Study On The Characteristic Of Outer Insulation In The Qinghai-Tibet Railway Power Supply System

Since the 1950s, it has been studied how the atmospheric parameter affects the discharge characteristics of external insulation, and there are many achievements. However, there are differences among the achievements without a unified view. Because of the higher altitude, lower atmospheric pressure, and lower air density along the Qinghai-Tibet railway, the discharge voltage is lower. In the railway industry standard of our country, it's advised about how to choose the insulator which is lower than 4000m above sea level, but not that which is more than 4000m above sea level, even in the international railway industry standard.In various voltage levels (include 110kV,35kV,27.5kV, 10kV), the data has been get from the experiment which simulates more than 4000m above sea level. The data is analyzed, as well as the related standards and achievements are compared. And it comes to the conclusion that the pressure could represent the atmospheric parameters which effects the discharge voltage, and the relationship between lightning impulse discharge voltage and gap distance at high altitude is linear, as well as the air gap correction factor at high altitude are proposed. Then, based on the experiments and experimental data analysis of insulator contamination discharge characteristics under different air pressure, the value of n at salt concentration 0.30mg/cm2 is worked out. And the number of insulator under various voltage levels is determined with the effective coefficient of insulator leakage distance 0.95.The experimental result shows that the atmospheric pressure can reflect the air density, temperature and humidity, which would change as the pressure changes. And it is logarithmic relationship between the frequency discharge voltage and the gap distance in the Wang-Kun station, and the discharge voltage is much lower than that at the low altitudes. And at high altitudes, the lightning impulse discharge voltage of negative polarity is much higher than that of positive polarity, and the multiple is much higher than that at low altitudes, which are related to the air gap distance. The greater the gap distance is, the larger the multiple is, as well as the altitude's effect on lightning impulse discharge voltage is more obvious. By analyzing the experimental data, it is concluded that the characteristic coefficient of the suspension insulator is 0.414, and the one of rod insulator is 0.5. At last, the number of suspension insulator in the traction substation at 4000m above sea level is determined:there are 10 pieces in the 110kV traction substation,5 pieces in the 27.5kV traction substation,6 pieces in the 35kV traction substation, and 2 pieces in the lOkV traction substation. The research could provide reference for the design of power system in the Qinghai-Tibet railway or in other railways at highland.