Chuck Yung
Senior Technical Support Specialist
Electrical Apparatus Service Association
St. Louis, MO
In the paper "Unusual Winding Connections & Layouts," presented at the EASA Convention 2008, Chuck Yung explores various unconventional winding designs encountered in three-phase motors. These designs often appear to violate standard rules but ultimately adhere to the principles of symmetry and electrical balance. The paper reviews several exceptions to common winding rules and provides insights into how these designs function effectively.
Yung begins by discussing the fundamental rules of motor design, emphasizing symmetry in slot spacing, phase sequence, pole distribution, and the number of slots being divisible by phases and poles. He explains that deviations from these rules can lead to issues such as circulating currents, higher losses, electrical noise, and negative torque. However, certain designs manage to work despite appearing asymmetrical.
One notable exception is the use of unequal grouping, where parallel circuits do not have the same number of coils. This can be mitigated by ensuring that each circuit has the same total number of turns, even if the number of coils differs. Another exception involves equalized connections, where jumpers connect points of equal electrical potential within parallel circuits to reduce circulating currents.
The paper also covers part-salient, part-consequent windings, which combine salient-pole and consequent-pole designs to achieve a desired number of poles using an existing lamination stamping. This hybrid approach allows for the creation of motors with unconventional slot-to-pole ratios.
Interleaved windings are another unconventional design discussed by Yung. These windings divide each group into subgroups and parallel them, effectively doubling the number of circuits. Proper interleaving requires that the electrical center of each subgroup coincides to prevent circulating currents and ensure efficient operation.
Interspersed windings, primarily used in two-pole machines, are designed to reduce the adverse effects of harmonic waveforms. By interspersing coils of adjacent groups, the winding behaves as if each coil has a longer span, improving motor performance by reducing harmonic distortion.
Yung emphasizes the importance of understanding these unusual winding connections and layouts to avoid repeat failures and improve motor efficiency. He advises service centers to proceed with caution when encountering unfamiliar designs and to consider the motor's history and performance when making repairs.
Key Points Covered:
- Fundamental rules of motor design and the importance of symmetry
- Exceptions to common winding rules, including unequal grouping and equalized connections
- Part-salient, part-consequent windings for unconventional slot-to-pole ratios
- Interleaved windings to double the number of circuits
- Interspersed windings to reduce harmonic distortion in two-pole machines
Key Takeaways:
- Unusual winding designs can function effectively despite appearing asymmetrical.
- Ensuring equal total turns in parallel circuits can mitigate issues with unequal grouping.
- Equalized connections reduce circulating currents and improve efficiency.
- Part-salient, part-consequent windings allow for unconventional slot-to-pole ratios.
- Proper interleaving prevents circulating currents and ensures efficient operation.
- Interspersed windings improve motor performance by reducing harmonic distortion.
- Service centers should proceed with caution when encountering unfamiliar winding designs and consider the motor's history and performance.
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