Mechanism of Copper Sulfide Deposition on Oil-Paper Insulation Partial Discharge Under Extremely Uneven Electric Field

The corrosive sulfur in transformer oil reacts with the copper winding to form copper sulfide (Cu2S) deposits, which cause partial discharge (PD) and accelerate the degradation of the oil-paper insulation. Currently, the mechanism of the influence of Cu2S deposition on PD is not clear. This article presents a simulation model for oil-paper insulation PD with Cu2S depositions under point-plane electrodes and studies the PD process and the influence law on PD at different distributions of Cu2S deposits under extremely uneven electric fields. The findings indicate that the presence of Cu2S deposits enhances the intensity of the electric field within the oil gap, thereby expediting the progression rate of the streamer. Upon reaching the Cu2S surface, the streamer will cause severe surface discharge. Increasing the deposition width is beneficial for the diffusion of charge on its surface but not the accumulation of charge. The surface charge density of Cu2S deposition with a large width climbs more slowly, the smaller the peak, and the smaller the final density level maintained. Meanwhile, the increase in deposition thickness not only shortens the streamer’s diffusion distance and increases the electric field intensity within the oil gap, but also reduces the onset and development time of surface discharge. Within a certain distance range, Cu2S deposition generates more charge when discharged away from the surface of the needle tip. The studies of PD under the influence of Cu2S deposition partially reveal the physical process and influencing factors of Cu2S-induced PD. This information is instrumental in developing a more accurate deposition detection method and is conducive to the optimization of the insulating structure and the research on the technology of suppressing PD.