Effect of Copper Sulfide Deposition on the Partial Discharge of Oil-Paper Insulation Under Plate-Plate Electrodes

The copper sulfide (Cu2S ) generated by the reaction of corrosive sulfur, as occurs in transformer oil and copper windings, is an important factor that induces partial discharge (PD) in power transformers. In this article, the development process and influence trend of PD under Cu2S deposition were studied. The process images of PD caused by Cu2S deposition were obtained through the oil-paper insulation charge transfer model applied to plate-plate electrodes. The law of PD varies when the polarity of the voltage excitation applied to the upper electrode plate varies. Charge build-up will be greater when applying a positive voltage to top plate, whereas reverse discharge will occur with a negative voltage applied. Based on these changes in charge density and electric field strength during PD, the influence of the thickness, width, and spacing of the Cu2S deposition was determined. The increase in deposition thickness increases the intensity of PD development, and the increase in width is conducive to greater diffusion of charges. If the distance is too small, it delays the development of discharge in multiple deposits. This research reveals the physical mechanisms underlying PD caused by Cu2S deposition.