Key elements to be controlled in the structural design of AC motors

1. Determination of stator structure

After initially determining the overall structure, the design usually starts from the stator. For the stator core, the axial and circumferential fastening methods should generally be determined, as well as the structure of the radial ventilation channel components (this is not required for those without radial ventilation channels); When using fan-shaped plates, it is also necessary to determine how the fan-shaped plates are divided, the number, size, and arrangement of dovetail grooves. In large motors, the specific structure of the stepped parts at both ends of the iron core needs to be determined. For stator windings, the end dimensions should be calculated first and the fixing method should be determined.

2. Draw stator assembly diagram

When drawing, first draw the stator core, pressure coil, and winding end, and then arrange the connecting wires between the coils and the pole phase group (which is important for high-voltage motors). If the radial size of the stator core yoke is large (such as in a two pole motor), this connecting wire can be placed radially between the winding end and the machine base; If the radial size of the yoke is small (such as in multi pole motors), it should be placed axially between the winding end and the end cap. Then the axial length of the machine base can be roughly determined.

For the base of small enclosed asynchronous motors, if the installation size permits, appropriately extending the base will be beneficial for heat dissipation and protecting the stator winding ends from damage. It can also reduce the depth of the end cover, improve the stiffness of the end cover, simplify the shape of the end cover, and improve the stability of the base itself. This is generally applicable to large hydrogen cooled steam turbine generators that use bearing end caps. For the machine base where the cooler is installed inside the motor, its axial length or cross-sectional shape should be considered accordingly. After determining the cross-sectional dimensions of the machine base, it is necessary to calculate whether its stiffness meets the requirements. Then determine the foot position based on the requirement for the center height of the machine base (this is not done for motors without feet). In small motors using end cap bearings, the foot should be lower than the lowest point of the machine base; For medium and large motors, it is required that the rotor can be removed without lifting the base for easy disassembly and assembly.

3. Rotor structure design

The main content of rotor structure design is the design and calculation of the iron core (synchronous motor includes magnetic poles and yokes) and the shaft, as well as the combination between the two. The size of the rotor winding has already been calculated in electromagnetic design, but necessary supplementary calculations need to be made here. For the rotor of a transition synchronous motor, the detailed structure, dimensions, and fastening method of the magnetic poles and yokes need to be determined. For other rotor cores, except for those with axial air ducts, the corresponding structure needs to be determined, and the situation is similar to that of stator cores. There are two types of combinations between the rotor core (or yoke) and the shaft: sleeve type and bracket type. The choice of one mainly depends on the radial size relationship between the rotor core (or yoke) and the shaft. If it is a wound rotor asynchronous motor and a synchronous motor, the structural type, size, and position of the collector ring still need to be determined. When arranging the position of the collector ring, consideration should be given to facilitating inspection and replacement of the electric brush. For wound asynchronous motors, the possibility of installing short-circuit and brush lifting devices should also be considered.

Other sizes should be determined as needed, but should gradually decrease towards both ends. In general, the shaft diameter at the bearings of the transmission end and non transmission end shall not exceed 0.8 and 0.7 times the shaft diameter of the rotor iron core gear (or intermediate gear), respectively.

4-end cap structure design

The structure and size of the end cap are determined based on the requirements of the ventilation system, the insulation distance between the winding and the ground, the bearing sleeve structure (seat type bearings do not need to consider this), and the stiffness and strength of the end cap (including those proposed from the process). There should be a certain distance between the inner cover of the rolling bearing and the parts on the shaft, so that there is sufficient operating space when disassembling the bearing.

5 Comprehensive Design

On the basis of the stator, rotor, and end cap assembly drawings, the final assembly drawing can be drawn, and the fan can be arranged at the same time. At this point, it is necessary to verify the relative position between each component, whether the necessary gaps or spaces are appropriate, whether the installation dimensions and external dimensions meet the requirements, and whether manufacturing, assembly, disassembly, and maintenance are convenient, etc. After the final assembly sketch is drawn, necessary modifications can be made to the sub assembly drawing based on it, and part drawings can be gradually drawn. Finally, a detailed and accurate final assembly drawing and verification of the final assembly dimension chain can be drawn. When drawing part drawings, it is necessary to determine the dimensions, materials, and processing requirements of the parts.