How does a furan test transformer oil assess paper degradation?

A furan test measures furanic compounds in oil that are byproducts of cellulose insulation breakdown. Because transformer paper aging produces characteristic furans that migrate into the oil, furan concentration trends can be used as an indirect indicator of paper condition and remaining life. The test is especially valuable when combined with loading history, moisture, and DGA, because paper aging accelerates with heat and water content. Operators typically interpret furans using trend analysis and asset specific context, since absolute values depend on oil volume, oil changes, and whether the transformer has been filtered or regenerated.