Switching Surge Study of EHV Station Posts: I

Results of tests and research are given for EHV station post insulators from 900 to 2050 BIL (basic imnpulse insulation level), including flashover and withstand on switching surge, wet and dry. Also studied are variations in withstand and flashover as the insulator height above ground is varied, as the mounting structure is changed, and as the number of insulators in parallel in the test is varied. Using the probability method of determining flashover and withstand under switching surge, it is shown that many tests and curves are needed to deternine the average value for only one set of test conditions. All tests were made outdoors and some comparisons are made with present indoor published data. Further information dealing with substation clearances in air as well as porcelain insulation will be published in the future.