A. Transformer Oil serves mainly two purposes 1. It acts as liquid insulation in electrical power transformer 2. It dissipates heat of the transformer i.e acts as coolant. In addition to these, this it serves other two other purposes, it helps to preserve the core and winding as these are fully immersed inside oil and also prevents direct contact of atmospheric oxygen with cellulose made paper insulation of windings, which is susceptible to oxidation. During 1970s, polychlorinated biphenyls (PCB)s were often used as a dielectric fluid since they are not flammable. But, They are toxic, and under incomplete combustion, can form highly toxic products such as furan. Presently, non-toxic, stable silicon-based or fluoridated hydrocarbons are used. Combustion-resistant vegetable oil-based dielectric coolants and synthetic pentaerythritol tetra fatty acid (C7, C8) esters are also becoming increasingly common as alternatives to naphthenic mineral oil.