Vibration Magnitude Analysis on Induction Motors of Different Efficiency Classes Due to Voltage Unbalance

Small efficiency improvement in induction motors (IMs) often lead to large monetary savings over time. These monetary savings justify the current movement toward the use of higher efficiency IMs. In many cases replacing a standard efficiency IM with a higher efficiency one is transparent to the user. In other cases, however, there are side effects which need to be considered. In this paper, we present data showing that vibrations due to voltage unbalance are significantly more pronounced on higher efficiency IMs than in standard efficiency ones. We first show analytically that for a given condition of voltage unbalance and motor load the power driving the vibrations are larger for higher efficiency IMs. Then we present laboratory tests on three IMs of increasing efficiency and present the measured power and vibrations level.