Relation between Extension of a Filamentary Channel from a Water Droplet Placed on a Hydrophobic Sheet under AC Field and Flashover via the Droplet

Flashover phenomena via a single water droplet located on a hydrophobic surface under an ac field was investigated. A water droplet under an ac field vibrates strongly only at the particular frequency range, which corresponds to resonant vibration with natural frequency of the droplet. The effect of deformation of the droplet by resonant vibration on flashover was investigated. Flashover voltage via a de-ionized water droplet with a volume ranging from 20 to 50 mul placed between the parallel rod electrodes was measured. The flashover voltage drastically decreased at the definite frequency smaller than the resonant frequency, regardless of droplet size. To make clear the mechanism of the decrease of flashover voltage at a particular frequency, the time variations of the shape of the water droplet for various frequencies were observed with a high-speed camera. Deformation of the droplet and formation of a water channel for non-resonant frequency would be effective to a flashover event. Ejection of several fine water droplets as well as electrification of the surface by corona discharge would also affect the extension of a water channel.