The Accuracy of Statistical Methods in Evaluating the Insulation of EHV Systems

The insulation of a 400 KV transmission line as far as switching overvoltages are concerned has been evaluated through the probabilistic approach. The statistical data of switching overvoltages have been obtained by means of one thousand line reclosing operations simulated through an appropriate computer program The switching tests have been grouped to study the influence of the statistical pattern. The risk of failure as calculated by means of three approved statistic al diagrams has overlapping regions resulting in low- reliability insulation values. To increase the reliability of the results it looks necessary that some relevant universal criteria should be specified.