Motor rotor imbalance noise reduction
To reduce the noise caused by rotor imbalance, the key is to improve the accuracy of the dynamic balance, or limit the rotor imbalance to a reasonable limit. The International Organization for Standardization (ISO) has promulgated the most economically and reasonably balanced quality grades for different rotors of electrical machines and the corresponding residual unbalances per unit rotor mass (kg). In general, increasing the rotor dynamic balance accuracy may reduce the noise by 3 to 5 dB.
Technical documents specify residual imbalance values or allowable total eccentricity values per unit rotor mass. The higher the speed, the stricter the requirements. However, this applies only to "rigid" rotors, which are rotors whose operating speed is much lower than their first critical speed. For an actual "flexible" rotor, that is, a rotor whose operating speed is between its first and second critical speeds, it allows the total eccentricity to be smaller.
It can also be pointed out that for a fully balanced motor, if it is combined with other equipment, the stiffness and vibration form of the bearing support changes due to the shaft coupling, and other reasons, for example, the connected equipment itself is unbalanced, not found. Good center, etc., unacceptable vibration and noise may still occur. Therefore, the entire rotating system should be dynamically balanced in the actual operating state.
In addition, attention should be paid to the stability of the balance, especially after running the heat. At the same time, the dynamic balance of other components such as fans, keys, etc. mounted on the coaxial shaft cannot be ignored. In the rotor of a 2-pole turbo generator, the bending stiffness of the two main axes is inconsistent due to the slotted winding. In this case, even if the rotor is balanced, mechanical noise with twice the rotational frequency of the rotor cannot be completely eliminated. . In particular, if the natural frequency of the bearing support or some components is equal to or close to twice the rotational frequency of the rotor, the noise and vibration at that frequency may be prohibitively high.
Reprinted from the network