Modernization of Transformer Insulation with Ester Oil by Replacing Mineral Oil

Transformers require high-quality insulating oil to operate safely and reliably over long periods. Traditionally, mineral oil has been used, but it deteriorates with time, is highly flammable, and poses environmental risks. To address these limitations, this study experimentally compares natural ester oil derived from plant sources with conventional mineral oil under controlled laboratory conditions. Tests such as breakdown voltage, viscosity, and flash/fire points were conducted using standard IEC and IS procedures. The results indicate that ester oil exhibits approximately 5-10% higher dielectric strength and more than double the fire safety margin compared to mineral oil, confirming its suitability for modern green transformer applications. Based on these findings, natural ester oil can effectively replace mineral oil in high-voltage transformers, offering improved safety, slower aging, and enhanced environmental sustainability. The study contributes practically by performing laboratory-based comparative testing under Indian grid conditions, validating that natural ester oil offers superior dielectric and fire-safety characteristics without requiring major transformer design changes.