Induction motor condition monitoring: Vibration analysis technique — diagnosis of electromagnetic anomalies

Vibration analysis is one of the most successful techniques used for condition monitoring of rotating machines. Vibration analysis is a very efficient and convenient tool for diagnosing mechanical problems in induction motors. The aim of this paper is to show that vibration analysis is an efficient tool for diagnosing electromagnetic problems in induction motors, which are very specific for this type of machines. The industry today widely uses different kinds of nonlinear systems operating in the power lines, for example, adjustable speed drives, which cause voltage distortion on the induction motor supply and in the power lines. Faulty operation of adjustable speed drives very often creates unusual voltage content on the induction motors input. Single phase load in three phase power systems may cause voltage imbalance. Induction motors operating under non-sinusoidal voltage (voltage distortion) or under non-symmetrical three phase voltage (voltage imbalance) have usually experienced significant vibration of electromagnetic nature. Vibration of an electromagnetic nature may also be a result of an internal fault in the motor. Motor vibration data contain substantial analytical information about internal motor electrical problems such as: stator and rotor winding and core condition, air gap eccentricity; and information about external electrical problems: current/voltage imbalance, voltage distortions in the power line, etc. A short theoretical analysis of electromagnetic excitation forces is included to exemplify how the internal and external electrical faults create parasitic radial forces (rotating waves) and tangential forces (pulsating torques) inside the induction motors, which deteriorates equipment health. Faults are illustrated in numerous case histories of electromagnetic problems from different industries, which result in machinery vibration that is significantly above acceptable standards. Among them are: voltage (current) imbalance, voltage waveform distortion, faulty control of ASD, motor eccentric air gap, induction motor winding (stator and rotor) damage, //and combinations of mechanical and electrical problems//.