Contact Resistance and Over-Current Characteristics of No-Insulation High-Temperature Superconducting Coils Impregnated With an Electrically-Conductive Epoxy

This paper examines the electrical characteristics of no-insulation (NI) high-temperature superconducting (HTS) coils impregnated with an electrically conductive epoxy. The NI winding technique refers to a method of winding HTS coils without insulating materials between the winding turns and is regarded as the most promising method to protect the HTS coils from the quench phenomenon. Thus far, many analytical and experimental studies focusing on the electrical characteristics of NI HTS coils have been conducted. From these studies, the quench tolerance levels of NI HTS coils were verified, and the possibility of using NI HTS coils in high-field-magnet applications was confirmed. In addition, studies have recently attempted to apply NI HTS coils to electrical rotating machines. The use of NI HTS coils as field coils in electrical rotating machines is expected to enhance their thermal/electrical stability, but there may also be technical issues related to charging/discharging delays and mechanical reliability. In this paper, we propose a NI HTS coil impregnated with an electrically-conductive epoxy to resolve these issues. In the proposed method, a commercially available epoxy resin is mixed with electrically conductive particles, after which HTS coils are wet-wound using the electrically conductive epoxy. In addition, it was confirmed in charging/discharging tests and in a quench test that HTS coils manufactured by the proposed method show reduced charging/discharging delay times in conjunction with quench-tolerant characteristics. The results here demonstrate the potential of the proposed electrically conductive epoxy impregnated NI HTS coil for electrical rotating machine applications.