Motion characteristic of copper particle in insulating oil under AC and DC voltages

The solid suspended particles originating from the process of installation and operation of converter transformer can affect the insulation performance of insulating oil, thereby, leading to equipment failure. Previous studies show that the difference of motion characteristic can cause the DC breakdown voltage of contaminated insulating oil is lower than that of AC voltage. Therefore, the motion characteristic of metallic particles in insulating oil under AC and DC electric-field needed to be further investigated. This paper studied the influence of voltage levels and voltage types on the motion characteristic of copper particles in insulating oil. The motion process of copper particles under different voltage levels of AC, DC and combined AC and DC voltage were recorded by high-speed camera, and the motion trajectory of copper particle in insulating oil under different voltage levels of AC, DC and combined AC and DC voltage was established through COMSOL simulation. Experiment and simulation results show that the copper particles will move to high electric field and form a bridge between electrodes over a period of time. The motion characteristic of copper particles can be influenced by voltage levels and voltage types. At the same time, the rate of bridge formation may increase along with voltage increasing. The copper particles are more likely to form a bridge between electrodes under DC voltage than that under AC voltage, and the combined AC and DC voltage is in between.