Simulation for the Chain Formation of Cellulose Particles in Flowing Transformer Oil Under DC Voltage

The formation of impurity bridges in transformer oil can be altered by the oil flow, which in turn influences the breakdown progress of contaminated oil. In this paper, a solid–liquid two-phase flow model that incorporated both uniform and non-uniform electric fields was developed. The chain-forming behaviors in oil were simulated under various flow velocities and the experimental verification was carried out. It was shown that in stationary oil, the cellulose particles would gradually converge along the direction of electric field. Then particle chains were established across the gap, starting and ending with the adsorbed particles on the electrode surface. In non-uniform electric fields, the chains were broader and particles accumulated more tightly. However, the formation of particle chains was inhibited when the transformer oil flowed. Furthermore, complete chains could not be formed after the flow velocity increased to 20 mm/s. Finally, the mechanism of particle chain formation and the effect of flow velocity on the bridge-forming were discussed in relation to the changes in the force conditions.