What key properties define high quality transformer oil?

High quality transformer oil has strong dielectric strength, low moisture, low acidity, low dissipation factor, good oxidation stability, appropriate viscosity for cooling, adequate flash and fire points, and low corrosive sulfur risk. It should meet relevant specifications and show clean DGA baseline values. Practical quality is confirmed by acceptance tests such as BDV, moisture ppm, acidity, DDF, resistivity, IFT, and inhibitor content where applicable, plus cleanliness checks for particles and sludge tendency.