Motor efficiency standards create new challenges
Big brother or helpful partner? The federal government's Department of Energy (DOE) has been working hard to change the old stereotype of government as a heavy-handed regulator.
Big brother or helpful partner? The federal government's Department of Energy (DOE) has been working hard to change the old stereotype of government as a heavy-handed regulator. "We realize that the maintenance department is in competition for corporate dollars," says Michael McCabe, Director of the DOE's Office of Codes and Standards. According to Marsha Quinn, Director of Technology Access, Office of Industrial Technologies, "Under our voluntary programs, government doesn't dictate to industry how things will be done. We want to work as partners."
Just bureaucratic posturing, or is it for real? In fact, the DOE is making a noticeable effort to help industry adapt to new minimum standards for electric motor efficiency mandated by congress. Although it wields both carrot and stick, the DOE has chosen to emphasize the carrot, especially toward end users.
The push for higher efficiency motors has its roots in the oil-energy crisis of the early 1970s. A sweeping piece of 1975 legislation called the Energy Policy and Conservation Act (EPCA) launched all sorts of initiatives to reduce the nation's energy consumption, covering products ranging from reduced-flush toilets to fuel-efficient automobiles to energy-efficient electric motors. In 1992, President George Bush signed the Energy Policy Act (EPAct), which amended EPCA and specified particular motor efficiencies to be mandatory 5-yr later, in October 1997.
In addition to the original motivating oil crisis, the "greenhouse" issue has become important. Improved motor efficiencies reduce consumption of fossil fuels for power generation, thereby reducing the quantities of greenhouse gases released from fossil-fueled power plants. Roughly two-thirds of U.S. electric power goes to motors of all kinds, and by far the bulk of that goes to industrial motors over 5 hp.
EPAct affects you
The intent of the EPAct law is to raise the efficiency levels of motors "gently," by placing requirements on the manufacture and importation of designated motors. The law does not require any motor user to replace an existing motor with a higher efficiency model. The initial burden has been entirely on the motor manufacturers, who faced a deadline on October 24, 1997. Designated motors can no longer be manufactured or imported after that date unless they meet specific efficiency requirements.
"Aha!" you may say, "I'm off the hook. I don't need to worry about this stuff until some covered motor dies." That approach could be risky, because as EPAct motors fill the distribution pipeline, buying a "drop-in" replacement motor is becoming a thing of the past. If you're not already EPAct-knowledgeable, you're not alone. Motor manufacturer field representatives indicate that they find lots of misinformation, and report reactions such as "surprise," "disbelief," and "sticker shock." A very good way to avoid pitfalls is to determine the likely replacement for each of your motors before it dies.
Motor types affected by EPAct
EPAct establishes energy efficiency standards and test procedures for commercial and industrial electric motors, and directs the DOE to establish labeling and compliance certification requirements. Only motors having the following characteristics are covered by EPAct:
- General purpose
- T-frame (143T-447T)
- Foot mounted
- Single speed
- NEMA Design A or B performance
- Continuous duty
- 1-200 hp
- 2, 4, or 6 pole
- 230/460 V, three phase, 60 Hz
- IEC frame motors with frames equivalent to NEMA T-frames
- Custom motors that could be used in general-purpose duty (example: a 12-hp motor)
- Imported motors meeting the other criteria.
It's important to be aware that motors having features in addition to those listed above are covered by EPAct, as long as they can be used in general purpose service. For example, a washdown-duty motor or a firepump motor could be used in general purpose service, so they are covered.
Motor types excluded from EPAct
Clearly, the intent is to cover only general purpose motors. "Definite purpose" or "special purpose" motors are excluded. The law defines a definite purpose motor as "any motor designed in standard ratings with standard operating characteristics or standard mechanical construction for use under service conditions other than usual...and which cannot be used in most general purpose applications." An example would be a motor with a special shaft that prevents general purpose use.
