No-insulation (NI) and metal-insulation (MI) high-temperature superconducting (HTS) magnets require three-dimensional (3D) models to describe the current distribution around critical current defects. In this work, we design and validate the EXTRA homogenisation method, standing for explicit turn resolution with anisotropic homogenisation method. It allows 3D magneto-thermal finite-element (FE) simulations of large-scale magnets to be performed with high accuracy at a reasonable computational cost. The method combines the anisotropic homogenisation of turn-to-turn contact layers (T2TCLs) and their neighbouring winding turns with the explicit resolution of specific T2TCLs. In particular, the inner- and outermost winding turns and adjacent contact layers are explicitly resolved to properly describe the current distribution near current leads. In addition, the method is able to simulate local $J_{\textrm{c}}$ defects for a broad range of turn-to-turn contact resistances, provided the winding turns and T2TCLs next to the defect are explicitly resolved. For efficiency, the resolved T2TCLs are modelled using the surface contact approximation. The consistency of the proposed method is first verified on a 50-turn single pancake benchmark. It is shown to reproduce AC losses and temperature distributions obtained with a turn-resolved FE reference model, for both nominal operation and during thermal runaway. The computational efficiency of the EXTRA method is demonstrated with the simulation of a stack of three 150-turn pancake coils, for which computation time is reduced by a factor of up to 13 with respect to a turn-resolved FE reference model. Finally, the results of a large-scale 3D FE simulation, currently out of reach of turn-resolved models, are provided for an insert HTS magnet with 10,000 turns. The EXTRA method is open-source and input files to reproduce all results are made available.

翻译：无绝缘（NI）与金属绝缘（MI）高温超导（HTS）磁体需要三维（3D）模型来描述临界电流缺陷周围的电流分布。本文设计并验证了EXTRA均匀化方法，即各向异性均匀化显式匝间解析方法。该方法能够在合理计算成本下，对大规模磁体进行高精度的三维磁热有限元（FE）模拟。该方法将匝间接触层（T2TCLs）及其邻近绕制匝的各向异性均匀化与特定T2TCLs的显式解析相结合。具体而言，对最内层和最外层的绕制匝及相邻接触层进行显式解析，以准确描述电流引线附近的电流分布。此外，该方法能够模拟宽范围匝间接触电阻下的局部$J_{\textrm{c}}$缺陷，只要对缺陷附近的绕制匝和T2TCLs进行显式解析即可。为提升效率，解析的T2TCLs采用表面接触近似进行建模。该方法的一致性首先在50匝单饼基准模型上得到验证：在额定运行和热失控过程中，其重现了匝间解析有限元参考模型获得的交流损耗和温度分布。通过模拟三个150匝饼式线圈堆叠体，证明了EXTRA方法的计算效率——相较匝间解析有限元参考模型，计算时间最高减少13倍。最后，本文给出了目前匝间解析模型无法实现的大规模10,000匝插入式高温超导磁体的三维有限元仿真结果。EXTRA方法为开源方法，复现所有结果的输入文件均已公开提供。