I. Single-layer winding
Definition: A winding in which only one effective side of a coil is embedded in each stator slot, and the total number of coils is half the total number of slots in the motor.
advantage:
a. Fewer winding coils mean the manufacturing process is simpler.
b. Since there is no interlayer insulation, the utilization rate of the slot is high.
c. Single-layer structures will not experience phase-to-phase breakdown faults.
Disadvantages: The electromagnetic waveform generated by the winding is not ideal, the iron loss and noise of the motor are relatively large, and the starting performance is also slightly poor.
Application scope: Generally used only in small-capacity asynchronous motors.
Classification:
a. Chain winding: Composed of single-layer coil elements with the same shape and width, characterized by winding coils looping one after another, resembling a long chain. Mainly used in small three-phase asynchronous motors with a limited number of slots per pole and phase. Advantages include uniform coil size, ease of manufacturing, and the ability to use short-pitch coils with shorter ends.
Special attention should be paid to the fact that the coil pitch of a single-layer chain winding must be odd; otherwise, the winding cannot be arranged.
b. Cross-link winding: The arrangement method of cross-link winding is the same as that of chain winding, but the number of coils in the pole phase group is not equal and the coil pitch is not equal. When the number of slots per pole per phase is an odd number greater than 2, the chain winding cannot be arranged. At this time, a cross-link winding with single and double coils is required.
c. Concentric winding: This winding consists of coils of different sizes and pitches within the same pole phase group. It is named for the fact that all the coils within the pole phase group surround the same center. It is mainly used in 2-pole asynchronous motors. It is convenient for winding, and the ends of the two groups of coils in the same phase are staggered, with little overlap, which facilitates arrangement and provides better heat dissipation.
d. Crossed concentric winding: When the number of slots per pole per phase is an even number greater than 2, a crossed concentric winding is used. The advantage is that the winding and inserting of the coils are relatively simple. The disadvantage is that the coil ends are too long, consuming too much wire. It is now rarely used except in small-capacity 2-pole and 4-pole motors.
II. Double-layer winding
Definition: Each slot contains two coil elements. When one coil element is placed in the lower layer of a slot, the other coil element is placed in the upper layer of another slot. The number of coils and the number of slots are exactly equal.
advantage:
a. The most favorable pitch can be selected, and distributed winding can be used at the same time to improve the waveforms of electromotive force and magnetomotive force.
b. Fractional slot windings can be used to reduce higher harmonics.
c. The electromagnetic performance, power performance and starting characteristics of the electric motor are better than those of a single-layer winding.
d. All coils have the same pitch, making winding convenient.
e. The coil ends have minimal deformation, are easy to shape, and the neat arrangement of the ends is beneficial for heat dissipation and enhances mechanical strength.
shortcoming:
c. The number of coils is twice that of a single-layer winding, so the winding process is more labor-intensive.
b. Due to the embedding of out-of-phase coil sides in the same slot, short-circuit faults are more likely to occur compared with single-layer windings.
c. Insulation is required between layers, resulting in a low slot fill rate.
Application scope: Larger capacity motors can generally use double-layer windings, and medium and large motors also generally use double-layer windings.
Classification:
a. Double-layer lap winding
Two coil elements are embedded in each slot of the lap winding, arranged in upper and lower layers. The two elements of each coil are located in the upper and lower layers of the two slots of the winding pitch, respectively. That is, during winding, any two adjacent coils are "tightly stacked" on top of the other. It is commonly used in the stator and rotor windings of three-phase asynchronous motors.
Lap windings allow for flexible selection of coil pitch to improve the waveforms of electromotive force and magnetomotive force, and are easy to manufacture, but overall winding is more difficult, especially for the last few coils of the motor. Short-pitch coils can save copper at the ends, but due to the large number of interconnections between coil groups and the high number of poles, copper consumption is greater. They offer excellent electrical performance.
b. Double-layer wave winding
Wave winding coils are typically single-turn, meaning any two coils advance in a wave-like pattern along the wire direction. A key characteristic is that one coil is connected in series with a coil under an adjacent magnetic pole of the same polarity. This reduces the number of connecting wires between coil groups, making them commonly used in the electronic windings of hydroelectric generators and the wound rotor windings of induction motors. However, because wave winding coils are mostly made of bent flat copper wire, their manufacturing process is relatively complex.
III. Single- and double-layer hybrid winding
Definition: Essentially, it is a variation of short-pitch double-layer winding. The upper and lower layers of short-pitch coils in the same slot are merged into a single layer by removing the interlayer insulation strip, while the slots of different phases in the upper and lower layers remain as double-layer sides. Their ends are reconnected according to the needs of the current flow direction in the slot, thus becoming a single-double layer hybrid winding.
Advantages: Single and double layer windings can exhibit different characteristics and properties when used in different situations, which can improve motor efficiency, reduce temperature, improve starting characteristics, and save copper in the windings.
Notice:
a. The single-double layer hybrid winding is best obtained by equivalent transformation of double layer lap winding. It is not recommended to improve it by single layer winding, as it will reduce the fundamental winding coefficient and require rewinding and embedding of the coil, which is a waste of time.
b. It is not recommended to change the winding with ≤2 slots per pole per phase to a single-double layer mixed winding, because the winding span before and after the change cannot be reduced, and materials and energy cannot be saved.
c. It is not recommended to change the winding with fractions per phase and per slot (when the denominator is ≥4) to a single-double layer mixed winding, because there is an asymmetrical distribution between phases and between pole groups of the same phase. If it is changed to a single-double layer winding, the winding and winding are very inconvenient and the average span is not shorter than that of a double layer winding.
IV. Comparison
1. For some special needs, such as pole changing, double-layer windings can achieve this, but single-layer windings cannot.
2. Double-layer windings are more economical than single-layer windings.
3. At critical low voltage, double-layer windings can start, but single-layer windings cannot.
4. In double-layer windings, the upper and lower windings are not always on the same phase. Therefore, the phase-to-phase insulation of single-layer windings is better than that of double-layer windings.
