Breakdown in Flowing Transformer Oil Contaminated with Cellulose Particles under DC Field

The effect of transformer oil flow on the insulation strength of the oil gap cannot be ignored. In this paper, the breakdown characteristics of flowing transformer oil contaminated with cellulose particles in slightly nonuniform DC field were investigated. The characteristic breakdown strengths and breakdown images at different flow rates were extracted. The results show that the dielectric strength of the oil gap at low flow rates was about the same as that of stationary oil. The introduction of oil flow can significantly improve the insulation strength of the oil gap only when the flow rate was above a certain critical value. In stationary and low speed oil flow, the cellulosic bridge across the electrodes formed at low voltage would break and form cellulose clusters on the surface of the electrodes in the process of raising the voltage. The breakdown occurred on the side closer to the center of the electrodes in the clustering region. In high-speed oil flow, the cellulose particles were neither bridged nor agglomerated, and breakdown was triggered by local electric field distortion caused by the end of the short cellulosic bridge.