Interfacial tension (IFT) is a sensitive indicator of oil oxidation and contamination by polar compounds. As oil ages, oxidation products and sludge precursors lower IFT. A low IFT often correlates with reduced dielectric reliability and increased risk of sludge deposition, which blocks cooling ducts and raises temperatures. IFT is especially useful as an early warning because it can decline before catastrophic breakdown voltage changes appear. Maintenance teams use IFT trends together with acidity, moisture, and DGA to decide whether the oil needs reclamation, inhibitor adjustment, or replacement.
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