I,

Gordon Duffy,

high=eff iciency Specifying an

energy-e f ficient

motor can pay back

with a quick ROI

and in savings for

years to come.

30 ENGINEERED SYSTEMS JUNE 1993

a n d A n n e M. Hayner

motors

Electric motors consume more than half of all elec- ticity in the U.S.

U.S. businesses spend an estimated $75 billion each year to run motors.

Motors are the largest single user of electricity in most industrial plants.

Electricity consumed by a typical motor costs five to ten times its purchase price each year.

Despite these facts, of the 2 million motors sold nationwide each year, only 15% are energy-efficient models.

Why? Perhaps it’s the critical nature of motors. A downed motor needs quick replacement. Or perhaps it’s because motors are an invisible workhorse of most systems. In a survey of motor manufacturers conducted by the Washington State Energy Office, efficiency ranked fifth, behind availability, quick delivery, reli- ability, and price.

That doesn’t make sense. With a thumbnail analysis, it’s clear that the efficiency tag is more important than the price tag. When specified correctly, a few percentage points of improved efficiency returns tenfold.

Todd Litman, energy specialist, Washington State Energy Office, says that many efficiency improvements will pay for themselves in less than two years.

“For example, even with the low energy cost of $O.O4/kW, a single per- centage point of efficiency improve- ment for a fully loaded, continuously operating 50-hp motor can save as much as 3,564 kWh, valued at $142 annually,” says Litman. “If you spent up to $852 more (than on a standard motor) for a motor,with a 3% im- proved performance, it would still be cost effective, given a two-year simple payback criteria.”

When it comes to selling your im- portance to the bottom line, a thor- ough analysis of motor stock and a planned progression to savings is the stuff from which promotions are made.

What makes efficiency? An energy-efficient motor produces

the same shaft output power (hp), but uses less electrical input power (kw) than a standard-efficiency motor.

Energyefficient motors raise output by lowering motor losses, as detailed in the diagram on page 32.

The National Electrical Manufactur- ers Association (NEMA) defines an energy-efficient motor as one with a nominal full-load efficiency rating that meets or exceeds the NEMA Table 12.6 standard (Figure I).

Manufacturers who sell motors with efficiencies signrficantly higher than the NEMA standard designate these as high- or premium-efficiency motors,

Energy-efficient motors typically cost 10% to 30% more than standard models. Depending on the application, that cost can be recouped, with simple payback, in less than two years.

When to choose efficiency The first step is to inventory all mo-

tors in your facility, estimating their efficiency. Give attention to motors with high downtime costs or which run more than 4,000 hours each year.

Using a strobe tachometer and watt- meter, measure and calculate the volt- age, amperage, rpm, power factor, and

I power draw for a motor under its nor- mal operating conditions. Use the slip, or difference, between the synchronous and the operating speed for the motor to estimate the output kW, process load, and, subsequently, the efficiency of the motor.

Testing each motor in a facility is not always practical or necessary. Newer motors have efficiency ratings stamped on their nameplate. The effi- ciency of other motors can be esti- mated based on the efficiency of cur- rent standard models.

When estimating the efficiency of rewound motors, take into account that motors may lose one to three points of efficiency if they have been improperly rewound.

Once you have conducted your in- ventory, use the following equations to calculate the value of annual energy saving if you replaced a standard mo- tor with an energy efficient one:

NEMA Standard 12.6 1 1.5 2 3 5 7.5 10 15 20 25 30 40 500 SO 75 100 125 150 200

12-6s ODP 77 82.5 82.5 86.5 86.5 88.5 88.5 90.2 91 91.7 91.7 92.4 92.4 93 93.6 93.6 93.6 94.1 94.1 TEFC 72 81.5 02.5 84 85.5 87.5 87.5 88.5 90.2 91 91 91.7 92.4 93 93 93.6 93.6 94.1 94.5

126C ODP 80 84 84 86.5 87.5 88.5 89.5 91 91 91.7 92.4 93 93 93.6 94.1 94.1 94.5 95 95

TEFC 80 84 84 87.5 87.5 89.5 89.5 91 91 92.4 92.4 93 93 93.6 94.1 94.5 94.5 95 95

Figure 1: NEMA Standard MGl, 126, threshold nominal load efficiencies for energy-effiient 4 p d e (1800 rpm) motors. Standard 12- 68 is currently in place. Standard l2dC is currently “recommended for new designs.” It is also part of the Energy Policy Act of October. 1992. The Act requires that, by five years of its signing, all manufacturers produce motors which meet these minimum standards. Note that efficiency generally increases with motor size. A value that is considered “efficient” at 5 hp may be considered ”standard“at 50 hp.

