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A 3 phase, 8 pole, 50 Hz star connected alternator has 72 coils in 72 slots. The coils are short pitched by 3 slots. The value of the pitch factor is
1. \(\frac{\sqrt{2}}{3}\)
2. \(\frac{1}{2}\)
3. \(\frac{\sqrt{3}}{2}\)
4. 1

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Correct Answer - Option 3 : \(\frac{\sqrt{3}}{2}\)

Concept:

Pitch factor:

Pitch factor is defined as the ratio of the induced emf per coil when the winding is short-pitched to the induced emf per coil when the winding is full pitched.

It is given by Kp = cos (α/2)

Where α is the short pitch or chording angle

Calculation:

Given that, 

Slots  S = 72

Slots/pole/ph = m = 72/ (8×3) = 3

Pole pitch = S/P = 72 / 8 = 9

Pole pitch = 180° = 9 slots

⇒ Each slot = 20° 

The coils are short pitched by 3 slots.

⇒ Chording angle α = 3 × 20 = 60° 

Pitch factor is given by Kp = cos (60°/2) = cos 30° = √3 / 2

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