Influence of particles on partial discharges and breakdown in oil

Particles influence both AC and DC voltage breakdown in insulating oil. Larger and conducting particles decrease the breakdown voltage most. For both DC and AC the ratio of breakdown voltage for clean oil to oil with non-conducting particles is nearly the same. For conducting particles the ratio for DC is generally larger than for AC. Particle concentration and motion is influenced by DC and AC stress in different ways. Particles may be drawn into or expelled from high stress regions. Fine particles may agglomerate or be dispersed. Particle chains may develop. These complex physical factors have not been related directly to voltage breakdown in the oil. Particles may cause partial discharges to develop in oil but these discharges also have not been related directly to short time breakdown of the oil.