Distributed Characteristics of Free Metallic Particles in Flowing Transformer Oil Under DC and AC Voltages

Transformer oil is inevitably contaminated by metallic particles during manufacturing and operation, which will accumulate in the oil gap and poses a serious threat to the oil insulation in the power transformer. However, the distributed characteristics of particles in oil channels will be influenced by oil flow. In this article, a circulation flow device of transformer oil was established, and the distributed characteristics of metallic particles in flowing oil were obtained under direct current (dc) and alternative current (ac) voltages, respectively. It was found that particle counts between parallel plate electrodes and rod–plane electrodes would decrease monotonously with increasing flow velocities under dc application, whereas the concentration between spherically capped electrodes would increase slightly first and then decline. When the electrodes were energized by ac voltage, the reduction of the particle concentration was more significant with the addition of flow velocities. What’s more, the temporal changes of particle amount under different conditions were obtained. Then the impacts of flow velocities and applied voltages on particle distribution were discussed based on the force analysis on metallic particles.