HVDC flashover on the surface of conductive ice

For a generalized and systematic study of the flashover performance of iced insulators, we investigated the flashover characteristics of HVDC iced insulators on a physical model with different ice temperatures. Iced insulator was simulated by a frozen electrolyte channel connected to the low voltage electrode. HV electrode, made of tungsten, is at an adjustable distance above the electrolyte. Investigation was done in a small refrigerated chamber in which temperature can be obtained at any desired value between 20°C and −50°C. Results show that discharge characteristics do not change with temperature and the flashover voltage obtained with positive polarity is slightly higher than that obtained with negative polarity for high-resistivity liquids. Furthermore with relatively high resistivity liquids (r≥20 kΩcm⁻¹) during icing period (decreasing temperature from 0° to −40°C) the ice resistance is higher than that measured during de-icing period (increasing temperature from −40°C to 0°C) therefore the minimum flashover voltage is lower in the latter case. At −40°C and below it is unlikely to have flashover on ice because ice resistivity is excessively large. Flashover voltage on ice covered with water film is always lower than that obtained with “dry” ice. In the case of uniform voltage stress of our experimental conditions the combination of both de-icing and water-film conditions of ice leads to worst possible situation.