Electro-magnetic-mechanical characteristics of 3D HTS INS and NI racetrack coils in complex physical fields

Abstract

To investigate the impact of insulation structure on the electromagnetic and mechanical properties of high-temperature superconducting (HTS) coils, numerical simulations are employed. A comparative study is conducted on the electrical, magnetic, and force distribution characteristics of three-dimensional (3D) racetrack insulating (INS) HTS coils versus non-insulating (NI) HTS coils under identical operating conditions and dimensions. To balance computational complexity and time, a 3D racetrack-type homogenization equivalent model is developed. INS HTS coil has no inter-turn resistance so that the current dimension is reduced by one level. A homogeneous T-A formula is used to establish anisotropic equivalent model, which enables addressing the 3D computational challenges of high aspect ratio superconductors. NI HTS coil is solved by H-method due to the presence of radial resistance. In this pure FEM model, which is not coupled with the circuit model, the real geometry in arc segment of the NI HTS coil can be equated to a concentric circle structure by using the rotational anisotropic resistivity method. It can be achieved by setting the resistivity matrix ρ_coil. Meanwhile, to explore the weakening effect of the strain inside superconducting coil on superconducting performance under multi-physical fields, the application scope of the strain dependence formula of I_c under one-dimensional (1D) mechanical loading (Ekin’s power-law formula combined with Weibull distribution function) is extended from 1D loading to 3D complex stress state. And its accuracy is verified. Then the extended formula is applied to two 3D coils. The influence of mechanical loading on the critical performance of the coil under multi-physical field conditions is compared and investigated.