Corrosive sulfur phenomena mitigation by using natural ester dielectric fluids - field experience in Latin America

Beginning in the 1990s, failures of large power transformers and reactors have occurred which are attributed to the presence of corrosive sulphur in mineral oil. In Brazil, one regional G&T utility reported multiple large power transformer failures. Intensive investigations of the failure phenomena, associated detection, and remedies have been pursued by many experts on an international scale. This paper address the used of natural esters as a means to eliminate the introduction of corrosive sulphur components that may be present in petroleum based mineral oil dielectric coolants. This paper provides a summary of our comparative test data, including samples representing retro-filled power transformers. It also discusses the field performance history of natural ester filled 230 kV power transformers that have been put into service, including installations replacing mineral oil filled transformers that were reported to have failed due to corrosive sulfur.