Why is ester oil used in transformer insulation and cooling systems?

Ester oil is used for a combination of fire safety, environmental compliance, and insulation life support. Its high fire point reduces fire risk, and biodegradability reduces remediation impact after leaks. Ester fluids can also support insulation aging management by improving moisture distribution between oil and paper. Utilities select ester oils when siting constraints require safer fluids, such as near buildings, waterways, or critical infrastructure. Engineering validation is needed for viscosity, temperature rise, compatibility, and dielectric performance under the transformer’s voltage and cooling class.