How does a transformer oil acidity testing kit detect oil degradation?

An acidity kit measures the neutralization number, indicating how much base is required to neutralize acidic compounds in the oil. Acidity increases as oil oxidizes and produces organic acids, which correlate with sludge risk and insulation deterioration. Field kits use titration methods with reagents and color endpoints, while laboratories provide higher accuracy using standardized procedures. Rising acidity often signals that oil has aged beyond acceptable limits and that filtration alone may not be enough, making regeneration or replacement more appropriate to restore long term stability.