Dynamic analysis due to eccentricity in asynchronous machines

In asynchronous motors exist several kinds of excitations that can cause vibrations. In addition to the mechanical excitations, such as unbalance, there are also electromagnetic forces, which can cause vibrations. This report focuses on the influence of a dynamic rotor eccentricity on the vibrations in an asynchronous motor. After the coherences between rotor eccentricity and magnetic pull are shown, a theoretical rotor model is presented, which consists on the superposition of three different kinds of excitations - magnetic eccentricity, eccentricity of the rotor mass and a bent shaft - which cause a dynamic rotor eccentricity. An analysis of the theoretical rotor model and a finite element rotor dynamic calculation is presented, showing the calculation of the shaft vibration, caused by a rotor core eccentricity. Thus a comparison with the real measured shaft vibration is possible. The calculation is based on the separation of the calculated shaft vibrations into several components of excitation. With this separation the influence of each excitation on the shaft vibration can be evaluated, and the rotor design can be optimised for the operating speed range. This calculation method is useful to support the analysis of the measurement.