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Abstract

Provided is an electrical insulating oil composition containing, as base oils, (A) one or more selected from hydrorefined mineral oils and synthetic hydrocarbon oils, and (B) a naphthenic solvent-refined mineral oil that has a ratio of carbon atoms in the naphthene content (% C_N) of 50% or more and 70% or less in ring analysis according to an n-d-M method, an acid value of 0.03 mg KOH/g or less and a sulfur content of 0.1% by mass or less. The electrical insulating oil composition contains the component (B) in an amount of 50% by mass or more and 70% by mass or less based on the total amount of the base oils, and has a flash point of 135° C. or higher as measured according to a closed cup flash point test method, a pour point of −40° C. or lower, and a density of 0.895 g/cm³ or less. The oil composition is more excellent in point of both electrical insulation characteristics and oxidation stability than before.

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First Claim