Transformer oil samples are tested for dielectric breakdown voltage, moisture content, acidity or neutralization number, interfacial tension, dissipation factor, resistivity, and color. Dissolved Gas Analysis is used to detect internal electrical and thermal faults. Additional tests may include furan analysis for paper insulation aging, particle count, inhibitor content, and corrosive sulfur testing. The exact test package depends on transformer criticality and oil type. Results are trended over time to support condition based maintenance and asset life assessment.
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