Why is acidity of transformer oil monitored?

Acidity measures the concentration of acidic oxidation byproducts formed as oil ages. Rising acidity indicates oxidation and degradation that can accelerate sludge formation, reduce interfacial tension, increase dielectric losses, and attack solid insulation. Higher acidity can also correlate with increased corrosion risk and reduced cooling performance due to deposits on heat transfer surfaces. Monitoring acidity helps determine when oil needs inhibitor replenishment, regeneration, or replacement. Trending acidity alongside interfacial tension and tan delta provides a strong picture of oil aging severity.