What is "Asymmetric Winding"?
 

Fractional-pitch three-phase windings with q = b + c/d becomes asymmetric if the denominator "d" is a multiple of  "3".

In general,  asymmetric windings are avoiding. Nevertheless, it is sometime possible to design polyphase windings with little asymmetry in order to use existing punching tools.

If "d" is a multiple of "3",and the total number of slots  can be divided by 3, it's possible to construct three-phase winding with small degree of asymmetry.

 

How frequent are unsymmetrical windings in practice?

They are very common: mostly 6 * k (k = 1,2,3 ...) pole windings, for example:

- 6 pole, in 24, 30, 42, 48, 60, 66, 96, 120 etc... slots

-multiples of 6 pole windings, i.e. 12 pole, 18 pole etc.

 

What kind of coils are used in practice?

There are various types of windings, single or double -layer, lap or concentric. Each winding is dealt with on a case by case basis.

Common to all is:

- getting winding with asymmetry at the angle and amplitude (because it is unbalanced winding),

- inability to use multiple parallel circuits, (because of circulating currents) and

- a very high content of harmful harmonics (see example below 24 slots, 6 pole, single-layer),

First table shows the leakage coefficient of 0,2415. This coefficient is high even in some improved double-layer windings.

- winding is a complex and often difficult to make.

 

What are the characteristics and benefits of the new winding layout and the aforementioned procedure?

- This is combined single-double layer winding,

- The procedure is applicable to asymmetrical windings if the number of slots per pole is an integer ( whole number), for example: 

 6 pole, in  24, 30, 42, 48, 60, 66, 90, 120 slots etc.,  and multiples of 6 pole windings, i.e. 12 pole, 18 pole etc.

This is a brief overview:

     - 6 pole, 24 slots  and all multiples 6*k poles, 24*k slots ( 12 pole-48 slots, 18 pole-72 slots etc....),

     - 6 pole, 30 slots  and all multiples 6*k poles, 30*k slots ( 12 pole-60 slots, 18 pole-90 slots etc....),

     - 6 pole, 42 slots  and all multiples 6*k poles, 42*k slots ( 12 pole-84 slots, 18 pole-126 slots etc....),

     - 6 pole, 48 slots  and all multiples 6*k poles, 48*k slots ( 12 pole-96 slots, 18 pole-144 slots etc....),

     - 6 pole, 60 slots  and all multiples 6*k poles, 60*k slots ( 12 pole-120 slots, 18 pole-180 slots etc....),

     - 6 pole, 66 slots and all multiples 6*k poles, 66*k slots ( 12 pole-132 slots, 18 pole-198 slots etc....),

     - 6 pole, 96 slots and all multiples 6*k poles, 96*k slots ( 12 pole-192 slots, 18 pole-288 slots etc....),

     - 6 pole, 120 slots and all multiples 6*k poles, 120*k slots ( 12 pole-240 slots, 18 pole-360 slots etc....),

       etc, etc.................

 

- incredibly  LOW content of harmful harmonics (see example below for 24 slots, 6 pole, single-layer),

The second table shows the leakage coefficient of 0,0557 ( 4,3 times lower).

This coefficient is significantly lower even in comparison with some improved double-layer windings.

 

- Each 6 pole winding can be performed with 3 parallel circuits,

- Each 12 pole winding can be performed with 3 and 6 parallel circuits,

- Each 18 pole winding can be performed with 3, 6  and 9 parallel circuits etc...

  There is no possibility of circulating currents, at all.