Development of an axial flux type PM synchronous motor with the liquid nitrogen cooled HTS armature windings

We developed an axial gap permanent magnet type high temperature superconducting synchronous motor (PMHTSSM) at liquid nitrogen temperature. There are two distinctive differences between this motor and the conventional HTS motors. The permanent magnet is applied to the field, iron cores and HTS wires are used as the armature. The motor has eight field poles, and six armature windings. The armature is put between the two fields. The field composes eight permanent magnets which are arranged as a circle. Four poles share three armature coils and there are two coils for every phase. The BSCCO wires, which are applied to armature windings, work at the temperatures of between 66 K and 70 K. The rated output is 400 kW at 250 rpm. It is known that superconducting wires have AC loss if they are operated at alternating magnetic fields. That is why there are few motors developed with superconducting armature windings. Also, there is no report of motors applying HTS wires such as BSCCO wires to armature windings. Furthermore, this motor adopted the revolving field type structure, so the brushes were not needed and the cooling system can be fixed. Also because of the axial-flux type, the structure of the cryostat can be simplified.