Study on Current Behavior and Thermal Stability of No-Insulation Coils With Parallel HTS Tapes Under External Magnetic Field Fluctuation

No-insulation (NI) coil has been developed as a means to enhance thermal stability. A notable characteristic of NI coils is the charge delay resulting from the absence of turn-to-turn insulation. In order to mitigate this charge delay in NI coils, a winding technique has been suggested, involving parallel high-temperature superconducting (HTS) tapes without insulation between layers. However, the external magnetic field fluctuation causes a large induced current in the NI coil with parallel HTS tapes. In such a situation, heat generation at the contact resistance in the path of the large induced current can be significant. In this paper, authors analyzed the current behavior of NI coils when the external magnetic field fluctuates for various number of parallel tapes. Also, a thermal analysis of the NI coil was conducted to assess the impact of induced current behavior on thermal stability. In this study, a Partial Element Equivalent Circuit (PEEC) model is utilized. Furthermore, a coupled analysis of current behavior inside the coil and thermal analysis was performed utilizing the PEEC model to analyze detailed electromagnetic phenomena. The calculation results of current behavior revealed the induced current concentrates at the particular turn to turn contact resistance. Therefore, the temperature at the point of heat generation increased to very high temperature and there is a possibility of burnout in the case of large number of parallel tapes.