Electric motors are the most fundamental source of motion generation mechanisms in both industrial and household products. Noise and vibration problems in such products can be remedied in general at each of the three stages ; source - transmission path - receiver. Some problems, however, caused inherently by the motors can not be successfully resolved by working on the transmission path or the receiver alone. In this regard, importance of the noise and vibration problems in the motor itself has been increasing so far.
In order to improve the vibration characteristic of structure which is closely connected to the structure born noise of induction motor, it is necessary to analyze the excitation forces as well as the dynamic properties of the structure.
This thesis presents a simple method for calculating electromagnetic excitation forces in the air gap between stator and rotor of a 5 horse power 3-phase squirrel cage induction motor, which are significantly responsible for the noise and vibration in the high frequency range under operating conditions. The proposed method adopts the classical transformer model to represent the electromagnetic circuit in the motor and takes into account skew of the rotor slot and fluctuations of the permeance due to rotor rotations in estimating the electromagnetic excitation forces at each tooth of the stator. Then, the effects of rotor eccentricity and slot opening on the excitation forces are analyzed.
Although it is well known that the sources of structure born noise of small induction motor are the electromagnetic excitation forces at the air gap between stator and rotor, there are not many studies on measuring those forces. In this thesis, also, a method to identify those forces related to vibration, using operational vibration data of frame and experimentally synthesized modal model of structure, was proposed.
The estimated and identified electromagnetic excitation forces were compared with forces measured by traditional flux-detecting coil method.
