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. Index Terms-Axial flux type, BSCCO HTS wire, permanent magnet, permanent magnet HTS synchronous motor. I. INTRODUCTION W E developed a liquid nitrogen cooled axial flux type Permanent Magnet High Temperature Superconducting Synchronous Motor (PMHTSSM). In order to pursuit a high efficiency and small size HTSM and PM synchronous machine, this motor used liquid nitrogen temperature HTS wires as the armature windings instead of copper wires. Since the permanent magnets are used in the field, the armature iron core is necessary to obtain large magnetic flux density.
A liquid nitrogen cooled axial flux type high temperature superconducting (HTS) synchronous motor was designed. This motor is an eight-pole inductor type synchronous motor with six armature windings. The field windings and armature windings are made of the BSCCO HTS wires. We called it Inductor type Flux Control Superconducting (IFCS) motor, and its output is 400 kW at the rated speed of 250 rpm. Until now, there were few armature windings using HTS wires, because of AC losses generation when the wires are used in the alternating magnetic field. In this motor, we used iron cores to decrease AC loss. Also because of the help of iron cores, it is possible to make use of armature winding at liquid nitrogen temperature. Furthermore, inductors were employed in the rotor. As a result, the cryostats that contain field HTS windings and armature HTS windings can be fixed; also we do not need the excitation devices such as the brushes and slip ring and the cooling devices such as the rotary joint to offer the path for coolant to flow. Index Terms-Axial flux type, BSCCO-HTS wire, inductor type flux control superconducting (IFCS) motor, liquid nitrogen coolant, stator cooling system.
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