There can be two types of winding in a DC machine, one is called the lap winding and another is called the wave winding.
Lap winding :
Lap Winding is the winding in which successive coils overlap each other. It is named “Lap” winding because it doubles or laps back with its succeeding coils.
Lap winding are of two types –
- Simplex Lap Winding
- Duplex Lap Winding
This winding is necessarily required for large current application because it has more parallel paths.
- It is suitable for low voltage and high current generators.
- It gives less emf compared to wave winding. This winding requires more no. of conductors for giving the same emf, it results in high winding cost.
- It has less efficient utilization of space in the armature slots.
In this winding, the end of one coil is connected to the starting of another coil of the same polarity as that of the first coil.
This winding forms a wave with its coil, that’s why it is named as wave winding. It is also called series winding because its coils are connected in series.
- In this winding, 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.
- This winding gives sparkles commutation. The reason behind is that it has two parallel paths irrespective of no of poles of the machine. The conductors in each of the two parallel paths are distributed around the armature in the entire circumference.
- For a given no of poles and armature conductors, it gives more emf than that of lap winding. Hence wave winding is used in high voltage and low current machines.
- Resultant emf around the entire circuit is zero.
Highlighting The Differences:
LAP – all the pole groups of the coils generating e.m.f in the same direction at any instant of time are connected in parallel by the brushes.
WAVE – In this winding all the coils carrying current in the same direction are connected in series i.e., coils carrying current in one direction are connected in one series circuit and coils carrying current in opposite direction are connected in other series circuits.
LAP – The number of parallel paths is equal to the number of poles in the machine.
WAVE – The number of parallel paths is always 2.
LAP – The number of brush required by this winding is always equal to the number of poles.
WAVE – The number of brushes required by this winding is always equal to 2.
LAP – Generally used for machines with ratings above 500 kW.
WAVE – generally used for machines of ratings below 560 kW.