### Generalized Expression for E.M.F. Equation of an Alternator

E.M.F. Equation of an Alternator : Part4
Considering full pitch, concentrated winding.
Eph   = 4.44 f Φ Tph   Volts.
But due to short pitch, distributed winding used in practice, this will reduce by factors and . So generlised expression for e.m.f. equation can be written as

For full pitch coil, Kc = 1.
For concentrated winding K= 1.
Note : For short pitch and distributed winding Kc and Kare always less than unity.
Example 1 : An armature of a three phase alternators has 120 slots. The alternators has 8 poles. Calculate its distribution factor.
Solution :
n = Slots/Pole = 120/8  = 15
m = slots/pole/phase = n/3 = 15/3 = 5
β = 180o/n = 180o/5 = 12o

= 0.957

Example 2: In a 4 pole, 3 phase alternator, armature has 36 slots. It is using an armature winding which is short pitched by one slot. Calculate its coil span factor.
Solution :
n = Slots/pole = 36/4 = 9
β = 180o/ = 20o
Now coil is shorted by 1 slot i.e. by 20o to full pitch distance.
...     α = Angle of short pitch = 20o
...      Kc = cos (α/2)  = cos (10)