Charging Characteristics of Micrometer-Sized Metal Particles and Their Effects on Partial Discharge of Insulating Oil in Flowing

In this study, the motion behavior of micrometer-sized metal particle swarm in the case of flow–electric field coupling is observed in a noncontact manner based on the experiments. According to the results of observation, the charging characteristics of metal particle swarm in insulating oil flow under dc electric field are analyzed in detail, and the effects of electric field intensity, voltage type, and oil flow velocity on the charging process and motion of particle swarm are studied. The obtained results show that the applied electric field will cause the streamlines of velocity of the metal particles to oscillate along its direction, where such an effect becomes more obvious as the electric field intensity increases. The increase of oil flow velocity can weaken the influence of electric field and make the streamlines of velocity tend to be flat. The oscillation effect of streamlines of velocity under ac electric field is much weaker than that of dc electric field. In addition, based on the measured kinetic parameters of particles, it is found that the charge quantity of the moving particles in the gap of electrodes has the characteristics of temporal and spatial variations, and the particles have a variety of charging modes, including collisional charging, charge transfer, neutralization, and accumulation. The high velocity of flow and the alternating electric field hinder the charge transfer between particles, resulting in a decrease in the overall charge of the particle swarm. Finally, from the perspective of microdischarge and electric field distortion, we explain the influence mechanism of flow velocity and voltage type on the discharge characteristics of oil flow containing metal impurities.