Survey on Structure-Property Relationship of Vegetable Esters

In the current scenario, mineral oil is mostly used in correlation with Kraft paper (insulation paper) as the dielectric medium in most of the transformers. The raising concerns on environment, lack of petroleum reserves and disposal problems with used mineral oils has motivated researchers to focus on biodegradable and renewable insulating fluids. The search for new insulating fluids is guided by factors such as environmental requirements and other safety and economic considerations. Vegetableoil based transformer fluids meet most of the above criteria. Hence, a lot of research has been taken up in the field of Bio-based dielectric fluids over past few decades. Their performance as dielectric fluid is on par with mineral oils to a greater extent. However, they fail to meet some of the requirements. This paper reviews the properties of water content, kinematic viscosity, pour point, ageing and oxidation stability that have to be enhanced, and furnishes their correlation with the chemical structure of the oils based on unsaturation, side chains and carbon count. Finally, the structural modifications that can be carried out for upgrading its properties are discussed, providing an insight to performance enhancing additives.