Under drizzle, light rain, heavy fog and other adverse weather conditions, polluted insulators may flashover under an operating voltage which serious threat to reliable operation of power systems. Therefore, it is very important to understand the natural pollution accumulating rule of insulator energized in the operating voltage. This paper takes the XP-70 insulator string being suspended without voltage in a certain power network in Shantou as the sample, tests and analyzes the pollution depositing rules of it. Test results indicate that: The performance of natural pollution deposit is related to geographic location and voltage class. The accumulation rate of non-soluble salt deposit density (NSDD) on the surface of insulator is more serious than that of equivalent salt deposit density (ESDD). The pollution depositing situation of insulator is different under different voltage classes, the pollution accumulating situation of the 110kV line is the most severe, while that of the 220kV line is a bit lighter and the 500 kV line is the lightest. The pollution levels of transmission lines in Shantou area are mainly c and d. The test results can be used to draw the map of pollution areas, help workers to clean insulators and direct external insulation coordination and design in the pollution area.
I.INTRODUCTION Pollution-flashover accidents caused by natural pollution accumulating will do great harm to the electric power system. So the work of pollution prevention is becoming the priority to ensure the safety and normal operation of power grid [1][2][3]. However, the pollution-flashover on the surface of insulator must go through the process of pollution deposit firstly, and it is the main reason that causes flashover [3].In view of this, large amount of researches have been carried out both at home and abroad. Some of the results show that, the performance of natural contamination of insulator is affected by several factors, such as sources of pollution, rainwater situation, weather conditions and geographic location [4][5][6]. Reference [7] elaborates the research of natural pollution depositing characteristics of porcelain insulator strings on the 500kV line, and the results show that natural pollution depositing degree is related to tower height and voltage class.The test results in references [8,9] show that both ESDD and NSDD will independently influence the flashover voltage of artificial pollution test, satisfying a relationship of power function.At present, there are not complete tests of ESDD and