Page 762 - Basic Electrical Engineering

coils used for winding may be of full-pitch type or short-pitch type. In a full-
pitch coil, the distance between the two coil sides is 180° electrical. The coil
span of short-pitch coils is reduced by a certain angle. Windings made with

short-pitch coils is called fractional-pitch winding. By use of fractional-pitch
winding, any specific harmonic present in the generated EMF can be

eliminated so that we get a sinusoidal EMF. Fig. 10.5 shows a single-layer
distributed stator winding where the windings can be connected in the lap,

wave, or spiral form. The connections for only one phase has been shown.
The number of coils used per phase is three only. Full-pitch coils have been

used in the winding shown in Fig. 10.5 (a).
Use of short-pitch coil improves the wave shape of the induced EMF
making it more towards a sine-wave. However, the EMFs induced in the two

coil sides when added vectorially in a short-pitch coil will be less than that of
a full-pitch coil.

Figure 10.5 (a) Single layer stator winding; (b) lap-type winding; (c) wave-type winding; (d) spiral-
type winding