More about energy-efficient motors

Control Engineering’s July 2005 cover story, “Energy-Efficient Motors Deliver Savings,” drew a number of comments from readers.


Control Engineering ’s July 2005 cover story, “ Energy-Efficient Motors Deliver Savings ,” drew a number of comments from readers. Given the large consumption of electric power attributed to these motors and rising energy costs, users in industry and everyday consumers should be concerned about efficiency of their motors. I am sharing snippets of comments from a couple of readers and users/specifiers of motors.

John Atkins, plant engineer for a division of Vertis Inc . (Newark, NJ), says, “More people need to understand that the initial price of a typical electric motor used in industry represents only 20% of the total cost for the motor in the first year or two of operation.” Moreover, effect of initial cost continues to diminish with longer operating life.

He mentions that various software tools can help assess motor efficiency and select motors. He is especially keen on MotorMaster+ from the U.S. Department of Energy (DOE), which includes a catalog of more than 20,000 ac motors. Now in Version 4.0, MotorMaster+ lists motors rated by efficiencies or cost for any given operating scenario, provides good costing information, and includes an “excellent first time life-cycle costing module,” according to Atkins, who says he used the database software for more than eight years. The software also “has great capabilities to show actual costs of repair versus buy and to show costs in life-cycle analysis,” he states. MotorMaster+ 4.0 and other software tools can be found by clicking here .

When making his purchase requisition with a completed costing module for a motor that costs more than the one found by the purchasing department, “It just blows away the questions,” adds Atkins. “And financial reviewers are very interested to see that someone besides them looks at all the variables, such as internal rate of return, installation and operating costs, depreciation, and tax considerations.”

Another reader, who did not want his name or company affiliation used, mentioned that not all “energy-efficient” motors are created equal. He referred to numerous “cost-optimized designs” of energy-efficient (EE) motors in the market that are susceptible to lower efficiency when applied in a poor-power-quality environment. He differentiates between these lower cost EE motors and premium EE motors with respect to design, frame materials, and manufacturing. “These cheap EE motors are what the multitude is buying and they are not aware that their reliability and productivity will suffer as a result,” he says.

This reader also references a technical paper, “A Comparison of Two Energy Efficient Motors,” published in IEEE Transactions on Energy Conversion, Vol. 13, issue 2, June 1998—which “provides evidence (based on limited testing) that a particular energy-efficient motor appears to have a unique susceptibility to reduced negative sequence impedance.” This allows flow of higher negative sequence current under conditions of voltage unbalance or harmonic distortion in bus voltage, leading to more rotor heating and other conditions that may combine to cause premature failure. “Existing industry guidance for application of three-phase 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,” the paper says.

My question to energy-efficient motor manufacturers: Are today’s EE motor products adequately addressing this concern?

—Frank J. Bartos, executive editor, Control Engineering,

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