Cast foil wound distribution transformers

Through most of its eighty year history, the basic structure of the transformer has not been fundamentally altered. The coils have been wound using round or semi-round copper wire, insulated turn to turn with enamel or paper. The insulation between layers and between separate coils has been paper or a similar material such as pressboard. This entire structure is then vacuum impregnated with mineral oil to develop the necessary insulation strength.