Prebreakdown current pulses in n-hexane and other dielectric fluids

A point-plane electrode geometry was used to apply negative DC stresses to n-hexane, trimethylpentane, and transformer oil. The resulting prebreakdown currents and light were observed with a state-of-the-art, low-noise amplifier and a high-speed digitizer. Currents appear as bursts of fast (on the order of 100 ns) negative pulses with progressively increasing amplitudes, and a wide bandwidth (at least 10 MHz) is required to resolve individual pulses. Light pulses occur coincidentally with current pulses, but are narrower. The effect of adding particles to the sample or increasing the applied high voltage is primarily to increase the burst rate, with little or no effect on other pulse characteristics such as shape, amplitude, or rate of increase. These observations suggest a model describing the source of the current pulses as a series of discharges inside an expanding low-density region