Long-Term Behavior of Natural Ester Filled Power Transformers in Eletronorte Transmission System

Back in 2006 Eletronorte developed a specification for power transformers filled with natural ester liquids and started purchasing units. Most relevant motivations were the mitigation of the risks of fires and for the environment, as many substations are in remote and environmentally sensitive locations. Starting with small units on the 69kV voltage class, the good results motivated the use up to 245kV units. More than a decade later, a review of the transformer assessment parameters of over 20 units confirms natural ester as a proven technology, offering improved reliability and resilience to the grid.