Phenomenology of conduction and breakdown in transformer oil

Abstract

In a coaxial test apparatus enabling the measurement of voltage and current at the test gap, dc conduction and breakdown in transformer oil caused by the application of dc voltages are investigated. Current measurements cover the range from 10." A to 1 kA, with temporal resolutions of milliseconds at the lowest current amplitudes to sub-nanoseconds for currents larger than IO4 A. The dc currentlvoltage characteristic for sub-breakdown voltage amplitudes point to the injection of charge carriers, allow us to characterize the transport mechanisms, and the influence of space charges. For voltages approaching breakdown thresholds, quasi dc-currents rising from nanoamperes to microamperes are superimposed by current pulses with amplitudes of milliamperes and above, and durations of nanoseconds. The onset of these current pulses occurs up to 10 ps before breakdown. One of these current pulses reaches a critical amplitude causing voltage breakdown and current rise to the impedancelimited value within 2 ns. Additional optical diagnostics using photomultipliers and high-speed photography with gated microchannel plates yield information on hydrodynamic ' processes and charge carrier amplification mechanisms associated with the current pulses and fmal breakdown, such as bubble formation, as well as on the development of the spark plasma finally bridging the gap.

Electrical conduction and dielectric breakdown characteristics of alkyl ester dielectric fluids obtained from palm kernel oil

“…This turbulent motion in oil between the electrodes causes the temperature of the liquid to rise locally. It also significantly affects the local pressure 12 . The injected energy could also result in a phase change in the oil or liberation of simpler molecules from the dissociation of part of the oil molecule.…”

Optical high voltage breakdown prediction using thermal lensing effect in transformer oil

“…When it comes to HV breakdown prediction, just before this event, partial discharges of high energy lead to the rapid development of gas channels between the electrodes [6]. These create shockwaves [6] and lead to the disruption of the laminar flow between the electrodes [4,9] within the charge channel (the host of the discussed thermal cylindrical lens).…”

“…These create shockwaves [6] and lead to the disruption of the laminar flow between the electrodes [4,9] within the charge channel (the host of the discussed thermal cylindrical lens). We expect that these events are disrupting the uniformity of this lens strongly affecting the passing laser beam.…”

“…This is known as partial discharge, PD [6]. A presence of the electric current due to discharge events is another factor leading to the localized oil heating [6].…”

Streamer Propagation in a Long Gap in Model Liquids

“…4, and reduces the breakdown voltage by about 50% (Table 3). The possible explanation is that a reduction in pressure will either reduce the boiling point of oil or facilitate bubble formation [17,18]. This eases the formation of gaseous channels and by this streamer propagation.…”