Energy Management for Motor-Driven Systemsiv Energy Management for Motor-Driven Systems Throughout this guidebook we identify sources of additional informa-tion, such as MotorMaster+

OFFICE OF INDUSTRIALTECHNOLOGIES

OFFICE OF INDUSTRIAL TECHNOLOGIESENERGY EFFICIENCY AND RENEWABLE ENERGY • U.S. DEPARTMENT OF ENERGY

EnergyManagement forMotor DrivenSystems

Energ

y M

anagem

ent fo

r Moto

r Driv

en S

yste

ms

The energy savings network—plug into it

EnergyManagementfor Motor-DrivenSystems

Prepared byGilbert A. McCoy andJohn G. DouglassWashington State UniversityCooperative Extension Energy ProgramOlympia, Washington

Funded byThe Bonneville Power Administration

Reproduced byThe U.S. Department of EnergyOffice of Industrial Technologies

Revision 2 March 2000

i

AcknowledgmentsThe authors wish to thank theBonneville Power Administration(BPA) for funding this project.Particular thanks are due to CraigWohlgemuth of Bonneville’s Techni-cal Assessment/R&D Group for hisencouragement, direction and sup-port. Portions of this guidebook havebeen adapted from two unpublished1994 reports prepared by Carroll,Hatch & Associates for theBonneville Power Administration.Appreciation is extended to JohnVranizan of Carroll, Hatch & Associ-ates and to Rob Gray of the Washing-ton State Energy Office’s Spokaneoffice for information and/or reviewsprovided. Vicki Zarrell providedreview, proofing, and technicalediting services.

A first version of this guidebook wascompleted in 1996 by the WashingtonState Energy Office with fundingfrom BPA contract No. DE-B179-93BP08158, Task Order No.96AT63464. Subsequently, enhance-ments and research results wereincorporated into this revision by theWashington State University Coop-erative Extension Energy Programusing Power Washington oil over-charge funds.

The U.S. Department of Energy,Office of Industrial Technologieswould like to thank the BonnevillePower Administration for theirefforts in producing this document.

This publication has been repro-duced by DOE/Office of IndustrialTechnologies.

DisclaimerThis guidebook was prepared bythe Washington State EnergyOffice and Washington StateUniversity Cooperative ExtensionEnergy Program with fundingfrom the Bonneville PowerAdministration. Neither theUnited States, the BonnevillePower Administration, the State ofWashington, the Washington StateEnergy Office, the WashingtonState University CooperativeExtension Energy Program, norany of their contractors, subcon-tractors, or their employees,makes any warranty, expressed orimplied, or assumes any legalresponsibility for the accuracy,completeness, or usefulness ofany information, apparatus,product, or process disclosedwithin this guidebook.

ii Energy Management for Motor-Driven Systems

iii

Executive Summary

This publication will assist you to establish a facility energy-manage-ment program, to identify and evaluate energy conservation opportu-nities involving motor-driven equipment, and to design a motorimprovement plan. These actions will help you:

� Reduce energy costs,

� Improve motor-driven system reliability andefficiency,

� Increase productivity, and

� Minimize unscheduled downtime.

In the Guide you will find:

• How to set up a successful energy management program(Chapter 1).

• How you can use utility bills, plant production data, and utilityrate information to “target” potentially cost-effective energyconservation, demand reduction and power factor correctionopportunities (Chapter 2).

• Plant distribution system troubleshooting and “tune-up” tips(Chapter 3).

• A description of motor testing instruments and field survey tech-niques (Chapter 4).

• Methodologies for analyzing motor improvement opportunities(Chapter 5). Chapter 5 illustrates how you can use measuredinformation to determine the load imposed on the motor by drivenequipment and its efficiency at that load point.

• How to determine the dollar benefits associated with appropriateenergy conservation and demand reduction actions (Chapter 6).

• Motor improvement planning basics (Chapter 7). This chapterprovides advice regarding the assessment of new motor purchase,repair, downsizing, and replacement decisions and shows how toincorporate findings into your motor improvement plan.

• Power factor correction assessment techniques (Chapter 8). Thischapter gives examples illustrating the sensitivity of power factorcorrection benefits to utility rate schedules.

• How to establish both preventative and predictive maintenanceprograms (Chapter 9).

iv Energy Management for Motor-Driven Systems

Throughout this guidebook we identify sources of additional informa-tion, such as MotorMaster+. MotorMaster+ is an energy-efficientmotor selection and energy management software package. Thecapabilities of MotorMaster+ include:

• Automatic motor load and efficiency estimation based upon fielddata measurements.

• Ability to select replacement motors from an internal database ofover 27,000 one-to-2,000 hp NEMA Design B, C and D motors.

• Ability to analyze conservation benefits due to purchase and use ofenergy efficient motors in new, rewind, or retrofit applications.

Call the OIT Clearinghouse

(800) 862-2086 to obtain

your copy of MotorMas-

ter+. Both the OIT Clear-

inghouse and the Electric

Ideas Clearinghouse (800)

872-3568 [(360) 956-2237

outside BPA’s service

territory] stand ready to

assist you regarding motor

and motor-driven equip-

ment efficiency issues.

v

Contents

Chapter 1 Energy Management for Motor-Driven Systems.......... 1-1Elements of a Successful Energy Management Program .......... 1-2

1. Secure Top Management Commitment ............................. 1-22. Appoint an Energy Coordinator ........................................... 1-23. Obtain Employee Cooperation ............................................ 1-34. Conduct Energy Surveys ..................................................... 1-35. Organize Energy Data .......................................................... 1-46. Analyze Survey Results ....................................................... 1-57. Set Conservation Goals ....................................................... 1-58. Develop Organization-Wide Energy Management Plan .. 1-59. Implement Engineering Changes ........................................ 1-5

10. Monitor and Evaluate Results .............................................. 1-7Conclusion .......................................................................................... 1-7

Chapter 2 Understanding Your Utility Bill ................................... 2-1Organizing Utility Bills and Production Data ................................... 2-1

Interpreting Utility Charges ................................................................ 2-4

Service Charge ............................................................................. 2-5Energy Charge .............................................................................. 2-5Demand Charge ........................................................................... 2-6Power Factor Charges................................................................. 2-6

Optional Rate Schedules .................................................................. 2-9

Time-of-Use Rates ....................................................................... 2-9Interruptible, Curtailment and Customer Generator Rates ..... 2-9

