In the lap winding, the two ends of a coil are connected to adjacent commutator segments. In the wave winding, the two ends of a coil are connected to the commutator segments that are approximately 360 electrical degrees apart (i.e., 2-pole pitch) and coil span = pole pitch. The result is that the coils under consecutive pole pairs will be joined together in series thereby adding together their e.m.f.s.This way all the coils carrying current in the same direction are connected in series. Therefore, there are only two parallel paths between the brushes, i.e., a=2 , independent of the number of poles. This type of winding is used for low-current, high-voltage applications.
Wave winding design procedure :
- Both pitches YB and YF are odd and of the same sign.
- Back and front pitches are nearly equal to the pole pitch and may be equal or differ by 2, in which case, they are respectively one more or one less than the average pitch.
- Resultant pitch YR = YF + YB.
- Commutator pitch, YC = YA (in lap winding YC = ±1 ). Also YC = (No.of commutator bars ± 1 ) / No.of pair of poles.
- The average pitch which must be an integer is given by YA = (Z ± 2)/P = (No.of commutator bars ± 1)/No.of pair of poles.
- The number of coils i.e NC can be found from the relation NC = (PYA ± 2)/2.
- It is obvious from 5 that for a wave winding, the number of armature conductors with 2 either added or subtracted must be a multiple of the number of poles of the generator.This restriction eliminates many even numbers which are unsuitable for this winding.
- The number of armature parallel paths = 2m where 'm' is the multiplicity of the winding.