Assessment of the Effect the Height and Relative Position of Support Insulation Components Have on the Insulation Electrical Strength
Abstract
The article presents the results from studies of the effect the height and relative position of extra high voltage class support insulation components have on the insulation electrical strength when subjected to positive polarity switching impulses, at which the insulation minimum permissible overall dimensions are determined. It is shown that the highest values of the insulation flashover voltage are achieved when a leader discharge develops along purely air trajectories: screen--pedestal or screen-- plane. A similar result is obtained in the case of cascade flashovers from the screen over the column elements if the upper insulator structural height is significantly larger than that of the lower one. The reverse mutual arrangement of these insulators leads to a significant drop in the insulation flashover voltage during cascade flashovers. It is shown that at the final jump onset moment, the main contribution to the insulation flashover voltage value is introduced by the voltage drop across positive streamers, which is directly proportional to the length of these streamers. Hence it follows that the ambiguous effect of the height and mutual arrangement of the support insulation components on the insulation electrical strength during cascade flashovers is mainly due a significant difference in the lengths of the positive streamer zones at the final jump onset. With the upper insulator height equal to 2.7 m, the length of positive streamers at this moment is commensurable with the length of streamers when the flashover develops along purely air trajectories, whereas decreasing the upper insulator height by almost a half entails a significant decrease in the streamer lengths. Measures to eliminate undesirable cascade flashovers and ensure the highest electrical strength of support insulation are proposed.
References
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