# An alternator has 18 slots per pole and the first coil lies in slots 1 and 16. Calculate the pitch factor of the coil for 3rd harmonic.

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An alternator has 18 slots per pole and the first coil lies in slots 1 and 16. Calculate the pitch factor of the coil for 3rd harmonic.
1. 1.5
2. 2.5
3. 0.707
4. 3.0

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Correct Answer - Option 3 : 0.707

Concept:

The pitch factor for nth harmonic is given by,

${k_c} = \cos \frac{{nα }}{2}$

where α is the slot angle

Calculation:

The first coil lies in slots 1 and 16

Coil span is 16 – 1 = 15 slots

Number of empty slots = 18 – 15 = 3 slots

$\therefore \alpha = 180^\circ \times \frac{3}{{18}} = 30^\circ$

Pitch factor for 3rd harmonic, ${k_{{c_3}}} = \cos \left( {\frac{{3 \times 30^\circ }}{2}} \right)$

= 0.707