Simulation of the Dynamics of Cellulose Impurity in Oil-Paper Insulation under DC Electric Field

The oil-paper insulation of valve side winding within converter transformers needs to withstand the effect of the DC electric field component in actual operation, under which cellulose impurities are easy to accumulate and form cellulose impurity bridges, leading to partial discharge in the oil gap, and even causing insulation failure. In order to explore the migration and accumulation process of cellulose impurities, this paper conducts the analysis and simulation study of the dynamic model of cellulose impurities in oil-paper insulation under a DC electric field, summarizes the force situation of cellulose impurities, and quantitatively analyzes the variation laws of velocity and lateral migration distance during the movement of cellulose impurities. The results show that under DC voltage, cellulose impurities in oil-paper insulation mainly subject to gravity, buoyancy, electric field force, drag force, additional mass force, dielectrophoretic force, Basset force, pressure gradient force, Magnus force, and Saffman lift force, among which the latter six forces can be ignored due to their low amplitude. Under the action of various forces, cellulose impurities in the sphere-plate electrode move towards the strong field area, and their movement speed increases with the increase of the electric field intensity, but the offset between every two collisions between the impurity and the paper decreases, eventually approaching 0. When multiple cellulose impurities collide, they can be attracted to each other by Coulomb force, forming cellulose impurities with larger mass, and eventually accumulate at the surface of insulating paper, and gradually forming cellulose bridges. The above research realizes the quantitative calculation of impurity dynamic characteristics, which can provide a theoretical basis for the subsequent assessment of the insulation hazards of cellulose impurities.