What insights does transformer oil analysis provide about insulation aging?

Oil analysis reveals how both oil and paper insulation are aging. Rising acidity and falling interfacial tension indicate oxidation and sludge risk. Moisture levels show insulation wetness and reduced dielectric strength. Dissolved gas patterns reveal overheating, partial discharge, or arcing. Furan compounds correlate with cellulose paper degradation and loss of mechanical strength. Trending these indicators helps estimate remaining life, plan maintenance, and reduce failure probability by catching problems early rather than after an outage or catastrophic fault.