Experiment and Mechanism of Bridging Effect of Cellulose Particles in Natural Ester Oil Gap under DC Voltage

With the years use of transformer, there may be a large number of fiber particles in it. During the operation of the converter transformer, due to the effect of the DC electric field component, the cellulose particles in the oil will form a "fiber particle bridge" within a period of time, which will induce PD and even damage the overall insulation. In this paper, slightly uneven electric field in transform oil is simulated by a spherical cap electrode, and the movement of cellulose particles in natural ester oil FR3 is observed under the DC voltage. The development law of particle bridge is summarized, and the difference of the positive and negative electrodes is pointed out. Simulation software is used to solve the electric field distribution in the field and the results show that the electric field distortion caused by the aggregation of cellulose particles in the gap could promote the further growth of the "particle bridge". This positive feedback relationship is the key to particle aggregation and bridging in slightly uneven electric fields.