What types of transformer oil tests are performed during maintenance?

Maintenance programs typically include BDV, moisture ppm, acidity, tan delta or power factor, resistivity, and interfacial tension. DGA is often included for fault detection, especially for critical transformers, and furan analysis is added to assess paper insulation aging. Particle count and color can indicate contamination. Inhibitor content is checked if inhibited oil is used, and corrosive sulfur testing may be required by utility policy. For legacy assets, PCB testing is performed during decommissioning or when contamination risk exists. Results are trended to guide filtration, regeneration, or replacement.