Switching Impulse Flashover Performance of Different Types of Insulators at High Altitude Sites of above 2800 m

This paper explores the influence of air pressure, temperature and humidity on the switching impulse (SI) flashover performance of different types of clean and dry insulators at different high altitude sites of 2820 m to 5050 m along the Qinghai-Tibet Railway, the highest elevation railway in the world. Seven types of insulators are used in the flashover tests: one is a composite insulator, two are glass insulators and four are porcelain insulators. At the test sites, the ambient temperature varies between 6.7 degrees C to 28.5 degrees C and the absolute humidity is between 4.11 g/m(3) to 9.69 g/m(3). The test results show that the 50% switching impulse flashover voltage of different types of insulators at high altitude sites is independent of the materials and sheds of insulators but has a multi-factor non-linear relation with the shortest are distance, the dry air pressure, the absolute humidity and the ambient temperature. The relative flashover voltage decreased with the ambient temperature is dependent on the voltage polarity, with 0.152% to 0.165% /degrees C for negative SI and 0.099% to 0.108% /degrees C for positive SI at the ambient temperature of from 6.7 degrees C to 28.5 degrees C. The relative flashover voltage increased with the absolute humidity and is dependent on the air pressure. The higher the altitude is, the more the influence is of the absolute humidity on the flashover voltage of insulators.