Study On AC Flashover Performance Of Insulation Surface Under Wind Sand Environment

Recently, frequent sand storm has caused great damage to the industry, agriculture and people's lives in many provinces of China, especially to the high voltage transmission line external insulation,which has brought about large area flashover accident of the transmission line. Regarding the external insulation,the influence of sand storm is mainly reflected in two aspects, serious contamination and the change of medium environment surrounding the insulators. On one hand, when sand storm breaks out, the sand and mineral salt and other solid particles in the air are increasing significantly, which is very likely to cause contamination on the surface of insulators, and that can then make the pollution flashover more possible to happen; on the other hand, in the background of sand storm, medium environment changes from pure air medium into the mixed medium of multi-material content,which brings great changes to the operating environment of transmission line's insulation structure. Based on the analysis of the literature and the research results relating to this topic, taking XP-70 porcelain insulators as the research object, with the methods of the combination of theory and experiment , this paper mainly researches the laws of the above two aspects' influence to AC flashover performance.Through a number of tests, it is found that the flashover voltage of the XP-70 porcelain insulator increases with the increase of the wind speed in wind sand environment under the AC voltage, and that the flashover voltage in weather of wind dust is lower than in the weather of wind. The flashover voltage of the XP-70 porcelain insulator decreases with the increase of the sand specific charge, and the flashover voltage of the sand with positive charge is lower than it with negative charge. When the sand particles deposit on the surface of the insulator, the changes of insulator's flashover voltage is related to the sand dust deposition. In low deposition density situation, the flashover voltage decreases with the sand dust deposition density increasing, and when the deposition density exceeds 20mg/cm2, the flashover voltage appears to go up.Different insoluble pollution materials have different influences on insulator flashover voltage. In this paper, the two pollution materials, sand particles and diatomite are compared and analyzed, and through the artificial pollution test, this paper researches the differences of the two insoluble pollution materials'influences to insulator flashover voltage. The result proves that, with the same deposition density, sand on insulator's surface causes less decline of its flashover voltage. Therefore, it is safe that using diatomite to simulate sand particles in order to set pollution grade standards in heavy sand storm area.This paper sets up an electric field simulation model of XP-70 porcelain insulator in sand storm environment, and then calculates the electric field distribution on insulator's surface in sand storm environment. The result proves that sand particles surrounding the insulator have less influence on the electric field distribution on insulator's surface,however, charged sand particles can cause the aberrance of its electric field distribution. In the area with charged sand particles, the strength of the electric field on insulator's surface increases evidently; when there appears areas without sand particles, the electric field strength increases in that area. Using the high speed camera, the process of the flashover of the insulator in wind sand environment and sand particles deposition on surface is photographed. The arc is blown from the insulator surface by the strong wind, which extends the development of the arc. When there is little sand dust depositing on surface, with the voltage going higher, sand particles jump and expand, areas without sand particles appear, but when plenty of sand dust deposits, there are sand particles jumping in discharge path, but no areas without sand particles.