Temperature-Dependent Nonlinear Conductivity and Carrier Mobility of Silicone Rubber/SiC Composites

An electrical field distorted by the complicated cable accessory structure and non-uniform temperature distribution is a significant threat to high voltage direct current (HVDC) cable. Thus, the field grading material (FGM) with nonlinear conductivity which can uniform local field receives attention. This paper focuses on the temperature-dependent nonlinear conductivity of the FGM based on high temperature vulcanized (HTV) silicone rubber (SiR). The nonlinearity was achieved by mixing silicon carbide (SiC) particles with the SiR matrix. The conductivities of the samples were measured at temperatures of 30-90 degrees C. In addition, the carrier mobility and trap distribution of different samples at different temperatures were obtained by analyzing the surface potential decay (SPD). The experiment results showed that the SiR/SiC composites had nonlinear conductivity when the SiC content exceeded 30 phr in the entire temperature interval. The conductivity increased, and the threshold field of conductivity decreased at high temperature. In the SiC mixed samples, a convergence trend appeared at high field at temperatures below 70 degrees C. The trap distribution moved to a higher energy level, and a higher shallow trap proportion appeared at high temperature. The mobility increased with the increase in temperature. This trend became more obvious at high temperature. In addition, compared with voltage, the temperature had a more remarkable effect on the carrier mobility.