Using Billing Data to Identify Opportunities .................................. 2-10

Checklist for Electricity Cost Savings ...................................... 2-11

Chapter 3 Industrial Electrical Systems ......................................... 3-1The Plant Electrical Distribution System ........................................ 3-2

Over and Under Voltage ............................................................... 3-2Voltage Unbalance ........................................................................ 3-3

Troubleshooting and Tuning your In-Plant Distribution System ... 3-5

Troubleshooting Poor Contacts .................................................. 3-5Voltage Drop Survey ............................................................. 3-6Infrared Thermography ......................................................... 3-6

Troubleshooting Voltage Unbalance ........................................... 3-7Troubleshooting Over and Under Voltage .................................. 3-8Troubleshooting Low Power Factor ........................................... 3-9Troubleshooting Undersized Conductors .................................. 3-9Troubleshooting Insulation Leakage ........................................... 3-9

vi Energy Management for Motor-Driven Systems

Chapter 4 Taking Field Measurements ........................................... 4-1Safety Considerations ....................................................................... 4-1

Constructing the Motor List and Inventory Database .................... 4-2

Acquiring Motor Nameplate Data ..................................................... 4-2

Load-Time Profiles ............................................................................. 4-3

Measuring Operating Values ............................................................ 4-4

Data Gathering Approaches ............................................................. 4-5

Safety Issues in Data Gathering ................................................. 4-6Voltage Measurements ................................................................. 4-6Current Measurements ................................................................ 4-7Power Factor Measurements ..................................................... 4-7

Purchasing Motor Testing Instruments ........................................... 4-8

Voltage Meters ............................................................................... 4-8Current Meters .............................................................................. 4-8Tachometers .................................................................................. 4-9Power and Power Factor Meters .............................................. 4-10Multi-channel Power Loggers .................................................... 4-11Motor Analyzers ........................................................................... 4-11

Industrial Practices .......................................................................... 4-12

Chapter 5 Motor Load and Efficiency Estimation Techniques ........ 5-1Input Power Measurements .............................................................. 5-1

Line Current Measurements ............................................................. 5-2

The Slip Method .................................................................................. 5-3

Variable Load Levels .......................................................................... 5-5

Determining Motor Efficiency ........................................................... 5-6

Computerized Load and Efficiency Estimation Techniques ... 5-8

Chapter 6 Energy, Demand, and Dollar Savings Analysis .............. 6-1Calculating Annual Energy and Demand Savings ........................ 6-1

Assessing Economic Feasibility ...................................................... 6-2

Chapter 7 Motor Improvement Planning ........................................ 7-1Energy Efficient Alternatives ............................................................. 7-1

Upon Failure Alternatives ............................................................. 7-2Without an Existing Motor Failure ............................................... 7-5

MotorMaster+: Motor Energy Management Software ................. 7-2

Motor Resizing .................................................................................... 7-6

Conclusion ........................................................................................ 7-10

vii

Chapter 8 Power Factor Correction ................................................ 8-1The Concept of Power Factor .......................................................... 8-1

Power Factor Penalties ..................................................................... 8-2

Power Factor Improvement .............................................................. 8-3

Sizing and Locating Power Factor Correction Capacitors .......... 8-4

Sizing Capacitors for Individual Motor and Entire Plant Loads .... 8-6

Benefits of Power Factor Correction ............................................... 8-8

Additional Benefits of Power Factor Correction ........................... 8-10

Power Factor Correction Costs ..................................................... 8-11

Avoiding Harmonic Resonances When Installing Capacitors ... 8-12

Chapter 9 Preventative and Predictive Maintenance Planning ........ 9-1Cleaning ............................................................................................... 9-2

Lubrication ........................................................................................... 9-3

Mountings, Couplings, and Alignment ............................................. 9-5

Operating Conditions ......................................................................... 9-6

Thermal, Vibration and Acoustic Tests ........................................... 9-9

Electrical Tests ................................................................................. 9-10

Storage and Transport ..................................................................... 9-11

Appendixes ................................................................................. A-1Appendix A: Motor Nameplate and Field Test Data Form ........... A-1

Appendix B: Average Efficiencies for Standard and Energy EfficientMotors at Various Load Points .................................................. B-1

Appendix C: Motor Energy Savings Calculation Form ............... C-1

Appendix D: Power Factor Correction Capacitor Suppliers ......D-1

viii Energy Management for Motor-Driven Systems

Figures

1-1 Typical Energy Management Team Organization Chart

1-2 Steps in an Energy Management Program

2-1 Energy Use Profile Reports

2-2 Sawmill Energy Consumption Disaggregation

2-3 Billing Statement

2-4 Electric Demand Meters

3-1 Typical Facility Single-Line Diagram

3-2 Acceptable Voltage Range for Systems and Motors

3-3 Motor Voltage Unbalance Derating Curve

3-4 Effects of Voltage Unbalance on Motor Losses

4-1 Motor Nameplate

4-2 Industrial Three Phase Circuit

4-3 Instrument Connection Locations

5-1 Relationships Between Power, Current, Power Factor and Motor Load

5-2 Depiction of Motor Losses

7-1 Motor Performance at Part-Load

7-2 Motor Efficiency Improvement Action Plan

8-1 The “Power Triangle”

8-2 Power Factor as a Function of Motor Load

8-3 Locating Capacitors on Motor Circuits

8-4 Apparent Power Requirements Before and After Adding Power FactorCorrection Capacitors

9-1 Effect of Voltage Variation on Induction Motor PerformanceCharacteristics

Figures and Tables

ix

Tables

2-1 Sawmill Energy End Use Summary

3-1 Acceptable System Voltage Ranges

4-1 Typical Motor Load Types

4-2 Coupling Types

5-1 Induction Motor Synchronous Speeds

5-2 Characteristics of Motor Loads

7-1 Motor Repair Versus Replace Analysis

7-2 Existing Motor Replacement Analysis

7-3 Motor Downsizing Example

8-1 Industries That Typically Exhibit Low Power Factor

8-2 Sizing Guide for Capacitors on Individual Motors

8-3 Multipliers to Determine Capacitor Kilovars Required for PowerFactor Correction

9-1 Grease Compatibility

x Energy Management for Motor-Driven Systems

Glossary forEquations

The following variable names are used in equations in this publication:

