Liquid insulation is widely used in high voltage equipments. In particular case, electric arc may occur in the liquid insulation. The existence of the arc may affect the performance of the insulation. This paper reports the experimental results on the effects of arc on the partial discharge (PD) characteristics in mineral oil. Electric arc treatment was conducted by applying AC voltage in needle-plane electrode. The arc intensity was adjusted by the distance between electrode. The effects of arc intensity and duration on the PD characteristics were elaborated. The experimental results showed that arc treatment significantly reduced the PD inception voltage. Positive PD inception voltage was slightly higher than negative PD in all samples. Phase-resolved analysis indicated the important role of instantaneous applied voltage on the PD magnitude as well as PD occurrence. The PD number drastically increased with arc treatment. The increase of PD number implied the increase of total charge with the arc treatment. DGA data indicated that high activity of PD was in line with the increase of dissolved gases in the oil samples.
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