Furals in Oil

Furaldehydes (Furals) are chemicals formed when cellulose-based insulating paper degrades due to overheating. The condition of the solid insulation can be assessed by testing for the presence of furaldehydes dissolved in the insulating oil.

Degrees of Polymerization (DP) is another test performed on the insulating paper to reveal its mechanical strength. An inverse relationship exists between the DP (paper test) and the Furals (oil test); the higher the Furals in the oil, the lower the DP of the cellulose paper. This relationship holds, however, only if the paper is degrading evenly. The DP of the paper usually varies within the solid insulation.

Since it is difficult to sample paper from an operating transformer, Fural Analysis in the insulating oil can indirectly reveal the status of the solid insulation.


We require at least 10 mL of insulating oil, which should be collected and transported in an amber bottle, as Furals are light sensitive. Our laboratory can also analyze a portion of oil sample collected in a glass syringe for DGA. Sample the oil before reclaiming it, since Furals will be absorbed.


High Pressure Liquid Chromatography (HPLC) is used to measure all the relevant furaldehydes (2-Furaldehyde, 5-Hydroxy-Methyl Furaldehyde, 2-Furyl Alcohol, 2-Acetyl Furan, 5 Methyl-2-Furaldehyde) along with any associated phenolics (phenol, m-Cresol, O-Cresol, 2,3-Dimethylphenol, and 2,3,5-Trimethylphenol).