Experimental Investigation on Outdoor Insulation for DC Transmission Line at High Altitudes

This paper presents the results of a study on the contamination characteristics of porcelain, glass and composite insulators in natural high altitude areas (1970 m). The test used the solid layer method, in which a contaminant solution consisting of sodium chloride, kaolin powder and water was used to coat the insulator surfaces. The insulators were wetted by steam fog in fog chamber. The 50% withstand voltage (
U

_50%
) was determined by the up-and-down method. Experimental results indicate that insulator profiles have a significant effect on the flashover voltages. The flashover voltages for bell-type porcelain insulator are higher than tri-shed porcelain insulator. The glass insulator with bigger spacing has a higher flashover voltage than that with smaller spacing. The flashover characteristics of composite insulators can be greatly improved for about 20% by optimizing the shed parameters. In addition, the suspension patterns (I-, V- and Y-string) also have a significant influence on the porcelain insulator flashover voltages. The Y-string configuration appears to lead to much lower flashover voltages than I- and V-string insulators. The flashover voltages for V-string insulators are influenced by the angle between two insulator strings. The flashover voltage for V-strings of 120
^°
is highest, which is higher than that of I-string for 7.5%.