Partial Discharge Characteristics of Oil-immersed Paper with Metal Impurities under AC and DC Compound Voltage

In the actual working process of the converter transformer, due to the metal impurities in the oil pump and the metal debris remaining in the manufacturing process, there will be metal impurities remaining on the transformer insulating paper, which threatens the safe operation of the transformer. In this paper, the partial discharge characteristics of oil-impregnated paper containing metal impurities under the action of AC and DC composite voltage are studied, and an experimental platform for partial discharge test of AC and DC composite voltage is established. Two experimental models were designed: the normal model and the metal impurity model. The experimental results show that the partial discharge and gas production characteristics of the two experimental models are very different under the action of AC and DC composite voltages. The PD onset voltage of the impurity model is lower, and the discharge volume and pulse repetition rate are higher than those of the normal model at different stages of PD development. The gas production in the oil of the two models is also different during partial discharge. It is found that the electric strength of the model containing metal impurities is significantly lower than that of the normal model, and the obtained results can provide a certain reference for the operation and maintenance of the converter transformer.