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

Rotating machines with high-temperature superconductors (HTS) usually consist of pole-field magnets having coils wound with Bi-2223 HTS wire. We have successfully used Gd-Ba-Cu-O bulk HTS in pole-field magnets in an axial-gap type rotating machine. These HTS pole-field bulk magnets were assembled in the rotor plate. They are cooled down with a liquid cryogen supplied via a rotary joint and circulated inside the rotor plate. The present design provides a small air gap and a bulk HTS gives a high magnetic field around the armature coils. Successful mechanical design has enabled us to magnetize the pole-field bulk 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 generators with a HTS bulk magnet for a sub-megawatt class propulsion system. We report several essential techniques for both mechanical and cryogenic designs, and deduce the characteristic features of the present axial-gap type machine using a HTS bulk magnet.