INTRODUCTION
Mineral oils are the most widely used fluids for electrical insulation and heat transfer in equipment
such as transformers, capacitors, bushings etc. Their technical characteristics have been optimised
during the last century to fit the requirements of these application fields. Nevertheless, even if mineral
oils still represent an excellent technical vs. cost solution, their environmental performance has to be
addressed.
In the frame of the sustainable development principles, the search for “green products” as an
alternative to mineral oils has to be carried out. Because of its non fossil origin, vegetable oil could be
an appropriated response to environmental, safety and health problems, and could reduce the
exploitation and end-life costs of transformers.
Some vegetable oils meet the technical requirements of conventional dielectric liquids. Their high
biodegradability and non toxicity are other qualities making these natural oils interesting raw materials
for the development of new environmental friendly dielectric fluids.
About Vegetable Oils
Vegetable oil basically consists of triglycerids, naturally synthesized by esterification of the tri-alcohol,
called glycerol, with three fatty acids.
The fatty acids are composed of linear hydrocarbon chains ended by a carboxylic function. These
molecules have an even number of carbon atoms (typically from 8 to 22 in triglycerids) and the chain
can be saturated or mainly mono-, di- and tri-unsaturated. Stearic acid is an example of a saturated
fatty acid. Its raw formula is HOOC–(CH2)16–CH3 and it is symbolized by the expression C18:0,