Furaldehydes (Furals) are chemicals formed when cellulose paper degrades due to overheating. The status of solid insulation can be measured using liquid oil insulation.

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

There are two ways to do Fural Analysis (Furaldehyde analyze):

Screening Test (low cost, colour test)

HPLC Test (complete analysis of furaldehydes and phenols)

Screening Test

This test will measure only 2-furaldehyde which is also the most prominent of the furaldehydes.

HPLC Test

High Pressure Liquid Chromatography test will measure all the furaldehydes (2-Furaldehyde, 5-Hydroxy-Methyl Furaldehyde, 2-Furyl Alcohol, 2-Acetyl Furan, 5 Methyl-2-Furaldehyde and Phenols, m-Cresol, O-Cresol and Dimethyl Phenols).