Aging Characteristics of Transformer Oil-paper Insulation Under Continuous Lightning Impulses

As climate becomes increasely warm, extreme weather with thunderstorms occurs frequently. Transformers are threatened by continuous lightning impulse voltage, which damages the oil-paper insulation and impairs the safe operation of transformers. In order to simulate the operation of transformers in extreme thunderstorm environments, a experimental platform of lightning impulses was built. Lightning impulses were applied to the oil-paper insulation model in different time. The influence of continuous lightning impulses on the aging characteristics of oil-paper insulation was studied. The polarization and depolarization current tests were performed on the samples with different number of lightning impulses. The micromorphology changes of insulation paper were observed by scanning electron microscopy. The tensile strength of each paper and the moisture content of the oil were measured. Subsequently, the effect of fiber structure on the strain of insulation paper was analyzed. Finally, the depolarizing trap density spectrum was obtained through the id(t)t−lnt curve. The change rules of trap level and density with aging degree were discussed. The results indicate that, with the increase in the number of applied lightning impulses, the deterioration degree of the fiber structure will increase and the stress maximum will decrease. The polarization/depolarization current and the depolarizing trap density curves of oil-paper insulation move upward. The peak value of depolarizing trap density curve and its peak time will increase. In the macroscopic view, the deterioration of the fiber structure of the insulation paper can be reflected by the decrease of the stress peak value. Under the effect of lightning impulses, the peak of depolarizing trap density curve and its peak time can be used as the aging characteristic quantity of oil-paper insulation. © 2023 Science Press. All rights reserved.