Motion behaviours and PD characteristic of free metallic particles in flowing transformer oil with paper‐covered electrodes

Abstract

The introduction of solid dielectrics to electrode surfaces will change the motion behaviours of free metallic particles and in turn affect partial discharge (PD) characteristics in transformer oil. To estimate the influence, the metallic particles movement in flowing oil was compared between different cases with and without insulating paper covering electrodes here. When the electrodes were bare, particles executed up-down movements repeatedly in the vertical direction. As the electrodes were paper-covered, the particles would settle on the paper surface for a period of time. Simultaneously, the PD characteristics caused by metallic particles were measured. When the electrodes were bare, the discharges concentrated in 0–90° and 300–360° and the PD magnitude reached 390 pC. When the double electrodes were paper-covered, the PD magnitude decreased by 67% and the concentration phases of PDs would migrate to 45° and 160°. In order to analyse the experimental results, a simulation model with a paper-covered boundary was constructed. Simulated trajectories of particles were in accord with the experiment results. Base on the model, the particle motion characteristics were obtained and the electric field distribution between the particle and electrode was calculated. Finally, the influence of paper-covering on PD characteristics was discussed.