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   Products > ... Baldor Super-E Motors  > 10 Ways to Save Motor Costs

Motor energy efficiency legislation passed in the past two decades has focused on the efficiency of general-­purpose motors. The Energy Policy Act (EPAct) of 1992 covered only AC induction motors of 1 to 200 horsepower (HP) with rigid mounting bases. The Energy Independence and Security Act of 2007 (EISA), passed by Congress and signed into law Dec. 19, 2007, built on this legislation and expanded coverage through 500-HP motors. The updated EISA-mandated efficiency standards apply to general-­purpose, three-phase, AC industrial motors from 1 to 500 HP manufactured for sale in the U.S. This legislation goes into effect Dec.19, 2010.

The U.S. Department of Energy (DOE) is responsible for establishing the rules to implement and enforce EPAct and EISA.

Federal Motor Efficiency Standards Based on NEMA Premium® Motors

The National Electrical Manufacturers Association (NEMA) recommended and helped draft minimum efficiency levels for motors regulated by EISA. The U.S. DOE adopted NEMA energy-efficient and Premium efficient motor standards as its federal motor efficiency performance standards specified in the act. NEMA Premium motors are designed for high efficiency.

The efficiency standards under EISA for each general-purpose rating (Subtype I) from 1 to 200 HP that were previously covered by EPAct 1992 specifies a nominal full-load efficiency level that is based on NEMA Premium efficiency as shown in NEMA MG 1, Table 12-12 (see Figure 1 and Figure 1a). All general-purpose motors (Subtype I) rated from 1 to 200 HP currently under EPAct and manufactured after Dec. 19, 2010, must meet or exceed this efficiency level.
Figure 1

General-purpose electric motors (Subtype II) not previously covered by EPAct 1992 will be required to comply with energy efficiencies defined by NEMA MG 1, Table 12-11. The term general-purpose electric motor Subtype II means that the motors must incorporate the design elements of a general-purpose electric motor Subtype I and also must be configured as one of the following:

  • U-frame
  • Design C
  • Close-coupled pump
  • C-face or D-flange footless
  • Vertical solid shaft normal thrust (as tested in a horizontal configuration)
  • 8-pole (900 RPM)
  • Polyphase (with voltage other than 230 or 460 and not more than 600)
  • 201 to 500 HP

Generally, efficiency levels mandated by EISA for Subtype I motors fall under the present efficiencies of existing NEMA Premium efficient motors for general-purpose 1- to 200-HP motors as covered by EPAct 1992.

The Subtype II 1- to 200-HP and general-purpose 201- to 500-HP motors may require manufacturers to raise the efficiency of some designs to comply with EISA, as defined in NEMA MG 1, Table 12-11; however,  many designs may already comply. NEMA Premium efficient motors meet or exceed the EISA requirements for either of these motor types.

EISA requires that all custom motors built into OEM equipment that fall within the parameters of the act comply with the efficiency levels for that type of motor.
Figure 1a

Motors with IEC metric frame dimensions of IEC 90 frame and larger also fall under EISA.

EISA makes no distinction between stock or custom motors, only whether the motor falls within the guidelines of the definitions and parameters as defined within the act. The determining factor under EISA is whether a particular motor meets the law’s definition of "electric motor."

EISA also applies to motors manufactured outside of the U.S. and imported for use. This also includes motors as a component of another piece of equipment.

Every OEM should prepare for the changes by developing new designs immediately—and well before the Dec. 19, 2010, deadline—particularly when UL or CSA approvals are required.

Exempt Motors

Motor configurations not covered by EISA are:

  • Single-phase motors
  • DC motors
  • Design D with high slip
  • Adjustable speed with optimized windings
  • Customized OEM mounting
  • Intermittent duty
  • Integral with gearing or brake where motor cannot be used separately
  • Submersible motors

Not every three-phase, 1- to 500-HP electric motor falls under EISA, such as some special OEM designs with proprietary mounting configurations, but most do. The following motor configurations are exempt from EISA compliance:

  • Integral gearmotors
  • Integral brake motors  
  • Inverter-duty motors with windings optimized for adjustable-speed drives (ASD) that cannot be line-started
  • Design D high-slip motors

Fractional-HP and 48- or 56-frame motors are not mandated under EISA. Only 1- to 500-HP motors with 3-digit frame NEMA numbers (143T and up) are ruled by EISA. This also includes equivalent IEC frame designations or 90-frame and larger.

