IWAIS XII, Yokohama, October 2007 Abstract—In this paper, ice surface resistance, measured on a simplified physical model, was investigated because of its relevance to the flashover of high voltage ice-covered insulator. Special attention was paid to three experimental parameters, electric field, freezing water conductivity, and surrounding air temperature. All experiments were performed by placing the physical model inside a climate chamber kept at the investigated temperatures of -12 and - 2°C. From the obtained results, it can be seen that the temperature and freezing water conductivity tend to considerably influence ice surface resistance. Possible mechanisms, which control these variations, are discussed. I. NOMENCLATURE DC : Direct Current R SH : Shunt resistance R 0 : Direct Current Ice surface resistance σ : Freezing water conductivity, μS/cm t : Time, minutes T : Temperature inside the cold room, °C E : Applied electric field, V/mm d : Electrodes clearance II. INTRODUCTION CE accretion on transmission lines and outdoor hardware can cause mechanical and electrical damages [1-5]. Particularly, ice accretion on outdoor insulators can sometimes decrease considerably the electrical performance of these devices [1-5]. Under certain circumstances, insulator may leads to flashover and consequent power outages. Such phenomena have been reported in Canada and many other countries [1-10]. The mechanisms of flashover of ice-covered insulators are not yet fully understood. Some tentative explanation has been reported in the scientific literature in this field [3-5]. Basic studies are essential to the elucidation of the mechanisms involved in the initiation of discharges, and their transition to arc propagation. However, researchers do agree that ice flashover is caused mainly by the combination of several factors, including [1, 3, 5, 8]: - Ice type and density, amount and distribution along the insulator surface, - Decrease in “effective” leakage distance caused by ice bridging; - Increase in surface conductivity caused by presence of a water film created by various factors, such as process of wet ice accretion, condensation, heating effect of leakage current and partial arcs, rise in air temperature or sunshine; - Formation of air gaps caused by the heating effect of partial arcs, rise in air temperature or ice shedding; - And, finally, presence of a pollution/impurities layer on the surface of the insulator. Among those factors, ice surface resistance appears to be one of the most important parameter governing flashover processes. Indeed, the development of leakage current and arcing on an ice surface, whose resistance has been reduced due to the presence of contaminants and impurities, as well as to melting and pre-melting, is responsible for flashover. It is therefore important to be able to specify accurately the resistance of the ice surface. Over the years, partial discharge intensity, surface conductivity of various materials has been investigated. But little work has been done onto ice surface under DC voltage. Of considerable interest is the manner in which the ice surface resistance changes with freezing water conductivity, ambient temperature or electric field [11]. P. G. Buchan [12] measured the electrical conductivity of ice and its variation with temperature. He found that wet ice can be considered to have both volume and surface conductivity. H. T. Bui studied ice resistance during the icing and de-icing period [13]. He found that at the same temperature the former is higher than the latter. In order to close gaps on those investigations, the present study focuses on determining the influence of electric field, ambient temperature and freezing water conductivity on the ice surface resistance. Since, industrial insulator has a complex shape and is difficult to use for fundamental process investigations, a simplified physical model was used as a mould to form ice. These investigations can help improving our basic understanding of ice surface flashover processes. The results will also be helpful in establishing mathematical models for predicting flashover on ice-covered insulating surfaces. III. TEST PROCEDURE AND EXPERIMENTAL SETUP The actual ice on insulators being very irregular in shape and difficult to investigate, it is therefore practical and more convenient to use a simple model to calculate the ice surface resistance. This configuration can ensure the formation of uniform leakage current distribution on the ice surface. Figure 1 shows the physical model used in these investigations. H. Hemmatjou, M. Farzaneh and I. Fofana NSERC / Hydro-Quebec / UQAC Industrial Chair on Atmospheric Icing of Power Network Equipment (CIGELE) and Canada Research Chair, tier 1, on Engineering of Power Network Atmospheric Icing (INGIVRE) at Université du Québec à Chicoutimi, Québec, Canada, G7H 2B1, (hossein_hemmatjou@uqac.ca) Ice Surface Resistance Measurements I