Assessment of Hysteresis Losses in HTS Coils Designed for a Rotating Electrical Machine

The development of superconducting machines has long been pursued due to their relevant power density advantages and high efficiency compared to conventional technologies. However, using superconductors under alternating current and/or magnetic field poses considerable challenges as they demonstrate non-negligible energy dissipation from the generated AC losses. This work investigates the electrical behaviour of a High-Temperature Superconducting (HTS) coil designed for rotating electrical machines. Both experimental activities and simulation studies are conducted with the primary aim of estimating the AC transport current losses. Accordingly, a circular-shaped coil in a double-pancake configuration is assembled using GdBCO tape (12 mm x 0.15 mm) manufactured by SuNAM Co. Ltd.; it is subsequently tested under DC and AC conditions at cryogenic temperature. Simultaneously, numerical simulations are performed using the commercial software Comsol Multiphysics. Considering the anisotropic field dependence of the critical current density J_c(B), a 2D axial-symmetric model based on H-formulation is developed. Various applied frequency and peak current conditions are examined to optimise the design of an HTS coil for assembling the armature of superconducting electrical machines. Finally, the numerical results are validated by comparing them against the experimental data obtained.