Control of Polymeric Outdoor Insulators Stress by Using Nonlinear Field Grading Materials

In this study, the effect of nonlinear field grading materials for controlling the high electric fields along the polymeric insulator surface has been investigated. The combination of polymeric material with Zinc Oxide microvaristors results in obtaining the required nonlinear properties (field-dependent conductivity). The extreme electric stresses under polluted and wet conditions lead to dry bands forming. Consequently, surface electrical discharges could be happened, which may develop under appropriate circumstances to a complete flashover. Furthermore, these electric discharges accelerate the degradation of insulation materials thus, the flashover voltage would be decreased because of surface tracking and erosion of the polymeric material. To get rid of these consequences, mitigate of electric field strength is considerably useful to minimize the influence of discharges on polymeric insulator surfaces. In this work, two configurations of the insulator equipped with microvaristor compounds have been modeled. Thereafter, the electric field, equipotentials, and the power dissipation are computed along an 11 kV polymeric insulator profile under different scenarios using the Finite Element Method. The use of nonlinear field grading materials enables reducing the electric field as well as the power dissipated in the polluted layer, particularly near both terminals. Hence, decreasing the possibility of dry band formation and discharge activities, providing better insulation performance has been achieved by using nonlinear field grading materials with optimum design and characteristics.