High-field saturation of nonlinear field grading materials used in AC applications

Semiconductive materials having an electric conductivity σ that is an increasing function of the electric field E, so-called nonlinear resistive field grading materials (FGM), are frequently used to reduce excessive field stress in various high voltage equipment. Design optimization often involves simulations where simplified expressions for the relation σ (E) are employed. In this paper we investigate numerically the impact in a representative AC application of the experimentally observed saturation of σ at very high values of the field amplitude.