Following are some commonly asked questions regarding energy efficient motors. As time goes on different questions and answers will be put on this page for the purpose of educating industry. The Department of Energy has developed the MOTORMASTER+ program. This is a sophisticated software based program which can analyze electric motors in a plant and will determine their efficiencies and costs. EASTLAND INDUSTRIES, INC. is a MOTORMASTER+ PARTNER and also an ALLIED PARTNER with the Department of Energy.
Please contact Eastland Industries at 1-888-547-6500 for further information in developing your program. Remember October of 1997 starts a new era in electric motor manufacturing and usage.
1. What is an energy efficient motor?
An "energy efficient" motor produces the same shaft output power (hp), but uses less input
power (kW) than a standard-efficiency motor. Energy efficient motors must have nominal
full-load efficiencies that meet or exceed the NEMA threshold standards.
Many motor manufacturers produce models significantly exceeding the NEMA standard. These may have the term "premium" or other superlatives in the model name, but there is no NEMA standard for any terminology other than "energy efficient."
2. How is an energy efficient motor different than a standard motor?
Energy efficient motors are manufactured using the same frame as a standard T-frame motor, but
have:
Starting in October 1997, however, the Energy Policy Act of 1992 requires most general purpose induction motors between 1 and 200 horsepower (hp) to meet more stringent minimum efficiency standards.
4. Where can I buy an energy efficient motor?
Energy efficient motors can be purchased directly from Eastland Industries at 1-888-547-6500
.
5. Are energy efficient single-phase motors available?
NEMA has no standard for "energy efficient" single-phase motors, but efficiency ranges widely
among models. A few manufacturers are beginning to produce higher efficiency lines of
single-phase motors.
6. Do energy efficient motors require more maintenance?
No. Energy efficient motors have the same maintenance requirements as standard motors.
7. What horsepower, speed, and voltage ranges are available?
Energy efficient motors are available for most sizes 1 to 500 hp at speeds of 3600, 1800, 1200,
and 900 rpm and three-phase voltages of 208, 230, 460, 575 and higher.
8. Can an energy efficient motor replace my present U- or T-frame motor?
Yes. Since T-frame energy efficient motors generally use the same frame casting as a standard
motor, standard T-frame to energy efficient T-frame should be a straight replacement. An adapter
or transition base is required for a U-frame to T-frame replacement. In addition, some
manufacturers now make energy efficient U-frame motors. Contact Eastland Industries at 1-888-547-6500
for specifics.
9. Should I rewind my standard-efficiency motor or purchase an energy efficient motor?
An energy efficient motor will result in lower energy costs when compared with a rewound
standard-efficiency motor. Its cost effectiveness will depend on the hours operated, motor
efficiencies, utility rates, and the difference in cost between the rewind and the energy
efficient motor.
Current rewind shop practices are outlined in the EPRI/BPA report Industrial Motor Repair in the United States: Current Practice and Opportunities for Improved Energy-Efficiency and the companion document Quality Electric Motor Repair: A Guidebook for Electric Utilities.
10. Can a standard motor be rewound as an energy efficient motor?
It is sometimes possible for a standard motor to be rewound with slightly larger diameter wire. This rewind
procedure can slightly improve the efficiency and adversely increase the starting current of a standard motor
above its initial level. However, the efficiency would still be lower than that of a new energy efficient
motor because of its unique physical characteristics. Energy efficient motors can be rewound to
maintain their original efficiency.
11. What is the efficiency of an energy efficient motor at different load points?
The efficiency of any motor varies with such factors as size, speed, and loading. Energy
efficient motors offer performance improvements over standard-efficiency motors under
full, partial, and unloaded conditions.
12. Do energy efficient motors maintain the same percentage edge over standard?
Yes. Most manufacturers are designing their energy efficient motors to provide peak efficiency
at 75 percent to 100 percent load. Typically efficiency stays fairly constant from full down to
50 percent load, but the power factor drops significantly.
13. Do energy efficient-motors require more starting current?
Sometimes. There are two terms (often misused) pertaining to starting current, "inrush" current
and "locked rotor" current. The familiar "locked rotor" current begins after contact closure
and tapers off over several seconds while the motor accelerates. Locked rotor current is
limited by NEMA standards to roughly six times full load current for both standard and
energy efficient Design B motors. Design E motor standards are consistent with European
standards and allow a higher locked rotor current in most horsepower ranges, roughly
10 times full load current.
The more insidious aspect of starting current is the momentary "inrush" current, which persists for less than a hundredth of a second and can substantially exceed locked rotor current. Inrush current can spike as high as 13 times full-load current in standard motors and as high as 20 times full-load current in Design E and energy efficient Design B motors. Inrush current is too brief to trip thermal protection devices, but energy efficient motors powered through magnetic circuit protectors can sometimes experience nuisance stating trips.
14. What is the power factor of an energy efficient motor?
Power factors vary tremendously depending on motor loading manufacturer. While some energy efficient motor models offer power factor improvements of two to five percent, others have lower power factors than their standard motor counterparts.
Overall, replacement of a standard with an energy efficient motor isn't likely to have much influence on power factor. On the average, a power factor improvement of less than one percent is expected. In any event, power factor correction is easily achieved by adding external capacitors.
15. I have heard different types of efficiencies quoted. What are they?
The following motor efficiency definitions are used: Quoted, Nominal, Average, Expected, Calculated, Minimum, Guaranteed, and Apparent. The most commonly used are Nominal and Minimum, defined as:
18. Is the service factor any different from that of a standard motor?
No. Service factors for both standard and energy efficient motors range from 1 to 1.25 with about 88 percent of motors at 1.15.
