Transformer oils are specified in several categories, including uninhibited mineral oil, inhibited mineral oil with antioxidants, natural ester fluids, synthetic ester fluids, and silicone based insulating fluids. Each type is governed by its own standard and application profile. Mineral oils are widely used for general power applications, esters are chosen for higher fire safety and environmental performance, and silicone oils are used where very high fire resistance is required. Specifications define electrical, thermal, chemical, and safety properties.
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