Two layer Winding of Transformer:

One important and commonly used way of neatly arranging the end connection of coils in a winding is to place two coil-sides per slot. Each coil then has one coil-side in the bottom half of one slot and the other coil-side in the top half of another slot (one pole pitch away for full-pitched coils). Such a winding is known as a Two layer Winding of Transformer.

All the coils of a Two layer Winding of Transformer are of similar shape so that these can be wound separately and then placed in the slots. The end connections at each end of such a coil are given an involute kink so that the coil-sides can be conveniently placed in the bottom of one slot and top of the other. A formed two-layer, mutli-turn coil is shown in Fig. 5.21.

The winding connections of a two-layer winding are best illustrated by means of a developed winding diagram which imagines that the stator has been cut and laid out flat. One phase of a 4-pole, two-layer lap winding is shown in Fig. 5.22.

The upper layer is indicated by a thick line and the lower layer by a dotted line and both are drawn side-by-side in the diagram. This figure illustrates the simplest case of 4-poles with 1 slot/pole/phase. The four coils could be series connected or various series-parallel connections could be employed.

In Fig. 5.22 the four coils of one phase are connected in parallel in two series groups of two coils each. Obviously the phase current i_a and the conductor current i_c are related as i_c = i_a/2.