A special purpose motor, according to EPAct, is "any motor, other than a general purpose motor or definite purpose motor, which has special operating characteristics or special mechanical construction, or both, designed for a particular application." An example would be an integral brake motor where the brake is within the motor. Following is a summary of motor types excluded from EPAct:
- Single phase
- Motors with no base or provision for a base (such as C-face)
- Motors having special shafts precluding general purpose use
- Two-digit frames (such as NEMA 56)
- TENV and TEAO
- Multispeed motors
- Frame size larger than NEMA assignment for the horsepower
- 50-Hz motors (but not 50/60 Hz)
- 200 V, 575 V, or other voltage motors that cannot be used at 230 or 460 V
- NEMA Design C or D performance
- Close-coupled pump motors
- U-frame motors
- Integral gearmotors
- Motors below 1 hp or above 200 hp
- Rebuilt, rewound, or repaired motors.
There are two reasons why large motors (above 500 hp) are not likely to come under efficiency mandates any time soon. First, large machines already tend to be particularly efficient. Second, they are usually custom designed for specific applications, and appropriate efficiency could vary with application.
EPAct and efficiency
Motors are converters, not users, of energy. Their job is to convert electrical energy into mechanical energy. Efficiency ratings indicate how well they do that job. By definition, efficiency is the ratio of output power (mechanical) to input power (electrical).
Straightforward indeed; yet, applying the definition in the real world gets a good bit more complicated. If an efficiency number is specified for a motor, under what operating conditions does it hold true? How should efficiency be measured? If the efficiencies of two of the same model motor are measured, they are unlikely to be exactly the same. How then should efficiency be stated for a group of same-model motors? (It isn't economically feasible to perform an individual efficiency test on each production motor.)
EPAct incorporates the nominal efficiency values published in NEMA Standard MG-1, Table 12-10, and requires that covered motors meet these values. These nominal efficiencies are for operation at full rated load and are the values found on motor nameplates. Nominal efficiency is arrived at by first calculating the average measured efficiency of a number of samples of a particular motor, and then selecting a value from the list of standardized efficiency values in Table 12-8 of NEMA MG-1 that is closest to, but does not exceed, the average.
The purpose of Table 12-8 is to simplify motor labeling. Rather than permit motor manufacturers unlimited freedom in indicating nameplate efficiency, they are required to choose from a standard set of closely spaced values. This requirement helps prevent advertising claims based on differences in efficiency numbers that might be too small to have any valid significance.
Since the nominal efficiency number is based on an average of measured values for a group of motors, it tells nothing about how much the measured values deviate from the average. For example, the two groups of numbers, 10, 11, 12 and 6, 9, 18 both have the same average value: 11. Therefore, in order to limit the spread of efficiency values about the average, every nominal efficiency number in Tables 12-8 and 12-10 has an associated minimum efficiency number listed.
EPAct's impact now
Make no mistake about it, there are higher efficiency motors in your future. Since October 24, 1997, replacing a general purpose motor almost certainly means buying an "EPAct motor." (The exception would be any motors manufactured before that date that are still in stock.) The characteristics of EPAct motors, also referred to as energy efficient motors, now on the market differ from pre-EPAct motors in three areas: price, mechanical characteristics, and electrical characteristics. EPAct motors also differ from manufacturer to manufacturer in those areas.
Motor manufacturers will have to amortize the large investment made in motor redesign to bring the old Design A and B models up to energy efficiency standards. More importantly, energy-efficient motors simply cost more to build.
The new designs aren't based on technological breakthroughs. Rather, motor manufacturers have attacked the known areas of inefficiency. The result is motors that contain more materials and are more carefully fabricated and assembled. The unavoidable consequence is higher prices, with increases generally in the 10% to 20% range.
Because energy efficient motors contain more materials than the old standard models, they are larger and heavier. Most motor dimensions remain the same; the extra volume is usually accommodated by greater length, which creates the fewest interchangeability problems.
Although some manufacturers are touting lower running temperatures for their EPAct motors, an energy efficient motor may run either hotter or cooler than its old version. Keep in mind that while there is indeed a correlation between efficiency and wasted heat energy, heat energy and temperature are two different things.
