Development of a low viscosity insulating liquid based on natural esters for distribution transformers

Environmental considerations demand alternatives for the current mineral oils used in many electrical equipment, such as transformers. Because of their excellent biodegradability and non-toxicity, relative to petroleum derived products, the use of the vegetable oils is on the rise as insulating and heat transfer liquid in electrical devices. In addition such natural esters have a favourable lower flammability, but their viscosity and low temperature behaviour is not well suited to applications in cold climate and/or with natural cooling system. That is why a new insulating composition, based on modified vegetable oil, has been developed to present very similar properties to those of the standard insulating mineral oils and to meet the specific needs of current distribution transformers. This article presents the formulation of this low-viscosity ester fluid, and it reports the results of the tests carried out to assess its performance in laboratory and real conditions.