Cryo-stability of quasi-insulation winding method for hts coils regarding the width of insulation tape at over-current operation

According to growing demand for high power electric machines, HTS coils which are able to transport high current have been widely researched. For application of HTS coils to electric devices stable operation should be verified so that protection schemes of HTS coils have been investigated by many researchers. Among the many insulation methods for protection, the Quasi-Insulation (QI) winding scheme which improves thermal stability without charging-discharging delay has been proposed. The performance of the QI is affected by exposure area to coolant so that thermal stability depending on the width of the insulation tape should be considered. In this study, the magnetic characteristics and cryo-stability of the QI HTS coils using HTS tape according to the different width of the insulation tape were experimentally analyzed. A wider HTS tape (12 mm) was used to wind tested QI coils for transporting higher current, and QI coils with narrower insulation tape than half of the HTS tape were especially analyzed. The temperature estimation was also carried out to support the experimental results. Even though the width of insulation tape was narrower than an half of the HTS tape, field delay, generated field saturation and degradation were not observed from the experimental results. Therefore, the QI coil with narrower insulation tape can provide better thermal stability without any weaknesses of field generation so that the QI coil can be adopted in high current application such as SMES with higher operation margin.