How does transformer oil chemical composition affect performance?

Composition affects viscosity, oxidation stability, moisture behavior, gas formation tendencies, and dielectric losses. Naphthenic rich mineral oils often offer good low temperature viscosity and solvency, while paraffinic oils can have different pour point behavior. Additives such as inhibitors slow oxidation and sludge formation but must remain compatible with paper insulation and metals. Ester fluids have higher fire points and biodegradability but also different moisture saturation and aging interactions with cellulose insulation.