The Right Motors Can Empower Savings
Using motors and ancillary equipment that’s well designed and matched to the application can cut energy costs significantly.
“Sustainability” is more than a material issue. It’s a power trip.
When it comes to saving both money and the environment, cutting back on packaging material is perhaps the most obvious (and visible) strategy. But reducing power consumption, while not as attention-getting, has the potential to be just as rewarding. And one of the best ways to do that is to specify, use and maintain electric motors, drives and power transmission equipment in a way that maximizes a line’s overall energy efficiency.
With motors, those who buy packaging and material-handling equipment operate at one step removed from original equipment manufacturers (OEMs). But knowledgeable end users can make sure that the equipment they buy comes with the most energy-efficient motors and accessories possible. And they can follow maintenance and rebuilding practices that will further increase their energy advantage.
Servo motors are the motors that tend to attract the most attention on packaging lines, for various reasons: their explosive growth over the last dozen or so years, their versatility and the increasing sophistication of their motion controllers. But in terms of potential energy savings, the best candidates on a packaging line are the workhorse, analog, three-phase AC motors that power main machinery components and conveyor driveshafts, along with their accessories: the drives that feed them current and the gearboxes that convert their shaft rotation into torque.
These motors are often considered plain-vanilla, commodity items, interchangeable within certain parameters (such as washdown resistance or extra-sanitary construction). This perception has been furthered by consolidation among motor suppliers, the most recent being Baldor’s acquisition of the Reliance and Dodge units of Rockwell Automation early this year.
“The customers have not for the most part caught on to energy savings through more efficient motors,” says Chris Medinger, stock product manager for Leeson Electric. “They’re still buying based off of cost.”
But when it comes to energy consumption, it pays to be aware of two important, standardized distinctions that exist among AC motors: EPAct and NEMA Premium.
Efficiency MandatesEPAct refers to the Energy Policy Act of 1992, which mandated that general purpose electric motors of 1 to 200 horsepower (HP) manufactured in the United States had to meet specified efficiency standards by October 1997. (At press time, Congress was considering tightening the standards further.) That includes most AC motors on today’s packaging lines-but there are exceptions, says John Malinowski, a product manager for Baldor.
For example, if a motor is mounted to a gearbox but doesn’t have a mounting base, it can legally operate at less than EPAct-specified efficiency standards. Therefore, it can pay for a purchaser who is mindful of energy efficiency to make sure that all motors on new equipment, even those that fall within EPAct loopholes, meet the standard or are specified with NEMA Premium efficiency.
NEMA Premium is another, higher standard. NEMA is the National Electrical Manufacturers Association, a trade and standard-setting organization. The NEMA Premium standards for electric motor efficiency, generally speaking, exceed the EPAct standards by one to two percentage points.
That extra efficiency can translate into significant energy savings over the life of the motor, says Ted Jones, senior program manager for the Consortium for Energy Efficiency, most of whose members are electric and gas utilities. Southern California Edison is among electric utilities that now base rebate programs on industrial customers’ use of NEMA Premium motors, rather than the lower EPAct standards. “The biggest message [for equipment buyers], I would say, is request NEMA Premium,” Jones says.
NEMA Premium motors cost about 15% to 20% more than standard motors, but the energy savings often give a quick return on investment, says Rob Boteler, director of marketing for motor supplier Emerson Motor Technologies. That situation applies to aftermarket motors replaced by end users as well as those that come with original equipment.
“If I’m [a beer bottler] and I have an old conveyor with 20-year-old motors on it, can I just pop on NEMA Premium and enjoy the benefits of a more efficient motor?” Boteler asked. “The answer is, you can.”
Repair, not replaceIn many cases, end users find it more cost-effective to repair motors instead of replacing them. When motors are repaired, they also can have their energy efficiency enhanced, Jones says: “The common wisdom out there is, you take a hit every time you have a repair done to a motor-it loses performance. [But] that’s not a law of physics; it need not be the case.”
Jones says end users can insist that repairs be done according to ANSI/EASA (American National Standards Institute/Electrical Apparatus and Services Association) standards. The most common repair option to improve energy efficiency is rewinding the copper wire in the stator (the motor’s stationary inner core). Switching to a traditional, hand-inserted lap winding and increasing the slot fill (the overall amount of copper in the stator’s hollow slots) can improve heat transfer and reduce copper loss and winding temperature, improving the motor’s overall efficiency.
No matter how efficient a motor is, a packaging line will lose efficiency if its motors are mismatched to the job. The tendency in many cases is to specify motors that are more powerful than necessary, to avoid straining them with an overmatched application. But using motors with too much horsepower can be just as wasteful.
The “sweet spot” for motor use, in which the motor will operate at peak efficiency, is between 75% and 100% of load capacity. A too-powerful motor that consistently runs below capacity will waste electricity.
Unfortunately, that happens often, Boteler says: “Every engineer looks at [an application] and says, ‘Well, a 5-horsepower motor would probably work here, but you know what, we know how these maintenance guys are, so we’ll put a 7½-horsepower in.’ Well, then what happens is, you get out in the field and something changes in production and you don’t even need 5 horsepower, the motor’s running at 4 horsepower, but you’ve sized it at 7½.” Once a motor is running at 50% or more below rated capacity, its efficiency drops dramatically, Boteler says.
Use the off switchAnother way to match the motor to the load is to avoid running it unnecessarily. “The most energy-efficient motor in the world is the one that’s not running,” Malinowski says. A conveyor belt that frequently has nothing to carry, for instance, can be started and stopped via feedback from sensors, he says: “I don’t know how many plants you walk through that you look out there and all the conveyors are just sitting there churning and there’s not anything running on them. Shut ’em off.”
In some cases, a conveyor consumes less power by starting repeatedly than by running when it doesn’t need to. However, this consideration needs to be carefully balanced against a possible decrease in motor life caused by too-frequent starts and stops.
One way to lessen the power impact of frequent start-ups is to use an inverter drive, Medinger says: “If you use an inverter with a soft start, you would gain [energy efficiency] because you don’t have that high inrush of current as you do from across-the-line starting.”
The use of variable-speed drives is an energy-saving strategy that is coming into increasing use. Standard drives for AC motors simply keep them running at a single speed; a variable-speed drive enables a motor to run at different speeds by varying the amps it feeds to the motor.
Variable-speed drives can be useful in material-handling equipment, says Mike Hosch, engineering director for Dorner Manufacturing, a supplier of conveyor systems. They can be a good choice in applications where the load varies, where the conveyor speed has to change with product changeovers, or where the end user wants some leeway to scale up speeds in the future.
Power-transmission equipment also presents an opportunity for energy savings. The most common such devices are gearboxes, also known as speed reducers, which mechanically convert the rotation of a motor’s shaft into torque that turns machine components or moves conveyor belts.
As with motors, more expensive equipment can lead to long-term savings. Worm-gear speed reducers have been commonly used because they have relatively few moving parts, which makes them inexpensive to buy and maintain. The downside is that they can lose up to 50% of efficiency in translating the motor’s power into torque. Devices like helical-gear reducers are more expensive but can operate at up to 98% efficiency. For this reason, worm-gear devices are being phased out, but some equipment manufacturers still use them, either to save money or because their smaller size warrants their use in a given machine.
Electric motors and their accessories may not be the highest-priority concerns of equipment buyers. But being aware of energy issues, both before and after purchase, can improve a plant’s “green profile”-in terms of both environmentalism and dollars.
For more informationBaldor Electric Co.
Dorner Manufacturing Corp.
Emerson Motor Technologies
Leeson Electric Co.