Last week, we talked about the basic mechanism of how furanic compounds form in transformers as the solid insulation breaks down. Next we are going to look at the furanic compounds we test for. Interpreting the results can tell us whether the paper has broken down and, maybe even more importantly, whether it still is. We test for five different furanic compounds. Increases in the concentrations of these compounds indicate that the paper is breaking down. Further, the particular furanic compound(s) present provide some useful information on what conditions caused the paper to break down, and may even indicate whether those conditions are still present.
We test for five different furanic compounds. We have cross referenced the incidence of finding those compounds with particular conditions that we see in transformers, and we have been able to identify that certain types of destructive conditions are frequently associated with specific furan compounds. The following table is a summary:
Table of Furanic Compounds
Conditions Associated with Formation
| Furanic Compuond |
Abbreviation |
Associated with paper breakdown
in the presence of: |
2-furaldehyde |
2FAL |
General or low level overheating |
2-furfuryl alcohol |
2FOL |
High moisture content |
5-hydroxymethyl-2-furaldehyde |
5H2F |
High oxygen content |
2-acetyl furan |
2ACF |
Rare, may be associated with abnormal electrical stress |
5-methyl-2-furaldehyde |
5M2F |
Hot spot overheating |
Four of these furanic compounds, all of them except for 2FAL, are not completely stable in an operating transformer. After they are formed, they start to break down. Further, they break down to form more 2-furaldehyde. In a normally operating transformer, it takes three or four months for all of furans to break down to 2FAL. So, if we run a furans test, and we find any of the furanic compounds other than 2FAL, we know that the condition causing the paper to break down continues to be active. Or, at the very least, it was active within the past three or four months.
If 2FAL is the only furanic compound present, you cannot really tell whether the condition is active or not. Mild or general overheating will form 2FAL. You will need to do a retest in a few weeks or months to determine whether the condition is active.
Next week, we will talk about when we run furans and what we might do with the information we get back from the test.
