Abstract:To investigate the influence of cellulose impurities on the characteristics of partial discharge (PD) in oil-paper insulation, a DC oil-paper insulation experimental platform is established. Processes including the generation and bridging of cellulose impurities in oil are observed, where the dynamic basis of bridging of cellulose impurities is analyzed. The characteristic parameters of PD in oil-paper insulation affected by cellulose impurities, including discharge frequency, average discharge magnitude and maximum discharge magnitude are studied. The results show that the cellulose impurities in oil under DC voltage are influenced by electric field force, gravity, buoyancy and oil viscous resistance. When the electric field strength is higher than 2.12×105 V/m, the cellulose impurities begins moving to high-voltage electrode at a slow speed and bridging along the maximum direction of voltage gradient. The distorted electric field of bridged impurities can cause an increase of PD frequency and a decrease of discharge magnitude. Further experiments show the cellulose bridge can increase the leakage current of oil gap, which leads to the local overheating and gasification of water contents in oil into tiny bubbles. Bubbles with low conductivity under DC voltage withstands stronger electric field, resulting in discharging before transformer oil and more concentrated PD with lower intensity.