SCHNELL TRANSFORMER OIL – Outperforms Naphthenic Electrical Insulating Oils. SCHNELL Transformer Oil family of electrical insulating fluids represents a breakthrough in electrical insulating fluids technology. Unlike naphthenic mineral oils, Transformer Oil uses SCHNELL ultra-pure severely hydrotreated isoparaffin base fluids to help minimize power loss and maximize productivity. These fluids contain no corrosive sulphur that may lead to transformer breakdown.