Furans in transformers: calculating the Apparent Age of cellulose insulation

FURANS and the Diagnostic Value to transformer owners and operators:


This Blog is for the discussion of how engineers use furan results:

I’ll start off by providing a short discussion the two methods of using Furan Analysis in dielectric fluids (mainly transformer mineral oil) to evaluate how transformer operational conditions affect the degradation rate of cellulose insulation (Kraft and Thermally Upgraded Kraft "TKU" paper).

Transformer oil labs, in addition to providing the concentration level in parts per billion (ppb) of the five (5) types of furans, generally provide a calculated degree of polymerization (DP) of the cellulose. All labs but one use the Chendong equations (based on the type of Kraft paper) to calculate this value. Many labs also provide either the "Apparent Age of the Paper" based on the Chendong equation or they may provide “Remaining Life” based on the calculated DP compared to the range of acceptable in-service DP (1000 to 250) of cellulose.

New TUK paper has a DP of 1000 or greater while a DP of 250 is considered as "end of life" indicating the paper has no mechanical strength remaining. Paper with a DP of less than 250 is brittle and easily breaks up under handling or with transformer vibrations. The paper is incapable of withstanding any electrical surge to the transformer and thus is at high risk of failure.

Those using the "End of Life" also reported as "Remaining Life" of the transformer give a number such as:

"100% or 30% of life (of the paper and thus the transformer) remains.

Lab's such as the now closed GE "Denver LIL" (Liquid Insulation Laboratory) used the "Apparent Age of Paper" and then compared this result to the "Actual On-line Chronological Age" of the transformer. The lab then provide a detailed conditon assessment or operational discussion based on three main classes:  a) Apparent age is less than...thus paper has low rate of degradation.   b) Apparent Age = +- 5% of Chronological Age thus paper is aging at the normal or standard rate.    c) Apparent Age is higher than Chronological Age thus indicating "several types" of damaging conditions which will reduce the life expectancy of the transformer.

The questions I pose to transformer and utility engineers or others involved in the maintenance and servicing of fluid filled electrical transformers is:


1) Are you aware that there are two diagnostic methods (Age of Paper or Remaining Life) used in evaluating the past operational effects on the condition of the paper and what future operational loading or "external faults" will have on the life of the transformer?


2) If you answered YES above, which diagnostic comment (Remaining Life or Apparent Age) do you prefer?


3) Please explain the reason for your preference.


4) Provide you questions or comments for further discussions.

Thank you for participating.

Mel Wright, Consultant
LICA Consulting LLC’ "Transforming Data into Solutions"