What is Furan Testing?
Paper insulation is an important part of an oil filled transformer. Mechanical properties of the insulation paper can be evaluated by its tensile strength or degree of polymerization. This is then used to evaluate the end of reliable life of the paper insulation. Since it is not practical to obtain a paper sample from a de-energized, in-service unit, other methods have been developed and employed. Dissolved Gas Analysis can be the first step in diagnosis but a need for a more detailed analysis was needed.
The main component of insulation paper is cellulose which is a natural polymer of glucose. The fibers consist of a bundle of molecules of different lengths that are side by side which held together by hydroxyl groups on adjacent molecules.
The paper begins to break down under certain conditions which are elevated temperatures, oxygen, acids, and moisture within the transformer.
This depolymerization results in glucose and degraded forms of glucose. The compounds further degrade into products such as Furans. These compounds are stable in the transformer fluids and can be extracted and analyzed.
5-hydroxymethyl-2-furfural (5HMF)
2-furfural (2FAL)
2-furfuryl alcohol (2FOL)
2-acetyle furan (2ACF)
5-methyl-2-furfural (5MEF)
Each compound can be indicative of various conditions of degradation from oxidation, high, moisture, overheating, arcing or lightning, to local severe overheating.
The 2FAL concentration can be correlated to provide an estimated Degree of Polymerization (DP) and be used as a guideline to life remaining in the paper insulation.
DP > 800 Paper is in good condition.
400 < DP < 800 Paper is in a mid-life condition.
DP < Paper is in the last part of life.
DP < 250 Paper is in very poor condition.
DP < 150 Paper is near end of life.
