Fabrication and Test of a 400 kW-Class Fully Superconducting Synchronous Motor Using REBCO Tape for an Electric Propulsion System

Advanced electric propulsion systems have been developed by utilizing superconducting technologies to reduce carbon dioxide emissions from aircraft. This study presents the progress in the development of a 400 kW-class fully superconducting synchronous motor using REBa
₂
Cu
₃
O
_7−δ
(REBCO) tape. REBCO tapes have high critical current densities; thus, they can generate a strong magnetic field without an iron core, permitting the fabrication of small-sized motors compared with conventional motors that use copper wires and iron cores. The 400 kW-class fully superconducting synchronous motor comprises field and armature coils. The field coil was wound with cos-theta-like racetrack distribution to generate a dipole field without an iron core. The maximum magnetic field is 1.45 T when the operating current is 110 A DC. The armature coil comprises six racetrack-shaped pancakes wound with six-strand parallel conductors. The parallel conductors were transposed inside the windings, resulting in a uniform current distribution in each conductor. The motor utilized carbon fiber-reinforced plastic (CFRP) for the casing instead of stainless steel for weight reduction. Foam insulation was adopted to further reduce the mass, in which an adiabatic material was wrapped around the external part of the CFRP casing. The armature coil was cooled using sub-cooled liquid nitrogen (LN
₂
), with high electrical insulation and a stable liquid phase. In contrast, the field coil was cooled by utilizing helium gas instead of LN
₂
because sealing the LN
₂
with a magnetic fluid seal is challenging. The motor was tested in a synchronous generator mode and subsequently rotated by utilizing three bipolar power supplies. The motor successfully rotated at 441 rpm when the field current was 72 A, the armature current was 103 Arms, and the frequency was 7.35 Hz.