In redesigning motors to meet EPAct requirements, manufacturers attacked energy loss due to motor cooling fans and airflow patterns. Cooling fans have tended to become smaller so that less energy has to be diverted to drive them. Depending on other changes made in the frame and cooling system design, the resultant redesigned motor may run hotter or cooler than the previous model.
For some motor buyers, torque may be a source of surprise problems. EPAct Design A and B motors must meet the torque requirements of NEMA MG-1, just like their predecessors. Nonetheless, application problems can arise in these two ways.
- NEMA MG-1 specifies three minimum values of torque for each motor design: locked rotor, pull up, and breakdown torque. MG-1 does not include any torque-speed curves. Since many different curves could exceed the three specified points, performance variations are not only possible, but likely. "Typical" torque-speed curves for Design A and B motors are often published, but they do not come from the MG-1 standard.
- It was common for pre-EPAct motors to exceed the MG-1 minimum torque requirements by a considerable margin. EPAct-compliant motors can meet the MG-1 torque requirements and still produce significantly less torque than the older versions. In some situations, a Design A or B EPAct replacement motor may not be able to successfully start a load that the old motor could start without problem.
Higher efficiency motors also run at slightly higher speeds. Speed differences can cause problems or wipe out the benefits of efficiency gains in certain applications. The horsepower requirements of some loads are highly speed-dependent, so installing an EPAct motor could shift the motor-load system to a new operating point. The new, higher speed operating point may result in undesirable energy consumption, or it may even upset a process.
The balancing act involved in designing energy efficient motors has resulted in somewhat higher locked rotor (starting) currents. Although the MG-1 standard does specify maximum locked-rotor currents, the new generation of motors appears in many cases to barely meet the requirements. Locked-rotor current is very important in sizing motor control components.
In any motor replacement, ratings of components such as starters, overloads, and fuses should be checked against the requirements of the new motor in order to avoid nuisance tripping.
EPAct does not apply to rebuilt, repaired, or rewound motors. An obvious question, though, is "What happens to efficiency if an EPAct motor is overhauled?" The traditional rule of thumb is that rebuilds result in lower efficiency.
The Electrical Apparatus Service Association (EASA) recently published details of an elaborate study to determine the effect of repairs on efficiency. Methods of tear-down, effects of burn-out ovens, and methods of rewinding were examined. The study concluded that properly done repairs do not degrade motor efficiency. Clearly, the key words are "properly done."
To verify compliance, EPAct specifies efficiency testing in accordance with NEMA MG-1 and IEEE Standard 112, Test Method B. The tests are quite elaborate, involving measurement of the various loss mechanisms in a motor. Very few labs are qualified to conduct such tests.
Jim Raba, DOE Office of Codes and Standards, says that the "DOE is currently in the process of developing the final regulations, which will cover accreditation of efficiency testing laboratories and establish procedures for national recognition of certification programs."
There aren't enough independent motor testing labs in existence to achieve the certifications and do all the testing. The immediate goal is to have motor manufacturers' test facilities accredited by third parties.
DOE's proposed regulation also permits some efficiency determinations to be based on alternative methods of calculating efficiency. Motors might then be spot checked by independent labs. Meanwhile, motor manufacturers self-certify EPAct compliance. Motor testing, particularly efficiency testing, is a difficult and complex process. To date, no manufacturer has been accused of fudging data.
How accurate and honest are the motor manufacturers being on their nameplates? In independent tests by Advanced Energy, a lab considered highly accurate, the following trends were noted in a small sample, 15 motors from 15 manufacturers.
- Efficiency : A significant percentage of the motors tested at less than EPAct efficiency.
- Temperature rise : A 40-deg C variation in temperature rise amongst the motors shows how widely similar motors can vary.
- Locked-rotor torque : All units met MG-1 requirements.
- Locked-rotor current : A considerable percentage of the motors failed to meet the MG-1 locked-rotor current limit.
Some other considerations
There are a number of other factors that should be considered for any specific situation or motor application.
- EPAct compliant motors are not all the same. A given efficiency number does not fix motor parameters, only the net combination of parameters.
- Efficiency can vary with motor loading, and EPAct specifies only full-load efficiency. Most motors reach peak efficiency at 60% to 80% of rated load.