Pi

= Three phase power in kW

PJ

= Power dissipated in a junction in watts

P2

= Corrected input power

P1

= Input power before correction

PApparent

= Apparent power in kVA

PApparent1

= Apparent power before PF correction in kVA

PApparent2

= Apparent power after PF correction in kVA

PR e a c t i v e

= Reactive power in kVAR

Pir

= Input power at full rated load in kW

Po

= Actual output horsepower

Po 2

= Corrected output power

Po 1

= Output power before correction

Por

= Nameplate rated horsepower

P F = Power factor as a decimal

PF1

= Original power factor

PF2

= Power factor after correction

V = RMS voltage, mean line to line of 3 phases

Vmaxdev

= Line to line phase voltage deviating most from mean of3 phases

VJ

= RMS voltage across a junction

Vr

= Nameplate rated voltage

I = RMS current, mean of 3 phases

IJ

= RMS current through a junction

Ir

= Nameplate rated current

kWh = Electric energy in kWh

kWhsavings

= Annual electric energy saved in kWh

kWbilled

= Adjusted or billable demand

kWdemand

= Measured electric demand in kW

kWsaved

= Savings from efficiency improvement in kW

xi

kVAdemand1

= kVA demand before PF correction

kVAdemand2

= kVA demand after PF correction

N = Number of days in billing period

e = Efficiency as operated in %

e2

= Corrected efficiency

e1

= Efficiency before correction

es t d

= Efficiency of a standard motor as operated in %

eE E

= Efficiency of an energy efficient motor as operated in%

efl

= Efficiency at full rated load as a decimal

Load = Output power as a % of rated power

S = Measured speed in RPM

Sr

= Nameplate full load speed

Ss

= Synchronous speed in RPM

Slip = Synchronous speed - Measured speed in RPM

hours = Annual operating hours

$savings

= Total annual dollar savings

$demand

= Monthly demand dollar charge

$energy

= Dollar charge per tailblock kWh

$premium

= Price premium for energy efficient motor comparedto standard

$rebate

= Utility rebate for energy efficient motor

$new

= New motor cost

$inst

= Installation cost

PB = Simple payback in years

% reduction = Percent reduction in distribution losses

R = Resistance in ohms

Unbal = Voltage unbalance in %

xii Energy Management for Motor-Driven Systems

Energy Management for Motor-Driven Systems 1-1

Chapter 1Energy Managementfor Motor-DrivenSystems

profits, industries that takeadvantage of energy efficiencyopportunities often gain addi-tional benefits such as:1-4

� More productive state-of-the-art-technology that improvesa facility’s competitive edgeand improves global competi-tiveness;

� Improved environmentalperformance and compliancewith environmental andpollution abatement regula-tions; and

� An enhanced public image asan environmentally friendlyor “green” company.

Energy management is not a one-person responsibility or a one-time investment in conservationmeasures. Energy management isan ongoing effort marked bygradual improvements in energy-efficiency.1-2 A successful energymanagement process is markedby:

� Maximizing productionefficiency,

� Minimizing energy consump-tion,

� Maintaining a high energyload factor,

� Correcting for low powerfactor, and

� Acquiring and using economi-cal supplies of energy.

Energy management does not justhappen. Effective energy man-agement occurs when the ideaand practices associated withenergy management become partof the “corporate culture.”

IntroductionThis energy management guidebookis designed to assist the industrialfacility engineer to reduce energycosts through:

� Identifying and analyzingmotor driven system energyconservation opportunities,

� Troubleshooting and tuningthe in-plant electrical distribu-tion system,

� Correcting for power factor,

� Understanding utility billingstatements, and

� Establishing a preventativeand predictive maintenanceprogram.

Why should industrial plant staffwork to save energy? One answeris money.1-1 Ever-increasingutility costs reduce profits, erodecapital and maintenance budgets,increase product costs, andreduce competitiveness.

A common misconception withinindustry has been to equate anenergy reduction or conservationprogram with the concept ofturning off equipment and shut-ting down processes. Instead, theprogram of energy managementchallenges plant staff to producethe products or services with theabsolute minimum energy con-sumption.1-2 The objective is tominimize energy usage throughproduction efficiency gains, whileprocuring the lowest cost andmost reliable supplies of fuel andpower.1-3

In addition to reduced energycosts and potentially increased

1-2 Energy Management for Motor-Driven Systems

Elements of a SuccessfulEnergy ManagementProgram

Energy-management consists of awell structured team effort tocreate energy awareness: collectand organize energy cost andconsumption data; identify,analyze and implement energyconservation opportunities; andmonitor results. The programmust be accomplished withoutplacing an undue burden onplant maintenance or engineeringstaff.1-2

Ten “Key Elements” that arecrucial to success of an energymanagement program are:

1. Secure Top ManagementCommitmentTop management must becommitted to a motor-drivensystems energy conservationprogram.1-6 To a substantialdegree, management’s atti-tude toward energy conserva-tion will determine the suc-cess of the energy plan.1-1

Management must be willingto provide both personnel andfinancial resources.

Employees will apply theirbest efforts to an energyconservation program only iftheir management displaysawareness of the program’simportance.1-6

2. Appoint an EnergyCoordinatorA plant energy coordinatorshould be appointed to guideenergy management efforts.1-2

The energy coordinatorshould have an energy back-ground with energy manage-ment being a primary duty.1-7

The energy coordinator can belikened to a coach: mobilizingresources, providing soundadvice, motivating others, andproviding support.1-1 Thecoordinator should be respon-sible for energy managementactivities such as:1-2

� Making energy manage-ment an integral part ofevery department.

� Providing operators,foremen, and maintenancestaff with tools they needto be part of an energymanagement team.

� Analyzing trends inenergy use and efficiencyand identifying areas ofconcern.

� Informing plant manage-ment of roadblocks toenergy use reductionwhile suggesting ways toremove them.

� Stimulating interest in theinstallation of energysaving measures.

� Assisting in the develop-ment of energy use stan-dards.

� Reviewing plans for plantexpansions, processmodifications, and equip-ment purchases to ensurethat energy is used effi-ciently.

� Directing the activities ofoutside consultants, and

� Preparing monthly or bi-monthly facility energyefficiency reports so thatmanagement can becontinuously updated onmotor-driven systemimprovements, energysavings, and cost reduc-tions.

A rule-of-thumb is oneperson-year for each$1 million of annual energyexpenditures.As progress is made, thecommitment can bereduced to one person-yearfor every $2 - $5 millionspent annually.


