The Analysis of Cellulose Particles Bridging in Natural Ester Oil under DC Voltage

The existence of cellulose particles in insulating oil is regarded as one of the major reasons for insulation failures in power transformers. Therefore, this research conducts experimental study and theoretical analysis of cellulose particle bridging mechanism in natural ester oil (FR3) under DC electric field. First, the spherically capped electrodes are used to test the natural ester oil (FR3) with cellulose particles in the experiment. The cellulose particles motion and the bridge-forming process in natural ester oil (FR3) are observed under the experiment of DC voltage. Then based on the experimental observation results, the numerical simulation model of cellulose particles in FR3 insulating oil under DC voltage is established, and the physical mechanism of cellulose particles at different bridge stages is simulated and analyzed. The results indicate that the presence of cellulose particles distorts the electric field distribution in the oil gap. Finally, based on the analysis and comparison of the dielectrophoretic force of cellulose particles at different positions in the electrode gap, the adsorption, aggregation and growth rule of the cellulose particles near the electrode are explained. The interval leakage current measured during the bridge-forming process shows that cellulose particles lead to interval conductance increases and the insulation performance decreases.