CASE STUDY:
Conversion from Concentric to Double-Layer Lap Winding (and much more)
Prompted by a discussion on a forum, we were contacted by a visitor named EngRepair for additional information related to the topic at hand.
Specifically, he is interested in a table below he found online, and in particular, a section marked with an asterisk (*), i.e., why it is not advisable to use 'full pitch = slots/poles' when converting a single-layer concentric winding.
The publication in question provides an explanation that this is due to the excessive presence of harmful harmonics in the equivalent lap, double-layer winding with a full pitch.
He is curious to know if this is true and seeks an explanation for this scenario.
First, let's take a look at how the diagrams of these two mentioned windings appear.
Considering that the two most important factors to consider and compare during the conversion process are:
- the fundamental winding factor and
- the content of harmful harmonics,
we have conducted an analysis of both windings, checking all of the aforementioned aspects as well as the symmetry of both windings. The obtained winding factors for windings 1 and 2 are shown below.
So, from the above data, it is evident that the winding factor for both windings is completely identical and cannot be a reason to avoid such a conversion.
Furthermore, if this conversion must be carried out for any reason, then a double-layer lap winding with full pitch is the ONLY CORRECT SOLUTION (in terms of winding factors). Replacing the lap winding with any other arrangement ( smaller pitch) significantly affects the motor's power/torque and worsens the motor's characteristics.
Next. We have calculated several of the most important harmonics for both windings.
The tables below for winding 1 and winding 2 show that the harmonics in both cases are the same, and there is NO REASON TO AVOID THE MENTIONED CONVERSION to a double-layer, lap winding with full pitch.
DRAW YOUR OWN CONCLUSION. For those who want to delve deeper, an extended article is prepared, containing additional explanations: - the calculated values of the differential leakage coefficient, which indicate the content of ALL harmonics, not just the first few, for both cases. - There will also be an analysis of another contentious, highlighted case from the table at the beginning (1-9*), especially since it is 2/3 of a full step, which is often used in the case of a double-layer, two-pole motor. - Additionally, images showing air-gap MMF curves for all mentioned cases will be included. The extended version of this article will be available at the following link: https://winding.wixsite.com/design/buy-now
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