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In order to improve the quality of motors, motor noise has been included as one of the quality assessment indicators in recent years, especially for the situation where the motor operating environment is in close contact with people , the noise of the motor has become a very important assessment requirement.In order to control the noise of the asynchronous motor, in addition to selecting the appropriate stator and rotor slots in the design, the inclined slot can be used to reduce the electromagnetic noise of the motor. However, it is still necessary to further test and verify how much groove slope is suitable.
In general, the pitch of the rotor slot of an asynchronous motor can take one stator pitch, which can basically meet the requirements. However, in order to further improve the motor noise, it is necessary to explore the optimal slot slope, which requires a lot of calculation and verification.
From the perspective of manufacturing, the production and processing of straight slot motors is relatively simple, but when necessary, the stator slots or rotor slots need to be skewed. It is relatively difficult to skew the stator slots, so in most cases, the rotor slots are skewed. The skew of the rotor slot is generally realized by machining the skewed keyway on the shaft. Enterprises with more advanced equipment use spiral punching to realize it in the manufacturing process of the rotor core.Causes of Electromagnetic Noise and CountermeasuresMotor noise has always been a problem that is difficult to solve. It is mainly caused by three reasons: electromagnetic, mechanical and ventilation. Electromagnetic noise in the asynchronous motor is caused by the electromagnetic force wave generated by the interaction of the harmonic magnetic field established by the stator and rotor currents in the air gap, which causes the vibration of the iron core yoke and forces the surrounding air to vibrate. The main reason is due to improper groove fit, stator and rotor eccentricity or too small air gap.
Electromagnetic noise is caused by magnetic pull forces that vary in time and space and that act between parts of the motor. Therefore, for asynchronous motors, the causes of electromagnetic noise include:
●The radial force wave of the magnetic field in the air gap space causes radial deformation and periodic vibration of the stator and rotor.●The radial force wave of the higher harmonic wave in the air gap magnetic field acts on the iron core of the stator and rotor, causing them to produce radial deformation and periodic vibration.●The deformation of different order harmonics of the stator core has different natural frequencies. When the frequency of the radial force wave is close to or equal to a certain natural frequency of the core, resonance is caused.
●The deformation of the stator causes the surrounding air to vibrate, and most of the electromagnetic noise is load noise.
●When the iron core is saturated, the component of the third harmonic is increased, which increases the electromagnetic noise.●The stator and rotor slots are all open, and there are many "slot opening waves" generated under the action of the fundamental magnetic potential in the air-gap magnetic field. The smaller the air gap and the wider the slot, the greater their amplitude.In order to avoid this problem, it is necessary to improve the product design stage through some effective means, such as: selecting a reasonable magnetic flux density, selecting a suitable winding type and the number of associated circuits, increasing the number of stator punching slots, and reducing the number of stator windings. The harmonic distribution coefficient of the winding, the proper processing of the stator and rotor air gap of the motor, the selection of the slot fit between the stator and the rotor, and the use of rotor chute and other specific measures.
XINDA