Exclusive: High-temp superconducting wire aids motor development

Rockwell Automation reports it successfully demonstrated in June 2005 the first use of second-generation (2G) high-temperature superconducting (HTS) wire in a 2-hp Reliance Electric HTS motor. The firm adds that HTS wire remains key to making HTS technology practical for use in large, industrial motors.

HTS wires and coils promise to make these super-efficient machines cost-effective and available in the not-too-distant future. HTS’ premise is to virtually eliminate resistance to current flow, allowing an HTS motor to cut power losses 50% compared to the best traditional motors now available.

Rockwell conducted its demo in cooperation with the U.S. Department of Energy’s (DOE) “Superconductivity Partnerships with Industry” (SPI) program. For more than 10 years, Rockwell has worked with DOE’s SPI program and partner supplier companies in a series of HTS motor demonstrations that showed impressive progress, reaching 1,600-hp output in 2001—all using first-generation (1G) HTS wire.

However, because cost per motor of 1G wire likely exceeded total cost of an existing motor; something new was needed, according to Dr. Rich Schiferl, Rockwell’s director of advanced technology for Reliance. “First-generation HTS wire technology was just too expensive to be successful for motors,” he told Control Engineering .

2nd-gen HTS wire needs less cooling

The HTS motor used for the 2-hp demonstration was a synchronous machine with superconducting field windings (rotor) and a conventional stator. Cooling for the HTS coils came from liquid nitrogen introduced into the center of the rotor and exhausted through the motor frame (for demo purpose only, see photo). It provided temperature of about -321 °F (-196 °C) inside the rotor. In an actual motor, coolant would be recirculated. “In large industrial HTS Motors, the superconducting-coil coolant will be recaptured from the rotor and rechilled in a closed-loop cooling system, so no cold gas or liquid will escape from the motor,” adds Schiferl.

The 2-hp demo motor used 14 meters (46 ft) of ceramic-based, coated conductor 2G HTS wire—wound into two rotating field coils—supplied by SuperPower Inc., a subsidiary of Intermagnetics General Corp. Second-generation HTS wire is expected to provide performance superior to the previous generation. SuperPower currently produces 2G wires in continuous lengths up to 100 m, and this capability is reportedly growing rapidly. Actually, about 10 times the present continuous wire length will be needed for motors around 5,000 hp, where the large hoped-for energy savings can be achieved. Splicing will add to total wire length. “Kilometers of wire will be required for large HTS motors,” adds Schiferl. Manufacturing the wire relies on SuperPower’s proprietary MOCVD (metal organic chemical vapor deposition) process that reportedly yields much higher production rates (throughput) and uniformity of performance than earlier pulsed laser deposition (PLD) processing.

So, when can we expect to see HTS motors at work? Schiferl replied that he believes in about five years HTS motors will be applied in industry in small numbers. Ramp up to wider use of such motors will come later. “Smallest unit sizes expected will be around 1,000 hp, with most at 5,000 hp and above. Also, 2G HTS wire available in the next five years will likely meet cost and length requirements,” he says. Electricity production and ship propulsion are likely first applications.

For more information, visit www.rockwellautomation.com , www.reliance.com , www.igc-superpower.com .

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