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In this paper, the principal pollution flashover models are reviewed and then an impedance criterion for arc propagation is proposed. This criterion differentiates the case in which the arc elongates until total flashover occurs from the case in which the arc stops before it reaches the end of the insulator. It is shown that the Hampton criterion is not a sufficient condition for initiation of the arc. Indeed, the latter can expand, under certain conditions, even if the Hampton criterion is not satisfied. An analytical model allowing one to determine the critical voltage that insulators can withstand is also established. This is based on an energetic balance, an equivalent electrical circuit and the physical characteristics of the arc. The critical voltage, the critical current and the critical arc length for polluted insulators are calculated using the elaborated model. The results so obtained are found to be in accordance with the experimental ones represented by known empirical relations.

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This paper is aimed at the determination of the leakage current and the flashover voltage of discontinuously polluted insulators submitted to ac voltages, using a predictive dynamic model based on an equivalent electrical network. This model is an extension of the one we developed for uniformly polluted insulators. The influence of the width and conductivity of polluted layers is investigated. The simulated results are validated experimentally on a plane insulator model using electrolytic solutions of different conductivities.