AC loss calculation of no-electrical-insulation HTS magnets using a field-circuit coupling method

Abstract

No-electrical-insulation (NEI) magnets gradually exhibit significant appeal due to their robust thermal stability and elevated mechanical strength. However, when exposed to AC conditions, the magnets would suffer more significant AC losses in dynamic electromagnetic devices, such as motors and maglev systems. Presently, the numerical methods for predicting the electromagnetic and loss behaviors of large-scale NEI magnets entail high computation costs due to the substantial degrees of freedom or complicated modeling strategies. Thus, we propose a fully finite-element method referred to the field-circuit coupling method to efficiently assess the overall behaviors of NEI magnets while preserving adequate accuracy. This method couples the T-A formula and the single-turn equivalent circuit through global voltage, to avoid the costly and complicated inductance calculation, and to simultaneously consider the induced current. By further integrating the homogenization method, the calculation speed can be increased up to ten times. Additionally, we study the critical current, electromagnetic and loss behaviors of the NEI magnets based on the proposed model. We identify some measurement methods that offer more precise estimations of the critical current and the turn-to-turn contact resistance of NEI magnets. Meanwhile, the results indicate the severe impact of high AC fields on the losses, and emphasize the importance of a reliable shielding structure for operational safety. Finally, the influence of turn-to-turn contact resistivity on the loss behavior is also investigated, which can provide valuable insights for the design of the NEI magnets in dynamic electromagnetic devices.