Vibration of induction motors operating with variable frequency drives — A practical experience

Variable Frequency Drives (VFDs) are widely used today in different industries due to many advantages including: energy savings, easy speed control, soft start, low motor start up current etc. However, VFD creates a number of problems for normal operation of induction motors, which require special attention. Excessive motor vibration is one of the serious problems related with this type of drive. The aim of this presentation is a comprehensive analysis of the origin of vibration in induction motors operating with VFD. This presentation is based on the author´s many years of experience in the field of electrical machinery vibration diagnostics. Case histories from VSC´s field service files covering assorted industries represent typical vibration problems of induction motors operating with VFD. Among them are: a resonance condition on the equipment at a certain operating speed, motor bearing deterioration due to high frequency current impulses coming through the motor shaft and bearings and voltage and current distortion, resulting in motor casing vibration, shaft torsional vibration and speed pulsation. Practical recommendations to prevent excessive vibration on the motor operating with VFD are also presented.