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ORNL superconducting motor has big possibilities
OAK RIDGE, Tenn.,
April 18, 1995
A table-top superconducting motor developed by researchers at the Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL) is helping people see up-close the potential for high-temperature superconducting wires.
ORNL and American Superconductor Corp. (ASC ) of Westborough, Mass., are working to develop electric power applications of superconductors. These devices will be used to produce more compact and efficient underground transmission cables, industrial motors and generators, and electric distribution equipment. Researchers also believe superconducting motors could play a role in a variety of other applications, including mass transportation systems and in generating electricity.
The motor's designer, Bill Schwenterly of ORNL's Fusion Energy Division, built the motor using a superconducting coil supplied by ASC and parts from a hobby shop and hardware store. In this instance, Schwenterly's main goal was to design and build a motor as an educational activity of the laboratory's Superconductivity Program for Electric Power Systems, sponsored by DOE. Schwenterly has demonstrated the motor to lab visitors and to students at an environmental fair, where it drew a crowd of curious youngsters.
"It's a nifty gadget to show superconductivity," said Bob Hawsey, manager of ORNL's Superconductivitiy Program. "We're getting to the point where we can show practical applications using superconductors." Several teachers and groups in nearby Knoxville have requested demonstrations using the motor.
"I am very pleased to see that ORNL is helping to educate students about superconductivity and the benefits this technology will provide to them," said Greg Yurek, president and chief executive officer of ASC. "ORNL's innovative use of ASC's high-temperature superconductor components in an educational demonstration of this new and exciting technology is another example of how our national laboratories bring value to the American public."
A superconducting motor is like a conventional motor, with two major differences: It uses special, zero-resistance, high-temperature superconducting (HTS) wire, and it operates at very low temperatures. Because of these features, a superconducting motor uses less electricity to do the same amount of work when compared with other motors. A superconducting motor is also dramatically smaller in size. These traits are what make superconducting motors and materials potentially so useful.
"Using these materials amounts to a gain in efficiency of a few percentage points. This does not sound like much until you think in terms of the huge utility and industrial power plants that stand to benefit from this technology," Schwenterly said. For example, over the 10-year life of a 1,500-horsepower motor, a superconducting version offers cost savings of more than $325,000 when compared with a conventional motor, Schwenterly said. Energy savings pay off primarily for large motors, 1,000 horsepower and greater.
Like a typical motor, a superconducting motor has two main components: the field coil and the armature coil. The field coil produces a magnetic field using an oxide of bismuth, strontium, calcium and copper oxide (BSCCO), a high-temperature superconducting wire. In a superconducting motor, BSCCO is surrounded by pure silver to protect it from air and moisture.
Silver is also much better than copper - used in conventional motors - at conducting electricity, and it produces a path for the current to travel if the superconductor breaks down.
In ORNL's small demonstration motor, two D-cell batteries provide power the BSCCO uses to produce a magnetic field. Meanwhile, the armature coil, which is made of copper wire and operates at room temperature, produces a rotating magnetic field rather than a steady field. The current in the armature coil oscillates, causing the field to change direction. A commutator, which is a rotating switch that energizes the armature, is mounted on the motor frame. In the demonstration motor, it runs on five nine-volt batteries. In motors like the one Schwenterly built, the armature coils rotate with the shaft.
The direct current magnetic field from the superconducting coil interacts with the alternating current flowing in the copper armature to produce the force that causes the armature assembly to rotate. The shaft rotates to try to get the opposite poles of the field and armature lined up with each other. The motor shaft continues to rotate as the armature coils always try to line up their opposite poles with the field coils. They never catch up because of the switching action of the commutator. When fully chilled to -196 degrees Celsius (-321 degrees Fahrenheit), the superconducting coil loses all electrical resistance, allowing the motor to rotate at several hundred revolutions per minute.
The Superconductivity Program for Electric Power Systems is funded as part of DOE's national effort to develop the technology necessary for U.S. industry to proceed to commercial applications of high-temperature superconductivity.
In other advances in high-temperature superconductivity funded by DOE's Superconductivity Partnership Initiative, ASC is part of a team developing for demonstration later this year a 100-horsepower HTS motor. The design and components of this motor will be the same for 1,000-horsepower motors, the size targeted for commercial applications.
DOE created the Superconductivity Partnership Initiative to offer financial assistance to industry-led teams developing HTS components and equipment for electric power systems. HTS has been identified by the federal government as a critical technology for the U.S. to develop.
ORNL, one of DOE's multiprogram national research and development facilities, is managed by Martin Marietta Energy Systems, a Lockheed Martin company, which also manages the Oak Ridge K-25 Site and the Oak Ridge Y-12 Plant.