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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.

This paper describes the surface modification of high temperature vulcanized silicone rubber (HTV‐SR) resulting from corona discharges under atmospheric pressure. In this study, a plate‐shaped HTV‐SR specimen was exposed to corona stress generated by a needles‐plane electrode system; further, physicochemical analyses were conducted on the surface layer of SR before and after corona discharge treatment. The results showed that the plasma impingement from the corona discharge can cause physical and chemical damages to the SR surface. In addition, it was demonstrated that instead of hydrophobic CH3 groups, hydrophilic OH groups that are byproducts of ageing may be formed on the surface of aged SR; further, the corona discharge plays an important role in the loss of hydrophobicity.

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