4. Conduct Energy SurveysAn initial plant energy surveyshows where and how energyis being used and/or wasted.1-6

An inventory of energy-usingequipment should be pre-pared, showing basic energyuse data (usually obtainedfrom equipment nameplates)and indicating typical runningtime and operating profiles.Without basic audit informa-tion, it is impossible to tellwhether equipment is operat-ing unnecessarily or waste-fully. The basic survey infor-mation is also needed to setstandards, and to measure theperformance of an individualpiece of equipment, a process-ing line, or a department.1-6

Survey information also assiststhe energy coordinator to“target” and focus efforts onthe most energy-intensiveequipment in a facility. Poten-tial conservation savings aregreatest where losses are thelargest. Auditors shouldconcentrate on motor-drivensystems where:1-8

� The motor running timeexceeds 1,000 hours peryear;

Figure 1-1 Typical Energy Management Team Organization Chart

3. Obtain EmployeeCooperationThe cooperation of operationsand maintenance staff is vitalto the success of any energymanagement effort.1-2 In mostcases, the effectiveness of anenergy improvement programis proportional to the effortand time the energy coordina-tor and department represen-tatives are allowed to spendon it.1-6 Recognize and sup-port internal “idea champi-ons”. An idea champion is theprime mover: the person withthe vision, desire, and persis-tence to promote a conserva-tion project or approach andto see it through to comple-tion.1-1

An energy committee shouldbe established, with represen-tatives from each departmentexpected to make recommen-dations and conduct investi-gations. Participants in anenergy committee help createthat “critical mass’ that iscrucial for success. A sense of“ownership” develops com-mitment.1-1 A typical energymanagement team organiza-tional chart is depicted inFigure 1-1.1-6


� Applications require largerhorsepower motors.Typically, motors above 20hp represent only 20percent of the overallmotor population yetconsume 60 percent ofmotor driven equipmentenergy.

� Loads are nearly constantand operation is at or nearthe full-load point for themajority of the time.

� Energy and power ordemand charges are high.In some locations, energyrates are as high as $.12/kWh. With higher electri-cal rates, expenditures forconservation measuresyield a much more rapidpayback on investment.

� Utility rebate or demandmanagement programincentives exist.

The initial physical plant surveyshould be conducted departmentby department. It should docu-ment wasteful operations andidentify obvious sources of lossesthat can be corrected immediately.The survey will also reveal whereenergy and/or process flowmetering should be installed.(One rule of thumb states that in-plant metering is economicallyjustified when the annual cost ofenergy exceeds five times the costof the meter.)1-6

One survey approach is to:1-2

� Determine the energyconsumption rates andcosts for major equipmentin each department.

� Ask the department-levelenergy committee mem-bers to determine howlong equipment operatesand how long it is inservice without perform-ing a useful task.

� Determine the cost ofenergy wasted.

� Request that department-level energy committeemembers develop proce-dures to reduce waste orto identify barriers orequipment limitationsthat prevent waste reduc-tion.

5. Organize Energy DataTo convince plant manage-ment of the value of motorsystems management, youmust make them aware ofenergy’s impact on opera-tions. High-energy costs maynot be perceived as a concernuntil energy costs can becompared with other costs atthe facility level.1-1 In orderfor energy conservationopportunities to compete forresources, top level managersmust understand the scope ofthe problem.

The logical place to begingathering information onenergy use is with utility bills.Obtain a copy of your rateschedule from your electricutility and determine whetheralternative schedules areavailable for your facility.Obtain electrical energyconsumption and cost datafor at least a one-year periodin order to establish a baseperiod.1-5 Check whetherpatterns exist in the use andcost of energy. Is the amountof money spent for energyhigher during certain portionsof the year? It is helpful tograph energy use and costsusing an energy accounting orspreadsheet program.

Chapter 2 shows you how tointerpret your utility’s rateschedule and use billing data


to target potentially cost-effective energy-conservation,power factor correction anddemand reduction opportuni-ties.

6. Analyze Survey ResultsAfter the plant energy surveyis complete, construct energybalances for each department,process, and piece of energy-consuming equipment inyour facility. An energybalance quantifies the totalenergy output against thetotal energy supplied to asystem, indicating howeffectively the suppliedenergy is utilized.1-6 Bycomparison with processrequirements or knownenergy intensity standards,you can detect whetherenergy is being used ineffi-ciently and, if so, to whatextent? On-line monitoringsystems may have to beinstalled to compute energybalances at the department,process, or equipment level.1-6

Energy surveys and balancesprovide the basic informationnecessary for analyzingenergy conservation opportu-nities. The analysis is typi-cally conducted by a plantengineer and examines thecapital and installation costs,and annual energy and dollarsavings associated withalternative conservationactions. The analyst mustaddress considerations suchas disruption of industryoperations, effect on productquality and yield, technologi-cal risk, maintenance require-ments, technology availabil-ity, vendor reliability, andtraining and skilled personnelrequirements.1-4

7. Set Conservation GoalsEnergy management programstypically set yearly goals forspecific reductions in baselineenergy intensity, usage, or cost.Although realistic goals maybe difficult to set initially, goalsare absolutely necessary.Without goals, there is nomethod for measuring perfor-mance.1-2

8. Develop an Organization-Wide Energy ManagementPlanGood energy managementbegins and ends with decisionmakers. The energy manage-ment program, depicted inFigure 1-2, illustrates informa-tion necessary for makinginformed decisions.1-9

The energy management ormotor improvement planincludes policies, goals, assign-ments, training needs, anassessment of the costs andbenefits (energy savings,demand reduction, productiv-ity gains) associated withconservation opportunities,implementation time-lines,and a description of feedbackand reporting mechanisms.

9. Implement EngineeringChangesEnergy audits or technicalassistance studies gatheringdust represent lost opportuni-ties to save money.1-1 Imple-ment engineering changes!

The energy-management plangenerally calls for identifyingand implementing the mostcost-effective measures first.Ideally, all measures meetingthe company’s return-on-investment criteria are funded.


Figure 1-2 Steps in an Energy Management Program

Often, however, the first stepin starting an energy manage-ment program is to installmeasures that enable energysavings to build quickly.1-7

This approach builds confi-dence and trust and allows

momentum to build, which isnecessary to overcomebarriers and change anorganization’s culture.

