Influence of the Flowing Speed of Transformer Oil Contaminated by Dry Cellulosic Particles on its Breakdown Characteristics

The insulation properties of transformer oil will be compromised by the presence of cellulose particles. And these particles can gather in areas with high field strength and around the main windings due to the oil flow. Nonetheless, there is a need for additional exploration into the breakdown characteristics of contaminated flowing transformer oil. In this paper, a circulating transformer oil flow device was constructed and breakdown tests were carried out. The results unveiled that, in both AC and DC fields, the characteristic breakdown voltage generally displayed an initial decreasing trend (or exhibited slight fluctuations) first, then increased with the increase of flow velocity. At low flow velocities, the breakdown voltage with preload was consistently lower than that without preload, while the disparity became less pronounced at high flow velocities. The severity of cellulose bridges formation (in a bridge-like structure, influenced by oil flow and electric field) was found to be inversely proportional to the breakdown voltage, indicating that the creation of cellulose bridges played a crucial role in initiating oil gap breakdown. This paper contributes valuable insights into comprehending the breakdown mechanism of contaminated liquid dielectric in a flowing state.