The Path of Least Resistance

The Path of Least Resistance

HTS rotating machines on the slow road to commercialization and widespread use

Conventional motors account for 64% of the nation's energy use, according to the U.S. Department of Energy (DOE), Washington, D.C. Of that amount, half — one-third of the total energy use in the United States — is used by motors rated more than 1,000 horsepower. By virtue of their ability to carry current with almost zero resistive losses when used in industrial motor applications, high-temperature superconducting (HTS) materials offer the potential to double the power output and significantly reduce energy loss by as much as 50% in comparison to conventional motors of similar size with copper windings.

In addition to energy savings, there are also practical mechanical advantages to HTS motors: Besides lower noise emission, the iron teeth that conduct the magnetic field in conventional motors become redundant, resulting in a decrease in weight and volume. In fact, HTS materials are at their best when used in motors rated above 1,000 horsepower, where the additional costs of the superconducting technology can be offset by motor volume reduction and reduced energy-consumption costs, according the IEEE Transactions on Industry Applications, Vol 44, No. 5, September/October 2008 paper, “High-Temperature Superconducting Synchronous Motors: Economic Issues for Industrial Applications.” In the industrial arena, this could mean energy savings of up to $50,000 a year for a 5,000-horsepower motor that runs 24 hours a day, seven days a week.

Industrial motors aren't the only application that could benefit from widespread use of HTS technology. Superconducting wire in electric generators can increase machine efficiency beyond 99%, as well as decrease size by 50%, in comparison with generators wound with copper wire. A 1,000-megawatt superconducting generator could save as much as $4 million per year in reduced losses per generator. Industry analysts are estimating the potential worldwide market for superconducting generators in the next decade will reach between $23 billion and $30 billion.

Despite these advantages, HTS motors and generators are not yet available on a commercial scale. Granted, HTS is expected to be the future of large, industrial rotating machines, most likely replacing conventional motors and generators in the areas of electrical generating stations, petrochemical plants, wastewater treatment centers, and steel and paper mills where large pumps, fans, and compressors consume vast quantities of electricity. However, industry experts are reluctant to offer an estimated time line for their availability and adoption. “I've been saying HTS industrial motors will be available in five years for the last five years now,” says Rich Schiferl, director of advanced technology for the Baldor/Dodge/Reliance Advanced Technology Labs, Baldor Electric Co., Fort Smith, Ark., who, along with other scientists, has spent 21 years researching that application of superconductive materials to electric motors and generators.

So far, Schiferl's lab has been able to make several prototypes to test and demonstrate HTS large motor capabilities. Its largest one to date was a 1,600-horsepower model demonstrated in Cleveland in 2001. Other labs have created prototypes as large as 5,000 horsepower. “We demonstrate capabilities,” Schiferl says. “We understand how you build these machines and how you keep the rotor cold.”

All the same, development of large superconductor motors and generators for use outside the lab has been slow going. The major barrier that remains to commercial adoption is cost — for both the superconducting wire as well as the necessary cryogenic subsystems. “It's now a cost issue,” Schiferl says. “From our standpoint, it doesn't make sense to invest a lot of effort into developing a commercial motor unless we know that the costs are going to be met, so we're waiting for that to happen. We can't sell a superconductor motor that costs significantly more than a conventional motor; nobody would buy it.”

Experts working in the field of HTS generators agree. “We know how to go about making these generators,” says James Bray, a chief scientist at General Electric's Global Research Center, Schenectady, N.Y. “But if you want economically competitive machines, you'll need prices to go down more. You won't have widespread commercialization until the cost of wire and cryorefrigeration comes down.”

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