Numerical study of dynamic resistance and total loss in insulated and non-insulated HTS REBCO double-pancake coils at 77 K

No-insulation (NI) coils emerged as a viable alternative to traditional insulated (INS) high temperature superconducting (HTS) coils primarily due to their inherent ability to self-protect during quench and enhanced mechanical stability. When coils carrying direct current (DC) are exposed to an external alternating current (AC) magnetic field, total loss in the coil is the sum of magnetisation loss due to the AC field and dynamic loss arising from the interaction between the DC current and the AC field. In this work, we numerically study the total loss and its components in NI and INS double-pancake coils (DPCs) of identical dimensions, wound with 4 mm wide SuperPower Rare-earth barium copper oxide (ReBCO) coated conductor (CC) tapes at 77 K. The analysis is carried out for external AC magnetic fields up to 200 mT at 72.73 Hz, with the coil carrying DC current up to 90 % of the coil self-field critical current. The results show that under a perpendicular magnetic field, the total loss and its components in the INS-DPC are higher than in the NI-DPC, which is attributed to the presence of insulation which hinders the current bypass. The NI-DPC and INS-DPC coils show similar electromagnetic behaviour under the perpendicular field, and the evolution of dynamic resistance, which gives rise to dynamic loss, is also similar. Under parallel field the loss in the NI-DPC is higher than that for the perpendicular field, and the coil level shielding similar to bulk superconductor is also observed. Surprisingly, under parallel fields, a dynamic resistance higher than that under perpendicular fields is evident in the NI-DPC, arising from a finite average electric field over a cycle.