Study On Flashover Performance And DC Discharge Model Of Ice-covered Insulator Strings At Low Air Pressure

The external insulation discharge characteristic under the coexistent conditions of high altitude, pollution, and icing is an unsolved problem, and it is crucial to West-to-East Power Transmission Project, the UHV power transmission construction and the development of power grid. Supported by the National Nature Science Foundation of China and the key project of West-to-East Power Transmission, this paper systematically investigates the flashover performance, discharge process and arc characteristic of typical porcelain, glass and composite insulator long strings under the coexistent conditions of high altitude, pollution, and icing in the multi-function artificial climate chamber of Chongqing University. The study is shown as follows:①Based on numerous tests on flashover voltage tests on typical iced long insulator strings, the probability distribution of average flashover voltage and minimum flashover voltage obtained respectively by the average flashover voltage method and the U-curve method is investigated, the flashover voltage values gained by the average flashover voltage method, the U-curve method, the 50% withstand method and the maximum withstand method are also compared. The results indicate that the average flashover voltage and the minimum flashover voltage obtained respectively by the average flashover voltage method and the U-curve method is investigated are in normal distribution; the 50% flashover voltage gained by the two test methods mentioned above are about 8.0%~9.8% and 3.8%~5.9% higher than that gained by the 50% withstand method respectively.②The icing flashover performance tests of typical DC porcelain, glass and composite insulator are systematically carried out in the multi-function artificial climate chamber, and the DC icing flashover voltages of seven typical insulators under various icing thickness, SDD, string length and atmospheric pressure are gained. The flashover voltage model accounting for the influence of icing thickness, SDD, string length and atmospheric pressure is established. Besides, the DC icing flashover voltage correction method of typical porcelain, glass and composite insulator in the coexisting condition of high altitude, contamination and icing is put forward.③According to the experiments on two UHV composite insulators with typical shed profile, the DC and AC icing flashover performances of the two UHV composite insulators are analyzed. Moreover, the special exponents characterizing the influence of SDD and atmospheric pressure on flashover voltage of the two composite insulators under DC and AC voltage are calculated. And the influencing extent of SDD on the DC 50% flashover voltage is smaller than that under AC condition, while the influencing extent of the atmospheric pressure shows the contrary trend.④The DC icing flashover characteristics of XZP-210 under various arrangement such as I-type, II-type, V-type, reverted V-type,"2+1"and"3+1"insulator strings connected alternately with large and small diameter sheds are investigated. The influencing rule reflecting the effects of the arrangement type on the icing flashover voltage is thus obtained.⑤The DC discharge process of pre-pollutecd and iced XZP-210 insulator string under low atmospheric pressure is shot by the high-speed camera. Moreover, the influence of the SDD and atmospheric pressure on the discharge process of polluted and iced insulator is studied. The relation between the two factors above and the phenomenon that the arc derive from the surface of insulator is analyzed, the calculation model of the DC critical flashover current under the influence of SDD and air pressure is developed, the special index characterizing the influence of pre-polluting SDD and atmospheric pressure is derived. Besides, the propagation length and velocity of partial arc as a function of the time is analyzed.⑥Based on the triangular plane icing model and icicle-icicle model, this paper investigates the U-I characteristic of the surface arc of polluted ice and icicle air gap arc under low atmospheric pressures as well as the relation between the equivalent conductivity of the residual ice layer and the pre-polluting SDD, freezing water conductivity. Besides, the DC discharge multi-arc development model of iced and pre-polluted insulators under low atmospheric pressure is established. The model is composed with the series of different polarity arcs, air gap arc and the residual layer resistance which is applied to the calculation of the flashover voltage of the pre-polluted and ice-covered long insulator string with the concurrence of multi-arcs under low atmospheric pressure. The values calculated by the model agree satisfactorily with those measured experimentally with the errors within the range of 10%, which validates the rationality of the model.