Measurement of induced electrical pressure in insulating liquids under high electrical fields

Experimental results on the electrical pressures generated in liquid dielectrics under high direct voltages are presented. Nonuniform fields (cone-plane) were used in the experiments. A controlled air bubble was injected through a hole at the apex of the conical electrode via a bubble injection system. The internal pressure inside the bubble was measured under various test conditions. Experiments were carried out on silicone oil, transformer oil, and n-hexane. Results show that negative polarity gives higher electrical pressure than positive polarity. The p×d characteristics of the bubbles were determined as a function of the applied voltage. The ionization level of the bubbles, where the bubble changes from the nonconducting to the conducting state, was determined from the results obtained. The results show that time is needed for the electrical pressures to build up inside the liquid