Detecting mechanical problems by examining variable speed drive signals

Variable speed drives are becoming increasingly popular as the source of power for three-phase induction motors. In addition to providing significant energy savings over Direct-On-Line arrangements, drives measure and compute many signals (e.g., electrical currents, estimated speed, torque), which can be used to detect various conditions in the motor or other elements of the shaft train. Furthermore, no additional sensors are needed, thus system reliability is not compromised. In this paper we focus on rotor and mechanical conditions. In particular, results are presented for detection of broken rotor bars, eccentricity, torsional resonances, and load oscillations. Results of laboratory experiments are presented alongside some examples of industrial data.