Question

A 3-phase, 4-pole alternator has 48 stator slots carrying a 3-phase distributed winding. Each coil of the winding is short chorded by one slot pitch. The winding factor is given by ______________

(a) (cos7.5)/16

(b) (cot7.5)/8

(c) 1/(8sin7.5)

(d) (cot7.5)/16

The question was asked by my school teacher while I was bunking the class.

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

Answer 1

The correct option is (b) (cot7.5)/8

Explanation: Slots per pole = 48/4 = 12 ⇒ γ=180/12=15° and q=48/4∗3=4

coil of the winding is short chorded by one slot pitch ⇒ ε=γ=15°, Kw=Kp∗Kd = cos7.5(sin(4∗15/2))/(4∗sin(15/2)) = (cot7.5)/8.