A Fractional Power Disk Shaped Motor with Superconducting Armature

A disk-shaped, double stator, induction motor with High Temperature Superconducting (HTS) field coils is proposed in this paper. Copper, typically used in windings of classic machines, limits current density allowed in field coils due to Joule effect losses. Also iron, which is used in magnetic circuits, limits the magnetic flux density obtained in the air gap due to saturation. The application of HTS field coils and iron removal effect in fractional power disk shaped or axial flux motors is analyzed by comparison of two different stator topologies. Twelve HTS field coils made of Bi-2223 (Bi2Sr2Ca2Cu3O10) first generation tape, wrapped around a racetrack-shaped nylon core, are assembled. A simple topology was chosen, consisting of six filed coils per semi-stator arranged in the same plane with 60 o displacement. This topology is analyzed theoretically, based on a linear induction motor approach and simulated using a commercial finite elements program, based on the same approach. In order to study the effect of magnetic saturation two stators were built. In the first, the field coils are assembled in steel plates. In the second, the same coils are assembled on nylon plates. The rotor is composed of an aluminum disk assembled on a stainless steel shaft. The HTS coils were cooled by liquid nitrogen (77 K). Simulations, experimental and theoretical results are consistent, showing high space harmonic distortion for the chosen topologies. It is shown that for this type of low power motors operating at this temperature, as iron saturation is not achieved, ferromagnetic materials removal is not a good option. Besides, flux leakage is to high, degrading developed torque.