Motor vibration problems — Understanding and identifying

Vibration problems in large induction motors can be extremely frustrating and may lead to greatly reduced motor reliability. It is imperative, in all production operations that downtime be avoided or minimized. If a motor problem does occur, the source of the problem needs to be promptly identified and corrected. With proper knowledge of the sources of motor vibration, proper vibration measurement and diagnostic procedures, it is possible to more quickly identify the root cause of motor vibration. This paper intends to assist the operators of cement plants in avoiding erroneous conclusions that may be reached as a consequence of not understanding the root cause of the vibration; conclusions that may result in trying to fix an incorrectly diagnosed problem, wasting time and money in the process. By utilizing the proper data collection and analysis techniques, the true source of the vibration can be more accurately determined: This analysis includes, but is not limited to vibration related to: · Electrical imbalance - stator, rotor bar · Mechanical unbalance - rotor, coupling, driven equipment · Resonance and critical speeds · Mechanical effects - looseness, rubbing, bearings · External effects - base, driven equipment, misalignment. This paper includes a diagnostic guide (Table I) listing of the causes of electrically and mechanically induced vibrations in large motors, along with the characteristics of these vibrations. In addition, a field example is provided from a cement plant facility wherein a vibration problem was discovered, the root cause was determined and the vibration issue was solved.