Naphthenic mineral oil is often chosen for good low temperature flow and naturally lower pour point, which helps circulation in cold climates. It can show favorable viscosity at operating temperature, supporting heat removal. Many formulations also provide good dielectric properties when properly refined and inhibited. The tradeoff is that oxidation stability still depends heavily on refining quality and additives, so utilities rely on specification compliance and routine testing. In practice, the advantage is thermal performance and cold weather behavior without changing transformer design or materials.
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