Vibration causes and typical cases
There are three main reasons for vibration: electromagnetic reasons; mechanical reasons; mechanical and electrical mixing reasons.
1. Electromagnetic reasons
(1) Power supply: The three-phase voltage is unbalanced, and the three-phase motor is out of phase.
(2) Stator aspect: the stator core becomes elliptical, eccentric, loose; the stator winding breaks, grounds breakdown, turn-to-turn short circuit, wiring error, and the stator three-phase current is unbalanced.
For example: Before the boiler room fan motor was repaired, it was found that the stator core had red powder. It was suspected that the stator core was loose, but it was not in the standard overhaul project, so it was not processed. The motor screamed when the test was overhauled. Troubleshoot after replacing a stator.
(3) Rotor failure: the rotor core becomes elliptical, eccentric, and loose. The rotor cage strip is welded to the end ring, the rotor cage strip is broken, the winding is wrong, and the brush is in poor contact.
For example: in the running of the toothless saw motor of the sleeper section, the stator current of the motor is oscillated back and forth, and the vibration of the motor is gradually increased. According to the phenomenon, the rotor bar of the motor has the possibility of opening and breaking. After the motor is disassembled, it is found that the rotor cage has 7 breaks. The two serious sides and the end rings have all been broken. If they are not found in time, the accident of burning the stator may occur.
2, mechanical reasons
(1) The motor itself:
The rotor is unbalanced, the shaft is bent, the slip ring is deformed, the stator and rotor air gaps are uneven, the stator and rotor magnetic centers are inconsistent, the bearing is faulty, the basic installation is poor, the mechanical mechanism is not strong enough, the resonance is loose, the ground screw is loose, and the motor fan is damaged.
Typical case: After the factory condensate pump motor is replaced, the motor sloshing increases, and the rotor and stator have slight broom signs. After careful inspection, it is found that the rotor height of the motor is not correct, the magnetic center of the rotor and stator are not up, and the motor is re-adjusted. After the thrust head screw is provided, the motor vibration fault is eliminated. After the maintenance of the over-the-line lifting motor, the vibration has been too large, and there are signs of increasing gradually. When the motor is hooked, the vibration of the motor is still large, and there is a large amount of movement in the axial direction. The disintegration found that the rotor core is loose. There is also a problem with the balance of the rotor. After replacing the spare rotor, the fault is eliminated and the original rotor is returned to the factory for repair.
(2) Coupling with the coupling: the coupling is damaged, the coupling is poorly connected, the coupling is not centered, the load is mechanically unbalanced, and the system is resonant.
The linkage part of the shaft system is misaligned, the center line does not coincide, and the centering is incorrect. The cause of this failure is mainly caused by poor alignment and improper installation during the installation process. There is also a case where some of the center lines of the interlocking parts are coincident in the cold state, but after a period of operation, the center line is broken due to the deformation of the rotor fulcrum and the foundation, thereby generating vibration.
a. Circulating pump motor, the vibration has been too large during operation, the motor is inspected without any problems, the idling is also normal, the pump class thinks that the motor is running normally, and finally the motor is found to have too much positive center difference. The motor vibration is eliminated.
b. After changing the pulley of the boiler room, the motor will vibrate during the test run and the three-phase current of the motor will increase. Check all the circuits and electrical components without problems. Finally, the pulley is found to be unqualified. After the replacement, the motor vibration is eliminated, and the motor is three-phase. The current also returns to normal.
3, motor mixing reasons
(1) Motor vibration is often caused by uneven air gap, causing single-sided electromagnetic pulling force, and the single-sided electromagnetic pulling force further increases the air gap. This electromechanical mixing acts as motor vibration.
(2) The axial movement of the motor is caused by the gravity of the rotor itself or the installation level and the magnetic center is not correct. The electromagnetic tension caused by the motor causes the axial movement of the motor to cause the motor vibration to increase. In the severe case, the shaft is ground and the bearing is made. The temperature rises rapidly.
(3) There are problems with the gears and couplings associated with the motor. This kind of failure mainly manifests as poor gear occlusion, serious tooth wear, poor lubrication of the wheel, skewing and misalignment of the coupling, tooth profile of the gear coupling, incorrect tooth pitch, excessive clearance or serious wear, which will cause certain vibration.
(4) Defects in the structure of the motor itself and installation problems. This kind of failure mainly manifests as the ellipse of the journal, the bending of the shaft, the gap between the shaft and the bearing bush is too large or too small, and the rigidity of the bearing seat, the foundation plate, a part of the foundation and even the entire motor installation foundation is insufficient, and the motor and the base plate are fixed. Not secure, the foot bolts are loose, and the bearing housing and the base plate are loose. The excessive or too small gap between the shaft and the bearing bush can not only cause vibration but also cause abnormal lubrication and temperature of the bearing bush.
(5) The load transmitted by the motor is transmitted and transmitted. For example, the turbine vibration of a steam turbine generator, the fan driven by the motor, and the vibration of the water pump cause vibration of the motor.
