Optimization of Carbon Nanotube Doping on Nonlinear Conductivity, Surface Charge Dissipation and Electric Field Regulation of SiC/SR Composites Insulators Subjected to DC High Voltages

Adaptive material can alleviate the local high electric field in electrical devices, due to its nonlinear conductivity characteristics. To solve the deterioration problem caused by the high doping of large-diameter fillers in the adaptive material, carbon nanotube (CNT) was used as the second filler. And the effect of CNT doping amount on the conductivity of SiC/silicone rubber (SR) composites was explored. Experiments showed that CNT doping can improve the nonlinear conductivity. The threshold field of the material doped with 0.7 vol % CNT decreased by 97%, and the nonlinear coefficient was increased by 83.7%. With the increase of CNT doping content, the decay rate of surface potential increased, which was attributed to the increase of the carrier mobility and ratio of shallow-to-deep trap density. A new field grading material (FGM) coating structure was proposed, which was compared with the traditional structure. Through finite-element simulation, the field grading effect of the two structures can be analyzed. The results showed that the field grading effects of the two coating structures were almost the same. But considering the influence of surface charge dissipation, the new coating structure was selected. The electric field of insulator surface and interface can be reduced by more than 30% with the best CNT doping ratio. It was verified that the interface charge and leakage current of the insulator coated with the best FGM were at the compliance level.