Research On Icing Flashover Performance And Primary Mechanism Of Full-Scale Long Insulator Strings Under Constant Voltage

The EHV&UHV transmission lines of long-distance and large-capacity in China may cross iced districts, and in case of the security and reliability of its insulation on icing conditions, icing flashover performance of the full-scale insulator strings is studied in this paper, as well, the anticipation and mechanism of icing flashovers is primarily studied.A new icing flashover test method is proposed in consideration of the disadvantages and merits of existing methods. With the new method, the insulator string is energized under a constant voltage during icing and melting period until a flashover occurs or withstands. And then an Up-and-Down method is utilized to obtain the50%flashover voltage. Then the icing flashover performance of full-scale EHV and UHV insulators is acquired. Besides, the relationship between the icing flashover voltage and the length of full-scale insulator strings is analyzed, which is non-linear. During the research, the percentage of ice-bridges, as a parameter for describing the severity of icing, is also proposed. The percentage of ice-bridges impacts directly on the icing flashover voltage, which makes it more suitable to define the severity of icing in comparison of ice weigh and thickness, etc.Furthermore, the leakage current characteristics of500kV insulator strings during icing flashover tests are analyzed, as well as their spectrum analysis. The distortion of leakage current of icing tests with the new tests methods is a bit more critical than that with voltage-rising method. Besides, in percept of leakage currents, the procedures of pollution flashover and icing flashover are compared. In the beginning, the icing arcs act smoother than pollution arcs, and the duration of icing flashover is longer, too.Moreover, icing flashover mechanism is primarily studied with an ice model, especially on icing flashover arc characteristics and the melting water conductivity variation. According to different velocities, the development of arcs can be divided into two stages. Corresponding to the arc development characteristics, the icing flashover process is analyzed. In addition, researches on iced insulators reveals that, the melting water conductivity reaches the maximum value when melting starts, and decreases rapidly later. The surface conductivity of ice is highest, attributed by both the dirty freezing water and the contamination on insulator surface. During freezing period, the dirty freezing water contributes more in lower temperature while the contamination contributes more in higher temperature.