EISA does not apply to motors exported outside the U.S., including motors mounted on equipment. The DOE requires that these motors or their packaging be specifically marked "Intended for Export." Countries outside of the U.S. are enacting their own minimum efficiency performance standards (MEPS) that may require compliance.

The law applies only to new motors manufactured after Dec. 19, 2010. EISA does not require that electric motors in use be replaced, nor does the law affect the repair of older motors already in service. EISA does not affect any inventories of electric motors. Motors in inventory on that date can be sold or used as before the law.

Picking Low-hanging Fruit for Energy Savings

Electric motor-driven systems use over two-thirds of all industrial energy. Current technology is available to reduce this consumption by 18 to 20 percent, according to a U.S. DOE survey.

1. Specify NEMA Premium Efficient Motors. The use of Premium efficient motors can save significant amounts of energy—of increasing importance in today’s high-priced energy market. NEMA Premium motors are defined in Tables 12-12 and 12-13 of NEMA MG-1. These motors are rated at 1 to 500 HP in low and medium voltage with Design A and B characteristics. These higher efficiencies are used in most North American rebate programs, Federal Energy Management Program (FEMP), and the Energy Policy Act of 2005. Approximately 22 to 25 percent of motors sold in North America now are designed with these Premium efficiencies, and their use is growing.

NEMA does not designate the mechanical or mounting configuration for NEMA Premium motors. Motor manufacturers supply them in all the usual configurations and enclosures, including C-face and vertical pump-mount; explosionproof; washdown-duty; and IEEE 841. Almost any application requiring a Design B motor can be supplied with Premium efficiency.

In addition, 250- to 500-HP medium-voltage motors are also defined by NEMA Premium even though they are excluded from either pieces of legislation.

Additional benefits beyond reduced energy consumption generally include features that provide for longer life and reduced downtime. Lower temperatures and better balance result in longer grease and bearing life. Cast-iron frames with machined mounting bases provide easier alignment and help to reduce noise and vibration.

Motor upgrades offer an opportunity to reduce bearing and winding failures. Many manufacturers will find that savings from reduced downtime is more valuable than energy savings alone.

2. Specify Three-phase Motors. Many large capital machines are now supplied with three-phase motors for
Figure 2
operation. When specifying this equipment, you should look at life cycle cost, and select NEMA Premium motors when they are cost-justified. Some machinery may come with permanent magnet (PM) rotor servos.

But some of the auxiliary equipment, such as a chip conveyor on a high-tech CNC machining center, may be supplied with single-phase motors. Many single-phase motors are inefficient and should be replaced with a three-phase motor for electricity savings and to prevent downtime from potential failure of the starting switch or capacitor. Premium efficient motors are available for single phase, but they are not as efficient as general-purpose three-phase motors. Figure 2 shows typical efficiencies for single- and three-phase motors.

Usually the least efficient three-phase motor has a higher efficiency than the best available single-phase motor. Specify three-phase motors when possible.

3. Replace DC Motors With AC Motors. Many industrial machines such as plastic extruders continue to rely on DC motors for their main power. Extruders are powered by 40- to 400-HP motors that have 88 to 92 percent efficiency. While this is relatively efficient, it is not as efficient as NEMA Premium motors that are 94 to 96 percent efficient.

DC motors require a silicon controlled rectifier (SCR) (thyristor) adjustable-speed control. Energy savings are possible by switching from a DC motor to an AC motor and drive. In addition, the newer AC vector controls can offer more accurate process control than older analog DC controls.

At the typical rate of $0.10/kilowatt hour (kWh) for two 8-hour shifts, a 40-HP DC motor with 88 percent efficiency consumes $8,816 worth of electricity. Under those same conditions, a 40-HP AC motor with 94.5 percent efficiency consumes $8,210—a $606 savings per year.

Additional savings can be realized by eliminating the brush and commutator maintenance and eliminating downtime costs associated with removing the machine from operation.

4. Increase Productivity With New Motor Technology. As energy surveys are completed, benchmarking of

Figure 3

units produced per kWh should be established. Significant electric savings can be realized by using PM motors and servomotors. Figure 3 compares efficiencies of various motor technologies.

