| American Superconductor Corporation, USA, has recently delivered a 5MW high-temperature superconductor (HTS) ship propulsion motor to the US Navy. The motor and its drive system successfully completed factory acceptance testing under US Navy observation at a test facility at Alstom in Rugby, UK. �We are very pleased with the factory test results for this advanced electric ship propulsion technology, which confirmed that this HTS motor met or exceeded all of our performance requirements�, commented Mr Scott Littlefield, programme manager at the US Navy�s Office of Naval Research. �American Superconductor�s successful development and delivery of this motor on-time and on-budget is noteworthy and adds to our confidence that their much more powerful 36.5MW HTS motor, now in design, will deliver similar results and provide the sort of power dense, highly efficient propulsion system the Navy will require for its next generation of surface ships�.
The 5MW, 230rpm HTS ship propulsion motor feature a number of significant advantages over both conventional copper-wound rotor and permanent magnet motors. These include dramatically reduced size and weight, inherent quietness, greater durability and higher efficiency, (particularly during low-speed, partial load operations). These advantages result from the use of AMSC�s HTS wire in place of copper in the motor�s rotor coils.
A motor�s power and torque density is directly related to the strength of the magnetic fields created when electric current is passed through its rotor coils. Rotor coils made from HTS wire generate much stronger magnetic fields than those of similar size made from copper, which means that an HTS motor can have a power density up to five times greater than that of a conventional motor of similar size. Because HTS motors have greater power density, they are more compact than their conventional counterparts. This not only enables more flexibility in ship design, but also means that fewer materials and less labour are required in manufacturing, making HTS propulsion motors highly cost-competitive. HTS wire also eliminates electrical losses in the rotor, typically the main source of wasted energy in motors. This makes HTS motors much more efficient than conventional motors across a broad range of ship speeds. Higher efficiency reduces fuel usage and, according to a recent study by the maritime consultancy MSCL LLC, can produce savings of several hundreds of thousands of dollars per ship per year.
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