Q S s O l UOlVlS

11 H J

S I I O I O W A 3 N 3 1 3 1 4 4 3 - H 9 1 H 9 N l S O O H 3

kW reduction = hp x L X 0.746 X ( 1 2 - Eo)

4 S l 4 E(HE, where: hp - motor nameplate horsepower rating. L = load factor; percentage of full operating

load.

E ( ~ , ~ ) - standard motor efficiency under load conditions.

E(HE) = high-efficiency motor efficiency under load conditions.

Annual kWh saved = kW reduction x annual hours of motor use

Dollars saved - kWh saved x energy charge

If you also pay a monthly demand charge, use this formula: Energy and demand dollar savings = (kW reduction x 12 x monthly demand charge) +

To evaluate the payback for replac- ing operable motors with energy-effi- cient models use this formula: Simple payback, years - motor price + installation charge - utility rebate energy and demand dollar savings

When considering a scheduled mo- tor replacement program also consider the additional benefits of increased re- liability and ease of installation dur- ing a scheduled changeout compared with waiting for a motor to fail.

Another option is to go through your facility using a motor evaluation and selection program like “Motor Master” (See “Energy-efficiency payback analysis programs”).

I Motor specification (kWh saved x energy charge) /

Because many factors influence util- ity demand billing, calculated savings may or may not match actual savings. Use this formula as an approximation of utility bill reductions only.

Given motors’ high energy use, utili- ties have now moved into the rebate game. Although their methods vary widely, 128 electric utilities in 36 states offer incentives to commercial and in- dustrial customers who make the switch to three-phase energy-efficient motors or adjustable-speed drives.

At the bottom end, the incentive might only be a free energy audit. 0th- ers might offer $250 to $400/kW for peak reduction. Or another might of- fer $600/kW saved.

Some utilities pay for the incremen- tal cost of an energy-efficient motor over a standard model. Another offers a monthly billing credit of $0.78/hp. Several offer a formula such as $15/ hp for motors of 5 to 15 hp, $1O/hp for 20 to 30 hp motors, and $6/hp for 50 to 300 hp motors.

Those who can take advantage of the incentives should contact the com- mercial or industrial marketing depart- ments of the utility in their area.

Calculating simple payback is easy. When considering a motor pur- chase or evaluating the feasibility of rewinding a failed motor, use: Simple payback, years - price premium - utility rebate energy and demand dollar savings

Once evaluation is complete, you can divide your motor stock into three categories:

1. Motors to replace on next avail- able opportunity with an energyeffi- cient motor.

These motors offer rapid payback through energy savings and improved reliability. These include motors which run long hours, are currently ineffi- cient (including oversized motors, or uses which justify variable-speed drives), and demand high reliability.

These motors should be replaced during a scheduled changeout. Order an efficient replacement motor or drive system soon and install it at the next available opportunity, such as during regular plant downtime.

2. Moton to replace when they fail. If you have a critical motor that

should be changed out for an energy efficient one, consider buying it as a spare. This could eliminate a panicked scramble for a quick replacement - with the possible result of replacing standard efficiency with standard effi- ciency.

3. Motors to replace with standard- efficiency motors.

With long paybacks, these are rea- sonably efficient or are used less than 2,000 hours/year. They require no spe- cial treatment and can be replaced with a similar motor in the future.

If your inventory reveals a large number of motors which can be changed out for energy-efficient units,

. 1 . . C H 00s I N G H I G H - E F F I C I E N C Y M O T O R S

Ener iency payback analysis programs your analysis of payback for energy-efficient or highefficiency ry depending on local electrical rates. Utility companies offer

rebates to encourage the switch to energy-efficient motors. Several individual motor manufacturers have developed their own computer programs.

Each of the programs requires inputs of electric cost per kWh and hours of use per year for the applicatio

-

r and efficiency rating of the motor.

flow analysis to determine the value of adding adjustable-

motor versus an energy-efficient

Companies taking pa

34 ENGINEERED SYSTEMS JUNE 1993

keep in mind some guidelines to opti- mize overall system efficiency.

