Determination of Highly Stressed Volumes in Oil Dielectrics

The volume of oil under the highest stress has been shown to correlate well with the measured breakdown voltages of transformer oil in different electrode systems. The determination of the volume of oil that is most highly stressed in a given electrode system is not however an easy matter. It involves the location of equistress or equigradient surfaces followed by computation of the oil volume contained within the surfaces. This paper describes a differential probe and amplifier system, which has been developed to allow the direct plotting of equigradient lines on a conducting paper analog of any two-dimensional electrostatic field.