Study of cellulose particle motion effect on impulse breakdown in transformer oil

This paper conducts experimental research and theoretical analysis on the effect of cellulose particle motion on impulse breakdown in transformer oil. In the experiment, the spherically capped electrodes immersed in the bulk of the transformer oil are used to form a quasi-uniform electric field. The breakdown tests are carried out and the breakdown voltages for three cellulose contamination levels oil under four types of impulses, 1.4/50μs, 14/220μs, 80/850 μs and 240/2400 μs, are obtained. The experimental results show that both the impulse waveshape and cellulose contamination level have an effect on the breakdown of transformer oil. Longer impulse duration or higher cellulose contamination level of transformer oil can lead to the decrease of impulse breakdown voltage. Specifically, the effect of the high level cellulose contamination for U50% becomes much more significant under long-duration impulses. To verify the findings above, a numerical model is introduced for the cellulose particle dynamics in the transformer oil under these four kinds of impulses. Notably, the calculation result indicates the particles can accelerate with the action of the impulse, and particles can aggregate in concentrated area of the electric field in the oil gap with the action of the long-duration impulse. It is concluded that the particle motion can play a catalytic role in the impulse breakdown of the oil gap.