Abstract
The degradation of transformer oil-paper insulation is one of the major concerns for utilities and transformer owners. Temperature and moisture are amongst the key variables to be considered while determining the load profiles that can be safely applied to transformers. In this paper, important parameters used to monitor the degradation of the oil-paper insulation are introduced in the existing thermal and moisture models reported in the literature. The standard IEC 60076-7 loading guide model is improved by including the viscosity of the liquids with a controlled aging history to estimate the behavior under hot-spot conditions. Similarly, moisture model is improved by including the acidity of oils and degree of polymerization of the paper. This allows a better representation of the relative moisture saturation of the liquids and the bubble inception temperature. In this work, potential models are reported to understand the moisture dynamics of cellulose paper and predict the bubbling inception temperature under specific loading profiles. The simulation analysis is also spanned to different aging conditions of mineral oil and cellulose based oil-paper insulation. The developed models may be helpful to monitor the moisture in paper and predict the bubbling temperature while taking into consideration temperature variations along with the degradation of the insulation system inside the unit.