Phase-to-ground switching transients in EHV systems

The author outlines the effects of unequal pole closure of circuit breakers on the magnitudes of phase-to-ground overvoltages. A model of a short section of a 500 kV line is used. Results show that the mean value of the phase-to-ground voltage increases in both directions away from the zero switching angle where it shows a minimum. The minimum is more distinct in the case of sequential switching than in the simultaneous switching mode. Risk of insulation failure is calculated for both modes of switching. Although the mean values of phase-to-ground overvoltages are less with sequential switching, higher risks of failure are encountered. This is due to the increased scatter in overvoltages indicated by their standard deviation