What transformer oil testing methods are used to assess insulation health?

Common methods include breakdown voltage testing, Karl Fischer moisture measurement, acidity testing, dielectric dissipation factor or power factor, interfacial tension, resistivity, particle count, and inhibitor content. Dissolved gas analysis provides fault detection for electrical and thermal issues. Furan analysis indicates cellulose paper degradation. Additional tests can include corrosive sulfur screening, oxidation stability, and sludge assessment. Together these tests describe oil condition, contamination level, and insulation aging status, enabling trending based maintenance rather than time based oil replacement.