This paper describes the electrification characteristics of water droplets on a hydrophobic surface and their influence on the induced discharge in an ac electric field. Tests were conducted by placing water droplets with different conductivities and volumes on an electrically stressed silicone rubber (SR) sheet, and their electrohydrodynamic behaviours were observed using a high-speed video camera. It is demonstrated that a locally high electric field at the tip of a droplet can trigger corona discharges, and droplets are always charged negatively during a corona discharge process. The deposited droplets are deformed and synchronized with the ac field. Once the deformation becomes noticeable, it increases rapidly until the droplet becomes mechanically unstable and ejects water filaments from its vertices. This can bridge the electrode gap and result in a flashover. In addition, the volume and conductivity of the water droplets have a marked effect on the mode of corona discharge and flashover development.
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