Talking about the electromagnetic noise in the operation of three-phase asynchronous motor

Update:09 Sep 2021

The electromagnetic noise in the operation of a three-phase asynchronous motor is mainly caused by the magnetostriction and vibration of the iron core caused by the radial electromagnetic force of the periodic change in the motor or the unbalanced magnetic pulling force. Electromagnetic noise is also related to the vibration characteristics of the stator and rotor. For example, when the exciting force resonates with the natural frequency, even if the electromagnetic force is small, a lot of noise will occur.

Motor manufacturers can start from many aspects to suppress electromagnetic noise. To deal with a three-phase asynchronous motor, you must first select the appropriate number of stator and rotor slots.

Generally speaking, there is a large difference between the number of slots in the rotor and the number of slots in the stator, that is, when the so-called far slots are common, the electromagnetic noise is small. For slotted motors, the skew can make the radial force phase shift along the motor axis in the remote direction, thus reducing the axial average radial force, thereby reducing noise. If the double chute layout is recycled, the noise reduction result will be better. The double chute layout divides the rotor into two sections along the axial direction. The skew of each section of the groove is opposite. An intermediate ring is also provided between the two sections.

In order to reduce the harmonics of magnetomotive force, the three-phase asynchronous motor with high noise requirements of the motor manufacturer can recover the double-layer short-moment winding. And to prevent the recycling of fractional slot windings.

Sine windings should be recovered in single-phase motors. In order to reduce the electromagnetic noise caused by the cogging, the magnetic slot wedges can be recovered or the slot width of the stator and rotor can be reduced until the opening slot is used. When a three-phase motor is running, it is necessary to maintain voltage symmetry as much as possible, and a single-phase motor should run near a circular rotating magnetic field. In addition, in the motor manufacturing process, the ellipticity of the inner circle of the stator and the outer circle of the rotor should be reduced, and the stator and rotor should be concentric and the negative air gap should be symmetrical. Reducing the air gap magnetic flux density and recovering a larger air gap can reduce noise. In order to prevent the electromagnetic force from resonating with the natural frequency of the casing, an appropriate elastic layout can be recovered.

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