Torsional vibration monitoring using induction machine electromagnetic torque estimation

The heavy duty drives need a continuous monitoring to avoid sudden loss of operation. In these systems, the mechanical anomalies like load troubles, great torque dynamic variations and torsional oscillations, result in the fatigue of the shaft driving electrical machine and other mechanical parts as bearings and gearboxes. Then, the permanent on-site mechanical performance has to be evaluated to predict the residual life time of each mechanical part on the base of combined mechanical loads affecting them. In this way, this paper proposes an electromagnetic torque estimation using non invasive measuring as a mean for mechanical monitoring of torsional stresses. Different electromagnetic torque estimations can be obtained from the induction machine mathematical representation and the simplest one in term of implementation is proposed for grid or inverter-fed machines. A test-bed based on a 5.5 kW squirrel-cage connected to a wound-rotor 4 kW induction machine via a gearbox has been used to validate the proposed method.