Change of Mechanical Natural Frequencies of Induction Motor

Most electromagnetic acoustic noise of induction motors is generated when the mechanical natural frequencies of the stator coincide with or are close to the frequencies of magnetomotive forces. In order to avoid this, it is necessary to determine the motor´s mechanical natural frequencies by calculation or simulation. Variation of natural frequency from yoke steel ring to motor has been studied experimentally, analytically and by structural finite-element method analysis. It thus became clear that mechanical natural frequencies increased in number and natural frequencies gradually decreased from simple yoke steel ring to motor.