First, avoid oversizing motors. Mo- tors should be sized for a load factor of 60% to 100%. Lower load factors reduce efficiency and power factor.

Oversizing is common. Audits made

FIGURE 2

The following tables contain a representative sampling of the highefficiency motors offered by the companies listed. All possible combinations of hp, voltage, rpm, and efficiency could not be listed. Contact the manufacturer to determine the availability of highefficiency motors for your specific application.

HIGH-EFFICIENCY MOTORS

by the Washington State Energy Of- fice at industrial and commercial fa- cilities indicate that about 30% of all motors operate at less than 50% of full load, resulting in efficiency losses. At part load, efficiency can drop as much as four to six percentage points.

1800 nominal rpm, 230/460-3-60, NEMA frame sizes 143T - 215T HP Ef f~ ien~y Motor Endosure Types'

Manufacturer Trade Name Range Range ODP TEFC SD XP Oaldor Supxi Premium E f f i m y 1.10 85.5-91.2 e e - e GLMOton Energy Saver/X$O 1-10 beson Ekctric Cop. WATTSAVER 1.10 MagneTek Cenlucy €plus/cHtury Eplur 111 1.10 MagncTek Lwb Alii Spartan 1.10

serierf/alw chip XRI 1-10 R&nuEkchk E.2000 / XE 1.5-10 MiafKaLkcbic OMEGA XL 5-10 Lkmrw Medalion 1-10 Terhbr EQP 111 / EQP IILXS 1.10 US EkcMc Motwr Unimunt / coCro.Duty 1-10 Wltt(nPh0uK OPTIM HE / OPTM Mi[ and chemical 1 . 10

89.5.91.7 85.0 - 92.0 82.5-91.0 88.5 - 89.5 82.5 - 69.5 84.0 - 88.5 86.5 - 89.5 82.5 - 89.5 84.0 -91.0 84.0-91.0 86.5-91.7

e e e - e e - - e e - - e e e - e e e e

- e e e e e e - e e e e - e m -

e * - -

e - - -

1800 nominal rpm, 230/460-3-60, NEMA frame sizes 254T - 405T HP EfMency Motor Endosure Types

hlanuixtunr Trade Name Range Range ODP TEFC SD XP lwdor Super4 Premium E f f i 15.100' 92.4-95.0 m e - e C.E.kbW3 Energy Sawr/xID 15.100 Lnr#r Lkcek Cop. WATTSAVER 15-100 MagneTek Century Epls/Century Eplw 111 15 . lW rJ*onrTa Lwb Ak Spartan 15-1W Mwubn Serii?s.E/Slw Chip XRI 15-100 R&wKefkctric E. 2000 / XE 15.100 ReA.RcI Ekctrk OMEGA XL 15-100 Sknwnr Medallii 15-100' T O S k EQP 111 / EQP IlEXS 15-100 US Ehcbk Motors unimount / CmrMuty 15-100 -house OPTlMHE/OPTlMMi~andChemical 15.100

u s a p c o ~ br 1wtQ.Blym"tdfmd y60)4oUdrgc (or MtotW tQ. Blymw rot offnd. y 6 0 ) 6 0 ~ (or25 w 1w tQ, 23Cyw360 MI o w

93.0 - 95.4 92.4 - 95.2 92.4 - 95.4 91.0 - 95.0 89.5-94.1 89.5 -94.1 91.0 -94.5 89.5 - 94.5 93.0-95.4 93.0 - 95.4 92.4 - 94.6

1800 nominal rpm, 460-3-60, NEMA frame sizes 445T - 449T

Trade Name Super4 Premium Effkielwy

Energy Sawr/X$O Cenlury Eplus/ Century Eplus 111

Lwb A% Spartan s e r i i

Premium Bluc Chip XRI E-2000/ XE OMEGA XL Medallion EQP IlCXS

Unimwnt/Cmrc-Duty OPTlM HE / OPTlM Mil and Chem'cal

HP Range 125-400 125-300 125-200 125-400 125-250 125-4W 125.350 125.300 125-250 125-200 125-200 125.250

Efiiciency Range 95.0.96.2 95.2 - 96.2 94.5 - 95.8 95.4.95.8 94.5.95.4 95.4 - 962 94.1 - 95.4 95.4.962 94.5 - 95.0 95.4-962 95.4.962 94.7 -95.5

Motor Enclosure Types ODP TEFC SD e' e - e e e e e -

e - - - e e' e e e

e

e e - e e e - e e

e - -

- - - * e

C H O O S I N G H I G H - E F F I C I E N C Y M O T O R S 1 . 1 : .

