Movement Characteristics and Kinetic Analysis Model of Cellulose Impurities in Oil-paper Insulation Under DC Voltage
The valve side winding of a converter transformer bears DC electric field continuously during operation. Its internal cellulose impurities are easy to accumulate and form bridges, which seriously impairs the performance of the composite insulation. In this paper, the migration and accumulation characteristics of cellulose impurities in oil-paper in-sulation under DC voltage were investigated. The trajectory, speed, offset distance and other characteristic parameters of impurities were quantitatively analyzed. The kinetic analysis model of cellulose impurities under DC electric field was established thereafter, the whole motion trajectory of fiber impurities was reduced, and the kinetic mechanism of the vari-ation of velocity and offset distance was explained quantitatively. The results show that a single cellulose impurity reciprocates between sphere electrodes and plate electrodes, and moves horizontally to the stronger electric field region at the same time. The single motion cycle can be divided into three stages:'lifting', 'rising' and 'falling', and the maximum speed reaches over 102 mm/s during this process. As time increases, the cellulose impurities in the oil form impurity bridges in the stronger electric field region. The micro bridges present the characteristics of dense morphology in the cen-ter and sparse morphology in the edges due to the repulsion of charges with the same polarity. By simulation of the migration characteristics of cellulose impurities, it is found that the growth rate of particle velocity is fast firstly and then slow in the 'lifting' stage, while the velocity increases sharply to the maximum at first, and then decreases gradually in the 'falling' stage. Meanwhile, the maximum acceleration can reach over 102 m/s2. In addition, the horizontal offset distance decreases with the increase of collision times in the process of cellulose impurity movement. Offset distance and collision times have an exponential relation. This study clarifies the whole moving process of cellulose impurities under DC volt-age and realizes the quantitative calculation of the impurities kinetic characteristics, which can provide a theoretical reference for the subsequent harmfulness assessment of cellulose impurities.
oil-paper insulationcellulose impuritiesmigration movementfinite element methodkinetic model
万方数据
维普
