Progress of the research on external insulations in China

A series of research projects has been launched to tackle the problem of outdoor insulation performance under various atmospheric conditions. Since a large portion of China´s power transmission projects is located in the high-altitude plateau area with different weather conditions, special attention is paid to the problem of insulation in conditions of reduced air density and high humidity. The testing facilities are described, and a brief summary of previous work is given. Results of comparative tests at different altitudes, tests in an artificial weather chamber, and an investigation of humidity effects are presented and discussed. Results of research on insulator pollution are also presented. These include analysis of the flashover criteria for contaminated insulators under AC and DC voltages, development of the partial arc and its influence on the pollution flashover voltage, and studies of pollution discharge under low atmospheric pressure