I

i’

Utility incentives for motors A list of utilities known by ES to offer incentives for motor efficiency improvements follows:

ALABAMA

Ft. Payne Improvement Author

ARIZONA

Arizona Electric Power Coop. Tucson Electric Power Co.

CALIFORNIA City of Los Angeles City of Sacramento Pacific Gas & Electric Riverside Public Utilities Sacramento Municipal Utility

San Diego Gas & Electric Co. Southern California Edison Co. Sierra Pacific Power Turlock Irrigation District

COLORA

District

Setvice of Colorado te G&T Association

CONNECTICUT Connecticut Valley Electric Co. Northeast Utilities South Norwalk Electric Works United Illuminating Co.

DISTRICT OF COLUMBIA Potomac Electric Power

FLORIDA Florida Po Gulf Power Co.

GEORGIA

PSI Ene

IOWA Interstate Power Iowa Electric Light & Power Co. Iowa-Illinois G & E Iowa Power Iowa Southern Utilities Co. IPS Electric Waverly Light & Power

MAINE Central Maine Power Co. Maine Public Service Co.

MARYLAND Baltimore Gas & Electric

MASSACHUSETTS Boston Edison

Eastern Utilities Granite State Electric Co. Massachusetts Electric Co. Narragansett Electric Co. New England Electric System Commonwealth Electric

MICHIGAN Consumers Power Detroit Ednon Co. Traverse City Light 81 Power

MINNESOTA Minnesota Power & Light Northern States Power Co. Otter Tail Power Co. St. Peter Municipal Utilities

MONTANA Montana Power

NEBRASKA Nebraska Municipal Power Pool

NEVADA Nevada Power Sierra Pacific Power

NEW JERSEY Atlantic Electric Jersey Central Power & Light Public Service Electric & Gas

NEW MEXICO Plains Electric Generation & Transmission Continental Divide Electric Coop.

NEW YORK Central Hudson Gas & Electric Consolidated Edison (NYC) Long Island Lighting New York Power Authority New York State Electric & Gas Niagara Mohawk Power Corp. Orange & Rockland Utilities Rochester Gas & Electric

NORTH CAROLINA Carolina Power & Light Duke Power

NORTH DAKOTA Mountrail-Williams Electric Coop. Northern States Power Co. Valley City Municipal Utilities

DHlO Centerior Energy Corp.

DKLAHOMA Indian Electric Coop. Dklahoma Gas & Electric

DREGON bhland Dept. of dublic Utilities Bonneville Power Administration Eugene Water & Electric Board Zity of Portland

Emerald Peoples Utility District Pacific Power Umatilla Electric Coop.

PENNSYLVANIA Northwestern Rec Association Philadelphia Electric Co. West Penn Power Co.

SOUTH CAROLINA South Carolina Electric & Gas Co. Duke Power Carolina Power & Light South Carolina Electric l3 Gas

SOUTH DAKOTA rthern States Power Co.

EE Meriwether Lewis Electric Coop.

net Electric Cooperative El Pas0 Electric Co. Houston Lighting & Power

Northern States Power Co. Northwestern Wisconsin Electric Co. Superior Light & Power Waterloo Light & Water Commission

Energyefficient motors tend to run slightly faster at full-rated load. With centrifugal load appli- cations, a replacement motor can lose its efficiency gain if it doesn’t match the full-load speed of the original. This happens because load increases when operating speed is higher.

Some energy-efficient motors have high locked-rotor currents. Take this into account when siz- ing wiring and protective circuits. Some energy-efficient motors are NEMA Design A, which allows a higher start-up current. If your electrical system has enough ca- pacity or if your motor has a “soft start’’ control, this won’t cause problems. Soft start can be added later if problems develop.

