This paper presents the results obtained from an experiment which was carried out in order to identify a possible correlation between the presence of static charge and the loss of hydrophobicity on partially and highly hydrophobic surfaces (glass and RTV silicone rubber coating, respectively). Glass and RTV silicone rubber coating samples were initially exposed to corona impingement, and subsequent measurements of charge decay and hydrophobicity recovery (contact angle) were taken. Data obtained from such measurements clearly show that as surface charge decay takes place, hydrophobicity is correspondingly recovered. This observation is valid not only for RTV silicone rubber samples, but also for glass samples. In the silicone rubber compound, recovery could be attributed to a mechanism of migration of silicone oil from the bulk of the polymer to the surface, but in glass samples that mechanism can be totally excluded as the likely responsible agent for hydrophobicity recovery. Therefore, a mechanism different from that of silicone oil migration should be determining the trends observed. When a comparison between both calculated and real surface charge decay times was made, a fairly strong agreement was found. As an additional proof for supporting the hypothesis here presented, when the surface and volume resistance characteristics of the original RTV silicone rubber compound were modified and after exposure to corona impingement, its hydrophobic properties remained unaltered.
A computational study was carried out in order to verify the assumption of reducing the magnitudes of electrical stresses generated in standard suspension-type disc insulators energized with high voltage alternating current (JIVAC), by including a semiconducting insert within their geometry. As a consequence, an improved performance of these insulators was expected during flashover tests in polluted conditions. Grading of stresses in the region adjacent to the pin of insulators is the factor responsible for such improved performance. These computational and experimental results were compared to those obtained from similar calculations and tests, but considering conventional non-modified insulators. Two different conductivity characteristics of the semiconducting insert were considered during the simullations. Then, an electrical evaluation of the above referred alternatives, as well as an additional set of alternatives was also develolped in a clean fog chamber. Results from computational studies showed decreases in the maximum stress found in the test arrangement ranging from 29% up to 45%, with respect to those corresponding to the base case (conventional insulators). These values are in a reasonably good agreement with increases achieved in the flashover voltage of the corresponding alternatives, when evaluated in the clean fog chamber. Increases in the flashover voltage resulted 33% and 44 % for each simulated case, respectively. For every alternative evaluated, an increase in the corresponding flashover voltage was always achieved. In the worst case, a 12% increase was obtained; for the best case, an increaase even higher than 97% was found.
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