The behavior of a water droplet on a silicone rubber plate was observed with a high-speed camera under ac voltage application. It was confirmed that a water droplet vibrated and that a remarkable deformation from the original droplet form occurred at the mechanical resonance frequency. Vibration frequency of an uncharged water droplet was double the frequency of the applied voltage. On the contrary, in the case of an artificially charged droplet, vibration frequency was the same with that of the applied voltage. A macroscopic mechanical model was devised, to which the experimental data were well correlated. Flashover voltage via the water droplet was also measured. Lower flashover voltage was obtained at the mechanical resonance frequency.

Vibration of a water droplet on a polymeric insulating material subjected to AC voltage stress

Super-hydrophobic silicone rubber (SIR) was fabricated by hot-pressing template method, and its surface water droplet contact angle reached 153.5° and sliding angle 8°. The observation of microstructure showed that there were plenty micrometer-scale papillas and nanometer-scale particles on its surface, the mechanism of super-hydrophobicity caused by this micro-nano hierarchical structure was discussed. In order to study the influence of super-hydrophobicity on the electric field distribution, two-dimensional simulation was carried out in software platform ANSYS. The influence of contact angle, volume and location was discussed. The simulation results indicated that super-hydrophobic surface had a better effect of electric field shielding. The flashover experiments (for both single and double droplets on different SIR surface) were carried out and showed that the flashover voltage of super-hydrophobic SIR with droplets on its surface was higher than that of ordinary SIR, which confirmed the simulation.

Flashover characteristics of discrete water droplets on the surface of super-hydrophobic silicone rubber

Super-hydrophobic coatings have recently drawn considerable attention in research and applications towards self-cleaning materials. This paper presents experiments and analysis of water droplet behaviors on glass, silicone rubber, and super-hydrophobic surface in an ac electric field applied parallel to the surface. Experimental results show that a water droplet tends to move on a super-hydrophobic surface while it tends to stretch or deform on glass and silicone rubber surfaces. A physical model of the water droplet deformation and motion mechanism is presented. An electrostatic force acting as the domain driving force plays a key role in water droplet motion on super-hydrophobic surface. The electrostatic stress acting along the external profile of a water droplet cross section was simulated using a surface integral of the Maxwell stress tensor. The simulation for surfaces with different wetting properties are in good agreement with the experimental results. Super-hydrophobic coating demonstrates a prospective electric field enhanced self-cleaning property.

Investigation of the electric field driven self-propelled motion of water droplets on a super-hydrophobic surface

In HVDC transmission lines, corona could occur even on well designed hardware and insulators, which can significantly damage the polymeric insulators and inject the charge in the surface of insulators. Rain formed by cloud elements may be highly electrified and a mixture of positive and negative drops is usually produced. Once the charged droplet is deposited on the surface, insulation performance of the insulators will be affected. In this research, the characteristic of an electrified droplet on coronacharged silicone rubber nanocomposite surface was observed under dc voltage stress. The samples were made by dispersing nano-scale SiO2 powdered in silicone rubber with the weight ratios of 0, 1, 2, 3 wt%, and were charged for 5 minutes under a dc corona discharge system based on needle-plate electrode before the test. Then the flashover test was carried out under a dc stress between two aluminum plate electrodes. The effect of nano-silica weight percent on the surface charge density and the surface charge on contact angle was obtained. Electric field strength simulation was performed to analyze the effect on charged droplets and surface charge. The relationships among the charge density, the contact angle, and the flashover voltage via the droplet were obtained. The results show that charged droplet deposited on charged surface has a negative effect on the nano filled silicone rubber composites that can make the flashover occurs at lower voltage.

http://ieeexplore.ieee.org/iel5/94/6396934/06396967.pdf

Electrified droplet on corona-charged surface of silicone rubber/SiO 2 nanocomposite

The effect of dynamic behaviours of the water droplet on DC/AC flashover performance on silicone rubber surface: Experiment, simulation and theoretical analysis

Observations and analyses have been conducted on the behavior of water droplets deposited on the surface of polymer insulators. As an index to characterize the repellency of water droplets on the polymer surface, the contact angle was measured for different situations. Experiments were conducted to see the behavior of water droplets of different volumes and their size distribution on silicone rubber. Electric field strength calculation was performed to analyze the effect on water droplets. Finally, effects of the Maxwell stress and the Coulomb's force were compared, to conclude that, even if there is some true charge on the water droplet, the Maxwell stress is predominant.

K. Honsali

Papers

A basic study on the effect of voltage stress on a water droplet on a silicone rubber surface