The most important factor in ultra-high-efficiency motors is the level of process assurance. The continuous improvement of motor efficiency is a process of continuous product upgrading and replacement, and it is also an indicator of a country's overall level of motor industry.
The key to designing high-efficiency electric motors is to reduce various losses and improve motor efficiency. Measures taken include: using special finishing tools to increase stator slot fill factor and increase the cross-sectional area of copper wire; improving manufacturing precision, shortening coil end lengths, and strengthening the manufacturing quality of laminations and stator cores, thereby reducing iron losses and excitation current and the resulting copper losses; improving rotor slot insulation processes to reduce load-related losses; and rationally selecting silicon steel sheet grades to reduce iron losses and stator copper losses.
1. Factors affecting motor efficiency
Motor losses include stator and rotor copper losses, iron losses, mechanical losses, and stray losses. There are many ways to reduce motor losses and improve efficiency: measures to reduce stator copper losses mainly include reducing stator resistance, shortening the winding end length; thinning insulation, increasing slot fill factor, increasing conductor cross-sectional area, and using new materials to reduce the resistivity of electromagnetic wires, etc.
Measures to reduce rotor aluminum loss mainly include using rotor slots with larger cross-sectional areas and increasing the end ring cross-section, improving aluminum purity, and reducing rotor resistance. Measures to reduce iron loss mainly include using high-quality cold-rolled silicon steel sheets with low losses to reduce eddy current losses in the motor; adjusting the slot shape and selecting a reasonable magnetic flux density to reduce fundamental iron losses; increasing the core length to reduce magnetic flux density and thus reduce losses; and improving the manufacturing quality of the core to ensure the insulation of the silicon steel sheet surface. Measures to reduce mechanical losses mainly include high-efficiency fan structures and reasonable airflow paths, and improving the surface roughness of the blades. Roughness ensures smooth airflow, improves fan efficiency, and reduces air friction; the use of high-quality low-friction bearings and grease reduces friction loss; improved form and position tolerances ensure the overall assembly quality of the motor and reduce friction loss; measures to reduce stray losses mainly include using more stator slots to reduce the width of stator and rotor slot openings, using non-magnetic materials at both ends of the core; using sinusoidal windings to weaken higher harmonics in the magnetic field and reduce additional losses; appropriately increasing the air gap; using fewer slots in the rotor; using magnetic slot wedges; precisely controlling the skewness of the slots; and using special skewed slots.
2. Key manufacturing technologies for reducing motor losses
2.1 Technical measures to reduce mechanical consumption
The dimensions of components are adjusted using intermediate tolerances and improved geometrical tolerances to ensure that components do not deform during transportation and assembly, while also ensuring the overall assembly quality of the motor, thereby reducing frictional losses. Production experience shows that using bearing housing rolling technology can effectively improve the machining accuracy of the bearing housing mating parts and reduce a series of problems caused by bearing operating accuracy; the use of online quantitative grease injection technology can stably control the amount of grease injected, ensuring stable mechanical wear of high-efficiency motors in mass production. Small and medium-sized motors generally use rolling bearings with suitable high-quality lubricants. The traditional process involves manually applying grease to the bearing before assembly, then assembling the bearing, and finally using a grease gun to add grease to the motor again. This manual grease application method has the following problems: the amount applied is difficult to control, affecting lubrication and mechanical wear of the bearing; the grease is easily contaminated, and there is oil residue around the motor components after manual application; the process is complex and inconvenient.
Currently, there is no device capable of quantitatively adding grease to motors. To effectively control the amount of grease added, after extensive technical verification, it was determined that an automatic grease injector, oil pipes, and quick-connect couplings can be used to achieve automated quantitative grease injection during online motor assembly. This technology places the grease injector at the end of the motor assembly line. During assembly, the motor does not require grease injection; when the motor comes off the line, the quick-connect coupling of the automatic quantitative grease injector is connected to the motor's grease pipe, and starting the grease injector automatically adds a quantitative amount of grease to the motor. This device has the advantages of being convenient to use, accurate in dosage, and highly efficient and fast. It is currently widely used in high-efficiency motors and other motors and has obtained a national utility model patent.
2.2 Technical measures to reduce stray losses
Rotor outer diameter machining is commonly performed by motor manufacturers using turning technology. Due to the influence of the aluminum strips in the slots, the turning process alternates between hard silicon steel sheets and soft aluminum. Because of the relatively poor precision of the machine tools, the dimensions of the rotor outer diameter are unstable after machining. If a single-cut machining process is used, coupled with a small machining allowance for some rotor outer diameters, the surface quality of the rotor outer diameter will be poor, with large burrs, or severe adhesion between rotor surface plates. This leads to high motor losses, high temperature, and low efficiency. Therefore, it is particularly important to standardize the rotor outer diameter machining process, parameters, and quality inspection standards.
The rotor's magnetic field commutation frequency is very low, and the hysteresis and eddy current losses generated by the rotor's silicon steel sheets themselves are negligible. Stray losses mainly originate from the transverse current losses caused by the conduction between the aluminum conductor bars at the slots and the outer diameter of the rotor laminations. This requires precision turning, firing, and special outer diameter treatment to increase the resistance between the rotor's outer diameter conductor bars and laminations, and between laminations themselves, thereby reducing stray losses caused by transverse current. Analysis suggests that new cutting tools and processes can be widely applied during rotor precision turning. Most manufacturers use a 450° positive offset cutter when turning the rotor's outer diameter, with a positive inclination angle. Under the same cutting parameters, this cutter has a large axial force, easily causing silicon steel sheets to buckle and stick together. The new process uses a 930° positive offset Sandvik machine-clamped cutter. Because the axial force of this cutter is smaller, it reduces silicon steel sheet buckling and sticking, effectively improving the surface finish of the rotor.
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