Torsional vibrations during the start-up of electric motor

Torsional vibrations during the start-up of an electrical motor may be sometimes very harmful. In worst situation they can cause even a break off of the shaft. Often the torsional vibrations create also overloading problems in components fitted into the shaft for example in the cogged belt drives. Especially in the combustion engines, even if there is a damper for torsional vibrations in the crankshaft, torsional vibrations often occur with large amplitudes during the start-up. The present paper comprises two different simulation models of the transient torsional vibrations, which appear during the start-up situation of an electric motor. One model is based on the equations of mechanical motion and the other is based on the equations of electromechanics. The simulation results are verified with measurements carried out on a test rig, which consists of a DC-motor, an elastic shaft and a flier. The measurement results are also analyzed by using the Joint Time Frequency Analysis (JTFA) in order to determine the mechanical responses of the test rig.