Shell type transformers:

In this type of transformer the iron core surrounds the copper windings (fig. given below). The core is in the form of numeral 8. The entire flux passes by the central part of the iron core, but outside this central core it separates into two parts half going in every direction. Sandwich type winding is used in which the sections of the primary winding are sandwiched in among the sections of the secondary winding. In this manner the leakage flux is decreased to very small value. To minimize the amount of high voltage insulation low voltage coils are placed adjacent to the iron core