What is the name of the synthetic liquid often used in transformers for insulation?

The synthetic liquid commonly used in transformers for insulation is known as Askarel. This fluid is specifically formulated to provide both insulation and cooling for electrical equipment, particularly transformers. Askarel is significant because it includes polychlorinated biphenyls (PCBs), which were noted for their excellent electrical insulating properties. However, due to environmental and health concerns regarding PCBs, the use of Askarel has decreased significantly over the years.

Regarding the other liquids mentioned: silicone oil and mineral oil are also used for insulation but are not synthetic in the same way Askarel is; silicone oil has high thermal stability but is often more expensive, while mineral oil is a natural oil derived from petroleum. Vegetable oil is an alternative that is seen more frequently in modern applications due to its biodegradable and non-toxic properties, but it is not synthetic like Askarel. Therefore, Askarel is the correct choice based on its unique synthetic composition and historical usage in transformer insulation.