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

E.M.F. Equation of an Alternator : Part4 
       Considering full pitch, concentrated winding.

                   E_ph   = 4.44 f Φ T_ph   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, K_c = 1.

       For concentrated winding K_d  = 1.

Note : For short pitch and distributed winding K_c and K_d  are 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 = 180^o/n = 180^o/5 = 12^o

               = 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 = 180^o/ = 20^o

       Now coil is shorted by 1 slot i.e. by 20^o to full pitch distance.

.^..     α = Angle of short pitch = 20^o

.^..      K_c = cos (α/2)  = cos (10)

              = 0.9848