- Electrical imbalance in the circuitry
- Mechanical imbalances arise due to the defects in coupling, bearing, or other part.
- External imbalance effects that include base and shaft misalignment issues
- Speed of motor and the resonance produced can also lead to vibration unbalance
Though this appears to be a small issue, it is likely to lead to great problems. The type of harm caused varies according to the type of vibration unbalance. The various problems induced by vibration defects are as follows.
Driven Machine Imbalances
Producing this type of imbalance occurs when the moving parts of the machine are off-balanced. When this imbalance crosses a certain limit, it can affect the moving parts of the motor thereby leading to motor damage.
When there is an improper arrangement of key and couplings on the frame, or there is some problem with alignment and mounting capabilities of the machine, this sort of imbalance is likely to occur. This condition may even include the usage of an over-sized coupling. This may lead to bending of shaft, extreme imbalance, and rubbing of seals. If this imbalance goes beyond limits, it may result in catastrophic failure of shaft.
Rotor movement produces high temperatures, and when there is too much heating in an improper manner, the shaft may bend and the equipment alignment may be disturbed. This affects the rotor placement.
Modal Shape and Natural Frequency Unbalance
The stator core develops vibrations when applying a magnetic field. The frequency of these vibrations is associated with the modal patterns. In case, the modal pattern’s frequencies match, producing large resonance. This introduces serious vibration, and unbalances the running parts of the motor.
Rotor Bar passing Vibration Unbalance
When there is excess load on the motor, which induces stator current in the rotor bars, and this gives rise to passing frequency in the rotor bars. This frequency can be quite harmful to the motor if the tolerance limits are crossed. If this happens, the motor is unreliable, and the operations are unpredictable. The motor experiences imbalances in velocity, displacement, and stress in the stator core iron and stator tooth iron.