Water film for protecting insulator surface from lightning discharge

Summary form only given. With increase in number of wind power generators, the lightning damage on the windmill blade becomes a serious problem. In addition to the conventional lightning protection methods such as a lightning rod and a tower with rod, metal receptors connected to the ground are installed on the blade tip as a more direct method for protecting the blade. In this study, the protection method using water film is proposed and discharge progress on the surface of water film is examined from the point of lightning protection. The surface conductivity of the blade is influenced by some attached materials or salty wind damage in the actual condition. Therefore in addition to change the thickness of water film, the conductivity of water was changed from 0.16 to 3000 microS/cm. Positive impulse voltage of 270 kV-1.5/50 microsecond was applied between a rod with sharp edge and a grounded plane electrode. The rod electrode was placed 1 cm above the surface of water. The discharge developed on the surface of the water when the conductivity of the water was smaller than one microS/cm. In this case, the water breakdown was not observed at least over 0.25 mm thickness of water film. But with thinner and higher conductivity water film, the discharge current flowed in the water directly and the surface discharge was not expanded around the breakdown point. The water film thickness required for 50% breakdown of the water was estimated to be 0.43, 1, 1.75 mm for 50, 100, 170 microS/cm water, respectively