Very clear assessment. The rotor is absolutely healthy. Torque level is high enough and constant. Torque band is constant. The frequency plot shows side bands at frequencies other than the ones of interest. Rotor sidebands would have to be at 59.28Hz, yet the sidebands shown here are at 55.1Hz. These sidebands are probably caused by mechanical resonances; definitely not by a deteriorated rotor cage.
Early degradation; healthy rotor bar:
This signature is a typical example of a very early stage of degradation. The caution level is not reached, yet there is a distinct signature available. Torque level is sufficient, and constant during acquisition.
Course of action: increase frequency of predictive maintenance observation, and monitor test log closely in future.
Broken Rotor Bar Warning:
Classic case of broken rotor bar. Fundamental frequency is at 60Hz, the sideband is automatically identified and displays a vertical line showing a red condition through it. The torque ripple graph shows that during acquisition the torque level was constant. Looking closer, the internal frequency of the torque ripple shows the signature of a severe broken rotor bar under higher slip condition.
