Correct Answer - Option 1 : 1/5 × full-pitch
Pitch Factor or Coil Span Factor or Chording factor (Kp):
- It is defined as the ratio of emf generated in short pitch coil to the emf generated in full pitch coil.
- 1 full pitch = 180°
- It is denoted by Kp and its value is always less than unity.
- It can also be defined as the ratio of the vector sum of induced emf per coil to the arithmetic sum of induced emf per coil.
If α be the angle in electrical degrees, by which the span of the coil is less than a pole pitch in the alternator, then mathematically pitch factor is defined as
KP = resultant emf of short pitch coil/ resultant emf of full pitch coil = cos α/2
For nth harmonic
Kpn = cos nα/2
Where n is the nth harmonic
Calculation:
For eliminating 5th harmonic voltage
⇒ Kp5 = 0
cos (5α /2) = 0
⇒ 5α / 2 = 90°
⇒ α = 180°/5
∴ Short pitch angle α = 1/5 × full pitch
Distribution factor or belt factor or breadth factor or spread factor (Kd)
- It is a measure of the resultant emf of a distributed winding compared to a concentrated winding.
- Kd = emf induced in distributed winding/emf induced if the winding is concentrated
The mathematical expression of the distribution factor is given as,
\({k_d} = \frac{{\sin \frac{{m\beta }}{2}}}{{m\sin \frac{\beta }{2}\;}}\)
Where m is the number of slots per pole per phase
β is the slot angle in degrees
