Effects of contamination in the electric field distribution on polymer insulators: an experimental and computational investigation

Summary

The use of the polymeric insulators in transmission and distribution systems has become increasingly widespread due to their advantages over glass and porcelain. Recent studies report problems related to premature aging and degradation of high voltage polymeric insulators, especially when these insulators are exposed to contamination and moisture. These defects generally appear in areas along the insulator surface subjected to high levels of electric field and are associated with corona. The operation of the polymeric insulator under rain or moisture conditions form water droplets on its surface. The water droplet, when subjected to a certain electric field strength, undergoes deformations which, in turn, alter the distribution of the field in such a way that it may reach magnitude high enough to produce corona on the insulating surface. The present work investigates the distortion of the electric field caused by water droplets located on hydrophobic surfaces at different levels of contamination. To evaluate the deformation of the water droplet, experiments were performed in an arrangement specially built for this purpose in which droplets are exposed to a known uniform electric field applied. The dynamic behavior of the droplets was visually observed and recorded. Image processing software was later used to extract information about the droplets deformation. Additionally, the electric field levels were numerically calculated along polymeric insulators used in 138 kV transmission lines. COMSOL Multiphysics® computational package was used and, simulations were performed considering a threedimensional modelling. The results show that the dimensional model of the water droplet must be considered for the electric field calculation and that the tower and the conductors must be involved in the numerical modeling because it considerably affects the distribution of the electric field in the insulator. Another relevant result is that the distribution of the electric field is highly influenced by water drop deformation and that these conditions facilitate the appearance of corona.

Additional informations

Authors

BRAUN, EPPLE

Keywords

high voltage, polymeric insulator, contamination, corona effect, aging