A ship propulsion motor with superconducting coils hushes machinery noise and hollows out confined engine rooms. The promise of superconducting motors inched closer to reality in April this year after American Superconductor Corp. of Westborough, Mass.(USA), announced plans to build a high-capacity manufacturing plant for its superconducting wire. This will move the company's high-temperature superconductor, or HTS, wire from a developmental phase into large-scale production.

Picture - MotorScale model of a 33,000-hp superconducting
ac propulsion motor. The design marries a conventional
ac stator and a superconducting dc rotor.

The announcement follows an U.S. Navy statement in January that it would use electric drive for the main propulsion in its next class of combatant ships, the DD-21 land attack destroyer. The news improved the chances for superconducting motors being aboard the first of the new vessels when it is christened toward the end of the decade. Even if a superconducting motor does not propel the lead ship, the decision will put enough necessary systems and equipment on the ships so they could easily be back-fitted eventually with superconductor motors.

"It almost doesn't matter what the first motor is," said Maribel Soto, a program manager in the materials division at the Office of Naval Research. Whether the first vessel carries an induction motor, a permanent magnetic motor, or a superconducting motor, the decision to use an electric final drive vindicates much of Soto's work in heading up what she called the "basic science" of ONR's superconductor motor development. The Navy, she said, now recognizes the importance of electric drive. The superconductor motor program has moved into an applications phase, she added.

Both contractors bidding the DD-21 class—General Dynamics' Bath Iron Works in Maine and Litton Ingalls Shipbuilding of Pascagoula (Miss.) recommended electric drive to the Navy as propulsion for its next warship. Actually, electric drive is only a part of the larger recommendation to use an integrated power system in the next class of ships. Navy ships have carried electric propulsion before. An integrated power system, however, ties the production of the electricity consumed by propulsion motors and the rest of a ship's electrical equipment to shared generators. Although the Navy's decision does not automatically qualify superconductor motors for shipboard duty, the ONR's 1999 award to American Superconductor of a $1.5 million preliminary design contract for a 33,000-hp ship propulsion motor is a sure sign of Navy interest.

Full article in Mechanical Engineering Magazine Online, by Paul Sharke, Associate Editor.