Leakage current characteristics of long insulator string during DC pollution flashover test under various air pressures

In high altitude area, because of low air pressure, pollution flashover characteristic is different from that in the plain area. Based on up-and-down method, DC pollution flashover tests of long insulator string are carried out in the artificial climate chamber (diameter 22m, height 34m) of Pollution and Environment Lab at China Electric Power Research Institute (CEPRI). During the tests in climate chamber, various air pressures are simulated to achieve conditions at various altitude (0m, 3000m, 5000m above sea level). Insulator string is arranged vertically. Leakage currents before the maximum current occurring in each individual test are analyzed statistically. Current amplitudes and lasting times at various air pressures are obtained. Meanwhile, typical leakage current curves at various conditions are compared. Results show that air pressure significantly affects the leakage current lasting times and amplitudes, which reflects the flashover discharge mechanism at high altitude indirectly. Furthermore, from comparison of typical leakage current curves at various altitudes on various stages in pollution test, effect of altitudes on insulator string leakage currents is obtained, revealing discharge processes distinction at high altitude.