Prediction of the noise power level of squirrel cage induction machines in different operation points taking into account mechanical boundary conditions for modal analysis

The electromagnetic forces due to the interaction of harmonic rotor and stator fields of various origins such as slotting, saturation, eccentricity and harmonics of the supply voltage due to inverter operation in induction machines are introduced. A modal analysis has to be done to judge, if these forces excite vibrations of the stator, which leads to noise emission of the motor. The modal analysis should take into account the mechanical boundary conditions due to machine mounting and the influence of the terminal box. As an analytical solution for this task is only hard to find and the simplifications of the structure lead to only roughly correct results, a numerical time-stepping model for Finite Element (FEM) analysis with ANSYS code is used, introducing mechanical boundary conditions, which is combined with the analytical force calculation. Measurement results of the noise power level L_W for three TEFC-induction motors acc. to [1] show good coincidence with the calculation results and illustrate the improvement by using this modified calculation method.