Experimental studies on determination of V-I characteristics and insulation resistance of stacked PPLP layers with liquid nitrogen under AC and DC excitations

Cold dielectric based High Temperature Superconducting (HTS) power cables often use PolyPropylene Laminated Paper (PPLP) as the dielectric material for electrical insulation. PPLP helps withstand the rated voltage at cryogenic temperatures and is thus wrapped around the current carrying conductor. It coniines the electric field within itself resulting in electrical insulation of the cable from the cryostat which is at ground potential. The V-I charachteristics and the insulation resistance of PPLP immersed in Liquid Nitrogen (LN2) are of paramount importance and its study becomes crucial for superconducting devices as they operate at extreme conditions. This paper deals with the development of an experimental facility for investigating dielectric and insulation characteristics of PPLP for different temperatures, when subjected to various voltage levels. The V-I characteristics of PPLP at cryogenic temperatures (77 K when immersed in LN2) and room temperature have been determined. Additionally, the insulation resistance of PPLP at ambient temperature was determined and compared against its value when immersed in LN2 (at 77 K).