One approach to incremen-tally “growing” a compre-hensive program is to choose


a small, low-investmentproject from your list ofpossibilities that can becharged to a routine mainte-nance budget. Once you haveselected a small project,double check its payback.Errors can be embarrassingand you are out to prove yourand your energy committee’sabilities as energy managers.Complete the project andthoroughly document costs,performance and energysavings. Then submit aproject summary to plantmanagement. Once you havecompleted the first project,choose another. Size doesn’tmatter. Once the two projectshave been successfully com-pleted, approach plant man-agement with a larger en-deavor that cannot be fi-nanced within maintenancebudgets.1-10

10. Monitor and Evaluate Re-sultsMonthly, bi-monthly, orquarterly reports of energyuse are essential feedback formaking the energy manage-ment program visible to bothplant management anddepartment level staff. Evalu-ate conservation measureperformance and periodicallyreport energy intensity, usageand cost data so that manage-ment “sees” the benefitsassociated with conservationinvestments.

Share success to build sup-port. Make the programvisible. Monitoring data canalso provide recognition orawards for exceeding energyreduction goals or for exem-plary performance or team-work.

ConclusionThe average energy cost as aproportion of manufacturingproduction costs is about threepercent. Historically, industrialfirms have viewed energy costs aslargely outside their control, andas fixed costs that are not signifi-cant enough to warrant specialattention. Today, a host of en-ergy-efficient technologies, tech-niques, and approaches hasemerged and energy managementis being increasingly recognizedfor its potential to improve the“bottom line”. For example, ifenergy represents three percentof production costs, and profitsamount to 20 percent of produc-tion costs, then reducing netenergy costs by one-third canresult in a five percent gain inprofits.1-4

Energy management is worthpursuing, with the greatestbenefit potential within energy-intensive industries that have notimplemented aggressive energy-efficiency programs in the past.1-4

The level of effort justified de-pends on how much money isspent for energy each year. Arule-of-thumb is one person-yearfor each $1 million expendedannually. As progress is madeand energy management becomesthe normal way of operating, thelevel of involvement can bereduced to one person-year forevery $2 - $5 million spent annu-ally.1-2


1-1 Washington Association of School Administrators,“Energy Excellence in Public Schools.” WashingtonState Energy Office

1-2 Wayne L. Stebbins, “Keeping the Energy ManagementProcess Alive,” Plant Engineering, June 3, 1993

1-3 J. Smith,“Developing a Coherent Corporate EnergyStrategy,” Energy Management and EnvironmentalSourcebook, Proceedings of the 14th World EnergyEngineering Congress, October 23-25, 1991.

1-4 M.F. Hopkins, et. al., “Industrial Demand SideManagement: A Status Report,”Battelle PacificNorthwest Laboratory, PNL-10567, May 1995

1-5 Thomas Bear and Karl Peters, “Getting an EnergyManagement System Up and Running,”I&CS, July1994.

1-6 “Energy Management for Industry” Electric IdeasClearinghouse Technology Update, Bonneville PowerAdministration, February 1993

1-7 David L. Lewis, Washington State Energy Office“Turning Rust into Gold: Planned FacilityManagement,” Public Administration Review, Vol. 51,No. 6, November/December 1991

1-8 Reliance Electric, “A-C Motor Efficiency: A Guide toEnergy Conservation,” B-7087-5

1-9 A & C Consultants, Inc., “Managing Energy in LocalGovernment Facilities,” Washington State EnergyOffice, WAOENG-87-07, March 1987

1-10 “Selling Energy Management,” Energy AccessWashington State Energy Office, WAOENG-89-47,September 1989

ReferencesChapter 1

Understanding Your Utility Bill 2-1

The first step in reducing energycosts is understanding whereyour energy dollars go.2-2 Howmuch energy goes to lighting, airconditioning, air compressors, orto refrigeration systems? Whatportion of the electrical bill is forelectrical energy consumption(kWh) versus peak power de-mand (kW)? Are demandcharges ratcheted, i.e. monthlycharges linked to the highestpower draw over the precedingyear? Is a power factor penaltyor kVA charge levied? Are ratesseasonally differentiated orhigher during certain periods ofthe day? Is a declining or in-verted block structure used forassessing energy charges? Theanswers to these questions tellyou where to look for bothenergy and dollar savings.2-2

Organizing Utility Billsand Production DataEnergy accounting involvesrecording and analyzing bothenergy use and cost data. Thisprocess helps you:2-3

� Account for current energyuse,

� Identify or target areas withthe greatest savings potential,

� Justify capital expendituredecisions,

� Observe the results of conser-vation investments,

� Gain management support,� Detect consumption in-

creases,� Identify billing errors; and

� Compare the energy efficiencyof your facility or process tosimilar facilities or processes.

To initiate an energy accountingprogram:� Locate all meters and

submeters within a facility.� Determine which building or

process is served by eachmeter.

� Obtain copies of all utility billsfor at least a one-year period.

� Obtain monthly and annualfeedstock, production, orthroughput data at the facilityand/or process level.

� Sort utility bills by buildingand/or meter, and organizebills into 12-month blocksusing meter read dates.

� Organize historical energyand production data so thatenergy management perfor-mance can be measuredagainst a baseline year. Typi-cally, the year prior to initiat-ing an energy managementprogram is selected as thebaseline.2-3

� Ensure that your facility is onthe proper utility rate sched-ule. Often, electrical utilitiesoffer different schedules —such as General Service, LargeGeneral Service, PrimaryGeneral Service, High VoltageGeneral Service, or HighVoltage Interruptible Service— based upon the type andreliability of services pro-vided.2-1 The “best” schedulefor your facility may changeover time.

Chapter 2

Understanding YourUtility BillThis section illustratesvarious billing strategies thatmay be applicable at yourfacility. Contact your utilityaccount representative fordetailed information aboutyour rate schedule.


Figure 2-1Energy Use Profile Reports

Concepts of Power andEnergy

The basic unit of power in electri-cal terms is the watt. Since thisunit is very small, a unit onethousand times as large (thekilowatt) is frequently used. Onemegawatt is one thousand kilo-watts. One horsepower is 746watts or 0.746 kW.

