| In a complex atmospheric environment, not only acidic precipitation but a coexistence environment with insulator's icing, low atmospheric pressure in high altitude and contamination etc. will .severely influence transmission lines' external insulation performance so as to threaten electrical power system security. Therefore, a systematic study of all types of insulators discharge performance for the complex atmospheric environment has both a very important academic meaning and an engineering value. Upon existence theoretical and experimental results and based on a great of laboratory investigations carried out in Chongqing University, for the first time this paper studies systematically the insulators AC discharge performance and flashover voltage correction method of the complex atmospheric environment, which are the test and theoretical reference for HV and EHV transmission lines design and safety service. Furthermore, with a computer emluator it calculates the on-surface electric-field distribution of a suspension insulator with a large creepage and a column cap under AC and steep impulse voltage, which is made for use in the complex atmospheric environment. The main work and conclusion for this paper is as following:(1) According to the results obtained by analyzing the relation between the pH value of acidic precipitation and the conductivity of insulator surface wet-contaminant, this paper indicates that in the acidic precipitation environment, if choosing the external insulation for the transmission lines or sub-distribution with the traditional method, the flashover accidents may take place. And it also indicates that the flashover voltage of a insulator decrease with the fall of the pH value of the acid rain or fog, and that is, when the pH-value of the acid solution is between 3.0 and 4.0, its conductivity will decrease deeply and a turn-up point will appear, when the pH-value equals 3.0, the pollution flashover voltage of the insulator is correspond to that of a higher level SDD with pH=7.0 (clean fog). It concludes that the AC flashover voltage of the insulator in the acid-fog environment can be improved by increasing the insulator's creepage or taking the glass insulator.(2) Based on the laboratory investigations for AC flashover performance carried out on several suspension insulator with some typical structure under the coexistence environment of icing and low atmospheric pressure and contamination, it obtains the lawful relations between the minimum AC flashover voltage and icing, low pressure and contamination. The study results show that the AC flashover voltage of the iced insulator during thawing is of a minimum value, and that the minimum AC flashover voltage decrease with the increase of the ice amount accreted on the insulator surface, the rise of the altitude and contamination level, and the down-trend of the minimum AC flashover voltage will slow gradually, and that both the rise of the contamination level and the drop of the atmospheric pressure make the arc to increase in diameter and toburn more steadily and to extinguish more difficulty and more easy to develop into fleet-arc, which will bridge the shirt-shed of the insulator and so the flashover voltage will decrease, and that the minimum AC flashover voltage is also influenced with the ice density and ice shape accreted on the insulator etc.(3) Upon the study of insulator AC discharge physical process in the coexistence atmospheric environment of icing and low pressure and contamination, it indicates that the discharge process can qualitatively divide into four phases according the leakage developing, that is, the basic leakage current, corona- stream current, white-arc current and flashover current, that in the low atmospheric pressure, the main factor for the AC flashover voltage decrease of the iced and polluted insulator is voltage distribution aberration along the insulator string. At the two ends of the string, especially at the high voltage end, it takes most of the voltage; therefore, partial arcs al...
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