Grading of electric field distribution of AC polymeric outdoor insulators using field grading material

In this work, composite materials with nonlinear conductivity are used to enable grading of the electric field distribution along polymeric outdoor insulators, particularly near the high-voltage and ground terminals. A ZnO spherical microvaristor/carbon fiber (CF)/ silicone rubber (SR) composite is used as the field grading material (FGM). Finite element method-based numerical simulations are performed to analyze the electric field distributions of 220 and 500 kV composite insulators when the nonlinear conductivity type composite material is used. The 220 and 500 kV composite insulators are fabricated based on the results of the simulations and optical electric field sensors are used to measure their electric field distributions under normal operating conditions. The electric field distribution along the composite insulators are shown to be improved through use of the FGM, and the simulation results are consistent with the experimental results. These graded electric field distributions may reduce the degradation of the polymer materials used in composite insulators and extend their lifetimes. In addition, the dry flashover voltages of insulators with FGMs are higher than those of traditional insulators.

1 Introduction

In recent decades, polymeric outdoor composite insulators have been widely applied in power systems. When compared with glass and porcelain insulators, polymeric outdoor composite insulators offer advantages that include compact size, light weight, excellent surface hydrophobicity (even under severe pollution conditions), low maintenance and operation costs, and improved mechanical performance [1], [2]. However, locally intensified electric fields remain a fundamental problem for polymer insulators [3]–[5]. Because of the rod-like electrode structure, the electric field distribution along the insulator is nonuniform, particularly near the high voltage (HV) and the ground terminals where the maximum electric field can reach several times the average electric field. Additionally, heavily polluted or humid environments can intensify the inhomogeneity of the local field distribution, which may lead to flashover. Furthermore, locally high field strengths can also accelerate the aging of the insulation material and may lead to degradation of the polymer, which then threatens the long-term operation of the entire insulation structure.