Power is the rate of energy use.The amount of energy used by amotor-driven system is directlyproportional to the power draw ofthe system times the length oftime it is in operation. Sincepower is expressed in kilowattsand time in hours, the conven-tional unit of energy is kilowatt-hours (kWh).2-1

Power and energy measurementsare used to determine loads onequipment, energy consumption,running costs, and to verifyproper system sizing and opera-tion. To measure power, we use apower meter or take advantage ofthe fact that power is proportionalto the product of circuit voltage(V) amperage or current (I) andpower factor (PF).2-1 For a three-phase system:

Where:

Pi = Three phase power in kW

V = RMS voltage, mean lineto line of 3 phases

I = RMS current, mean of 3phases

PF = Power factor as a decimal

You can present informationabout your energy use in agraphical format as shown inFigure 2-1. Energy managementperformance is often indicated interms of 12-month rolling averageenergy consumption. Becauseindustrial plants may expand orundertake modifications toincrease production rates, therolling average is typically nor-malized to reflect an energy-intensity ratio such as kWh/square foot-year or kWh/unit ofproduction per year. For indus-trial facilities, energy efficiency isproperly expressed as a reductionin the energy required to produce

a unit of product. Informationtypically presented in graphsincludes:2-3

� Electricity consumption bymonth (kWh) for a givenfacility, meter, or process

� Electrical demand by month(kW)

� Energy and demand costsby month

� “Rolling Average” energyconsumption

� “Rolling Average” energyintensity (kWh/unit ofproduct)

� Facility production bymonth

iPV x I x PF x = 3

1000


In the rolling average method ofenergy accounting, you calculatebilling data each month by drop-ping the oldest month from thetotal and adding the newest. Thismethod eliminates widely-fluctuating values due to variablemeter reading dates or seasonalprocesses. It allows for simplecomparison of the present year’senergy use or energy intensitywith any previous year. A graphof this type remains flat if nosignificant changes in energyconsumption or process efficiencyoccur.2-3

Once a baseline energy consump-tion profile is established, you canidentify the load with the processand ultimately with the motor-driven equipment. You can thenbegin to identify where to focusyour energy conservation efforts.A summary of energy end uses ina sawmill is given in Table 2-1 andshown in Figure 2-2. You shouldalso examine seasonal loads,consumption trends, annualenergy and cost savings, andanomalies or unexplained peaksin energy use or demand. Suchpeaks may indicate equipmentmalfunction or a meter readingerror.2-3

Figure 2-2Sawmill Energy Consumption Disaggregation

Table 2-1.Sawmill Energy End Use Summary

Process Electricity Use, kWh Percentage of Total Use Cost

Blowers 484,600 4.8% $12,115Chippers 101,600 1.0% 2,540Air Compressors 1,911,200 19.0% 47,480Hog 76,700 0.8% 1,917Hydraulic Motors 857,800 8.5% 21,445Saw Motors 2,092,000 20.8% 52,300Planer Motors 132,700 1.3% 3,317Kiln Fans 2,033,800 20.2% 50,845Boiler Fans 268,900 2.7% 6,722Lights 376,400 3.7% 9,410Misc. 1,741,390 17.3% 43,534

Totals 10,077,090 100.0% $251,925


Interpreting UtilityChargesLook at your electric bill. Atypical bill is shown in Figure 2-3.The bill tells you how much topay, but generally does not tellyou where the total came from orwhy. In fact, most bills includetwo, three, or four separatecharges.2-1,2-2 These differentcharges vary widely from utilityto utility. Therefore, your strate-gies to reduce energy costsdepend heavily upon the ratestructure applicable to yourfacility.

While your utility bill indicateshow much energy and power youused, the rate structure is yourguide for determining how costsare allocated and computed.2-2

Let’s examine the most commoncharges shown in Figure 2-3, asample monthly commercial/industrial billing statement. Thedescriptions below relate tonumbers on Figure 2-3.

1. Service days - The number ofdays in the billing cycle.

2. Meter number - The numbershown on the face of the meter.

3. Meter type - You could have oneor more of the following types ofmeters;A. Energy and Demand - this

measures kWh (Kilowatt-hours) and kW (Kilowatt),

B. Reactive Energy only - thismeasures kVARh (Kilovolt-amp-hour reactance) whichis used to bill for powerfactor less than 95%, and

C. Energy, Demand, and PowerFactor - this meter has thecapability to measure allthree.

4. Meter Reading - The actualreading taken from the meter.

5. Multiplier - This meter multiplier

used in calculating the kWdemand, total kWh consumptionor total kVARh consumption ison the front of the meter.

6. Consumption - The actual meterreading multiplied by the metermultiplier in units of kWh orkVARh. Reactive power is thenon-working power caused bymagnetizing currents required tooperate inductive devices such astransformers, motors and lightingballasts and is used as the basisfor power factor charges.

7. Demand - This is the actual kWdemand and is calculated bymultiplying the kW meter readingby the meter multiplier. Thedemand kW shown is the highestkW recorded by the meter in anyone 15 minute period for thebilling period.

8. Power Factor - The Power Factor% shown on the bill is determinedfrom the kVARh consumptiondescribed above, along with thereal (working) power and appar-ent (total) power. The actualcharge for power factor below95% is calculated by multiplyingthe kVARh consumption by thekVARh rate.

9. Rate Code - This is the rate thatapplies to the meter numbershown. For customers withmultiple meters, more than onerate schedule may apply.

10. Unit Charge - The rate beingcharged for the rate code shown.If the rate is not shown, you havea time-of-use meter. In thiscircumstance, a second statementis included with your bill whichshows the off peak and on peakschedule charges.

11. Service Charge - A monthlycharge often referred to as thebasic, facilities, or customercharge. It is generally stated as afixed cost based on transformersize.


You may be able to loweryour plant’s electricity costsby revising operatingschedules, replacing ineffi-cient equipment, or selectinga different utility rateschedule that better fits yourpattern of electricity use.

Ask your electric utilityrepresentative for printedrate schedules that describethe various rates availableand illustrate how chargesare calculated. Most electricutilities are willing to changea customer’s rate schedulefree of charge.2-4

Figure 2-3

Billing Statement

Service ChargeThis monthly charge is oftenreferred to as the basic, facilities,or customer charge. The servicecharge is designed to recoverfixed utility costs associated withactivities such as operations andmaintenance, administration,metering, and billing. It is gener-ally stated as a fixed cost based ontransformer size. Some utilitiesestablish a minimum billingamount or offer a variable servicecharge which is dependent uponpeak demand.2-2 Typical servicecharge structures are given inExample 1.

