Suppression method for electrolytic corrosion of porcelain insulators´ iron caps on UHVDC transmission lines

In recent years, the phenomenon of electrolytic corrosion on porcelain insulators´ iron caps has occurred in many HVDC transmission lines in China such as the Yunguang, Xiangshang, Tianguang, Gaozhao and Xingan HVDC lines. The validity of using U-shaped zinc rings to restrain iron caps´ electrolytic corrosion is tested and verified in this paper. In order to research the influence of U-shaped zinc rings on the electric field intensity of insulators, Finite Element Method (FEM) simulation software was used to calculate the surface electric field of insulators with and without a zinc ring. The influence of zinc ring size on the inhibitory effect was studied by accelerated electrolytic corrosion tests, and the reason that zinc rings of the same size exert different inhibitory effects on insulators of different tonnage is explained in terms of iron caps´ curvature radii and water pocket characteristics. Test results indicate that the installation of U-shaped zinc rings is useful to suppress iron caps´ electrolytic corrosion, and that the inhibitory effect of zinc rings of the same size on insulators with larger cap curvature radii is better than that on smaller ones. Optimal designs of the structure and size of the U-shaped zinc ring and its service life are proposed in this paper, based on the test results and the actual engineering practice.