Servomotors are being used to increase throughput by moving parts from place to place more quickly than a conventional fixed-speed conveyor. These high-efficiency servos are replacing many air and hydraulic actuators. Servos also save in maintenance costs and production downtime.

Permanent magnet rotor motors up to 1,000 HP are producing higher outputs than before. The efficiencies may be up to 3 percent higher than NEMA Premium motors. An additional advantage is in the motor’s smaller size and increased power density.

With continuing development of PM rotor motors, efficiencies of 98 percent or more are now possible for 400- to 500-HP motor designs. The 4-pole TEFC versions of 250- to 500-HP AC induction motors would be at 96.2 percent efficiency, with standard versions in the 95.8 percent range. Although this difference may not seem significant, it can be over time. For example, with a 400-HP running for three shifts at $0.10/kWh, annual savings would be $1,134 and 11,340 kWh.

These new permanent magnet designs are more efficient than NEMA Premium motors. Some large motors have tested to 98.3 percent efficiency. A 400-HP at 98.3 percent would save $5,805 a year over the 96.2 percent Premium motor and $6,939 over the standard efficient motor.

Die cast copper rotors are replacing aluminum in AC induction motor construction in some motors because they can reduce rotor losses and increase efficiency. Although these copper rotors show efficiency improvements over aluminum, other technologies such as PM rotors may show even greater efficiency improvements. In addition, PM rotor motors also greatly increase the power density available from a particular frame size. A conventional AC induction motor provides 5 HP from a 180-frame design, and a PM rotor can provide 30 HP. Only 20 HP is possible from a conventional AC induction, 250-frame motor, but 100 HP is available from a PM rotor.

5. Review System to Maximize Savings. Although upgrading to Premium motors realizes significant electricity savings, existing technologies and best practices can reduce energy consumption by 30 to 50 percent, according to the U.S. DOE. The system should be analyzed for improvements that go beyond motor replacement, if possible.

6. Use Pump or Fan System Analysis Tools. The DOE report states that adding an adjustable-speed drive to a pump or fan can reduce consumption by 30 to 50 percent. The payback period for adding an inverter for an application can be as little as six months—without incentives. Generally, an upgrade of this type would be done while installing a Premium motor. The robust insulation system of the motor is suitable for use with the pulse width modulated (PWM) waveform supplied by inverters.

7. Upgrade Belts. Additional savings are possible by replacing V-belts with energy-efficient cogged belts. This can raise system efficiency by up to 2 percent and has a payback of less than six months.

8. Use High-efficiency Helical or Bevel Gear Reducers. Switching a right-angle worm speed reducer to an inline helical or right-angle bevel gear reducer can raise efficiency by 20 to 50 percent. This means that a lower-horsepower motor that consumes less electricity and with a lower price tag can be used to drive the load.

9. Access Utility, Government Incentives to Shorten ROI. Rebates and incentives for Premium motors are available in many states and all Canadian provinces.

Paybacks calculated to be more than two years often result in decisions to replace motors on failure. A U.S. DOE report, "United States Industrial Electric Motor Systems Market Opportunities Assessment," estimates that it would take 18 years to replace all motors on failure. Incentives, tax credits, and accelerated depreciation would help industry quickly upgrade to Premium motors.

Adding these newer technologies to programs proposing additional federal tax incentives such as accelerated depreciation and rebates would help push along the transformation to more efficient equipment, resulting in less electricity usage and lower CO2 emissions.

10. Consider Life Cycle Cost Versus Purchase Price. All of these efforts require a market transformation in
Figure 4
evaluating equipment and processes based on life cycle cost rather than first cost (see Figure 4). As electric rates continue to increase, more industrial companies are beginning to seek ways to help reduce their electricity costs. Any motor purchase decision should be evaluated based on the motor’s life cycle cost, rather than just its purchase price. Generally, the purchase price comprises only 2 percent of a typical AC induction motor’s life cycle cost, while energy comprises more than 97 percent.

References

NEMA Standards Publication, MG 1 – 2006 Motors and Generators.

U.S. Dept. of Energy, United States Industrial Electric Motor Systems Market Opportunities Assessment, December 2002.

M. Melfi, S. Rogers, S. Evon, B. Martin, Permanent Magnet Motors for Energy Savings in Industrial Applications, IEEE Petroleum and Chemical Industry Committee Conference, September 2006.




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