Electrical, mechanical and thermal properties of ZnO/SiR composite dielectric

High-voltage direct current (HVDC) cable accessories are the weakest part of the cable operation, and possess the highest failure rate due to the uneven distribution of electric field. The rubber materials with nonlinear conductivity can be used to homogenize the electric field distribution in cable accessories. To endow the silicone rubber (SiR) with nonlinear electrical conductivity, zinc oxide (ZnO) nanosheets were prepared by sol–gel method and filled into SiR for fabricating ZnO/SiR composite dielectric. The microstructure, electrical, thermal and mechanical performances of the composite dielectric are studied systematically, and the electric field distribution of the accessory is also simulated by COMSOL Multiphysics software. The results show that with the increase of ZnO doping content, the threshold field strength which corresponds to the nonlinear electrical conductivity decreases gradually. With the increase of temperature, the electrical conductivity of the composite increases, and the threshold field strength further decreases. The breakdown strength of the composite increases slightly and obtains the optimal value at a doping content of 5 wt % ZnO, and then decreases gradually. In addition, the tensile strength, elongation and thermal conductivity are improved by doping ZnO nanosheets into SiR. The simulation results reveal that the ZnO/SiR composites with nonlinear electrical conductivity can effectively to alleviate the electric field concentration at the stress cone of cable accessories.