High Power Density Marine Propulsion Motors with Double-Helix Coils

— A new class of marine propulsion motors, that achieves power density far superior from that obtained in conventional superconducting synchronous motor designs, is presented. This is accomplished through the use of a novel coil design called the " double-helix " (DH) coil for the superconducting rotor of a synchronous machine in conjunction with a superconducting stator. This configuration is especially suitable for use with high current capacity superconducting cables, which can be made as multi-strand cables from round wires or as several layers of thin flat conductors. When a high excitation current is applied to a DH coil wound from HTS conductor, the strong magnetic field that is produced can achieve a high power output in a relatively small machine. The rotor lends itself quite readily to high current excitation by means of a flux pump incorporated in a completely superconducting circuit without any external connection to the machine frame. The resulting low inductance, high current design facilitates the quench protection of high energy content coils. The high power is developed in conjunction with a close-fitting superconducting three phase stator that uses an interleaved structure of conventional saddle-shaped superconducting coils to achieve an efficient flux linkage between the rotor and stator. The AC losses in the superconducting stator may be reduced to an acceptable level by using a two pole configuration with a low frequency (i.e. 2 Hz current for 120 rpm) and small filament conductor.