Example 1: Basic Service ChargeStructures� Basic monthly charge:

$760

� Facilities charge:$2,865 per month

Energy ChargeAll rate schedules include anenergy charge.2-2 The energycharge is based upon the totalnumber of kWh consumed overthe billing period. Many utilitiesoffer energy charges that areseasonally differentiated whilesome offer rates which vary withthe time of day. Some utilitiescharge the same rate for all kWhused, while others charge differ-ent rates for different quantities or“blocks” of energy. You shoulduse the “tailblock” or marginalenergy cost when calculating thefeasibility of conservation invest-ments.

With a declining block schedule,the charge per kWh is reduced foreach successive block, making thecost-per-unit less when moreelectricity is used.2-1 With an“inverted” block structure, theunit price increases for each


Ratcheted DemandCharges

Some utilities use what iscalled a “ratchet” clause. Theconcept is that the demandcharge should reflect thegenerating, transmission, anddistribution capacity requiredto meet your peak demandover the year, not just for thecurrent billing period. Forexample, your monthlydemand charge may be thegreater of the metered de-mand or a percentage of thegreatest demand recordedduring the preceding 11months. With this type ofrate structure, indicated inExample 6, abnormal electri-cal consumption from usingbackup equipment during anupset period or from a plantrestart can affect charges overan entire year.

incremental block. Consolidatemeters to take full advantage ofdeclining block rate schedules. Asample declining block ratestructure is depicted in Example 2.

Example 2: Declining Block RateStructure

� 3.636¢ per kWh for the first40,000 kWh

3.336¢ per kWh for all addi-tional kWh

Demand ChargePeak demand charges can accountfor half of the electric bill in anindustrial plant. Demand is acharge based upon your maxi-mum or peak rate of energy use.The demand charge is designed torecover utility costs associatedwith providing enough generat-ing, transmission and distributioncapacity to meet your peak electri-cal load.

A typical demand meter averagesdemand over a specified “demandinterval,” usually 15 or 30 min-utes. (In this instance, shortperiods of intense use, such as aten-second start-up of a motor,have little or no effect on de-mand.) At the end of each inter-val, the meter resets to zero andthe measurement begins again.2-2

The meter, however, stores orrecords the largest average de-mand interval in the billingperiod. “Sliding window” de-mand meters record demand andthen scan for the largest demandinterval regardless of startingtime.2-2 You are then billed for apeak demand that is somewhathigher than that obtained with aconventional meter. A demandmeter is depicted in Figure 2-4.2-3

A few utilities base their demandcharge on a facility’s instanta-neous peak. In this case, shortperiods of intense use such as a

ten-second start-up of a motor (orstart-up of motors after a poweroutage) can significantly affectdemand. Eliminate spikes bysequencing the start-up of largemotors so that their peak de-mands are staggered.

Types of Demand Charges

Direct Demand Charges

You may be billed directly fordemand charges at a rate fromless than $2/kW per month toover $25/kW, depending uponyour utility.2-2 In the Northwest,both demand and energy chargesare higher in the winter monthsthan the summer months.

Like energy, demand charges maybe levied in a declining or in-verted block structure. Some-times the initial block is offered atno charge, with a fixed chargeassessed for all demand exceed-ing the minimum value. Typicalrate schedule language for directdemand charges is illustrated inExample 3.

Example 3: Direct Demand Charge

� For each kW of billing demandWinter Summer$1.69 $1.13

� All kW of maximum demandbetween 7:00 a.m. and 10:00p.m., Monday through Friday at$1.16 per kW

Demand Incorporated IntoService Charges

Some utilities incorporate ademand component into theirbasic charges. Others vary thebasic charge based upon thefacility demand. This type of ratestructure is indicated in Example4. This charge may be in additionto other demand charges.2-2


Example 4: Incorporation of Demandinto Basic or Service Charges� If load size is over 300 kW: $115

+ $0.80 per kW

Linkage of Demand and EnergyCharges

Some utilities have rate schedulesthat include demand payments intheir energy charges. The energycharge in this case is broken into ablock structure where block sizevaries according to facility de-mand. For instance, you mightpay a higher rate for the first 100kWh per kW of demand, with alower rate for all additionalenergy use. This type of ratestructure is depicted in Example 5.

Example 5: Linkage of Demand andEnergy Charges

� 6.510¢ per kWh for the first 85kWh per kW of demand but fornot less than the first 1,000 kWh4.199¢ per kWh for the next8,000 kWh3.876¢ per kWh for all additionalkWh

� 2.815¢ per kWh for the first 200kWh per kVA of demand but notless than 1,000,000 kWh2.394¢ per kWh for all additionalkWh

Racheted Demand Charges

Some utilities use what is called a“rachet” clause. The concept isthat the demand charge shouldreflect the generating, transmis-sion, and distribution capacityrequired to meet your peakdemand over the year, not just forthe current billing period. Forexample, your monthly demandcharge may be the greater of themetered demand or a percentageof the greatest demand recordedduring the preceding 11 months.With this type of rate structure,indicated in Example 6, abnormalelectrical consumption from usingbackup equipment during anupset period or from a plantrestart can affect charges over anentire year.

Example 6: Ratcheted DemandCharges� The minimum charge is 100

percent of the maximum demandcharge established during thepreceding eleven months.

� Billing months of April throughNovember: the highest demandestablished during the month,but not less than 60 percent ofthe highest demand establishedduring the previous winterseason.

Figure 2-4Electric Demand Meters

Reduce ratchet charges byreducing your maximumdemand. For example,avoid simultaneouslyoperating large pumps andcompressors that are neededonly occasionally. Carefullyplan when to operate largeequipment during themonths of your greatestelectric demand. The morelevel your month-to-monthdemand, the closer you willcome to paying only foractual demand eachmonth.2-4


If you are on a time-of-use rate,shift as many operations to off-peak as possible. Significantinvestments in added equipmentmay be justified by savings inenergy and demand charges. Youmay be able to use automation tocontrol start-ups, minimizing theneed for additional people to workduring off-peak hours.

If your facility is not on a time-of-use rate, find out whether yourelectric utility offers such rates.You may be able to reduce costsby switching to time-of-use rates.

Minimum Demand Charges

Some utilities build a minimummonthly charge into their assess-ment of demand charges. Withthis type of rate structure, givenin Example 7, energy conserva-tion or demand-limiting measureswould produce no additionalbenefit once the monthly demanddrops below the minimum value.

Example 7: Minimum DemandCharges� $5,500 for the first 3,000 kVA or

less. $1.10 for each additionalkVA.

