Voltage unbalance and harmonic distortion effects on induction motor power, torque and vibrations

Voltage unbalance and harmonic voltage distortion affect the power, torque and vibrations on induction motors (IM). In this paper, we compute the frequency of the oscillations of the power, torque and vibrations due to voltage unbalance and harmonics and we present laboratory results to verify the calculations. We also show that typical values of harmonic distortion combined with the maximum levels of voltage unbalance allowed by standards are sufficient to introduce vibrations levels under which continuous operation of IMs is not recommended. This result has important implications for root-cause analysis of IM trip due to vibrations because protection engineers can rule out mechanical problems by verifying that vibrations are only present during high levels of voltage unbalance and harmonic distortion.