Abstract
A short duration impulse voltage generator was constructed to study the onset and propagation modes of discharges in silicone oil. The events were captured using PC-based shadowgraphic optical system hooked up with a high resolution digital camera. Results show that positive discharges propagate with three distinct modes attaining supersonic velocity. Negative discharges initiate at much higher voltage amplitudes as compared to positive discharges and were found to expand as long as they remain attached with the stressed point electrode and collapse in size as they leave it. This phenomena was tested on Raleigh's model of cavity growth and collapse and proved that negative discharges are produced as an outcome of vaporization of liquid when it is stressed under high voltage pulses.