Some effects of particles on discharges in oil/paper systems

The influence of particles on partial discharges and voltage breakdown in oil has been summarized previously by the authors.¹ In this paper, the effect of particles on the breakdown of a more complex system of impregnated paper in series with an oil gap is discussed. Due to the long times involved for complete drying and impregnation, the number of test specimens employed was limited as was the number of complete voltage breakdowns. On the other hand, for paper in series with oil, partial discharges often occurred and these could be measured before breakdown took place. Under direct voltage, the leakage current and the desorption current were also measured. For the work described here, 2–5 μm iron particles were added to the oil. Particle motion was observed and photographed.