Effect of contact resistivity difference on steady-state characteristics of multi-pole no-insulation HTS field coils in synchronous motors

Abstract Several superconducting motor designs with a power density exceeding 20 kW kg −1 have been proposed and are under development. However, maintaining the stable operation of superconducting coils in a rotating environment remains a partially unresolved challenge. The no-insulation (NI) high-temperature superconductor (HTS) winding technique, which deliberately removes insulation materials between turns, has emerged as a potential solution for superconducting motors. NI HTS coils have demonstrated current bypassing characteristics, making them stable under external field disturbances and robust against local critical current drops. However, contact resistivity, which largely governs the ‘NI behavior,’ has been reported to fall within a broad range in prior studies, making it challenging to consistently obtain specific values. As a result, understanding and managing contact resistivity has become a significant area of research. This is especially critical in motors where the field winding is subjected to periodic external harmonic fields, and maintaining pole-to-pole balance is crucial. In this study, we investigated the influence of contact resistivity on the performance of field windings through simulation as part of our efforts to assess the potential risks associated with NI HTS motors. Torque, voltage, and current were analyzed using the finite element method coupled with a lumped parameter circuit model, and the results were compared.