According to the different arrangements of the winding coil elements in the slots, the motor windings can be divided into single-layer windings, double-layer windings and single- and double-layer mixed windings. The specifics are as follows: 1. Single-layer winding Definition: Each stator slot contains only one coil with an effective side, and the total number of coils is half of the total number of slots in the motor. advantage:a. The winding coils are few and the process is relatively simple.b. There is no interlayer insulation, so the slot utilization rate is high.c. Phase-to-phase breakdown failure will not occur in a single-layer structure. Disadvantages: The electromagnetic waveform generated by the winding is not ideal, the iron loss and noise of the motor are large, and the starting performance is slightly poor. Scope of application: Generally only used in small-capacity asynchronous motors. Classification: a. Chain winding: It is composed of single-layer coil elements with the same shape and width. The characteristic is that the winding coil is looped in loop, shaped like a long chain. It is mainly used in small three-phase asynchronous motors with the number of slots per pole and phase. The advantages are that the coils are of the same size, easy to manufacture, and the coils can be short-distance with shorter ends. Special attention should be paid to the single-layer chain winding that its coil pitch must be an odd number, otherwise the winding will not be able to be arranged. b. Cross-chain winding: The arrangement method of cross-chain winding is the same as that of chain winding, but the number of coils in the pole-phase group is not equal and the pitch of the coils is also 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-chain winding with single or double coils is required. c. Concentric winding: This winding is composed of coils of different sizes with different pitches in the same pole phase group. It is named because all coils in the pole phase group embrace the same center of a circle. It is mainly used in 2-pole asynchronous motors. It is convenient to unwind. The ends of the two groups of coils in the same phase are staggered, with a small overlap layer, which is convenient for layout and good heat dissipation. d. Cross-concentric winding: When the number of slots per pole per phase is an even number greater than 2, cross-concentric winding is used. The advantage is that the winding and inserting of the winding are relatively simple, and the disadvantage is that the coil ends are too long and consume too much wire. It is occasionally used in small-capacity 2-pole and 4-pole motors, but is rarely used at present. 2. Double-layer winding Definition: Each slot has two coil element sides embedded in it. When one coil side of the coil element is embedded in the lower layer of a slot, the other coil side is placed in the upper layer of another slot. The number of coils is exactly equal to the number of slots. advantage:a. You can choose the most favorable pitch and use distributed winding at the same time to improve the waveform of electromotive force and magnetomotive force .b. Fractional slot windings can be used to weaken high-order harmonics.c. The electromagnetic performance, power index and starting characteristics of the motor are better than those of single-layer winding.d. All coils have the same pitch, making winding easy.e. The coil ends have little deformation and are easy to shape, and the neat arrangement of the ends is conducive to heat dissipation and enhanced mechanical strength. shortcoming:c. The number of coils is twice that of single-layer winding, so embedding the wire is labor-intensive.b. Due to the embedding of the out-of-phase coil edges in the same slot, short circuit faults are more likely to occur compared to single-layer windings.c. Insulation is required between layers and the slot fill rate is low. Application scope: Larger capacity motors can basically use double-layer windings, and large and medium-sized motors generally also use double-layer windings. Classification: a. Double-layer windingTwo coil elements are embedded in each slot of the stacked winding, and the two elements of each coil are arranged in the upper and lower layers of the two slots of the winding pitch, that is, when winding, any two adjacent coils are "tightly stacked" on top of each other. It is widely used in the stator and rotor windings of three-phase asynchronous motors. The stacked winding can flexibly select the coil pitch to improve the electromotive force and magnetomotive force waveforms. It is easy to manufacture, but it is difficult to embed the wire as a whole, especially the last few coils of the motor. Short-pitch coils can save copper at the end, but due to the large number of connections between coil groups, the copper consumption is large when the number of poles is large. The electrical performance is excellent. b. Double-layer wave windingThe coil of the wave winding is generally a single turn, that is, any two coils move forward like waves along the line direction. The main feature is that a coil is connected in series with the coil under the adjacent same-sex magnetic pole. In order to reduce the connection wires between the coil groups, it is mostly used in the electronic winding of the hydro-generator and the winding rotor winding of the induction motor. However, since the wave winding coil is mostly made of flat copper wire, its manufacturing process is relatively complicated. 3. Single and double layer hybrid winding Definition: It is essentially a deformation of the short-distance double-layer winding. The upper and lower coils in the same slot of the short distance are combined into a single-layer side by removing the interlayer insulation strips, while the slots of the upper and lower layers with different phases are still kept as double-layer sides, and their ends are reconnected according to the direction of current flow in the slot, which becomes a single-double-layer mixed winding. Advantages: Single-layer and double-layer windings can show different characteristics and features when used in different occasions, which can improve motor efficiency, reduce temperature, improve starting characteristics, save winding copper, etc. Notice:a. Single- and double-layer hybrid windings are most suitable to be obtained by equivalent changes of double-layer stacking windings. It is not recommended to improve by single-layer windings, which will reduce the fundamental wave winding coefficient, and the coils must be rewound and embedded, wasting time.b. It is not recommended to change the winding with slot number per pole per phase ≤2 to single-layer and double-layer mixed winding, because the winding span before and after the transformation cannot be reduced, and it is impossible to save materials and energy.c. It is not recommended to change the winding with fractional number of slots per phase (when the denominator is ≥ 4) into a single- or double-layer mixed winding, because there is an asymmetric distribution between phases and between pole-phase groups of the same phase. If it is changed into a single- or double-layer winding, the winding and wire embedding are very inconvenient and the average span will not be shorter than that of a double-layer winding. 4. Comparison 1. Some special needs, such as pole changing, can be met by double-layer windings but not single-layer windings.2. Double-layer winding is more cost-effective than single-layer winding.3. When the voltage is critically low, the double-layer winding can be started, but the single-layer winding cannot.4. The upper and lower windings of a double-layer winding are sometimes not necessarily in the same phase, so the interphase insulation of a single-layer winding is better than that of a double-layer winding.
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