Imaging of negative polarity dc breakdown streamer expansion in transformer oil due to variations in background pressure

Abstract

The breakdown physics of transformer oil is investigated using high speed electrical and optical diagnostics. Experiments are done in self-breakdown mode utilizing a needle/plane geometry. Shadowgraphy combined with high-speed electrical diagnostics are aimed at measuring streamer expansion as a function of external pressure. Assuming a breakdown mechanism for negative needle based on bubble formation with subsequent carrier amplification in the gas phase implies a pressure dependence, which is observed in the experiments, i.e. the expansion velocity decreases with increasing pressure.

Streamer initiation and propagation in transformer oil under positive and negative impulse voltages

“…The temperature rise in negative streamers is considerably higher in a larger area. Experimental results have shown that in negative streamers initiated from needle electrode generate relatively large gas bubbles in transformer oil [14][15][16]. These observation supports the numerical results we have obtained for negative streamers, since in the bushy ionized body of around the needle as can be seen in Figs.…”

“…The field enhancement makes the positive streamer initiation possible at lower applied voltages. According to the model, for a given applied voltage, negative streamers travel slower than positive streamers, which is again in agreement with experimental records [14][15][16]. The results also reveal that the velocity and the shape of positive streamers are approximately insensitive to changes in electron mobility as long as it is about two orders of magnitude greater than the ion mobilities.…”

“…It should be noted that the results shown in Figs. 5 and 6 cannot be considered as streamer columns since firstly, experimental records show that the diameter of the negative streamers are in order of tens of micrometers [15]; secondly, again according to experimental results [16], the velocity of the negative streamer head will increase after an initial decrease (due to formation of the bubble).…”

Multi-frame interferometric imaging with a femtosecond stroboscopic pulse train for observing irreversible phenomena

“…At the micron scale, the imaging of dynamical processes such as fracture 1 , propagation of shock waves 2,3 , dielectric breakdown 4 , and plasma formation 5 require ultra-high-speed diagnostic tools with nanosecond temporal resolution or shorter. Reversible processes may be observed with high temporal resolution utilizing conventional pump-probe measurements with many repetitions, in which a single image is recorded at a variable probe time delay after a pump pulse initiates the event.…”

Inception and breakdown voltages of insulating liquids under DC stress

“…Partial discharges under negative polarity were found to closely resemble the structure and growth of the slowest (subsonic) cathode events emanating from a tip under the application of negative impulse voltages. In addition, effect of background pressure on streamer expansion was studied in [7]. The results indicated that the streamer expansion velocity decreases with the increasing pressure under negative polarity.…”