Fabrication and Testing of Racetrack-Shaped Double-Pancake Coil for Stator Windings of Induction-Synchronous Motor

We have fabricated a racetrack-shaped spliceless double-pancake test coil with GdBCO coated conductors and investigated its performance in air and magnetic cores. We have been developing a high-temperature superconductor induction/synchronous machine (HTS-ISM) for electric vehicles. To improve the specific power and torque density of the fully superconducting HTS-ISM, an increase in the current capacity of the HTS stator windings is crucial. The fabricated test coil was wound with two GdBCO conductors in parallel, which were transposed at a coil end. Thus, the self-inductances of the two conductors were equal, and the coil was free from splice resistances due to transposition. We confirmed the soundness of the transposition method by critical current measurements. We also investigated the critical currents of the test coil by placing it in a magnetic core and observed a decrease in the critical current compared with that in the air core. This is caused by the increase in the component of the magnetic field perpendicular to the coated conductors. To overcome this issue, magnetic materials were used for magnetic-field correction. We methodically compared the results of the critical current measurements and evaluated the results by numerical magnetic-field analyses.