Winding Secrets: Lap vs. Wave Windings in DC Machines

• Consider the machine has P poles and Z armature conductors, then there will be P parallel paths, and each path will have Z/P conductors in series.

• The number of brushes is equivalent to the number of parallel paths.

• The half of the brush is positive, and the remaining is negative.

• \(Y_B = Y_F \pm 2m\)

  • \(m\) multiplicity of the winding

  • \(m=1\) for Simplex Lap winding

  • \(m=2\) for Duplex Lap winding

• Progressive winding: \(Y_B > Y_F\)

• Retrogressive winding: \(Y_B < Y_F\)

• The back pitch and front pitch must be odd.

• Resultant pitch (\(Y_R\)) = \(Y_B – Y_F\) = \(2m\) ; even

• Average pitch \(\left(Y_{A}\right)=\frac{Y_{B}+Y_{F}}{2}=\text { pole-pitch }\left(Y_{P}\right)=\frac{Z}{P}\)

• Back pitch \(\left(Y_{B}\right) \approx \frac{Z}{P}\)

• Commutator pitch \(Y_c = \pm m\)

• Number of parallel path in the Lap winding = \(mP\)

• 1. Required for large current applications because it has more parallel paths.

  2. Suitable for low voltage and high current generators.

• Disadvantages of lap windings

  1. It gives less emf compared to wave winding.

  2. Requires more no. of conductors for giving the same emf, which results in high winding cost.

  3. It has less efficient utilization of space in the armature slots.

• If after one round of the armature the coil falls in a slot right to its starting slot the winging

• Retrogressive wave winding:

  If after one round of the armature the coil falls in a slot left to its starting slot the winging

• \(Y_B\) and \(Y_F\) are nearly equal to \(Y_P\) and maybe equal or differ by \(\pm2\). + for progressive winding, – for retrogressive winding.

• Resultant pitch \(Y_R = Y_B + Y_F\)

• Commutator pitch (\(Y_C\)) = average pitch (\(Y_A\))

• Average pitch \(Y_A\) = \(\dfrac{Y_B+Y_F}{2}\) = \(\dfrac{Z \pm 2}{P}\)

• Since \(Y_A\) must be an integer, this winding is not possible with any no. of conductors.

• \[\text { Then, } Y_{A}=\frac{Z \pm 2}{P}=\frac{8 \pm 2}{4}=\frac{10}{4}=2 \frac{1}{2} \text { or } 3 \frac{1}{2}\]
  Let us take 8 conductors in a 4 pole machine.

• Being fractional no the wave winding is no possible but if there was 6 conductors then the winding can be done.

• \[Y_{A}=\frac{Z \pm 2}{P}=\frac{6 \pm 2}{4}=\frac{8}{4}=2=\text { an integer. }\]
  Since,

• For this problem the DUMMY COILS are introduced.

• simplex progressive wave winding diagram having 34 conductors in 17 slots and 4 poles.

• Only two brushes are required but more parallel brushes can be added to make it equal to the no. of poles.

• If one or more brushes set poor contacts with the commutator, satisfactory operation is still possible.

• Gives sparkles commutation because it has two parallel paths irrespective of the number of poles of the machine.

• For a given \(P\) and \(Z\), it gives more emf than that of lap winding. Hence wave winding is used in high voltage and low current machines. This winding is suitable for small generators circuit with a voltage rating of \(500-600 \mathrm{~V}\).

Disadvantages of Simplex Wave winding

• cannot be used in machines having higher current rating because it has only two parallel paths.