Oil immersed inverted current transformer is vulnerable to overvoltage in the transmission line during operation. The accumulative effect of switching impulse voltage can degrade the main insulation and lead to a reduction in insulating property. Frequency domain spectroscopy (FDS) can be used to reflect the insulating property of oil-paper insulation. In order to investigate the FDS characteristics of oil-paper insulation under repeated switching impulse voltage, samples of oil-paper insulation with different thickness were made. Afterwards, the FDS of samples was tested with different number of repeated switching impulse voltage and applied voltage. The results show that more impurities occur in oilpaper insulation under repeated switching impulse voltage, which has a greater impact on the FDS results. Therefore, the FDS characteristic curves can reflect the deterioration characteristics of oil-immersed inverted current transformers under repeated switching impulse voltage. The role of impurities concentration and motion characteristics in the degradation process of oil-paper insulation was analyzed.
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