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      Analysis on Reason to cause Motor Electromagnetic Noise

      Electromagnetic Noise is caused by magnetic pull,which changes in time and space and acts on every part of motor.For asynchronous motor,reasons to cause electromagnetic noise are as follows:

       

      1. The magnetic field of air gap space is a kind of rotating force wave. Its radial fore wave makes stator and rotor occur radial deformation and periodical vibration to cause electromagnetic noise.

       

      2. There are high-order harmonic components in air-gap field besides power fundamental components.The radial force wave of high-order harmonic act on cores of stator and rotor separately,which make them occur radial deformation and periodical vibration.In general, for high-order harmonic, the stiffness of motor rotor is stronger and the radial deformation is primary, which many cause bigger noise.

       

      3. The deformation of stator core harmonic with different degrees has different inherent frequencies.When the frequency of radial force wave approaches or equals with one of the inherent frequencies, it will cause¡±resonance¡±.On this occasion,even if the amplitude of radial force is not big, it will also cause the deformation of core and periodical vibration to cause bigger noise.

       

      4. After the deformation of stator, it will cause vibration of ambient air to cause noise. By now, the stator is equivalent to a sound radiator.

       

      5. When the core is saturated, it will make the top of magnetic field withsinusoidal distribution become flat and increase the third harmonic components in field distribution, which causes the increase of electromagnetic noise.

       

      6. The grooves of stator and rotor are open and the air-gap permeance is changed and fluctuant.There are many harmonics introduced by the opening of grooves.

       

      Methods to reduce electromagnetic noise£º

       

      1. Choose air-gap flux density reasonably.

      2. Choose suitable winding form and multipled branch numbers

      3. Increase the quantity of stator grooves to reduce coefficientof harmonic distribution

      4. Suitable match of grooves

      5. Take advantage of magnetic groove carving

      6.Choose carbon brush

       

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