The authors describe the results of an investigation into the withstand voltage characteristics of an insulator string covered with snow or ice and the application of these results to the insulation design and maintenance of a transmission line in a heavy snow area. It was found that the characteristics of withstand voltage were affected by the specific gravity of snow, the conductivity of water melted from snow, the height of snow, and the ratio of snow-covered length. The lightning impulse flashover voltage of insulator string covered with snow is much lower than that of nonsnow-covered insulator, indicating that the efficiency of lightning protection greatly decreases under snowing conditions. When transmission lines pass through a heavy snow area, an extension of the transmission system fault is feared in 54 and 275 kV transmission lines because the existing insulator string length does not have sufficient dielectric strength for temporary AC overvoltage and switching surge.
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