Channel Evolution and Pressure Wave Characteristics of Low Energy Power Frequency Spark Discharge in Short Transformer Oil Gap

To study the channel evolution and pressure wave characteristics of spark discharge in transformer oil, a synchronized test platform for voltage, current, pressure wave measurement, and discharge channel morphology filming was built. The spark discharge under power frequency voltage can be divided into intermittent discharge and continuous discharge stages. The transition is caused by the breakdown strength reduction due to gas and carbon particle generation. The maximum of the pressure wave in the intermittent discharge stage is considerably larger, and the second pressure peak is the maximum. The maximum peak pressure is approximately proportional to the square of the applied voltage, with a power exponent of$2.15~\pm ~0.12$, and decreases with the increase of the electrode gap distance. The increase in plasma channel injection power under different voltages is the main reason since the conversion efficiency of deposited electrical energy to pressure wave mechanical energy remains around 19.8%, while the decrease in injection power per unit electrode gap distance and that of the conversion efficiency are the main reasons under different electrode gap distances. The conversion efficiency is sensitive to the channel length and can decrease to merely 11.0% when the electrode gap is increased to 7.5 mm.