- Operation with a PWM variable-speed drive significantly degrades motor efficiency, although the variable-speed capability may increase overall system efficiency.
- The benefit of higher efficiency can be offset by a simple, perhaps unnoticed matter such as slightly unbalanced line voltages. The percent increase in motor heating is about twice the square of the percent voltage unbalance. Thus a 3% voltage unbalance yields an 18% increase in heating.
- Actual motor speed is often rounded off to the nearest 5 rpm on motor nameplates.
- Life-cycle cost evaluations are needed to realistically evaluate replacements and retrofits. MotorMaster+ software is a great help with this. Focus should shift from "lowest initial cost" to "lowest life-cycle cost."
- Many motor manufacturers have prepared booklets summarizing EPAct requirements and related information. Check with your motor sales representative.
- Where several variations of the same type of motor are in use and spares must be stocked, it may be most economical to stock a single motor rated for premium efficiency and inverter duty, rather than several less-expensive motors.
- As the DOE itself says, there is a point of diminishing returns in increasing motor efficiency , where improvements run in the 2% to 8% range. The overall efficiency of electric motor-driven systems presents many more opportunities for improvement, with savings often in the 10% to 50% range.
Plant Engineering magazine extends its appreciation to the organizations in the motor resources listing for their assistance in the preparation of this article. Also providing valuable assistance were the Department of Energy (DOE), Electric Power Research Institute (EPRI), Richard L. Nailen, PE, consultant, and National Electrical Manufacturers Association (NEMA).
Photos courtesy of DuPont/Reliance Electric; energy bar chart data courtesy of EPRI.
Federal EPAct efficiency requirements governing many industrial motors are now in effect.
EPAct requirements affect electrical parameters, mechanical parameters, and purchase price.
Selecting a new or replacement motor can be a complex process.
Careful selection can result in lower overall cost.
MotorMaster+ began as selection software for energy efficient motors, then expanded into a larger database and powerful motor management tool. Packaged on four disks, the windows-based software is delivered with plenty of support, including a well written 124-p manual, online training, and a toll free help line.
The MotorMaster+ database contains both performance and price information for over 17,500 NEMA Design A, B, C, and D three-phase motors, 1 to 700 hp. It also includes close-coupled pump and IEEE 841 motors. Here is a sampling of the software's capabilities:
- Create inventory records for inplant motors and motor driven equipment
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- Display monthly and annual rolling average energy use and cost per unit of plant production
- Conduct life-cycle cost analyses
- Generate a greenhouse gas emissions reduction report
- Print reports and graphs of information.
Electric motor resources
The manufacturers and organizations listed below responded to a request for information from Plant Engineering magazine. For data on their products or services visit the listed website.
Company or organization Website
Baldor Electric Co. www.baldor.com
Boston Gear www.boston.gear.industry_net
GE Motors www.ge.com
Leeson Electric Corp. www.leeson.com
Lincoln Electric Co. www.lincolnelectric.com/motors
Louis Allis Co. www.louisallis.com
Marathon Electric www.marathonelectric.com
Rockwell Automation/Reliance Electric www.reliance.com
SEW-Eurodrive, Inc. www.sew-eurodrive.com
Siemens Energy & Automation, Inc. www.sea.siemens.com
TECO-Westinghouse Motor Co. www.teco-wmc.com
U.S. Electrical Motors, Div. Emerson Electric www.usmotors.com
WEG Electric Motors www.ajaxmotors.com
Advanced Energy (motor testing) www.aec.ncsu.edu
Danfoss Electronic Drives (motor drives) www.danfossdrives.com
Electrical Apparatus Service Association (EASA) www.easa.com (under const.)
Grundfos Pumps Corp. (VSD pumps) www.us.grundfos.com
Motor Challenge Program (motor information) www.motor.doe.gov
National Electric Coil (rebuilder -- large motors) www.national-electric-coil.com
Rockwell Automation/Allen-Bradley (motor controls) www.ab.com
W. W. Grainger (distributor) www.grainger.com
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