Electrical arc on polluted ice surfaces of insulators can affects the insulator operation. Ice accretion on power transmission lines can decrease the electrical insulation along the insulators.

Modeling of electrical arc on polluted ice surfaces of insulators:
Insulator flashover as a result of ice accretion is one of the causes of power outages dung ice knelt. For the first time, a research program on the modeling of electrical arc on ice surfaces has been undertaken in the High Voltage and Atrnospheric king Laboratory and the NSERC I Hydro-Quebec / UQAC Chair on Atmospheric king of Power Network Equipment of the University of Quebec in Chicoutimi (UQAC). As a part of this program, the present thesis aims at the modeling and characterization of the arc on wet-grown ice surfaces and the analysis of the flashover conditions on ice covered insulating surfaces. Some fundamental concepts of surface discharge, such as corona discharge, electrical arc, arc development, and mathematical mode1 of arc on polluted surfaces, are first introduced. Then the flashover problem of ice-covered insulators and the related research activities are summarised in the literature review. A cylindrical glass rod covered with wet-grown ice, the most dangerous type of ice associated to insulator flashover, was used in most of the experiments of the present thesis. Wet-grown ice samples were formed in the cold room of the High Voltage and Atmospheric king Laboratory of UQAC. By means of a high speed camera, a data acquisition system and high voltage test facilities, a series of dc and ac flashover arcs on ice surfaces were recorded and analyzed. Arc speeds in various periods of arc development, such as the arc-starting period, the arc-developing period, and the finial flashover period were measured. The relationships between arc current and arc foot radius were obtained using regression on the test results. The arc voltage current characteristics under dc and ac voltages for cylindrical ice samples were determined. The arc electrode voltage drops were also obtained from the regression on the observations. Arc resignation conditions must be satisfied under ac voltage in order to complete the flashover in the same manner as polluted surfaces. The relative constants for these resignation conditions were obtained using the regression method on the test results, using an approach that was adapted from polluted-surface flashover. The ice surface conductivity during flashover was also measured and an equivalent surface conductivity, y*, for both ac and dc voltage applications was defined. xii Several factors influencing the flashover on ice surfaces, such as freezing water conductivity, voltage type, arcing distance, and ice surface infinity were analyzed. The temperatures of ice surfaces and ice body were measured during the melting period. The influence of bulk ice current on the total ice current reassured was extirpated. It was observed that the leakage current passed principally through the ice surfaces in the cylindrical grommet ry. On the basis of the above studies and following the concept of Oberaus for pollution flashover, mathematical models were established for flashovers on ice surfaces under dc and ac voltages. Using these mathematical models, the flashover voltages, critical currents, and critical arc lengths were calculated. The mathematical mode1 was then applied to both short and long ice-covered facility insulator strings for different king conditions. The calculated results were in good agreement with the experimental results on short insulator strings.

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