Lap Winding

The windings are connected to provide several parallel paths for current in the armature. For this reason, lap-wound armatures used in dc generators require several pairs of poles and brushes.the finishing end of one coil is connected to a commutator segment and to the starting end of the adjacent coil situated under the same pole.

Following points are consider to design a lap winding 

1. The back and front pitches are odd and of opposite sign.But can't be equal. They differ by 2 or some multiple thereof.
2. Both YB and YF shpuld be nearly equal to the pole pitch.
3. The average pitch YA = (YB + YF)/2.It equals pole pitch = Z/P.
4. Commutator pitch YC = ±1.
5. Resultant pitch YR is even, being the arithmetical difference of two odd numbers i.e YR = YB - YF.
6. The number of slots for a 2-layer winding is equal to the number of coils.The number of commutator segments is also the same.
7. The number of parallel paths in the armature = mP where 'm' is the multiplicity of the winding and 'P' the number of poles.Taking the first condition, we have YB = YF ± 2m where m=1 fo simplex lap and m =2 for duplex winding etc.

• If YB > YF i.e YB = YF + 2, then we get a progressive or right-handed winding i.e a winding which progresses in the clockwise direction as seen from the comutator end.In this case YC = +1.
• If YB < size="1">F i.e YB = YF - 2,then we get a retrogressive or left-handed winding i.e one which advances in the anti-clockwise direction when seen from the commutator side.In this case YC = -1.