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

The insulation properties of transformer oil can be compromised by the presence of cellulose particles. 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 article, a circulating transformer oil flow device was constructed and breakdown tests were carried out. The results unveil that, in both ac and dc fields, the characteristic breakdown voltage (BDV) generally displays an initial decreasing trend (or exhibits slight fluctuations) first, then increases with the increase of flow velocity. At low flow velocities, the BDV with preload is consistently lower than that without preload, while the disparity becomes less pronounced at high flow velocities. The severity of cellulose bridge formation (in a bridge-like structure, influenced by oil flow and electric field) is found to be inversely proportional to the breakdown voltage, indicating that the creation of cellulose bridges plays a crucial role in initiating oil gap breakdown. This article contributes valuable insights into comprehending the breakdown mechanism of contaminated liquid dielectric in a flowing state.