Flux Deflection on Rotating Field Pole Magnets for HTS Machines

Intensified magnetic flux generated by high-temperature superconducting (HTS) windings makes feasible the industrial rotating machines with both high efficiency and high torque density. For those HTS windings, the superconducting characteristics are influenced by the magnetic flux interacting with the HTS tape. Especially, the magnetic flux perpendicular to the a-b plane of the HTS tape decreases the critical current property, according to the anisotropy of 1G/2 G HTS tape conductors. This leads to the drop of the operating current limit as well as a heat loss in the windings. To avoid these losses as much as possible, the magnetic flux deflection (MFD) was studied. In a previous study, the advantage to suppress the heat loss in the wire was verified on Bi2223 prototype windings by adopting MFD composed of flattened magnetic materials. To evaluate the effect of adopting flux deflection to industrial HTS rotating machines such as MW class industrial motors, we conducted the study by using a middle-scale field pole model stacked with HTS windings composed of 4 race-track double-pancake coils. We examined the effect of deflected flux on the winding at 30 K, which was the operating temperature of the field pole magnet. The reduction of the thermal loss was successfully confirmed by using MFD. The present study exhibits the importance of a flux deflection on the field pole magnet in the power applications.