Switching impulse Breakdown of EHV Trnasmission Towers

Tests were performed to evaluate the switching impulse (S.I.) breakdown voltage of tower window models of different sizes. Window models were tested with positive polarity S.I. and with conductor-to-structure clearances of 4.55, 5.90, 7.60 and 8.75 meters. With each size of model the 50% breakdown voltage was determined for seven different wave-fronts with a time-to-crest between 60 and 800 ps and a half-amplitude time over 3500 ps. The time-to-breakdown was also recorded and correlated to the time-to-crest of the applied wave and the breakdown voltage.