In the core type transformer, the magnetic circuit consists of two vertical legs or limbs with two horizontal sections, called yokes. To minimize the leakage flux, half of each winding is placed on each leg of the core. The low voltage winding is placed next to the core, and the high voltage winding is placed around the low voltage winding to reduce the insulating material required. Thus, the two winding are arranged as concentric coils.

And these cylindrical coils are wound in a helical layer with different layers insulated from each other by paper, cloth, micarta board, or cooling ducts. For reducing leakage flux, and H.V & L.V winding are placed one after another separating with high insulation cylinder on fuller board which is shown in fig.