Surface Charge Properties of SiR/SiC Composites in DC and Pulse Combined Field

The nonlinear conductivity layer has become a highly concerned method to modify the distorted electrical field caused by the complicated cable accessory structure. It is unavoidable for a HVDC transmission system to experience transient overvoltage caused by switching and lightning. A challenge still lies in the understanding of the charge property in the insulation with nonlinear conductivity. This paper focuses on the surface charge property of silicone rubber (SiR)/SiC composites at coupling voltage. The nonlinear conductivity was obtained by blending SiC particles with the SiR matrix. The sample conductivity were measured at 30°C. The surface potential decay (SPD) was measured at 30°C. The carrier mobility and trap distribution were calculated according to the SPD. The results proved that the SiR/SiC composites presented nonlinear conductivity. At DC voltage, the initial potential becomes higher and the decay rate increases. The cross-over phenomenon was observed. The high surface potential caused by the pulse voltage leads to a nonlinear conductivity which immediately dissipates the surface charge. The increase in DC voltage is proven to be more effective in accumulating surface charge. The nonlinear conductivity and the diffusion are two factors concern the initial surface potential.