Influence of Eddy Current Losses in Nonsuperconducting Layers of HTS in Superconducting Electrical Machines

Numerical analysis of high-temperature superconductors (HTS) commonly addresses ac losses in the superconducting ReBCO layer. However, alternating magnetic fields also induce eddy current losses in the metallic nonsuperconducting (non-SC) substrate, silver, and copper layers of the HTS, which cannot be overlooked for certain operating temperatures and frequencies. Previously, non-SC losses have been estimated numerically for simple geometries at 77 K. Using a multilayer H-A-formulated model, this article estimates the eddy current losses for a full-scale 2.5-MW SC aviation motor for frequencies between 50 and 1000 Hz and temperatures between 25 and 60 K. Furthermore, a sensitivity study is presented to show how ac losses are impacted by specific design parameters, such as the copper purity, angle of the external field, tapes per turn, tape height, and copper layer thickness. The results show that eddy current losses are negligible for high HTS temperatures and low frequencies. However, at low temperatures and high frequencies, these losses represent a significant share of the total, meaning that while they can be neglected for low-speed machinery, they must be considered for power-dense machinery, particularly if the planned cooling method involves liquid hydrogen temperatures.