Effect of Aged Nonlinear Resistive Field Grading Material on Electric Field Distribution of DC Cone Spacer

Nonlinear resistive field grading materials are widely used in the electrical and electronic applications, and are usually researched based on the initial nonlinear conductivity characteristics of synthetic materials. However, the long-term stability of these materials are rarely reported. In this paper, the effects of thermal ageing on nonlinear resistive field grading material and the electric field distribution of DC cone spacers are studied. The 30 wt.% SiC/epoxy micro-composites are prepared and are thermally aged at 180 °C for 1080 h. The infrared spectroscopy, dielectric properties, breakdown strength and nonlinear conductivity are measured, respectively. In addition, a simulation model for a cone spacer is built, and the electric field and power dissipation density are calculated. With the increasing thermal ageing time, the relative permittivity and loss tangent increase, and the breakdown strength decreases. Besides, the nonlinear coefficient of nonlinear conductivity almost increases, and the switching electric field of nonlinear conductivity decreases. Simulation results show that the aged micro-composites can homogenize the electric field in the cone spacer, but the thermal ageing causes the increase in power dissipation density and threatens the safe operation of the cone spacer.