Modeling of electric stress control in HV bushing using field grading material

The electric stress control is important for improving insulation performance and upgrading design of power devices. In recent years, the technique of applying field grading material (FGM) is proposed for the designs of cable accessories and machine insulation, but fewer applications in HV bushing realm. In this paper, modeling of electric stress control in a simplified HV wall bushing is presented. The hollow insulator employs an artificial field grading material (FGM) with linear (constant) and nonlinear (field-dependent) conductivity, respectively. First, the electric stress control theory of FGM is analyzed. Then, the COMSOL Multiphysics is used to solve a numerical model of bushing. In the process, the FGM is equivalent to a thin layer of surface conduction. Hence, an additional term of surface current density is added into the boundary equation. The simulation model is calculated under dc and ac (50 Hz sinusoidal) voltages respectively with both linear and nonlinear FGM. At last, the application conditions and effects of using FGM for HV bushing are discussed.