Electric motors are widely used in various industries, but many problems can arise during use, among which motor vibration is one of the most common issues encountered in daily production and life. 1. Hazards of Electric Motor Vibration Electric motor vibration accelerates bearing wear, significantly shortening the normal service life of the bearings. Simultaneously, it degrades winding insulation. Vibration loosens the end-end wiring, causing friction between the end windings, reducing insulation resistance, shortening insulation life, and in severe cases, causing insulation breakdown. Furthermore, motor vibration can damage the driven machinery, affect the normal operation of surrounding equipment, and generate significant noise. 2. Causes of Electric Motor Vibration The causes of electric motor vibration are mainly mechanical and electromagnetic. Mechanical causes include: loose foundation mounting, tilted or uneven foundation surface; damaged bearings, bent or deformed shaft, misalignment between the motor's axis and the axis of the driven machinery; misalignment of the stator and rotor core magnetic centers, and poor rotor dynamic balance. Electromagnetic causes include: unbalanced three-phase voltage, single-phase operation of the motor; unbalanced three-phase current, unbalanced phase resistance and reactance, and asymmetrical operation of the motor. The motor may have issues such as incorrect winding connections after rewinding, broken rotor squirrel cage bars, or cracked short-circuit rings. 3. Inspecting and Eliminating Motor Vibration When motor vibration is significantly higher than usual, a vibration meter should be used to measure the vibration values ​​of each part in both horizontal and vertical directions, and the results recorded. Listen to the sounds inside the motor stator cavity and the bearing rotation sounds, and check the mounting feet. If no obvious abnormalities are found, disconnect the driven machinery and run the motor alone to determine whether the vibration is caused by the motor itself or the driven machinery. In production, it may be found that after motor repair, due to various reasons, the three-phase winding magnetomotive force is asymmetrical. The vibration of the motor is not very obvious when it is unloaded or under low load, but it gradually intensifies once the load increases. In production, we often use the power-off method to check and distinguish whether the vibration is caused by electromagnetic or mechanical reasons. The power-off method involves suddenly disconnecting the power to the motor running at its rated speed. If the vibration suddenly decreases, it can be determined that it is caused by electromagnetic reasons; if the vibration value does not change significantly, it may be caused by mechanical reasons. For vibrations caused by mechanical factors, if the vibration is due to worn bearings, the bearings of the same model should be replaced immediately. If the vibration is due to a deformed or bent shaft, the shaft must be aligned or replaced. If the vibration is due to loose foundation fasteners, they should be tightened again. Insufficient foundation strength and uneven platform height may seem like minor issues, but they are often the most direct causes of vibration. One of our factory's high-voltage motors was vibrating excessively. Multiple attempts to center it failed to eliminate the vibration. After hoisting the motor, it was discovered that the foundation platform was made of two steel plates spliced ​​together, with one side slightly higher and the other lower. The weld seam was not ground smooth and was located directly under one of the motor's feet. Although the motor had been aligned, there were actually many point contact surfaces. The alignment of the motor center with the mechanical center was merely an illusion, and vibration was inevitable when the motor was running. The initial solution involved cutting the joint with gas welding, re-welding, and grinding it smooth. After realigning the motor, the vibration actually increased during test runs. Analysis revealed that the steel plate, having undergone both gas cutting and electric welding, had suffered thermal damage, significantly reducing its strength. The motor's rotation caused resonance with the steel plate, exacerbating the vibration. The problem was resolved by rebuilding the foundation platform. Another root cause was poor rotor dynamic balance. While the motor's rotor is factory-balanced, repairs (especially high-voltage motors) often neglect proper marking. Unauthorized removal and reassembly of balanced components inevitably leads to poor dynamic balance and vibration. Rebalancing is the only solution. For vibrations caused by electromagnetic factors, the inspection should begin with the power supply. Check if the three-phase voltage is balanced. Use a clamp meter to measure the three-phase current to check for balance and single-phase operation. During production, it was found that loose wiring at the motor terminal box frequently burned out, causing single-phase operation. This area should be thoroughly checked and the problem eliminated. If the clamp meter shows an imbalance in the three-phase current, and the needle fluctuates, it indicates a broken cage bar in the rotor. In this case, immediately stop the motor, disconnect the power, and remove the rotor for inspection and repair. Additionally, measure the resistance of the three-phase stator windings to check for symmetry. If the resistance values ​​are unbalanced, it indicates a weld breakage; the rotor should also be removed for inspection and re-welding.