Effect of Organic Acids and Thermal Ageing in Oil-Impregnated Kraft paper used in Power Transformers

The insulation system in a power transformer is basically comprised of oil and oil-impregnated paper. The lifetime of power transformer is very much dependent on the insulation health. Due to several years of continuous service related stress, the oil-paper insulation degrades. This degradation manifests itself through the generation of moisture and many by-products. One important by product is the formation of organic acids. Presence of acids further accelerates the ageing process of the oil paper insulation. Therefore, understanding the ageing of oil-paper insulation in presence of acidic components in transformer oil becomes very important from asset management point of view. This paper discusses the combined effect of acidified transformer oil and thermal ageing on different important properties of Kraft paper. The properties under investigation are polarization current, dissipation factor and mechanical strength oil impregnated kraft paper. The kraft paper samples were aged for a total 30 days, and the variation of abovementioned properties were studied throughout that period.