Development of a synchronous motor with Gd–Ba–Cu–O bulk superconductors as pole-fieldmagnets for propulsion system

Abstract

Rotating machines with high-temperature superconductors (HTS) usually consist ofpole-field magnets having coils wound with Bi-2223 HTS wire. We have successfully usedGd–Ba–Cu–O bulk HTS in pole-field magnets in an axial-gap type rotating machine. TheseHTS pole-field bulk magnets were assembled in the rotor plate. They are cooled down witha liquid cryogen supplied via a rotary joint and circulated inside the rotor plate. Thepresent design provides a small air gap and a bulk HTS gives a high magnetic field aroundthe armature coils. Successful mechanical design has enabled us to magnetize the pole-fieldbulk to more than 1 T by using a pulsed current applied to the copper armature coils.These techniques imply the possibility of smaller and lighter rotating motors or generatorswith a HTS bulk magnet for a sub-megawatt class propulsion system. We report severalessential techniques for both mechanical and cryogenic designs, and deduce thecharacteristic features of the present axial-gap type machine using a HTS bulk magnet.