Page 760 - Basic Electrical Engineering

Figure 10.4 (a) Two-pole stator winding; (b) four-pole stator winding

The direction of current flowing through the coils and the flux produced
have been shown. It is observed that when the coil span is 180° mechanical,

as in Fig. 10.4 (a), two poles are formed. In Fig. 10.4 (b), the coil span has
been reduced to 90° mechanical. Two coils have been used to complete the

winding distributed throughout the stator. The directions of the flux produced
show that four poles are formed in the stator. This shows how by using coils
of different spans, a winding can be made for a different number of poles.

The students are advised to draw a simple six-pole stator winding by using
three coils connected together. The coil span here should be 60° mechanical.

The distance between the two coil sides of a coil is always expressed as
180° electrical irrespective of the number of poles for which the winding is

made. For a two-pole winding, the coil span is 180° electrical which is also
equal to 180° mechanical. For a four-pole winding, the coil span is again