Harm, Cause and Solution of Motor Vibration

Motors are widely used in all walks of life, but there are many problems when using them. Among them, motor vibration is more likely to collide in daily production and life.

1. Motor vibration hazards

Motor vibration will accelerate the wear of the motor bearing, which will greatly shorten the normal service life. At the same time, the motor vibration will also cause the winding insulation to slide down. Due to the loosening of the wire at the end of the motor due to the vibration, the end windings may wear each other, reduce the insulation resistance, shorten the insulation life and other problems, which may lead to insulation breakdown in severe cases. In addition, the vibration of the motor will cause damage to the towed machinery, affecting the normal operation of the surrounding equipment, and the noise will be louder.

Second, the reason for the vibration of the motor

The reasons for the vibration of the three-phase asynchronous motor are nothing more than mechanical and electromagnetic reasons. In terms of machinery, the main problems are that the footing is not tight, the base is inclined, and the level is uneven; the bearing is damaged, the rotating shaft is bent and deformed, the center of the motor shaft does not match the center of the mechanical shaft it is dragging; the magnetic center of the stator and rotor iron cores do not match, and the rotor is poorly balanced. Wait.

The electromagnetic aspects are mainly problems such as unbalanced three-phase voltage and single-phase operation of the motor. The three-phase current is unbalanced, the resistance of each phase is unbalanced, and the motor runs asymmetrically. After the motor is rewound, the winding wiring is wrong, the rotor squirrel cage is broken, and the short circuit is broken.

Three, the solution to the motor vibration

When the vibration of the motor is normal, use the vibration meter to measure the vibration value of each part along the horizontal and vertical directions, and make corresponding records. Listen to the sound inside the stator cavity of the motor and the sound of the bearing rotating, check the feet, if there is no obvious abnormality, etc., take a separate idling motor from the dragged machine, and judge whether it is the vibration of the motor itself or the vibration caused by the dragging machine. In the production process, it will be found that after the motor is repaired, the magnetic potential of the three-phase winding is asymmetric due to various reasons, and the vibration of the motor is not very obvious when there is no load or low load. The vibration of the motor will also gradually increase.

We often use the method of power failure during production to distinguish whether the vibration is caused by electromagnetic or mechanical reasons. The power-off method refers to the sudden power-off of the motor running at the rated speed. If the vibration suddenly decreases, it can be judged to be caused by electromagnetic reasons. If the vibration value does not change much, it may be caused by mechanical reasons.

For the vibration caused by the mechanical aspect, if the bearing is worn, the bearing of the same type should be replaced immediately; if the shaft is deformed, the shaft must be adjusted or replaced; if the corner of the ground is not fastened firmly, it will be re-tightened . The foundation strength is not enough, and the height of the platen seems to be a small problem, but it is often the most direct cause of vibration. A high-voltage motor in our factory vibrated a lot, and the center searched for many times, but the vibration was not eliminated. After turning on the motor, it was found that the basic platen was made of two steel plates. The welding seam is not polished and it is just under the foot plate on the side of the motor. Although the motor has found the correct position, there are actually many places where point contact surfaces are formed, and the motor center and the mechanical center have found only an illusion. Once the motor is running, it will inevitably oscillate.

Gas welding was used to cut the splices and re-weld and grind them to make them smooth. After the motor was found to be correct again, the vibration of the pilot turntable increased. After analysis, it was found that the steel plate was ground again and it was found that the steel plate was ground again, resulting in certain thermal damage, and the strength has been seriously reduced. The steel plate forms resonance, so the vibration increases, which can only be eliminated after the foundation table is remade. In addition, the poor balance of the rotor is also the source of vibration. The rotor has passed the calibration when the motor leaves the factory. However, when the motor is repaired (especially the maintenance of high-voltage motors), it is often not paid attention to the mark and scale, and the warp is removed without authorization. For a certain part of the whole balance calibration, after reloading, it will inevitably cause poor dynamic balance and cause motor vibration. The only way to eliminate it is to re-calibrate the dynamic balance.

For the shock caused by the electromagnetic aspect, it should be checked from the power supply. Check whether the three-phase voltage is balanced, whether the three-phase current is balanced with the clamp current, and whether there is single-phase operation, etc., and it is found that the terminal wiring in the motor junction box is not fastened tightly and often burns out, resulting in single-phase operation, etc. problem, we must increase the inspection of this place and eliminate it. If it is found that the three-phase current is unbalanced and the needle swings high and low when measuring with a clamp current, it means that the rotor has a broken cage. At this time, the operation of the electric vehicle should be stopped immediately, the power supply should be cut off, and the rotor should be pulled out for inspection and repair. In addition, the resistance value of the three-phase stator winding should be measured to check whether the winding is symmetrical. If the resistance value is unbalanced, it means that there is an open welding part, and the rotor should also be pulled out for inspection and re-welding.