**Short Pitched Coils (Chorded)**

Short Pitched Coils – So far it was assumed that the stator coils are full-pitched (a span of iv rad elect). Coils may have a span of less than the full-pitch. This arrangement offers certain advantages. Consider that the coil-span is less than the full-pitch by an elect. angle O_{sp} (short-pitching angle) as shown in Fig. 5.20(a). With reference to Fig. 5.15, Eq. (5.5) for the flux linking the coil now modifies as under:

The flux linking the coil and therefore the coil emf reduces by a multiplicative factor of

The meaning of the pitch factor can be arrived at from another angle. In Fig. 5.20(a) with positive direction of coil-side emfs marked in opposite direction, the coil emf is the phasor sum of coil-side emfs, i.e.

In the case of a full-pitch coil *E*_{a}*, ***and ***Ea *are in phase (they are *,r *rad apart but their positive directions are marked oppositely) so that

as shown in Fig. 5.20(b).

In a coil short-pitched by *O _{sp}, *

*K*

_{a}*,*will lead (or lag)

*K*

_{a}**by the angle O**

_{sp}as shown**in**Fig. 5.20(c). From the geometry of the phasor diagram

Hence the reduction of the coil emf due to short-pitching is governed **by **the factor

Because of short-pitching the expression of Eq. (5.15) for the phase voltage modifies to

Thus short-pitching helps in elimination of any particular harmonic or in reduction of the harmonic content of the induced voltage in general. It is easily seen from Fig. 5.20 that short-pitched coils have shorter end connections. Thus there is a saving in copper per coil but part of this saving is wiped off by the fact that more series coils/ phase would now be needed to generate a specified phase voltage. A designer has to weigh these factors in arriving at a decision on the angle of short-pitching.