According to Blaugher's estimate, all electric motors account for about 64 percent of demand side electrical consumption in the United States, which translates to about 6.4 quad. One quad of energy is about 10¹⁵ British thermal units—a measure of energy consumption worth about $20 billion in retail sales at 7 cents per kilowatt hour. Electric motors consume about $128 billion worth of energy every year, with one-half of that amount used by large motors, defined as those greater than 1,000 horsepower.

Assuming substantial introduction of large superconductor motors, Blaugher estimates that the users would save about $2 billion a year in efficiency improvements and a second $2 billion a year could be saved at the utility or electric power producer.

Blaugher notes the $500,000 to $750,000 current market price for a conventional 5,000-hp motor combined with an adjustable speed drive (ASD). If superconductor motor producers can compete with that cost, including ASD and cryogenic support, Blaugher believes there would surely be a market for many hundreds of SC motors.

Reliance Electric, the Rockwell Automation company based in Cleveland, has a small but ambitious HTS motor team, led by David I. Driscoll. Driscoll is superconducting motors manager in the Advanced Technology unit of Rockwell Auto's Euclid Labs.

Driscoll and his team are currently in the second phase of a multiyear collaboration with American Superconductor. The collaboration is one of the Department of Energy's Superconductivity Partnership Initiatives, which support much of the work here in the United States. The first phase was construction and load testing of a 125-hp motor, which performed well over 200 hp from an inverter. One of the key accomplishments of that project was finding that the performance of the HTS coil did not degrade under the mechanical stresses associated with rotational force.

The second phase is construction and testing of 1,000- and 5,000-hp motors. The 1,000-hp design is complete and under construction.

A recent paper by Driscoll and his team summarized that effort. The 1,000-hp motor is designed for operation from an adjustable speed drive using the same topology as the previously demonstrated 200-hp HTS motor, which was an air-core ac synchronous motor with HTS field-winding operating at 1,800 rpm. The ASD is a conventional rectifier/ inverter system as used with present ac induction motor products, Rockwell said.

In this topology, the HTS coils are located on the rotor and the stator is composed of more conventional copper winding.

"Most of the technology is really in the rotor," Driscoll said. To accommodate the side effects of an HTS rotor, like the very high magnetic field created, the stator is water-cooled and Litz wire is used to reduce eddy current losses.

The coils are mounted on their own support structure, which houses a conduction-cooling apparatus.

Rockwell is using a commercial reverse Brayton cycle helium refrigeration system for initial component and system testing, but is looking at other options.

The wire being wound to make the motor coils is BSCCO, which is superconductive at 77K and so only requires liquid nitrogen for cooling. However, the motor application requires helium for cooling to 20K to 30K, Driscoll said, to keep the superconductors behaving as desired.

Much of Reliance Electric's work today is in preparation for more progress on the materials front. "All of the engineering we're doing today to get a motor at 1,000 hp at 33K will only help us in the future, when we have wire that will actually be performing at 77K," Driscoll said.

These motors will go into the standard large-motor applications, such as centrifugal compressors, boiler feed pumps, induced and force draft fans, and industrial scrubbers, Driscoll said.

The efficiency losses of an HTS motor, Rockwell expects, will be half those of an energy-efficient ac induction motor. Also, the motor has an active volume that is 55 percent of that for a 1,800-rpm, 5,000-hp, high-efficiency induction motor. This leads to reductions in friction and windage, core, stray load, and armature I²R loss.

Meanwhile, the Naval Research Lab (NRL) pursues superconducting motors for ship propulsion, Donald Gubser, superintendent of the materials science and technology division at the NRL in Washington, noted.

"The Navy has had a superconducting motor program for almost 30 years for ship propulsion," Gubser said. "We've recently been attempting to ascertain the viability of converting one of our low T_c motors to high T_c," he said, referring in shorthand to the very first superconducting materials, those of niobium titanium, and their replacement high-temperature ceramic counterparts.

The NRL's demonstrator superconducting motor operates at the low, liquid helium temperature of 4.2K at 300 hp. During 1998, researchers operated it off a cryo-cooler at 27K, which allowed for a 200-hp motor. Gubser noted that this is a homopolar motor; it is completely direct current, which requires brushes to make contact with the superconducting stator windings. Improving the brushes is currently one of the things NRL is working on, Gubser said.

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