19. How much do energy efficient motors cost?
Generally, they average 15 to 30 percent more than standard motors, but depending on the specific motor manufacturer and market competition, they can be even less expensive. It is often possible to negotiate a lower price premium when purchasing a large quantity of energy efficient motors. The price premium per horsepower is lower for the larger motor ratings.
20. What is the payback period for selecting an energy efficient versus a standard-efficiency motor?
The payback period varies according to the purchase scenario under consideration, cost difference, hours of operation, electrical rates, motor loading, and difference in motor efficiencies. For new purchase decisions, the simple payback on the incremental cost of a continuously operated energy efficient motor can be recovered through energy savings in well under two years.
21. Do terms such as "premium", high", "super", "ultra", "plus", or "extra" describe specific motor efficiency characteristics?
Manufacturers are free to select descriptive terminology for use in identifying and marketing motor lines. The term energy efficient, however is restricted to motors meeting the NEMA MG1 Table 12-10 full-load efficiency standards.
22. Are oversized motors less efficient than motors that are matched to their load?
Surveys indicated that most motors are underloaded by one-fourth to one-third. The efficiency of typical motor designs peaks at three quarters load and remains relatively uniform down to the 50 percent load point. A motor replacement analysis should be conducted for motors operating below 40 percent of their full-rated load.
Oversized motors will require greater starting currents and operate with a lower power factor than motors that are closely matched to load.
23. Don't energy efficient motors always cost less to operate?
Energy efficient motors have a lower rotor and stator resistance and thus a higher inrush current and full-load speed than standard-efficiency motors. Speed changes significantly affect the power draw by centrifugal loads. The shaft power requirements for a centrifugal fan or pump loads varies as the cube of the speed while the flow of air or fluid discharge varies linearly with speed.
An increase in driven-equipment load can result in a greater power of kilowatt draw despite the lower inherent losses of the energy efficient motors.
The cost penalty due to operating at a higher full-load speed is related to load characteristics. For instance, a motor driving a pump which fills a reservoir tank may operate in an on/off mode. While the kilowatt draw may be higher, the operating time is reduced due to the provision of increased flow. In contrast, given a continuously operating system, the extra pumping capacity may be wasted in throttling and friction losses. The entire system of process should be examined prior to replacing a standard with an energy efficient motor. Also, not all energy efficient motors have higher speeds than their standard counterparts.
24. Don't energy efficient motors operate "cooler"?
External temperature readings are often interpreted as a measure of heat rejection.
If two motors are identical, the one with the lower losses will indeed operate at a lower temperature due to decreased internal heat production. Lower losses, however, result in diminished need for ventilation air, and fan cooled energy efficient motors are often equipped with a smaller fan to reduce windage losses. The consequence of fan design modifications is that an energy efficient motor may have a running temperature as high or higher than that of a standard-efficiency motor with significantly higher losses.
25. Do energy efficient motors suffer a loss in efficiency when they are repaired?
Not necessarily. Efficiency losses can occur in either standard or energy efficient motors when poor quality control is observed. The core can be damaged by excess heat during winding removal. Any deviation from original wire gage and winding pattern generally increases losses. Machine work that alters original clearance and tolerance, and substitution of nonequivalent parts such as sealed bearings for shielded bearings can also reduce efficiency. Standard and energy efficient motors have comparable susceptibility to these offenses.
26. Don't energy efficient motors have to be oversized because they don't develop enough starting torque?
The same minimum allowable locked rotor (starting) torque is specified by NEMA for all Design A and B motors regardless of efficiency. NEMA standards for Design E motor locked rotor torque are higher than Designs A and B levels for some horsepower and speed combinations and lower for others. While some energy efficient motors may exhibit a slightly lower locked rotor torque than their standard-efficiency counterparts, no problems should be posed except for special applications such as heavily loaded conveyors. NEMA Design C motors should probably be specified for such applications anyway. Full-load, breakdown and locked rotor torque values are available for most energy efficient and standard motor models within the MotorMaster+ Electric Motor Selection software.
27. Isn't the efficiency gain insignificant between large standard and energy efficient motors?
While the percentage improvement obtainable decreases as motor size increases, the energy and dollar savings per hour of motor operation increases substantially. A one-point efficiency improvement for a 100 hp motor will save more energy than a nine-point efficiency gain for a ten hp motor.
The price premium per kW saved is comparable across a broad range of hp. Small improvements are worth pursuing.
28. Don't energy efficient motors have a longer expected service life due to their being equipped with better and oversized bearings?
Most motor bearings are oversized. Improved bearings are available for both standard and energy efficient motors. Motor life is not significantly correlated to efficiency. Conversely, it is highly dependent upon proper application, maintenance, and environmental conditions.
29. Aren't energy efficient motors unsuitable for adjustable speed drive applications?
"Severe-duty" application conditions are not affected by motor efficiency. Energy efficient motors may, in fact, be more suited for variable speed drive use than their standard-efficiency counterparts. Many manufacturers now produce energy efficient ASD, inverter drive, or inverter duty motors. These motors are provided with a totally enclosed nonventilated enclosure or are equipped with a fixed-speed fan or blower system.
30. Isn't a quality rewind of an old motor just as good as purchasing a new energy efficient motor?
No. It is sometimes possible to slightly improve efficiency of an old motor by using larger diameter wire or replacing aluminum wire with copper, but it is rare. A quality rewind can usually equal, but not exceed original efficiency.
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