Resolve power quality prob- lems such as under- or over- voltage, phase imbalance, or low power factor. Consult the motor manufacturer if your power quality is questionable, especially if you are replacing a burned-out motor. If you make major electrical system changes, let an electrical engineer review your plans. Your local electric utility can also advise you about power quality.

There are solutions to correct power factor, such as installing capacitors in the ac circuit to de- crease reactive power, minimiz- ing idling of lightly loaded mo- tors, and avoiding operation of equipment above rated voltage.

Another way to improve drive efficiency in applications where loads fluctuate is to replace a single-speed motor with a vari- able-speed drive. For example, if a pump or fan is designed to meet a rarely occurring peak load, it may run in an inefficient load range much of the time. Often, dampers or throttling valves are used for output control. Litman likens this to driving a car under full throttle and controlling speed with the brake. Depending on cir- cumstances, adjustable-speed drives can reduce motor energy consumption by 10% to 70%.

36 ENGINEERED SYSTEMS JUNE 1993

shopping for motors “Often, two motors with the same

price have considerably different effi- ciency ratings,” says Litman. “It is im- portant to become familiar with motor efficiency terminology and the motor retail market in order to obtain the greatest efficiency at the lowest cost.”

The most important focal point is efficiency standards. Any specification you prepare should require identifica- tion of test standards and guarantee that all quotations are made on the same basis.

The U.S. efficiency test protocol is IEEE 112-Method B. This method uses a dynamometer to determine mechani- cal output. Rely only on this standard when comparing motor efficiency. Other testing standards, such as the Japanese Electrotechnical Committee (JEC) 37 standard and the Intemational Electrotechnical Commission (IEC) 34.2 standard tend to overstate motor efficiencies compared with IEEE’s.

The testing standards differ prima- rily in their treatment of stray load losses. The end result is that the effi- ciency of a motor, when tested under different standard conventions, can vary by several percentage points.

Nominal versus minimum Second, use “nominal” or “average”

efficiency values rather than “guaran- teed minimum.”

Nominal values are calculated so that half of all motors in a model class will measure above that value and half will measure below it. That is, the nominal value is the midpoint on a bell curve of tested motor efficiencies.

Guaranteed minimum values are a lower value associated with each NEMA nameplate nominal value. Mini- mum values assume that all motors in the model class can be expected to ex- ceed that value. Minimum values cor- respond (in the NEMA ratings and those of many manufacturers) to 20% below mean on the bell curve. NEMA’S formula for minimum efficiency is: Minimum efficiency =

1

1.2 - 0.2 nominal efficiency

Since both NEMA nameplate and guaranteed minimum values are

rounded off from the nominal values, they are less accurate. Never compare nominal against minimum values.

Some manufacturers lower their standard deviation when assigning minimum values. One question to ask

M O T O R R O U N D U P

is if they vary minimum efficiency by

equation, what is the value of the subtractor.) The lower the percentage of variation. the meater the mobability

1oyo or 20%. (I,, terms of the above

, Y

that the motor in question is closer to the nominal value.

Some variation in testing is prob- able, even with a standard test method. In the U.S. today, there is a standard test procedure but no standardized test- ing agency. The motor manufacturers assume that responsibility themselves.

In 1978, NEMA shipped three mo- tors of different sizes to nine motor manufacturers, with the request that they be tested in accordance with IEEE 112-Method B practices. A second test examined efficiency changes due to variations in materials and manufactur- ing tolerances. These tests showed that variation in measured losses frequently exceeded *lo% for some motor de- signs while the combined variation from manufacturing and testing can ex- ceed +-19%.

For purchasers that means you should select a unit that has a mea- sured efficiency value within 1.5% or less of the maximum value available within a given size, enclosure, and speed class.

The NEMA standard is not very re- strictive. Cost-effective motors are available which significantly exceed this criteria. The highest efficiency motors save up to three times as much as mo- tors which just meet the NEMA stan- dard. For this reason, comparison shop by efficiency ratings, not by labels such as “energy efficient.”

Effective shopping also means ne- gotiating a favorable motor purchase price. Industrial-size motors are sel- dom sold at manufacturers’ list prices. Typical dealer discounts range from 20% to 40%. Dealers repre- senting the same motor manufacturer may offer different retail prices. Prices depend on the dealer’s dis- counting policy, sales volume, and the number purchased. H