The gains might be small and the cost differential large if you change from a premium to a super-premium, or high-efficiency, motor. The extra expense can be worth it, though, given the duty cycle. However, other motor capabilities, such as being able to run efficiently enough at an appropriate and variable speed, might offer an even better payoff.
An illustration of these various ways to boost efficiency comes from Portescap. The company makes motors for smaller applications, with a line of stepper, dc and brushless products. The stepper motors have efficiency as high as 60%, while the brushless motors come in at +90%, roughly equivalent to the super-premium class of ac induction motors.
In the last half of 2013, the firm launched its Ultra EC series of brushless, slotless dc motors. These have several innovations, some of which are particularly important when it comes to efficiency, according to Dave Beckstoffer, Portescap’s project manager.
"One is the coil design," he says. "That allowed us to increase the power density, increase the speed and have the motor run much cooler."
That extra performance can be important in some settings. For instance, the motor could rapidly close a pick-and-place gripper about 80% of the way, with the final one-fifth completed at a slower and more part-friendly rate. The overall effect could be a faster cycle time, as well as an efficiency improvement.
Kollmorgen designs and makes ac induction and permanent magnet motors. Its products are found, for example, in the fans that circulate air within large buildings. In such applications, premium motors might have efficiencies around 90%, while super-premium motors might be in the low- or near-mid-90% range, says Tom England, Kollmorgen’s vice president of market development.
The efficiency gain is a few to, at most, 5%. But that small difference can be important.
"Once you get into some big motors, such as 50- hp motors that run pumps, fans and compressors 24 hours a day in your plant, a couple of percentage points efficiency end up being a fair amount of dollars over a year’s time," England says.
That efficiency gain is achieved because some of the design and construction techniques include a copper—instead of aluminum—bar rotor and very high slot-fill in the stator. Those add to the cost of the motor, but if the duty cycle is high enough, the extra expense is justified.
An even-better payoff can arise from varying motor speed to match the task at hand. A pump, for instance, might only need to run at full power half the time and lope along at three-quarters full output the rest of the time. The power savings grow as the cube of the speed, England says, so getting the latter right can outweigh other possible efficiency improvements.
NovaTorque manufactures brushless, permanent-magnet, ac motors. Alan Crapo, vice president of electromagnetics at NovaTorque, says the company chose to use low-cost ferrite materials instead of rare-earth magnets, as the latter can be expensive. Hitting efficiencies in the 95% range with this approach does require some careful choices that are designed to boost the magnetic performance.
"We focus the flux in three dimensions, and we have a cone shape, which gives us additional flux focus between the rotor and the stator," Crapo says.
Employing such motors can bring cascading benefits, he adds. Using a higher-efficiency motor for a fan, for instance, lessens the overall cooling load because the motor itself is producing less waste heat.
Finally, one of the best ways to boost motor efficiency could lie in doing some upfront work, notes Rahil Hasan, motion marketing manager at Rockwell Automation. This is based on the premise that right-sizing components can lead to less wasted power.
For that, Rockwell Automation offers software tools that optimize the sizing of the system. Motors, drives and, sometimes, mounting frames can be made smaller, potentially saving money and improving system efficiency.
To help this process, Rockwell Automation optimizes motors and drives, so they work better together. For instance, when the company launched its low-inertia VPL servomotors, it did so after having tweaked the guts of the motor to make it more efficient in the system. "We optimized the windings in the motor, the speeds they operate at and the peak currents they handle," says Hasan.