In the iron core, the part of the winding is called “core column” , and the part of the magnetic circuit that does not have the winding is called “Iron Yoke” .

Where iron core around the winding is called Shell Type; where the winding around the core column is called core type. Shell-type and core-type have their own characteristics, but the manufacture technology of transformer is different because the iron core is enough. Once a certain structure is chosen, it is difficult to produce a structure. In China, most transformer cores are stacked cores.