PHASE-TO-PHASE SWITCHING SURGE FLASHOVERS: DESIGN DATA.

Information for designing the switching surge strength of phase-to-phase gaps on transmission lines is given. The data were obtained from flashover tests on parallel conductor gaps of 3 to 12 feet. A Type I external relation is described as preferable to a Gaussian for calculating flashover probabilities. Simple factors allowing design for most of the variables affecting phase-to-phase performance are given for use with this relationship. Applications of the design information show that the withstand strength of parallel conductor gaps, and also the strength of long line sections compared to short test spans, are higher than previously assumed. This suggests that existing lines may have greater margins than previously thought. New test procedures and high measurement accuracies used during the flashover test provided the opportunity to develop new methods of statistical analysis with unusually broad capabilities for analysis of the test data. These methods should be useful in many other experimental situations.