Furanic compounds in dielectric liquid samples: review and update of diagnostic interpretation and estimation of insulation ageing

Commercial laboratories and electrical equipment owners have used analysis of furanic compounds in dielectric liquids for more than ten years to evaluate the continuing operation of transformers and to estimate the degree of ageing of solid insulation. The solid insulation of transformers is comprised mainly of Kraft paper. As the paper ages, the cellulose polymer chains break down into shorter lengths with a corresponding decrease in both tensile strength and degree of polymerization. Further, the paper breakdown is accompanied by an increase in the content of various furanic compounds in the dielectric liquid. Analysis for furanic compounds allows the laboratory or the owner to make a determination as to whether the breakdown of the paper is an active condition. It further allows a determination as to the relative degree of the paper breakdown that has occurred. This paper reviews the tools that have evolved to help perform these interpretations and presents a system to aid in the assessment of transformer insulation ageing.