Influence of Manufactory Asymmetrical Squirrel Rotor on Motor Current Responses

In current spectrum, the spectral sidebands at (1 ± 2ks)fs (s is rotor slip, k represents integer and fs is the fundamental supply frequency) are commonly used as the indicator of bar faults in induction motors (IMs). A symmetrical rotor should not show any peak at such frequencies. However, in the current spectrum of most of healthy IMs, the sidebands at (1 ± 2ks)fs also show observable peaks. That should be caused by the rotor machining error. Although the manufacturers try their best to reduce the asymmetricity degree to guarantee the rotor is balanced, the asymmetricity rotor still cannot be avoided. Although the sideband peak value increases along with the bar breakage level, it still hard work to recognize whether the IM diagnosed is with only machining error or with more breakage. To study how machining errors affect the rotor current and stator current and what kind of machining error factors will result in the fluctuation of sidebands peaks. Current model of symmetrical rotor, asymmetrical rotors with three level machining errors and with multiple breakage bars are investigated numerically. The results show the level of machining errors and the positions of the errors affect the sideband peak values significantly. These novel findings will provide foundation for accurate diagnosis of motor rotor health conditions.