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Authors:
S. M. El-Makkawy

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Abstract:
Outdoor insulators are subjected to electric stress and weather conditions like rain, fog and dew. This gives rise to the danger of leakage currents forming on contaminated or wetted surfaces and finally leading to insulation failure. They show a stable hydrophobicity, which forces moisture into the shape of small droplets rather than a wet layer. Yet at the triple junction between the droplet, the air, and the insulating surface, the electric fields are enhancement. If the onset level for water drop corona is reached, the surface locally loss its hydrophobicity. Dew has been found to be a more critical condition than rain or atomized spray. This paper describes experimental investigations on inception and breakdown voltages at water drops. Experimental investigations are made to describe and understand the phenomena accruing at water drops on insulating surface exposed to the electric field. In that direction, measurements are made using two different test arrangements: First when the applied electric field is tangent to the insulating surface and Second when it is perpendicular. The electrical field distribution around the water drop is calculated by Boundary Element Method. The water drop shape, spherical, hemispherical and a conical, and its dimensions were changed. The study was done on Polyvinyl- Chloride (PVC) and Bakelite (Ba) as insulating surface because of their important industrial application. The number of water drop was changed

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http://jee.ro/articles/WW1246994529W4a53a061cfed0.pdf