Influence of Cellulose Particle Aggregation on Transformer Oil Dielectric Strength

With increasing transformer voltage levels, the probability of unexplained insulation discharge failure also increases. These failures often occur despite normal insulation parameter readings prior to the event. Investigating and uncovering the mechanisms behind such failures is crucial for ensuring the safe operation of transformers. This paper focuses on the phenomenon of local aggregation and the cumulative effects of low-concentration particles in transformer oil during long-term operation, explores how these factors reduce the insulation margin of transformers, and reveals the mechanisms behind sudden unexplained failure. Using transformer oil samples containing low concentrations of cellulose particles, the aggregation of cellulose particles toward high-field regions was observed over time, and the impact of different aggregation levels on the breakdown strength of oil gaps was examined. These results indicate that the aggregation behavior of cellulose particles leads to increased impurity concentrations in high-field regions. In this experiment, after an AC voltage was applied to the electrodes for 7200 s at a field strength of ~2.78 kV/mm, the breakdown voltage of the oil sample decreased by ~79.57% compared with the breakdown voltage when the electrical field was directly increased until breakdown occurs. This is attributed to the aggregation effect, which causes particle clustering and increased local concentration, significantly reducing the dielectric strength of the transformer oil. The findings of this study help in understanding the relationship between impurity particle aggregation effects and the reduction in transformer safety margins, providing new theoretical support for tracing the origins of transformer discharge failures.