1. The motor blades are damaged or the screws that fasten the blades are loose, causing the blades to collide with the blade cover. The sound produced by the blades varies with the severity of the impact.
2. Due to bearing wear or improper shaft, the eccentricity of the rotor of the motor will cause the stator and the rotor to rub, causing the motor to generate severe vibration and uneven friction sound;
3. Due to the long-term use of the motor, the anchor screws are loose or the foundation is not strong, so the motor generates abnormal vibration under the action of electromagnetic torque;
4. Long-term use of the motor due to lack of lubricating oil in the bearing formed in the grinding operation or damage to the steel balls in the bearing, so that the motor bearing room makes an unusual snoring or grunting.
5. The abnormal sound of the normal running motor suddenly appears. When running with a load, the rotation speed drops significantly, and a low edge roar is issued. It may be that the three-phase current is unbalanced, the load is too heavy, or the single-phase operation.
6. For a normal running motor, if the stator and rotor windings are short-circuited or the squirrel cage rotor is broken, the motor will emit high and low Weng Weng sounds. The fuselage also vibrates.
Basic types of motor noise:
① Electromagnetic noise
Frequency doubling noise: multiple of power frequency
Tooth harmonic noise: stator, rotor eccentricity, improper slot coordination, rotor imbalance causes noise.
Slip noise: caused by inadequate cooperation between the blades and the shaft.
② duct noise
Flute noise: the rotation of the fan causes the gas cycle to pulsate and the airflow to collide with solid objects to generate sound, which is what we usually call the "whistle effect"
Vortex noise: The vortex sound generated by the surrounding air when the fan blades rotate, and its frequency spectrum is wide.
③ mechanical noise
It mainly includes friction noise generated by mechanical components such as bearing noise and bore.
1. The peak frequency of the frequency doubling noise is generally two or four times the power frequency, and does not change with the change of the motor speed.
2. The peak frequency of tooth harmonics and slip noise will increase or decrease accordingly with the change of the motor speed. The noise will disappear after the motor is powered off.
3. The peak frequency of air duct noise increases or decreases correspondingly with the change of the motor speed, but the whole machine noise will continue for a period of time after the motor is powered off.
4. Mechanical noise is relatively easy to distinguish. Generally it is caused by motor bore, bearing damage or poor assembly of the whole machine.
Method for reducing electromagnetic noise of asynchronous motor:
1. Reasonably choose air gap magnetic density.
2.Select the appropriate winding form and number of parallel branches
3. Increase the number of stator slots to reduce the harmonic distribution coefficient
4. Suitable slot fit
5.Using magnetic slot wedges
6, rotor chute
For products that have been produced, the electromagnetic noise is relatively large:
1. Properly increase the moment of inertia of the cross section of the machine base to avoid the resonance zone;
2.The synchronous salient pole machine can improve the magnetic field distribution by calculating and appropriately increasing or decreasing the width of the pole shoe, so that the fundamental wave is closer to the sine wave, thereby reducing the higher harmonic components and reducing the effect of electromagnetic noise;
3. Selecting a more appropriate number of stator winding wiring rounds can effectively reduce the reverse wave generated by the motor windings, thereby reducing noise;
4. For those with higher harmonic content, magnetic grooved boots can be used.
As for the newly designed motor:
1.Choose the proper slot number to cooperate;
2.Select the appropriate pole distance;
3.Increase the number of parallel branches;
4. For salient pole machines, choose the appropriate pole shoe width;
5. Under the condition of guaranteed motor performance, appropriately reduce the air gap magnetic density;
6. The concentricity of the stator and rotor is ensured through the process, so that the unilateral magnetic pull force approaches zero.
The main contradiction of the electromagnetic noise of the motor is the stator and rotor slot coordination, the rotor skew groove and the concentricity of the stator and rotor. Noise reduction measures are mainly to use high-quality stator and rotor slot coordination and reasonable rotor skew groove width, while making the motor air gap as uniform as possible.
Sound occurs through vibration, and without vibration there is no sound. Electromagnetic noise cannot be completely eliminated, and it is true for any motor. The key is to have a certain value. Some people can't wait to get into the motor when they hear the noise. The noise of the motor exceeds the standard. But to be completely noise-free, the motor must not turn.