Experimental Investigation of the Influence of Electric Charge on the Behavior of Water Droplets in Electric Fields

High voltage insulators in electric power transmission and distribution must withstand extreme weather conditions like rain or snow without long-term degradation. An increasing amount of outdoor composite insulators uses silicone rubber due to the various advantages over glass and ceramic. One difficulty is the presence of water droplets residing on the hydrophobic silicone rubber surface of insulators, which locally alter the electric field. Specifically, the electric field is strongly enhanced at the three phase contact line, which can lead to electrical partial discharges and affect the aging of the insulator's surface. The present contribution investigates the behavior of sessile water droplets exposed to strong electric fields with a high-speed camera. Electrically charged and uncharged droplets are generated under well-defined conditions and placed on a generic insulator model. The oscillation frequency of the droplet in resonance mode is investigated in detail with respect to the amount of charge, droplet volume, frequency of the electric field as well as the electric field strength. Significant changes in drop behavior are observed depending on the charge and the electric field strength. A regime map based on the experimental data as well as a mathematical model is developed to quantity the necessary conditions for the change of behavior. The performed experiments improve the understanding of droplets in electric fields as well as the ageing process of high voltage insulators.