The measurement of charge on single particles in transformer oil

The author addresses the role of particles in the breakdown of insulating oils by studying the motion of a single stainless steel ball as it transfers charge in an oscillatory manner between two DC planar electrodes immersed in transformer oil. The ball ranged in radius from 0.5 to 1.6 mm and the electrode gap from 8 to 12 mm. The maximum electric field within the gap was 3.5 MV/m. The ball was either levitated freely between horizontally oriented electrodes or constrained to move horizontally between vertically oriented electrodes to determine the charge carried by the ball. In both cases theory could be reconciled with experiment, but only if space charge, modified electric force due to the geometry of the system, effective density of the ball in the liquid for inertial force calculation and modified viscous drag due to a high Reynolds number of movement were taken into account. The paper presents recorded current waveforms and general observations of ball movement