DGA of natural ester filled transformers: Experience with retrofilled and new transformers

The use of Esters as a liquid insulation in transformers as a better alternative in place of mineral oil has been prevalent in Europe for quite some time. Its use in India is increasing and now on a noticeable scale. New natural ester liquid filled transformers and transformers retro filled with this ester liquid have been in service for more than two years and an analysis using various tests on these transformers will help gain better insights on the performance of these ester liquid filled transformers. This paper will highlight the electrical and chemical test results from these natural ester filled transformers, both in retro filled distribution transformers and new power transformers.