iv) If the applied voltage is high enough, the local arc will change to a white arc and extend along the ice surface. Therefore, the initial corona discharges and the consequent local arcs will develop at these sections of the insulator. This water film has very high conductivity and may cause predictably large voltage drops across the air gaps. However, due to the effects of sunshine, a rise in air temperature, condensation, and/or the heating effect of leakage current, a water film will form on the ice surface. iii) Dry ice has high resistivity and does not reduce significantly the electrical properties of insulators. These air gaps are caused by the melting or shedding of ice from some parts of the insulator. Also, for long insulators, no accretion usually occurs in areas of high electric stress, i.e., air gaps. The windward side is usually free of ice. ii) The distribution of ice on insulators is seldom uniform. Glaze with icicles is the most dangerous type of atmospheric icing. Precipitation icing can occur in several ways, including freezing rain and drizzle, as well as wet and dry snow. Flashover on ice-covered insulators i) Atmospheric ice accretion on insulator surface due to the hoar frost, in-cloud icing, or precipitation icing. The flashover of ice-covered insulators includes the following steps. shows an example of a flashover on standard line insulators covered with ice. FLASHOVER MECHANISM OF ICE-COVERED INSULATORSįlashover on ice-covered insulators is a very complex phenomenon, as arc is not only an electrical process, but also thermal and electro-chemical. The main objectives of the present study are to evaluate the critical flashover performance of a standard post insulator, as typically used in 735 kV Hydro-Quebec substations, under icing conditions and, based on the experimental results, to improve the mathematical model for application to long, ice-covered insulators. This situation makes it difficult to apply this model to long, ice-covered insulators for engineering purposes. However, mainly due to limited laboratory conditions, very few experimental results for the flashover voltage of full-scale EHV insulators under icing conditions are available. ![]() The flashover phenomenon on ice-covered insulators has been studied for over 25 years in the HV laboratories of Université du Québec à Chicoutimi (UQAC) critical flashover voltage of ice-covered insulators, and has been successfully applied to a short insulator string covered with a wet-grown ice layer. Reviews of most of these investigations were reported in previous work and recent papers by IEEE and CIGRE task forces. This problem has received a great deal of attention from many researchers and a large number of investigations and theoretical studies have been carried out in several laboratories. Also, power outages caused by ice and snow accretion have been reported by many authors in Canada, the United States, Japan. For example, on, at the Hydro-Quebec Arnaud substation, a series of six flashovers occurred on insulators covered with wet snow and resulted in a major power interruption for a large part of the province of Quebec. In addition to mechanical damages due to excessive ice accumulation and dynamic loads caused by wind, the presence of ice and snow on insulators may lead to flashover faults, and consequent power outages. In cold climate regions, one of the major problems for power systems is atmospheric icing due to freezing rain or drizzle, in-cloud icing, icing fog, wet snow, or frost.
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