What Insulating Liquids Are Used in Transformers?
Quick answer — The main insulating liquids are mineral oil (the standard, cost-effective choice), natural esters (biodegradable, high fire point, from vegetable oils), and synthetic esters (high fire point, often for transformers and flame-retardant applications). Silicone oil is used for a few fire-critical designs. Each has a different fire point, environmental profile, cost and compatibility.
Contents
What types of insulating liquid are used in a transformer?
Mineral oil
The traditional insulating oil, refined from petroleum. It is the standard for most oil-filled transformers, with good dielectric and cooling properties and sold to IEC 60296.
Esters
Natural and synthetic esters have a much higher fire point, are biodegradable and are used where fire safety and environmental risk matter (e.g. indoor, in fire-sensitive or protected areas).
Other liquids
Silicone oil is used in some high-fire-point designs. The choice depends on the fire risk, the environmental requirements, the cost and the compatibility with the insulation and the design.
References & standards
- IEC 60296 (mineral oil)
- IEC 61099 (esters)
- IEC 62770 (natural esters)
Related
Related manufacturers
Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp
Related components
Technical content is prepared from engineering references, standards frameworks, manufacturer documentation and industry sources. Contractual or compliance decisions should refer to current official standards. TransformerPath Technical Editorial.
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