Streamer and Breakdown Characteristics of Dielectric Liquids Under Impulse Waveforms With Different Tail-Times

Abstract

Impulse waveforms have been widely used in the studies of streamer and breakdown phenomena in dielectric liquids. In this article, both experiments and analyses were carried out to investigate the effects of impulse tail-time on streamer and breakdown characteristics of a mineral oil and a synthetic ester liquid. A range of positive impulse waveforms with the same front-time of 0.8 µs but different tail-times from 8 to 3200 µs were considered. Needle-plane electrodes with a needle tip radius of 10 µm and a gap of 10 mm were used. It was found that reduction of tail-time leads to an increase of 50% impulse breakdown voltage, while the instant breakdown voltage and the timeto-breakdown remain constant. On this basis, an analytical method is developed to estimate the 50% impulse breakdown voltage under waveforms with various tail-times. The method is valid when streamers remain of second mode and in divergent fields. It was also observed that some "self-regulation" by branching explains the constancy of streamer propagation velocity when the applied voltage is increased.

Statistical analysis and interpretation on lightning impulse breakdown voltages of ester liquids under varying field uniformity

“…For the streamer propagation dominated breakdown under lightning impulse, the propagation of streamer requires high enough local electric field to result in breakdown, otherwise it will be quenched without bridging the whole oil gap. To bridge the liquid gap, a high enough applied voltage will be required to maintain a sufficient duration of voltage above the minimum streamer propagation voltage under lightning impulse [73]. Alternatively, the streamer propagation velocity should be accelerated.…”