Question

In 48 slot, 4-pole,3 phase alternator, the coil-span is 10. Its distribution and pitch factors are respectively ____________

(a) 0.9717,0.966

(b) 0.9822, 0.9814

(c) 0.9577, 0.9814

(d) 0.9577, 0.966

The question was posed to me in an online quiz.

My question is from EMF Polygon topic in chapter Synchronous Machines of Electrical Machines

Answer 1

Correct option is (d) 0.9577, 0.966

For explanation I would say: Slots per pole = 48/4=12, for a coil span of 10 slots, the coil is short pitched by 2 slots and the chording angle is ε=2γ and γ=180/12 ⇒ ε = 30° ⇒ Kp=cosε/2=0.9659.

We know, Kd=(sin(qγ/2))/qsin(γ/2), here q=48/4∗3 = 4 ⇒ Kd=0.957662.