Why is the interfacial tension test of transformer oil important?

Interfacial tension reflects the presence of polar contaminants and oxidation byproducts in oil. As oil ages and forms acids and sludge precursors, interfacial tension decreases. Low values indicate degraded oil that may deposit sludge, reduce cooling efficiency, and increase dielectric losses. Interfacial tension is therefore a useful indicator of oil cleanliness and aging, especially when combined with acidity, dielectric dissipation factor, and color observations. Trending interfacial tension helps decide when oil regeneration, inhibitor management, or replacement is needed to protect paper insulation and maintain reliability.