Influence on Formation of Methanol and Ethanol in Oil-Filled Transformers Under Accelerated Thermal Aging

This contribution investigates the suitability of short-chain alcohols for estimating the condition of a cellulose insulation in power transformers. To model an accelerated thermal aging of a transformer, strips of insulation paper impregnated with different insulation liquids were kept in a glass vessel, filled with the dielectric liquid and catalyzer inclusions, in a heating chamber. After oil sampling at predefined intervals, the concentrations of furanic compounds, the degree of polymerization (DP) value and the concentrations of methanol and ethanol in the insulation liquid were measured. Three different types of insulation liquids were utilized, such as the well-known uninhibited and inhibited mineral oil as well as a new inhibited insulation liquid with different oil components, inhibitor content and manufacturing process. These insulation liquids were investigated to obtain their various aging behavior regarding the generation of 2FAL and short-chain alcohols by thermal accelerated stress.