Calculation, Analysis, and Verification of Natural Frequencies of Stators With Unequal-Length Casings of Rotating Motors

Overcoming the drawback of low accuracy in stator natural frequency calculation results caused by excessive simplification of the casing in existing analytical methods (AMs), a universal and accurate AM for the natural frequencies of stators with unequal-length casings of rotating motors is proposed. The stator yoke and frame are considered as a composite shell with uneven material parameters, inside which the continuous conditions of displacements and strains can be ensured, and complex structures such as teeth, windings, heat dissipation ribs, junction boxes, and feet can be accurately considered. Afterward, the energy equations of each part of the stator are derived and the characteristic equation of natural frequencies is accurately constructed based on the energy method. The natural frequencies of two prototypes of the stator with casing and the stator with windings and casing are quickly and accurately calculated. In addition, detailed finite element analysis and prototype testing are performed to verify the stability of the proposed calculation method for stator natural frequencies and the accuracy of calculation results. Finally, the vibration characteristics of the stator are analyzed, the excitation mechanism of strong electromagnetic vibrations and the suppression basis are accurately revealed, and the variation laws of stator natural frequencies with dimensional and material parameters are summarized, which lays a solid theoretical foundation for the rapid adjustment of stator natural frequencies and effective suppression of electromagnetic vibrations. The analysis shows that the extension lengths of casing ends significantly impact stator natural frequencies, and the dimensional and material parameters of the casing must be accurately considered in the analysis and calculation of stator natural frequencies.