Natural esters distribution transformers: A solution for environmental and fire risk prevention

The electrical transformers insulated and cooled with mineral oils remain, still today, the most widespread and effective solution for converting electrical energy. Mineral oils are used for their excellent dielectric and thermal properties, but have a low flash/fire points and biodegradability and these factors may negatively contribute in cases of fire and toxic release with contamination of soil and surface water and groundwater. For these reasons, innovative insulating fluids, such as natural esters (vegetable oils), have been suggested worldwide. Natural esters, compared to conventional mineral oils, in fact, have some advantages, such as high flash/fire points, lower toxicity, higher biodegradability and possibility of recycling. In addition, natural esters may have very positive heat exchange properties, allowing a more effective cooling of the electrical power transformers. Distribution transformers are often used as pole transformers, which, in case of failures and thefts, may release and spill in the surrounding environment their insulating liquid with possible soil contamination. Other distribution transformers are located in urban area, internally to buildings and, in this case, the flammability of their insulating liquid may create some limitation in compliance with the local fire regulations. This paper presents the first results of the experimental work performed by an Italian Working Group (WG) supported also by Experts of the Italian Firefighters Authority, the Department of Land Protection of the Ministry of Environment (ISPRA) and the Department of Safety of the National Institute for the Accidents at Work Prevention (INAIL). These results have shown as the use of natural esters in transformers may positively reduce the risk of fire and environmental accidents.