Update to preliminary study for use of vegetable esters in big power transformers

As the biggest European TSO the Terna's experience in managing the power transformer filled with mineral oil lasts many decades, but it is further acknowledged that operational and maintenance traditions rather the peremptory needs are sometimes the reasons for the preference accorded to mineral oils. But in recent times the new strategy, which is oriented to find the right balance between the country's energy needs and environmental respect and conservation, has addressed the research in direction of alternative from crude oil derivative. Vegetable esters are for many reasons the more promising and attractive substitute of mineral oil. Worldwide experience with low and medium class of power transformers is almost large, up to some thousands, but is extremely limited for big power transformers [1]. After a first [2] set of investigation on conventional chemical and physical parameters (like density, viscosity, DDF, BDV, oxidation stability and so on) a second stage with more specific test unconventional and long term chemical tests [3] for fluids characterization and comparison will be presented and discussed. The present study has demonstrated that despite of some drawbacks (oxidation stability, pour-point and viscosity) many other advantages (water saturation, paper endurance, flash point and biodegradability) make the natural esters as a real alternative to mineral oil. Anyway for prudential purpose big power transformers filled with vegetable esters need some reconsideration and precautions.