Wave Winding: Simplex, Duplex, Retrogressive And Progressive Wave Windings

What is a Wave Winding?

A wave winding, sometimes called a series winding, is one of the two main armature-winding arrangements used in DC machines. The other is lap winding.

Successive coils connect so that the winding passes under poles of alternating polarity before returning near its starting position. The coil side A-B progresses around the armature until it reaches the conductor A₁-B₁ under the starting pole.

This repeating path gives the winding its wave-like appearance. Coils in each path are connected in series, which is why wave winding is also called series winding. The diagram below shows the arrangement.

Wave windings are described by multiplicity and winding direction:

• Simplex wave winding has two parallel paths.
• Duplex wave winding has four parallel paths.
• Retrogressive wave winding progresses to the preceding commutator segment.
• Progressive wave winding progresses to the next commutator segment.

Progressive Wave Winding

In progressive wave winding, the connection advances to the next commutator segment after passing around the armature. In the diagram, this appears as a shift to the right of the starting slot.

Retrogressive Wave Winding

In retrogressive wave winding, the connection goes to the preceding commutator segment. In the diagram, this appears as a shift to the left of the starting slot and forms a retrogressive wave winding.

In the diagram, the second conductor, CD, lies to the left of the first conductor.

Simplex Wave Winding Pitch

In simplex wave winding, the back pitch (Y_B) and front pitch (Y_F) are odd numbers with the same sign.

The back pitch and front pitch are close to the pole pitch and usually differ by two conductors. The positive choice gives a progressive winding, while the negative choice gives a retrogressive winding.

Here, Z is the total number of armature conductors and P is the number of poles.

The average pitch (Y_A) must be an integer so that the winding closes after including all coil sides.

The plus or minus two in the numerator makes the connection finish one commutator segment ahead of or behind its starting segment.

Using Z/P without the correction would make the winding close before it includes every coil side.

Because the average pitch must be an integer, not every combination of conductor count and pole count permits simplex wave winding.

For example, consider eight conductors in a four-pole machine.

The result is fractional, so this simplex wave winding cannot close correctly. With six conductors and four poles, the pitch is an integer:

When the available slot and coil count does not meet the closure condition, designers may use a dummy coil.

Dummy Coil

Wave winding requires conductor, coil and commutator-segment counts that satisfy its integer-pitch condition. A standard armature stamping may have a slot count that does not match the required electrical design, so a dummy coil can occupy the unused slot.

A dummy coil helps preserve the armature’s mechanical balance but is not electrically connected to the active winding.

For a multiplex wave winding, the pitch relation includes the winding multiplicity:

Where:

• m is the winding multiplicity.
• m = 1 for simplex winding.
• m = 2 for duplex winding.

Construction of Wave Windings

The following example develops a simplex progressive wave winding for a four-pole machine with 34 conductors in 17 slots.

Average pitch:

The resulting conductor sequence gives the connection table below:

Wave Winding Diagram

Simplex Wave Winding Advantages

The main properties and advantages of simplex wave winding are:

1. Only two electrical brush positions are needed. Designers may install additional brushes in parallel to improve current collection.
2. The two parallel paths each include conductors distributed around the armature and under all poles. Equalizer connections are therefore not normally required.
3. Each path contains Z/2 conductors, where Z is the total number of armature conductors.
4. The generated emf between brushes is the average conductor emf multiplied by Z/2.
5. For the same poles, flux, speed and number of armature conductors, its two parallel paths give a higher emf than a lap winding. A wave winding is therefore suited to relatively high voltage and low current machines.
6. Each conductor carries the current of its parallel path.
   

   

   
   For simplex wave winding, each path carries approximately half the armature current I_a. The allowable current depends on conductor size, insulation, cooling and commutation design.
7. The series-connected emfs in each path add between opposite-polarity brushes, while the algebraic sum around the complete closed winding is zero.

Simplex Wave Winding Disadvantages

The main limitation of simplex wave winding is:

1. A wave winding is less suitable for high-current machines because a simplex winding provides only two parallel paths.