For better understanding of
advantages and disadvantages of Short-pitched winding, we shall first
understand the meaning of short-pitched coil and full-pitched coil. It will
take some 10 minutes of your precious time to go through the write-up but it
will really help you.

**Full Pitch Coil:**

A full pitched coil is
defined as the coil whose two coil sides are 180 electrical degree apart. As
the Pole Pitch, which is defined as the space electrical angle between two
consecutive poles is 180 degree, therefore in an alternate manner we can also
say that a Full Pitch Coil has its two coil sides one pole pitch apart. This
can be seen in the figure below.

**Short Pitch / Chorded Coil:**

If it happens that the two
coil sides are not lying under the pole, then obviously the space electrical
angle between the coil sides will not be 180 degree rather it will be less than
180 degree as shown in figure below.

Thus we can define a

*Short Pitch Coil as the coil having the coil span (Coil Span is defined as the space angle between the two coil sides of a coil) less than 180 degree. A short pitched coil is also known as Chorded Coil.*

Chording Angle ξ is defined
as the angle by which the coil span departs from a pole pitch i.e. 180 degree.

Thus, Chording Angle ξ = 180°
- Coil Span

If Chording Angle ξ is zero
then it is a full pitch coil.

So we are now familiar with
the Full Pitched Coil and Short Pitched Coil.

*But is it sufficient to judge the advantage and disadvantage of Short Pitched Coil?*

**But if we can see the effect of the above two types of winding on Generated EMF then we could have some idea. So we will just see the effect of short pitching on the generated EMF.**

*No, this much information is not enough to have an idea of advantage and disadvantage of short pitch coil.*
The rms value of EMF
Generated in a Full Pitched Winding of N turns

**E = 1.141**

**πfNØ**

Whereas the rms value of EMF
Generated in a Short Pitched Winding of N turns

**E = 1.141**

**πfNØCos(ξ/2)**

Here the term

**Cos(ξ/2)**is called Pitch Factor.**K**

_{p}= Pitch Factor =**Cos(ξ/2)**

Thus it can be seen that a
Short Pitched Coil reduces the output voltage by a factor Kp i.e. Cos(ξ/2).

*Thus is the disadvantage of Short Pitch Coil.***Advantages of Short Pitch Coil:**

- Short Pitching reduces the amount of copper needed for End Connection when compared with Full Pitched Coil as can be observed from the figure above.

- They improve the waveform of
generated EMF i.e. generated EMF can be made to approximate to a sine wave more
easily and the distorting harmonics can
be reduced or totally eliminated.
**How?**

^{rd}harmonic from the Generated EMF. So what we do is that we will select Chording Angle ξ in such a manner that Cos(nξ/2) becomes zero i.e. Pitch Factor becomes zero for 3

^{rd}harmonics only.

**Mind here that Pitch Factor for nth harmonic is Cos(nξ/2).**

**Therefore, Cos(nξ/2) = 0**

For eliminating 3

^{rd}harmonic from Generated EMF,

Cos(3ξ/2) = 0

3ξ/2 = π/2

ξ = π/3 = 60°

- Due to the elimination of high frequency harmonics, eddy current and hysteresis losses are reduced, thereby increasing the efficiency.

**Disadvantages of Short Pitch Coil:**

- The disadvantages of using short-pitch winding is that, the total voltage around the coils is somewhat reduced. In order to compensate for this reduction in Generated EMF, more number of turns and therefore more copper is required.

Thank you!

## 1 comment:

Very nice explanation.

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