The dependency of water droplet behaviour and leakage current pattern on electrode configuration

The ageing processes of composite insulators are heavily dependent on their surface hydrophobicity level. Corona discharges and dry-band arcing are the main phenomena associated with the degradation of polymer surfaces when insulators are exposed to pollution, humidity and electric fields. Additional environmental factors such as UV radiation, temperature and mechanical stresses act as accelerating factors for the ageing processes. Understanding of corona and dry band arc processes is crucial to evaluate, diagnose and monitor the insulators´ surface condition in advanced ageing stages. At the same time, different experiments to study the effect of electric field distribution and its influence on water droplet behaviour, leakage current patterns, insipient corona discharges and water droplets behaviour are needed to increase the knowledge about early degradation stages. The study summarized in this paper was focused on metal electrodes shapes and their influence on electric field distribution, water droplet behaviour and leakage current characteristics. Keeping the gap distance constant, five different shapes of elongated electrodes (flat, three different circle-sections, and rectangular bars) were simulated using Finite Element Analysis (FEM) and four of them were experimentally tested. Contact angles of water droplets were monitored using a high speed camera. Images were synchronized with leakage current and voltage signals. Significant differences were found between the cases under study, and the influence of electrode shape on processes seen on the material surfaces has been established.