Switching impulse of long oil gaps of natural ester fluid

Switching impulse breakdown values, negative and positive polarities, were measured for long oil gaps of natural ester fluid and mineral oil. A switching surge wave shape of 250×2500 μs was used for gaps of 50-150 mm between a high voltage bushing shield and a simulated tank wall (an electrode arrangement used to obtain previously published 60 Hz and 1.2×50 μs lightning impulse breakdown values). We compare these results with data obtained from 10-35 mm gaps using an electrode configuration developed by Weidmann Electrical Technology Inc. The results of this testing are consistent with previous results that showed natural ester fluid has equal or better dielectric breakdown characteristics compared to mineral oil for 10 to 150 mm gaps.