Charging characteristic of free metallic particles in transformer oil when the electrodes covered with insulation paper

The charging characteristics of free metallic particles in transformer oil will change when the electrode is covered with solid insulation dielectrics. In this paper, the motion behavior of the particles was recorded by the motion observation platform. The result showed that particles would temporarily settle on the electrode after touching the paper-covered surface, which would not occur after contacting the bare electrode. As applied voltages increased, the settling time decreased. Subsequently, a calculation method of the charge quantity was proposed based on the kinetic equilibrium equation and the charge quantity of metallic particles was solved. It was shown that the charge quantity after contacting the paper-covered electrode was about half of that for the bare electrode, which increased linearly with the rise of the applied voltage. Finally, it was qualitatively inferred that the particles were mainly charged through the conduction of insulation paper.