Studies on the partitioning of Furfural between liquid and paper insulation

Ageing status of transformer paper insulation is commonly assessed through measured 2-furfural in oil. Laboratory studies have shown an exponential increase in 2-furfural in oil with the reduction in the Degree of Polymerisation (DP) of paper insulation. While there have been various models proposed to estimate the DP of paper insulation through 2-furfural in liquid, their applicability has been a challenging task due to the complex partitioning process between oil and paper for in-service power transformers. This paper investigates the applicability of Van’t Hoff plots for temperature correction of measured 2-furfural in oil for oil-paper insulation systems through literature data and laboratory studies. Laboratory study was conducted with mineral oil and two types of paper: non-thermally upgraded Kraft paper and thermally upgraded Kraft paper. Furthermore, effects of temperature and water content on the partitioning process were evaluated. Results from both literature and experiments indicated that Van’t Hoff plots could be used for identifying temperature correction factors for 2- furfural measurements.