Withstand Voltage Characteristics of Snow Covering Insulator Strings of AC Transmission Lines

In recent years, it is noticed that flashover faults of snow covered insulator string due to AC operating voltage or switching surge may occur in heavy snow areas. AC, AC overvoltage, switching and lightning impulses flashover tests of strain insulator set artificially covered with snow were conducted in the Yonezawa testing station constructed in the northern part of Japan. Withstand voltages of snow covered insulator set for high voltage AC transmission line have been investigated with the obtained test results. The main points of the results are summarized as follows: (1) The investigation of nature of snow on insulator sets shows that the specific gravity of snow is 0.3_??_0.4 and the conductivity of water melted from snow is maximum 40 μS/cm. (2) Withstands voltages of insulator set covered with snow decreased as the specific gravity of snow increased. (3) In the case of the specific gravity of 0.3_??_0.4, AC minimum withstand voltage per unit length was 74_??_79 kV/m. (4) Switching impulse flashover voltage of snow covered insulator set with AC pre-stress was 10% lower than that without pre-stress. This is why snow condition is changed by leakage current under AC voltage application. (5) It is clarified to make an insulation design for AC high voltage transmission line in heavy snow areas, on the basis of actual snow and meteorological conditions.