Study of space charge characteristics and DC dielectric properties of PTFE/XLPE nanocomposite material

To enhance the long-term operational reliability of cross-linked polyethylene (XLPE) insulation material used in high-voltage direct current cables in a wide temperature range and high electric fields, this study investigated the regulatory effect of nano-polytetrafluoroethylene (PTFE) on the space charge and dielectric properties of XLPE. PTFE/XLPE composites with different PTFE doping ratios (0.1wt%, 0.3wt%, 0.5wt%) were prepared by melt blending. The dielectric properties of the material were systematically studied within the temperature range of 30~90℃ and the electric field strength of 5~40 kV/mm. Through thermal stimulation current (TSC), electro-acoustic pulse method (PEA), DC conductivity and breakdown strength tests, the trap characteristics, space charge distribution, conductive properties and breakdown behavior of the composites were analyzed. The results showed that when the PTFE doping content was 0.1wt%, the peak space charge density of the composite at high temperature (80℃) and high field (40 kV/mm) was approximately 49% lower than that of pure XLPE; at 15 kV/mm electric field, the conductive current in the 30~90℃ temperature range increased by only one order of magnitude, which was significantly better than pure XLPE (three orders of magnitude); the DC breakdown strength at 90℃ increased by 29.2%. The TSC test indicated that at this ratio, the composite exhibited a deep trap with a depth of approximately 1.16 eV at 135.5℃. The study demonstrated that PTFE effectively regulates charge transport by introducing both deep and shallow traps, thereby inhibiting space charge accumulation and enhancing insulation stability.