Electro-Thermal Homogenization of HTS Stacks and Roebel Cables for Machine Applications

This paper presents a homogenized electro-thermal model for high-temperature superconductor (HTS) stacks made of multiple REBCO tapes, which reduces the computational complexity of their thermal analysis. The electromagnetic analysis is performed in both the H - and T–A -formulation. An average heat capacity and an orthotropic heat conductivity are derived for the equivalent thermal properties of the HTS coil. The proposed homogenization method is verified to produce the same results as the full model with an error below 5% for a range of scenarios, including transport losses, magnetization losses, AC frequencies from 50 to 300 Hz and a temperature range from 25 to 80 K. Finally, the model is applied to study a permanent magnet motor with HTS armature windings and is verified to produce results with an error below 15 % as long as the stabilizer eddy current losses are low. Compared to the full multilayer model, the newly proposed model allows for the use of a significantly coarser mesh, which reduces the computation time by an order of magnitude.