Chuck Yung
EASA Technical Support Specialist

Sometimes when redesigning a motor, the desired speed requires more poles than are possible for the number of stator slots. Or, a motor arrives in the service center with a nameplate speed that does not seem to be compatible with the number of stator slots (e.g.,18 poles with 36 slots). In both cases, the answer may be a part-salient, part-consequent winding.

To understand how this winding works, let’s compare it to ‘normal’ winding designs. One winder’s trick for verifying the integrity of a connection diagram is to trace through each phase and “arrow-diagram” the groups. For a salient- pole winding, the polarities alternate with each physical group (Figure 1). With a consequent- pole connection, all the arrows point the same direction (Figure 2).

With a consequent- pole connection, an opposite polarity is induced between each physical group. The effect is as if there are twice as many groups. “Phantom poles” induced between the actual poles have polarities opposite the real poles.

Hybrid winding
By combining these two basic diagrams, it is possible to develop a hybrid winding that is partly salient-pole, and partly consequent-pole. That al- lows the designer to develop a winding such as a 10-pole with 24 slots, which would not otherwise be possible.

As long as some basic rules are followed, this method is reliable.

• Since each phase must be balanced, each phase must contain the same number of real groups.
• Each phase must have the same number of real poles and the same number of induced poles.
• The number of real poles and induced poles do not have to equal each other.
• Phantom groups must be placed so that the arrow diagram results in alternate polarity for the entire winding.

Follow simple process
To simplify this, use a template with the actual number of slots. Determine the number of groups required (poles x 3 phases) for a normal salient- pole winding, and subtract from that the number of groups possible with the number of slots in the stator. The difference is the number of phantom groups required. Divide by 3 for the number of phantom groups required per phase.

For the 24 slot, 10 pole example: 10 poles x 3 phases = 30 groups
30 groups – 24 slots = 6 phantom groups required The phantom groups must be uniformly distributed around the stator, so the next step is to determine the odd grouping sequence.

There are 24 groups of 1 coil, and 6 groups of zero. It may help to think of the “groups of zero” as placeholders for those phantom poles.
The groups of zero must be divided equally among the 3 phases, so group them A-B-C to visualize it better: 111,101,111,011,110; repeated once. This pattern places 2 zeros in each phase.

 
All that remains is to draw the connection, treating the zeros as place-holders. Use the direction of the arrows as a guide, and don’t be confused by the fact that some jumpers are “inside to outside” while others are “inside to inside” or “outside to outside.” Each time you get to a phantom group, simply bypass it and draw to the next group in that phase, following the direction of the arrows. Those two steps labeling the phases, and following the arrows that indicate the alternating north-south relationship of the groups are the key to making this a simple process.

The completed diagram should look like this:

With such a global economy, expect to see more small motors produced using this unique method. Manufacturers save money by using a few standard laminations for a variety of motor speeds. This method has been used successfully on motors up to about 10 HP (7.5 KW).

Tip: When tracing out an existing connection you suspect is part-salient, part-consequent, a sure clue is the mix of 1-3 jumpers or 1-6 jumpers with the expected 1-4 or 1-7 jumpers.

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Categories: Stators/windings, Design/theory/application

Tags: Winding connections Part-salient part-consequent

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