Updated experiences of DGA with natural esters and current state of international guides

Historically, transformers used mineral oil as dielectric fluid. With the new environmental trends, the use of natural esters as a dielectric fluid in transformers is increasing. Its biodegradable characteristics make it a possible substitute for mineral oil. Nevertheless, its application in power transformers is limited due to the lack of history in service. Traditional diagnostic techniques for mineral oils, such as dissolved gas analysis (DGA), must be readjusted for its application in natural esters. This work aims to present an updated review of experiences of DGA with natural esters, highlighting the main differences regarding mineral oils. In addition to the experiences reported in the specialized literature, these differences are treated by comparing and analyzing some of the current guides for the interpretation of gases generated in mineral oil and ester liquids used in transformers, such as IEEE C57.104 and IEEE C57.155 respectively.