Methanol as an Ageing Marker for In Service Transformers

Measurement of transformer remaining useful life has long been a goal for responsible asset management. Most testing laboratories offer furan concentration testing as a suitable method. The interpretive method of choice is usually the Chendong equation, expressed in practical terms as degree of polymerization of the paper with new paper at about 1000 and end of life at around 300. Typical mill transformers have thermal insulation ratings expressed as 55 °C rise for plain kraft or 65 °C, which corresponds to thermally upgraded kraft paper (TUP). It has been determined that TUP does not produce furans and, thus, provides a false indicator of the cellulose breakdown. There are several recent papers that have demonstrated that a measurement of methanol (MeOH) may be a better method to determine ageing of the TUP insulation and also better for transformers with plain kraft paper insulation. The objective of this paper is to provide an overview of the reasons why furans should not be used as the basis for measuring aging of thermally upgraded paper, why MeOH should be so used, and to compare actual furans and MeOH test data for service aged transformers in a process industry application