A Field-Circuit Coupled Model for Efficiently Simulating the Charging Characteristics and Losses in No-Insulation HTS Coils

Abstract

No-insulation (NI) high-temperature superconductor (HTS) coils introduce turn-to-turn electrical paths, enhancing their thermal stability and self-protection capacity against quenching. However, the extra turn-to-turn electrical paths complicate both the geometrical and physical modeling of HTS coils. This article presents a field-circuit coupled model where the HTS component is treated as a global voltage parameter that contains resistive and inductive voltage in the circuit model. The superconducting branch current in the circuit model serves as external current input to the NI HTS coil. The finite element method model is based on an anisotropic resistivity model governed by the $\mathbf {J}$–$\mathbf {A}$ formulation, considering the current-sharing effect of the metal layers in the coated conductor under overcritical current state. To validate the proposed model comprehensively, two key characteristics are illustrated: first, comparing experimental measurement data of sudden discharging, charging, and overcritical current state; second, comparing computing efficiency with the prevailing $\mathbf {H}$-formulation model. The results show that the calculated results are in good agreement with the experiment, the validity, and applicability of the proposed model are well verified. In comparison to the $\mathbf {H}$-formulation model, the computational efficiency of the proposed model is improved by more than 82% without sacrificing the computational accuracy. In addition, with the proposed model, it has been found that the current-sharing effect of the metal layers is negligible in the overcritical current state. To verify the wider applicability of the proposed model, we simulated charging the closed-loop NI HTS coils with a flux pump. The proposed model can better characterize the voltage source excitation properties and analyze the frequency saturation of the charging time constant. Based on this, we have further investigated the superconducting resistive losses as well as the turn-to-turn losses at different traveling wave frequencies.