Examining dielectric properties of paper ageing in scrapped transformers

Experimental Study of degradation of oil impregnated paper has attracted enormous attention over the past 20 years worldwide. Outside the controlled conditions of the laboratory, however the real situation is more complex due to loading change, ambient temperature, fluctuation and sudden impulse impact. Therefore, interests in forensic examinations of scrapped old transformers have increased in recent years since it may be a way to obtain under-service ageing information and connecting the laboratory ageing experiment with the reality. This paper presents the effect of ageing on the breakdown voltage and examines the effect of oil quality on the breakdown voltage of the paper. Tests results of service-aged papers taken from three failed power transformers. The result indicated that ageing has a small reduction effect on the breakdown voltage, whereas the breakdown voltage is affected more by the density of the paper and the quality of the oil.