ABSTRACT:

The influence of direct and alternating voltages on the density, weight and visual aspects of ice deposits at an intensity of 2g m-2 s·l on H. V. conductors was investigated in a laboratory. Numerical simulation employing a simple model was developed, enabling uS to explain the influences of electric parameters such as corona current, ionic wind, voltage polarity and. bombardments of the ice surface by positive ions and electrons. It was found, under our experimental conditions, that the above electric phenomena and parameters had significant effects on the amount and the mean density of ice deposits on H.V. conductors.

INTRODUCTION

In cold regions, such as the northern area of the United States and Canada, conductors· and insulators of transmission lines energized by ac or dc, are frequently covered with ice deposits accreted from supercooled droplets, such as those encountered in cloud riming, drizzle and freezing rain. These deposits consist of three main types of ice: glaze, a clear and semitransparent ice with a density between 0.85 and 0.92 g.cm-3; hard rime, an opaque, and white-colored ice with a density between 0.6 to 0.9 g.cm-3 and soft rime, an ice feathery in appearance, with a density lower than 0.5 g.cm-3. The amount and the characteristics of these atmospheric ice accretions grown on power lines depend not only on meteorological and environmental conditions, but also on the polarity (Farzaneh et aI, 1992; Farzaneh and Laforte, 1992) and the electric strength at the surface of the conductors submitted to icing. However, experiments in cold laboratories involving cylindrical collectors submitted to high voltage electric field strengths equivalent to those on real conductors, have shown that ice density properties can be altered under energized conditions, especially at low intensities of icing (Phan and Laforte, 1981; Laforte et al., 1982).

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