Study On Pollution Flashover Performance And DC Discharge Model Of Insulator (Long) Strings At Low Air Pressure

With the stratagem development of west-east electricity transmission, north-south power exchange and nationwide interconnection of power system, and China's Western Development Program, many more UHV/EHV transmission lines may pass by high altitude regions, whereas, the pollution may turn worse with the quick development of economics between urban and rural areas at high altitude regions and make more and more transmission lines'external insulation, especially insulator, face with the threaten of high altitude and pollution. The pollution flashover accidents take place sometimes in power system and the loss because of which is large, So it is significant to study deeply the pollution flashover performance and DC discharge model of long insulator string at high attitude.The work that research on the DC/AC pollution flashover performance of insulator (long) strings at low air pressure are carried out in the artificial climate chamber, furthermore, the test results validation of the difference between the laboratory tests results and the high altitude field tests were done in this paper. The paper also analyzes the DC pollution flashover process using insight from high-speed photography and thus the DC discharge model of polluted insulator string under low air pressure is proposed.The artificial pollution methods at high altitude, which was simulated by climate chamber, and at high altitude field is confirmed in this paper, furthermore, the influence of artificial pollution test program difference on pollution flashover performance is analyzed and thus the reasonable artificial pollution test program is discussed.The experimental researches on DC pollution flashover performance for different types of insulator (long) strings under low air pressure by laboratory are done by the numbers. The relationship between DC pollution flashover voltage of insulator (long) strings under low air pressure and units of insulator, pollution, air pressure and so on is discussed and the influence factor on DC pollution flashover voltage is analyzed at last.The research on AC pollution flashover performance under three high altitude locations of Wangkun Station (height of altitude 4484m), Nacitai Station (height of altitude 3575m) and Geermu (height of altitude 2820m) along by the Qinghai-Tibet railway was brought forward firstly and the results got by laboratory tests was validated using field test results. Comparing the field test results with laboratory test results, the paper brings forward that the relative error is in 8 percent and the research results got by laboratory can be applied to engineering design.Analyzing the DC pollution flashover process by insight from high-speed photography and the force characteristic of partial arc at low air pressure by theory, it is found that the air pressure influence on electrostatic force and thermal buoyant force is different and thus the reason that the partial arc derive from the surface of insulator more severe at high altitude is well explained.According to the DC pollution flashover process by insight from high-speed photography, the relationship between the length of partial arc and time, spread speed of partial arc and time is measured and the main reason make pollution insulator flashover at last is not electric breakdown is confirmed.The E-I characteristic of surface arc and air gap arc under low air pressure is measured and the difference between surface arc characteristic and air gap arc characteristic is obvious because of the different thermal delivery capability of materials.The circuit model explaining the flashover mechanism for a polluted insulator string at high altitude is put forward firstly, which can be expressed as an electrical circuit consisting of a surface arc and air arc in series with a resistance representing the wet pollution layer. The feasibility of model is validated by experimental resultsWith the model validated by experimental results, the relationships between the value of pollution flashover voltage and air pressure, pollution, profile of insulator and partial arc characteristic and so on are discussed. The main reason that makes the b and n of insulators different is the partial arc fluttering degree difference for insulators.