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Reference: ISH2015_271

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Electric Strength Enhancement Using Low-conductive Coating on Hard Dielectric Insulation



Application of a thin low-conductive coating to hard dielectric insulation allows increasing the breakdown voltage. A surface charge is induced on the coating. The induced surface charge can smoothen the electric potential. The electric field intensity is reduced in this case and becomes more uniform. However, there is an issue of coating parameters selection: conductivity and spatial dimensions. A thin low-conductive coating with given parameters can behave as either a dielectric or a conductor depending on the characteristic time of the voltage change: If the time is very large, the coating behaves as an ideal conductor. The strong electric field appears on the coating edges in this case and decreases the electric strength. If, however, the characteristic time of voltage change is very small, the coating behaves as a dielectric. It has no effect on the electric field in this case, and the aim of electric strength increasing is not attained. Finally, there is the optimal characteristic time for a particular coating – the electric strength is increased due to low-conductive coating application in this case. In different applications, the time can vary significantly: e. g., the period of the power-frequency voltage is 2·10-2s, while the durations of the leading and trailing edges of a standard lightning pulse are 10-6s and 5·10-5s, respectively. A quantitative criterion is proposed that establishes a relationship between the coating parameters and the characteristic time of the voltage change, which enables solving the problem of increasing the electric strength most effectively. It is showed the feasibility of describing a thin low-conductive coating using a computational model, where the coating is simplified as infinitely thin, with specific boundary conditions set on the corresponding surface. The model is compared with that based on the law of conservation of the surface charge, as well as a more complete one of a coating of finite thickness.

File Size: 118,8 KB

Year: 2015

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