Dynamic resistance and total loss in small REBCO pancake and racetrack coils carrying DC currents under an AC magnetic field

In many high-temperature superconducting applications, REBCO (Rare-earth barium copper oxide) coils carry DC currents under AC magnetic fields, such as the field winding of rotating machines, linear synchronous motors and the electro-dynamic suspension system of maglev. In such operating conditions, REBCO coils generate AC loss—total loss which includes the magnetization loss due to the shielding currents, and the dynamic loss arising from dynamic resistance caused by the interaction of DC currents and AC magnetic fields. In this work, dynamic resistance and total loss in a small double pancake coil (DPC) and a small double racetrack coil (DRC) are investigated via experiments in the temperature range between 77 K and 65 K. The DC currents are varied from zero to 70% of the self-field critical currents of the REBCO coils, with AC magnetic fields up to 100 mT. The experimental results in the DPC are well supported by the finite element simulation results using 3D T-A formulation. Our results show that the critical current of the DRC is approximately 2%-5% higher than that of the DPC in the temperature range. For given experimental conditions, the magnetization loss in both coils is much greater than the dynamic loss. The dynamic loss and magnetization loss in the DRC are greater than those in the DPC, which we attribute to the large perpendicular magnetic field component in the straight sections of the DRC.