Influence Of Electrical Stress On Insulator's Icing And The Discharge Characteristic Of Iced Insulator

China is a country suffering the severe problem of icing. As the development of power construction, insulator icing and flashover has become an important problem about the safety operation of transmission lines and the design of the external insulation. At present there are lots of researches about the characteristics of ice-covered insulators, however, there are still many problems. In the previous studies, the test methods were not unified and the theory analysis couldn't be combined with practice, especially there were not a standard about the insulator icing process with or without voltage, which led to the difficulty of applying the laboratory test results to practical projects. This paper focuses on the effect on the process of insulator icing and electrical characteristics, and the equivalence between charged test and uncharged test is analyzed. The results can not only provide valuable reference for practical projects, but also deepen the icing mechanism of line insulators and external insulation characteristic. Therefore, the paper is of great realistic significance and theoretical value.Based by NSFC, computer simulation and laboratory test were combined to carry out the project. The influence mechanism of electrical field on insulator icing and electrical characteristics was explained by the electrical effect and the heat effect; comparing the features of insulator icing and electrical properties, the influencing law of the electrical field was replayed. Through lots of laboratory tests and theoretical analysis, the main results were obtained as follows:The calculation results of the electrical field indicated that there was a close relationship between the electrical field properties on insulator and the ice type. The rime-ice with dry-growing process was mainly influenced by the applied voltage and the insulator configuration while the glaze-ice with wet-growing process was mainly influenced by the applied voltage, the insulator configuration, the insulator material, and the freezing water conductivity. The electrical field calculation provided theoretical basis for the test results.The values of leakage current and the ultraviolet photons were monitored in the icing regime of energized insulator, and the results showed that the electrical field could affect insulator icing indirectly, in the other word, the discharge activities and the joule heat influenced the energized insulator icing process. In order to explain the effect law of electrical field, the process of the energized insulator icing was divided into initial period, developing period and sTab period. In addition, according to the variation of the ultraviolet photons, the standard to evaluate the safety during the icing period and melting period was developed.As the configuration of insulator on severe icing condition was close to a cylinder and its icing and electrical characteristics were not clearly influenced by the insulator configuration and material, a model of smooth post insulator was used to research. Based on the model, the overall heating balance equation was built, and the critical equation of the leakage current and external electrical field strength was acquired by analyzing the dynamic balance process of the model. Moreover, results showed that the 15% to 35% of the heat during discharge activities feedback to ice surface and the other was used to ice melting, and most of the heat was used to arc burning and loss.To show the influence law of electrical field on different types of icing, four parameters were compared, which were the ice aspect and distribution, ice growth rate, ice quality, ice density and microstructure. In addition, three conditions of insulator, which were no corona existing, corona existing and no local arc existing, local arc existing, were investigated to explain the effect mechanism. The results showed that the mainly effect parameters were the ice type, the applied voltage, the freezing water conductivity, the insulator configuration and material.As for the rime-ice, the effect of the electrical field mainly reflected the polarization, the electric suction, the weak corona and spark discharge. The polarization effect would accelerate the droplets speed and increase the collision chances to improve the icing strength. Moreover, the corona discharge and the spark discharge would lead to dispersion and morphological change of the droplets. All the effects would accelerate the icing velocity and increase the ice quality as the increasing of applied voltage. Whereas, the ice density would be first increased and then decreased. As for glaze-ice, the main function of the electrical field was reflected in the ice-melting effect of Joule heating. Combined with other discharge activities, the whole effect weakened or restrained the ice bridged insulator to make the glaze-ice quality decreasing as the increasing of applied voltage. At the same time, the ice density was firstly decreased and then increased. Among the four insulators in the paper, the discharge was the most severe on the surface of the ordinary glass insulator, the second was ordinary porcelain insulator, the three-sheds insulator and the last one the composite insulator.The results showed that the results of electrical field calculation could explain the effect of electrical field on the insulator icing and flashover characteristics very well. In the icing regime, the variation of local electrical field strength and the existence of water film with high conductivity on the ice surface would lead to the discharge, which was the main reason influencing the insulator icing properties.As for the glaze-ice, the flashover voltage of iced insulator with voltage was lower than one without voltage in the same experimental condition. This was because the icing process changed the ice aspect, reduced the ice quality and increased the air gap and effective leakage distance. Also, the influence of the icing process was related with the applied voltage and the freezing water conductivity. In order to provide the experiment with and without voltage with valuable references, the paper put forward the power function relation between flashover voltage and applied voltage. Considering the applied voltage as an important parameter, unit number,the ice quality, freezing water conductivity and ice sewage were combined to put forward comprehensive correction formula of minimum AC voltage of the insulators in a complex environment.