Effect of Metal Ions and Suspended Particles on Streamer Propagation

Metal contamination in insulating oil is one of the main threats to the safe and reliable operation of oil-immersed equipment, such as on-load tap changers (OLTCs). The mechanism analysis of metal ions’ influence on the discharge process of insulating oil is rarely involved in previous studies. Herein, the generation mechanism of metal ions and suspended particles is summarized first for subsequent modeling. Numerical models are constructed to simulate the streamer propagation in oil, considering the effect of two forms of metal contaminant. The dissociation source term of ionic compounds is introduced into the charge continuity equation to elucidate the impact of metal ions on streamer propagation. The results reveal that adding metal ions increases the overall speed of the streamer and decreases the maximum field intensity at the head of the steamer compared to pure oil conditions. Excessive ion concentration hinders the streamer’s development by creating the space charge shielding effect. Charge accumulation on the surface of suspended metal particles is the leading cause for the branching or turning of the streamer channel. The size, quantity of the metal particles, and the landing location will significantly affect the streamer propagation characteristics, e.g., the landing location on the surface of the metal particle will determine whether the subsequent branching streamer head can further develop. The results contribute to a better understanding of the influence of ionic and particulate metal contaminants on the microscopic discharge process in insulating oil.