Sinusoidal Windings: Why They Should Never Be Replaced by Standard Windings
So-called sinusoidal windings, which offer improved performance compared with standard windings, have been used in practice for many years. Unfortunately, many motor repair shops pay little or no attention to this fact. Instead, they have developed their own simplified replacement procedure, apparently just to make the job easier!
Their procedure is fundamentally wrong. They simply add up the turns in all coils of a coil group and divide the total by the number of coils in that group. This produces a motor with significantly lower efficiency, higher operating temperatures, and a shorter service life. All this is done without even obtaining the customer's (motor owner's) consent to such a modification.
Motor repair shops that follow this practice should be avoided.
Using one motor we analyzed — a 55 kW motor with 60 slots and 4 poles — we will demonstrate the advantages of a sinusoidal winding.
In the first video, we will show a standard three-phase, double-layer lap winding and a double-layer concentric winding. The windings are shown with series-connected coils because the number of parallel branches does not affect this type of analysis.
In a sinusoidal winding, the number of turns per coil within a coil group is not uniform. Instead, it varies according to a calculated distribution designed to produce a stator MMF (magnetomotive force) waveform that is as close as possible to a sinusoid. For this example, the number of turns per coil is provided in the table.
Using our own software, we analyzed the fundamental winding factor and Td (the differential leakage coefficient) for both the standard winding, with the same number of turns per coil throughout each group, and the sinusoidal winding, with the number of turns per coil distributed according to the table.
The results showed that the sinusoidal winding has an almost 10% higher fundamental winding factor and an almost 50% lower Td, indicating a substantial reduction in harmful space harmonics.
These results demonstrate the significant performance advantages of the sinusoidal winding.
IT SHOULD NEVER BE REPLACED WITH A STANDARD WINDING WITHOUT PROPER TECHNICAL ANALYSIS AND THE MOTOR OWNER'S INFORMED CONSENT — especially not by using simplistic, technically unjustified procedures.
The video below provides a visual comparison of the MMF waveforms produced by the two windings. The standard winding is shown on the left, and the sinusoidal winding on the right.
Even to an untrained observer, it is clear that the waveform on the right is much closer to a true sinusoid than the one on the left. Wouldn't you agree?
See the video at: https://vimeo.com/1234596985
If you require further information, please contact us using any of the contact forms available on our website.
One final request: please do not expect our professional services to be provided free of charge. Just imagine a customer walking into your own repair shop with a motor, expecting you to provide your services for free. Would you consider that reasonable?
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