Switching-surge flashover characteristics of long sphere-plane gaps for UHV station design

The switching-surge behavior of UHV station electrodes was studied by investigating the performance of sphere-plane gaps. Design curves which show the effect of electrode curvature on the critical flashover voltage for spheres ranging in diameter from 0.5 to 2.5 meters and with gap spacings between 1 and 11 meters are presented. The influence of waveshape on large electrode flashover characteristics was obtained by varying the time-to-crest of the applied waveforms between 75 and 1220 µs. Test data are given for smooth and segmented spheres during dry conditions. The effect of precipitation on the switchlng-surge strength was investigated by wetting the sphere surfaces either by natural rain or artificial means. The results presented provide information required for the switchlng-surge design of outdoor UHV stations.