Dielectric and Electrical Insulation Properties of PTFE/PP for HTS Power Apparatus Application

Polypropylene laminated paper (PPLP) and liquid nitrogen (LN2) is widely used as insulation and coolant, respectively, in high-temperature superconducting (HTS) cable. Dielectric loss of PPLP plays an important role in the loss of HTS transmission system. In this paper, polytetrafluoroethylene (PTFE) filter papers were chosen to take place of Kraft paper (KP) in composite insulation system. Two layers of PTFE filter paper and one layer of polypropylene (PP) film were processed into sandwich structure through hot-press method. Experimental results show that the dielectric loss can be cut to half by replacing KP with PTFE filter in AC HTS transmission system. The trap level of PTFE/PP composite insulation is shallower. The surface discharge voltage of PTFE/PP is higher than that of PPLP. PTFE/PP also has stronger ability of resisting partial discharge and shows higher partial discharge inception voltage than PPLP does. And the breakdown voltage of PTFE/PP composite insulation is higher than that of PPLP, which mainly due to the stronger resistance to discharge.