Breakdown Characteristics of Liquid Nitrogen/Tetrafluoromethane/Polypropylene Laminated Paper Insulation System Utilized for Superconducting Energy Pipeline

Liquid nitrogen/tetrafluoromethane (LN $$_2$$ /CF $$_4$$ ) mixture with a wide liquefied temperature range of 50 to 100 K might be a promising coolant for high- $$T_\textrm{c}$$ superconducting (HTS) apparatus. However, certain features have not yet been clarified before further application, particularly the insulation properties regarding the composite insulation system consisting of such a cryogenic mixture and polypropylene laminated paper (PPLP). In this paper, AC and DC breakdown experiments and simulations of LN $$_2$$ /CF $$_4$$ - PPLP composite insulation system are carried out with various molar fractions of each constituent part taken into account using sample cables insulated by the foregoing composite insulation. Results indicate that such a mixture/PPLP composite insulation system possess a superior breakdown strength compared to pure LN $$_2$$ /PPLP system; LN $$_2$$ /CF $$_4$$ can therefore be an advantageous choice for HTS power apparatus.