In DC machines, the drum type armature windings are used. In the case of drum type winding, the armature conductors (in the form of coils) are placed in the slots around the surface of cylindrical or drum shaped armature core. The coils are connected in series through the commutator segments such that their EMFs are added to each other.
In DC machines, two types of armature windings are used −
In the case of wave winding, the armature coils are connected in series through the commutator segments in such a way that the armature winding is divided into two parallel paths irrespective of the number of poles of the machine, i.e.,
If Z being the total number of armature conductors, then each parallel path has Z/2 armature conductors in series. Each parallel path carry a current of Ia/2, where Ia is the total armature current. In the case of wave winding, the generated emf is equal to the EMF across each parallel path.
The wave windings are used in small machines, since in the case of small machines the current carrying capacity of armature conductors is not critical.
In lap winding, the armature coils are connected in series through the commutator segments in such a way that the armature winding is divided into as many parallel paths as the number of poles of the machine, i.e.,
If Z is the total number armature conductors and P is the number of poles in the machine, then there will be P parallel paths in the winding and the number of conductors in each parallel path will be,
If Ia being the total armature current, then
The EMF generated in the lap winding is equal to the EMF in each parallel path.
The lap windings are used in large machines, because in the large machines current carrying capacity is more critical.