A Study of the Composite Insulation Breakdown Properties for Wrapping Cables in Liquid Nitrogen

To optimize the insulation design of high-temperature superconductivity (HTS) cable, the multilayer wrapping cable insulation properties in the liquid nitrogen should be studied. In this paper, we investigated the breakdown properties of multilayer wrapping of cable insulation in liquid nitrogen. AC and dc breakdown tests of a minimodel cable with an insulation floor composed of polypropylene laminate paper (PPLP), PPLP/100HN (DuPont polyimide film), PPLP/100CR (DuPont polyimide film), and PPLP/150FCR019 (DuPont polyimide film) and of singer-layer sheets, including PPLP, 100HN, 100CR, and 150FCR019, respectively, were performed in liquid nitrogen. The breakdown characteristics of the sheets and model cable insulation consisting of PPLP and composite insulation schemes according to the arrangement of PPLP/HN, PPLP/100CR, and PPLP/150FCR019 were compared. For the sheets, the ac breakdown strength of 100HN is greater than that of 100CR; this may be because there are large amounts of organic–inorganic interface in 100CR. The dc breakdown strength of 100CR is greater than that of 100HN, which may be because the space charge of 100CR homogenizes the electric field. For the minimodel cable insulation, the dc and ac breakdown strengths of the composite insulation in which the third layer of wrapping tape insulation material was composed of three layers of 100HN, which is overlapped completely, are greater than those of the insulation consisting of PPLP and other composite insulations.