Insulation Characteristics of Cryogens for HTS Power Apparatus

A cryogenic cooling system is essential for high temperature superconducting (HTS) apparatus because cryogenic temperature is generated by using a cryocooler or cryogen. The cryogen method is widely applied to various HTS apparatus because its thermal stability is higher than that of the cryocooler. Furthermore, the cryogen not only performs cooling but also insulates electrically. Thus, the insulation performance of an HTS apparatus relies heavily on the insulation characteristics of cryogen. This study examines the insulation characteristics of cryogens to be applied to HTS apparatus, using nitrogen and argon in liquid and solid state as cryogen. Their electrical characteristics such as the flashover discharge and breakdown are also investigated and compared. We also discuss whether nitrogen and argon in solid state are applicable to HTS apparatus as cryogens.