Study Of AC Flashover Performance And Process Of Iced Insulators At Altitude Of 3500m Above

The severe atmospheric environment of low atmospheric pressure at high altitude with pollution and icing has an important effect on the external insulation performance of transmission lines and threatens the reliability of a power system. Therefore, a systematic study on flashover performance of several types of insulators at the severe atmospheric environment has both important academic meaning and engineering value. Based on a great of laboratory investigation carried out on the AC flashover performance of several types of insulators in the multi-function artificial climate chamber of Chongqing University, this paper studies systematically the AC flashover performance of several type of insulators and puts forward a flashover voltage correction method for the atmospheric environment at altitude of 3500 m above, and discusses the flashover process and mechanism of the iced insulator. The contribution of the paper can conclude as following:According to the laboratory investigations carried out on the AC flashover performance of two types of porcelain insulators and four types of composite insulators at the atmospheric environment of low pressure at a high altitude with pollution and icing, the relations between the minimum AC flashover voltage and the ice amount, the atmospheric pressure as well as the contamination level are obtained. The study results show that the minimum AC flashover voltage decreases with the increase of the ice amount accreted on the insulator surface by an exponential law, and the down-trend of the minimum AC flashover voltage will slow gradually with the bridging of the shed of the insulators by icicles, both the average saturated ice amount and the special exponent m of effect of ice amount for different insulators depend on the radius of shed and the air-gaps of the sheds of the insulators, and that the AC ice flashover voltage decrease with the decrease pressure ratio P/P0 (rise of the altitude) by power-law for different ESDD and icing-states when the altitude is from 4000m to 5500m. The special exponent n, which show the effects of altitude on the flashover voltage, is various with the type of insulator, icing-states and the surface status of iced insulator etc., and that the minimum AC flashover voltage of iced insulators decreases by power-law with ESDD or the freezing water conductivity for different ice amount and atmosphericpressure (high altitude), and the down-trend of the minimum AC flashover voltage will slow gradually.Based on a great of laboratory investigation carried out for insulators flashover voltage, it was put forward a calculation expression for correcting the minimum AC flashover voltage of insulators in the single or coexisting condition of high altitude above 3500m, contamination and icing. This paper analyzes the effect of ice-covering appearance, icing water conductivity and temperature etc., it was found that all of the above factors have effect on the minimum flashover voltage of iced insulators, and the flashover performance of iced composite insulator was a approximate linear function with arcing distance.Based on the measure result of the potential distributing at the surface of composite insulator before and after icing form, and the evolution process of local arc and leakage current, this paper discusses the flashover process and mechanism of the iced insulators. According to the statistic of the wave of flashover voltage, it was found that the flashover voltage of iced composite insulator hasn't evident effects on its polarity.