The winding is the circuit part of the transformer, which is wound with a paper-wrapped insulated flat wire or round wire.

The conductor element of the transformer bobina is made of copper wire with rectangular section and high conductivity, and the outer part is wrapped with two layers of kraft paper for insulation purpose. For insulating pads of the same material, the number of copper wires depends on the working voltage, so that the bobina elements have sufficient insulating strength between layers. Using glue on the outermost layer of insulating paper, each wrapping layer is glued together to form a tight coil. To reduce eddy current losses, line crossings are made at predetermined positions of the conductor elements. The coil of the shell-type transformer is fixed vertically. In order to prevent misalignment, a wooden wedge is inserted between the coil and the iron core. All ends of the coil are fixed by the wire core and the oil tank. The external force is distributed in a large area, which greatly improves the mechanical strength. .