The bottom coil-sides are shown with dashed lines, because they are hidden behind the top coil-sides when we look outwards from the axis. The coils are all identical, and they are laid up so that one coil-side is in the bottom of a slot, and the other at the top near the slot-opening. This is what is known as a double-layer winding, one of the most common types. Each coil has two coil- sides, so there must be two coil-sides in each slot. The developed diagram shows only a few slots, but we can see that altogether there are 36 coils. If we rotate our view through 360° we will see all 36 slots. We have to imagine that we are inside the stator, somewhere near the centre-line or axis, and looking radially outwards towards the slotted inside surface.

The term “developed” is borrowed from the geometry of cylinders, and it means that our view of the inside of the stator bore is rolled out on to a plane. The starting-point is the developed winding diagram at bottom left. In most respects it is a regular classical example, and the objective here is to review some of the features of the diagram and its conventions, rather than the winding itself or any particular machine.

This winding could in fact be used with any AC machine, including a synchronous reluctance motor or a wound-field synchronous motor or generator. Here we see a winding diagram for a 3-phase AC induction motor or brushless PM motor (IPM), having 4 poles and 36 slots.

Ac motor winding theory