Electromagnetic vibration caused by abnormal stator
Since the three-phase winding of the stator produces a rotating magnetic field, it rotates at a synchronous speed n0 in the air gap between the stator and the rotor. If the grid frequency is f0, the synchronous speed n0=60f0/P.
The force-bearing part on the base is constantly changing its position with the rotation of the magnetic field. As can be seen from Fig. 1c-e, when the rotating magnetic field makes one revolution, the magnetic pulling force and electromagnetic vibration change twice (2-pole motor).
Stator electromagnetic vibration characteristic frequency
Because the electromagnetic vibration is synchronized with the rotating magnetic field in spatial position, the electromagnetic vibration frequency of the stator should be the product of the rotating magnetic field frequency (f0/P) and the number of electromagnetic force poles (2P), 2f0, which is twice the power frequency.
It can be seen from this that when the motor is working normally, the base is subjected to a rotational force wave whose frequency is twice the frequency of the grid, which may cause vibration. The magnitude of the vibration is directly related to the magnitude of the rotational force wave and the stiffness of the base.
The main reason for the abnormal electromagnetic vibration of the stator
The three-phase magnetic field of the stator is asymmetric. For example, the three-phase voltage of the power grid is unbalanced, the single-phase operation due to poor contact, and the three-phase asymmetry of the stator winding will lead to the asymmetry of the stator magnetic field, resulting in abnormal vibration.
The loose stator core and stator coil will increase the electromagnetic vibration and electromagnetic noise of the stator. In this case, in the vibration spectrum diagram, in addition to the basic components of 2f0, the electromagnetic vibration can also appear 4f0, 6f0, 8f0 harmonics Element.
The loosening of the foot screws of the motor base is equivalent to the reduction of the rigidity of the frame, which causes the motor to resonate in the frequency range close to 2f0, thus increasing the vibration of the stator, resulting in abnormal vibration.
Characteristics of Electromagnetic Vibration of Stator
The vibration frequency is twice the power frequency;
Cut off the power, the electromagnetic vibration will disappear immediately;
Vibration can be measured on the stator frame and bearings;
The vibration amplitude is related to the stiffness of the frame and the load of the motor.