is very compact, with three phase conductors placed concentrically around a common central core, cutting the quantity of wire in half. This smaller surface decreases cooling requirements.
According to Heyeck, “The performance of the HTS Triax system has shown the potential for cost savings with excellent reliability in a variety of applications.”
With the Bixby performance success, Southwire now draws on over a decade of in field superconducting experience. Together with projects under way in New Orleans and New York City, these installations prove the in-field success of urban delivery of critical electric power through superconductivity and position Southwire as an experienced leader in this innovative offering.