The noises from the most industrial induction motor are mainly caused by the electromagnetic effects. This kind of noise can be amplified by the structure itself if the frequency components of the magneto-motive force are close to the resonance frequencies of the structure. So, there must be an intermediate process which usually called structure dynamic modification(SDM) to avoid this phenomenon.
To do this work, the dynamic characteristics of an induction motor(3.7 kW) were investigated for each assembling step experimentally and using finite element method(FEM). To obtain the input forces for the motor, analytical forms of magneto-motive force were obtained and those were feed to do response analysis. From these analysis, some design guides were suggested to reduce the vibration of the induction motor.
Thanks to this study, the design changes on some parts of stator, such as stator slots, circumferential cut, and several holes significantly affect to the stiffness of stator. On the other hand, the change on frame and bracket components can move the natural frequency of the oval mode which is known as the main contributor of the motor noise. The higher of the oval mode frequency gives the less radiation. Also the presence of eccentricity between rotor and stator can influence the magneto-motive force that has the wave number of 2. This frequency component dominates the magnitude of the modal force of the oval mode. So the eccentricity must be minimized as small as possible to reduce the input source.
