American Superconductor (USA) announced that it is delivering its 5-Megawatt (MW) high temperature superconductor (HTS) ship propulsion motor to the U.S. Navy after completion of factory acceptance tests. This 230 rpm motor offers 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).

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 labor are required in manufacturing, making HTS propulsion motors highly cost-competitive.

HTS wire also eliminates electrical losses in the rotor. Higher efficiency reduces fuel usage and, according to a recent study, can produce savings of several hundreds of thousands of dollars per ship per year. In addition, because HTS motors run “cold”, they are more durable since their rotors are not affected by the thermal stresses that are inherent to conventional motors. It is the thermal stress on rotors caused by the heat build-up in conventional and permanent magnet motors that necessitates costly motor repair and refurbishment.

According to industry experts, the current annual global market for electric motors and generators utilized for electric propulsion in commercial cruise and cargo ships is over $400 million. The market for ship propulsion motors is expected to grow rapidly to over $2 billion per year by 2010 because electric drives are becoming the propulsion system of choice for both commercial and military ships.