A COMPARISON OF 2 ENERGY-EFFICIENT MOTORS

Limited testing provides evidence that a particular energy efficient m otor (EEM) appears to have a unique susceptibility to reduced negative sequence impedance. The effect of the reduction in negative sequence impedance is to allow a higher negative sequence current now under con ditions of voltage unbalance or negative sequence harmonic distortion in the bus voltage. This higher current flow results in additional hea ting of the rotor and 120 Hz vibration, and may combine with other con ditions to cause premature failure. In addition, energy efficient moto rs operate at slightly higher speeds, and may sometimes cause the driv en loads to require more horsepower from the motor causing further ove rheating. Existing industry guidance for the application of three phas e motors in poor power quality environments may be inadequate because this guidance does not consider the combined effect of such conditions as voltage unbalance, harmonic distortion and over voltage. A specifi c application of an EEM is studied in this paper; the motor may be fai ling due to a combination of over voltage, voltage unbalance, harmonic distortion and loading the motor to full rated load, while the motor has a Service Factor of 1.0.