By Tom Bishop, P.E.
Senior Technical Support Specialist
Electrical Apparatus Service Association, Inc.
St. Louis, MO
The paper "How Winding Changes Affect Motor Performance" by Tom Bishop, presented at the EASA Convention 2016, explores the intended and unintended consequences of various winding changes in three-phase stator motors. The paper delves into common and less common winding modifications, examining their potential impacts on motor efficiency and reliability. One of the primary considerations is the connection type, with wye (star) and delta being the two options. Delta connections require more turns and less wire area per turn compared to wye connections, which can lead to higher volts per coil and potential electrical stress.
Bishop emphasizes the importance of ensuring that changes in winding connections, such as switching from wye to delta, do not result in excessive volts per coil. He provides formulas and examples to illustrate the calculations needed to determine volts per coil and the necessity of additional insulation if the volts per coil exceed 80. The paper also discusses the consequences of misconnecting a motor, such as reduced torque capability and increased heating, which can significantly affect motor performance and reliability.
The number of circuits in a winding is another critical factor. Increasing the number of circuits can lead to unbalanced windings and circulating currents, reducing efficiency and reliability. The paper highlights the importance of equalizing connections to mitigate unbalanced magnetic pull and electrical noise. Bishop also addresses the impact of turns count errors, which can result in increased current, higher operating temperatures, and reduced efficiency.
The paper explores the effects of changing winding pitch, noting that reducing pitch increases magnetic flux densities and developed torque, while increasing pitch has the opposite effect. Incorrect coil grouping sequences can lead to unbalanced windings and circulating currents, emphasizing the need for accurate grouping sequences. Bishop provides examples and tables to illustrate the correct and incorrect grouping sequences for various winding configurations.
The conversion of concentric windings to lap windings is discussed, with lap windings generally offering better performance due to their more sinusoidal magnetomotive waveform. However, the conversion process must be carefully managed to avoid issues such as increased losses and noise. The paper also covers the importance of wire area per turn and slot fill, noting that increasing wire area per turn can improve efficiency and reliability, while reducing wire area can have detrimental effects.
Bishop concludes by emphasizing the need for careful consideration of winding changes to ensure that motor performance and reliability are not compromised. He provides practical advice and examples to guide service centers in making informed decisions about winding modifications.
Key Points Covered:
- Differences between wye and delta connections
- Importance of volts per coil and additional insulation
- Consequences of misconnecting motors
- Impact of the number of circuits on winding balance
- Effects of turns count errors
- Influence of winding pitch changes
- Correct and incorrect coil grouping sequences
- Conversion from concentric to lap windings
- Importance of wire area per turn and slot fill
Key Takeaways:
- Winding changes can significantly affect motor performance and reliability.
- Ensuring proper volts per coil and additional insulation is crucial.
- Misconnecting motors can lead to reduced torque and increased heating.
- Balanced windings are essential to avoid circulating currents and unbalanced magnetic pull.
- Accurate turns count and winding pitch are critical for optimal performance.
- Converting to lap windings can improve performance but must be managed carefully.
- Increasing wire area per turn can enhance efficiency and reliability.
- Careful consideration of winding changes is necessary to maintain motor performance and reliability.
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