PHASE-TO-PHASE SWITCHING SURGE DESIGN.

Phase-phase switching surge design information has been obtained from a project, the purpose of which was to develop methods for the design of 115-138 kv compact transmission lines, but the results are applicable to all designs with spacings in the range tested. Advanced statistical methods were used. Switching surge flashover measurements were made for phase-phase spacings of 3, 6, and 12 feet, on line lengths of 30, 150 and 1200 feet. Effects of the surge ratio alpha, the surge voltage on the third phase, line hardware, and height were studied. Weather correction factors were obtained from the test results as concomitant variables. Methods developed offer capabilities for statistical analysis of large complex data sets. The techniques permit rapid initial approximations, followed by sophisticated analyses permitting Gaussian or extremal function behavior for the data. The techniques include procedures for automatic rejection of spurious readings, and for 'censored' analyses which utilize flashover voltage information in addition to the binary flashover/no flashover records. Results are presented in a simplified form for ready use by design engineers, and can be used with a complementary TNA-generated system performance data base prepared in an associated EPRI project RP260-2, 115-138 kv Bundled Circuit Design. The combination permits probabilistic designs using simple procedures.