Influence of composite insulator shed design on contamination flashover performance at high altitudes

The dc arcing performance of composite insulators with contaminated surfaces has been investigated at high altitudes because of the program of building ±800 kV dc transmission lines in China, because much of their intended routes will be at relatively high altitudes. As the length of the arcs on the composite insulator depends on the repeat distance and the arcs are initiated on the core rod between the sheds, the effect of the repeat distance and the shed dimensions on the dc flashover voltages was studied for composite insulators under contaminated conditions. The experimental results confirmed that the shed design parameters do have a great influence on the flashover voltages. It was found that, with the same insulation distance, the flashover voltage had a maximum at a particular value of the radial extent of the shed and of the between-repeat distance, and that the influence of these two factors on the flashover voltage was independent of each other. It was also found that, for the alternate large and small shed design, the ratio of the radial extent of the major shed to the minor shed should not be too great.