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Insulator flashover under icing conditions

Atmospheric ice accretion, combined with pollution, has been recognized as a significant risk factor in the reliability of line and station insulators in cold climate regions. Flashovers occurring on ice- and snow-covered insulators result from combinations of a number of factors and parameters. Electric fields modify the structure of ice, the shape and direction of icicle elongation, the distribution of liquid water and the geometry of air gaps that break up the continuous ice surface. Electric field strength and voltage polarity as well as corona space charge and ionic wind have demonstrable influences on the flashover process. Insulator icing flashover is also affected by changes in air temperature and several other environmental and meteorological conditions including ice type and structure. The presence of surface pollution and the rejection of ions from solid to liquid layers during the freezing and melting process also play a central role in the icing flashover of insulators, which can occur at normal operating voltage under the most adverse conditions. This paper presents an overview of these phenomena and describes the interactions that lead to the initiation and development of discharges on the ice surfaces covering the insulators, as well as their evolution to flashover. The lecture also includes the modeling of these phenomena, leading to successful prediction of the critical flashover voltage as well as to insight into the most practical solutions for improved insulator design and mitigating icing flashovers.