How do transformer oil testing labs evaluate insulation health?

Transformer oil testing laboratories evaluate insulation health by analyzing physical, chemical, and electrical properties of the oil. Key tests include dielectric breakdown voltage to assess insulation strength, moisture content to evaluate paper aging risk, acidity to detect oil oxidation, and interfacial tension to identify sludge formation. Dissolved Gas Analysis is used to detect thermal, electrical, and partial discharge faults. Furan analysis provides insight into cellulose insulation degradation. Trending results over time allows labs to determine aging rate, fault severity, and remaining transformer life.