In the DC machine, the fractional pitch winding is used

In the DC machine, the fractional pitch winding is used

Right Answer is:

To reduce the Harmonic in generated EMF

SOLUTION

  • In full pitched coils, as one conductor of a turn in a coil cuts N pole, the other conductor of the same turn cuts S pole resulting in the production of induced emf(E), i.e phase angle is 180 degree
  • In short-pitched coils, both conductors of the same turn in a coil don’t cut the respective poles simultaneously. so phase angle is slightly less than 180 degree As a result, the magnitude of induced emf gets reduced to E × Cos(nα/2)
    Where E × Cos(nα/2) is called a pitch factor

For eliminating 3rd harmonic from Generated EMF,
Cos(3α/2) = 0
3α/2 = π/2
α = π/3 = 60°

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