DC corona discharge from water droplets on a hydrophobic surface

Corona discharge occurring in water droplets placed on the surface of a hydrophobic polymer sheet under DC field was investigated experimentally along with the behavior of droplets. Two kinds of hydrophobic insulating materials, PTFE and silicone rubber, were used. Two water droplets were placed at the border of the foil electrodes and the insulating sheet. The two droplets elongated in different ways and a water filament extended along the surface by the electrostatic force. Corona discharge occurred at the tip of water droplets before the filament formed. The discharge aspect and the behavior of water droplets strongly depends on the polarity of the applied voltage. This would affect the surface flashover voltage via water droplets.