ELECTROMECHANICAL INTERACTION IN TORSIONAL VIBRATIONS OF DRIVE TRAIN SYSTEMS INCLUDING AN ELECTRICAL MACHINE

摘要

Electromagnetic field in the air-gap of an electric machine creates torque between the rotor and stator. In addition to this primary function the electromagnetic fields affect the torsional vibrations of rotating machinery. The aim of this paper is to introduce a new method to include electromechanical interaction in torsional rotordynamics of drive trains with an electrical machine. This aim is achieved by transforming the frequency response function between the electromagnetic torque and the oscillating rotor motion into the form of electromagnetically induced stiffness and damping coefficients. This method was applied successfully to explain the experimentally observed self-excited limit-cycle vibrations. In addition, the method was applied to real life examples representing two different types of electrical machines and drive trains. It was observed that the strength of coupling is dependent on the relative modal amplitude of the motor package. Furthermore, there is a frequency range, right below the supply frequency, where the electromagnetically induced damping is negative. One of the calculation examples was a blower driven by a 932 kW induction motor. In this case the interaction increased the natural frequency of the lowest mode about 4 %, and the electromagnetic damping ratio varied between -0.7 and +1.4.