Application of nonlinear finite element method in DC steady E-field calculation of composite insulation structure

The DC steady E-field is a state of composite insulation in the converter transformer outlet barrier system. The electrical properties of insulating material are both function of electric stress and temperature, thus, changes of electrical parameters due to temperature gradient will affect the DC steady E-field distribution of composite insulation structure. Based on this, to accurately simulate DC steady E-field of composite insulation structure with temperature gradient, this paper applied nonlinear finite element method to the coupling analysis of these two affecting factors. Firstly, relationship between electrical parameters of insulation materials and temperature, electrical stress was investigated. Then, the DC steady E-field calculation method with nonlinear finite element was proposed and verified by the simple coaxial insulation structure model. Finally, 2D simulation model of barrier system was established to simulate and analyze the DC steady E-field considering nonlinear characteristics of materials. The results show that the results of traditional simulation are quite different from those when considering material nonlinearity. The nonlinear finite element method proposed in this paper and the calculation results provide references for the design of converter transformer outlet barrier system.