To find natural frequencies a modal analysis is required. This analysis can be done in two different ways: using an effective numerical approach (Finite Element Method - FEM) or doing an experimental modal test [5].
In paper [6] it was developed an experimental modal analysis for the rotor of a two-phase induction motor. The rotor was considered as one 3D part defining materials properties for the shaft (steel) and the damping factor for the silicon steel core.
The theoretical and experimental modal analysis highlights the influence of the complex structure on natural frequencies.
In the present paper, based on the experience, the modal study was extended to the whole three-phase squirrel-cage induction motor.
There were found the natural frequencies of the assembly and there were compared with the vibration frequencies developed during operating regime for finding the resonance conditions. The theoretical values of the natural frequencies were found using finite element modal facilities and the values were validating using experimental method of impact hammer modal test [7], [8].