� The highest average 30-minutedemand recorded during themonth, or 4,400 kVA, whicheveris higher.

Power Factor ChargesInductive motor loads require anelectromagnetic field to operate.Reactive power, measured inkilovolt-amperes reactive, circu-lates between the generator andthe load to excite and sustain themagnetic field. Reactive powerdoes not perform “work” and isnot recorded on the utility’senergy or demand meters, yet theutility’s transmission and distri-bution system must be largeenough to provide it. Workingpower, measured in kW, andreactive power together make upthe apparent power (measured inkilovolt-amperes or kVA).

Power factor is the ratio of work-ing power to apparent power.Power factor measures howeffectively electricity is beingused. A high power factor indi-cates the efficient use of electricalpower, while a low power factorindicates poor utilization of theincoming electrical current sup-plied by the utility.2-6 Techniquesfor sizing and locating powerfactor correction capacitors andfor determining the cost-effective-

ness of power factor correctionactions are given in Chapter 7.

Utilities generally assess a penaltyfor low power factor. Variousmethodologies exist for calculat-ing the penalty. You need tounderstand your utility’s calcula-tion method in order to determinethe benefits associated withpotential power factor improve-ments.

Types of Power FactorPenalties

kVA Billing

As shown in Example 8, theutility may measure and bill forevery kilovolt-amp of apparentpower or primary period (peak)kVA supplied, including reactivecurrent.

Example 8: kVA Billing� Demand charge: $2.49 per kVA

of billing demand

� Primary kVA charge: $24,000which includes 2,000 primarykVA plus $12.10 for each addi-tional primary kVA.

Direct Reactive Energy Charges

As indicated in Example 9, reac-tive power may be measured anda reactive energy charge levied (in¢/kVARh).

Example 9: Direct Reactive EnergyCharges� Reactive power charge: 0.061¢

per reactive kilovolt ampere-hour(kVARh)

Demand Billing with a PowerFactor Adjustment

In the following calculation theutility bills at normal demandrates with a demand surcharge ormultiplier included to account forlow power factor.


Equation 2-1

kW kW x PFbilled

dem and= 0 95.

Where:

kWbilled = Adjusted or billabledemand

kWdemand= Measured electricdemand in kW

PF = Power factor as adecimal

Given a facility power factor of 84percent, the utility would obtain a13 percent increase in billabledemand.

Example 10 shows a rate schedulewith a penalty for facilities oper-ating below a 95 percent powerfactor.

Example 10: Demand Billing witha Power Factor Adjustment

� The demand charge, beforeadjustment for power factor, willbe increased 1 percent for each 1percent by which the averagepower factor is less than 0.95lagging.

Excess kVar Reactive DemandCharges

With this method the utilityimposes a direct charge for theuse of magnetizing power inexcess of some percentage of kWdemand. For example, if thecharge was 60 cents per kVAR foreverything over 40 percent of kW,and a 4,000 kW peak load existed,then the utility would provide upto 1,600 kVAR at no cost. ExcesskVAR is billable at the specifiedrate. This type of rate structure isillustrated in Example 11.

Example 11: Excess kVAR Reactive

Demand Charges� The maximum 15-minute

reactive demand for the month inkilovolt amperes in excess of 40percent of the kilowatt demandfor the same month will be billedat 45¢ per kVAR of such excessreactive demand.

Optional Rate SchedulesTime-of-Use Rates

By charging more during the peakperiod, when incremental costsare highest, time-of-use utilityrates send accurate marginal-costprice signals to customers. Peri-ods of heavy electricity use aretypically defined as “peak” hours;periods of lower use are “shoul-der” hours, with times of lowestuse deemed “off-peak.” Energycharges between peak and off-peak times might vary by over10¢/kWh .

Similarly, your demand chargesmay be computed at a muchhigher rate if your highest-de-mand interval occurs during the“peak” hours.2-4

Interruptible, Curtailment, andCustomer Generator Rates

Upon request from the electricutility, customers on interruptiblerates must lower their demand.They can do this by turning offsome or all of their large electri-cally-driven equipment or theycan use emergency generators orengine-driven pumps instead ofutility-supplied power.2-4

To obtain interruptible, curtail-ment, or customer generatorrates, the customer enters into aload management agreement tointerrupt or reduce plant loads atthe request of the power companyduring the occasional times ofpeak demand. In return, the

Find out whether your electricutility offers “interruptible,”“curtailment,” or “customergenerator” rates. If you arethinking of using an emer-gency generator on a regularbasis, analyze operatingconditions as well as yourability to maintain the genera-tor. Talk with your accountrepresentative about a loadmanagement agreement.


Ask your utility account represen-tative the following questions:2-4

� What other rate schedulesare available for the plant?Would they be less costly?

� What are the months in thepower company’s “peakseason?”

� Do time-of-use rates exist?How are the peak, shoulderand off-peak periods definedand what are the corre-sponding energy costs?

� Is there a ratchet clause?Which months in the pastyear were affected by theratchet clause? What wasthe additional annual cost?

� What was the peak monthkW demand? How muchlower must it be to elimi-nate ratchet charges in thefuture?

� Are there any power factorpenalties in effect for thisplant? What is the annualcost?

� Is a “customer generator”or other load managementrate available? What arethe requirements? What arethe benefits?

Example 12: Determining Your Load Factor

WhereLF = Load factor in %kWh = Electric energy in kWhkWdemand = Electric demand in kWN = Number of days in billing period

Sample Billing Information —

Energy Use Demand Period1,132,000 kWh 2,880 kW 30 Days

Sample Load Factor Calculation —

LFkWh

kW x 24 x Nx

demand

= 100%

LF2,880 x 24 x 30

x = =1132 000100% 54 6%

, ,.

With energy data in hand, youcan assess the feasibility ofdemand management measuresby computing the facility loadfactor. Load factor is the ratio ofyour facility’s average to peak-demand and indicates howeffectively demand is allocated.Calculate your monthly loadfactor for a 12-month period so aminimum, maximum, and annualaverage can be determined.2-5 Asample load factor calculation isgiven in Example 12.

If your load factor varies signifi-cantly from billing period tobilling period, your operationshould be carefully reviewed. Ifyour annual load factor is lessthan 80 percent, opportunities forin-plant demand reductionmeasures might exist. In contrast,if your facility has a load factorwhich is constantly above 80percent, there is likely littlepotential for demand-limitingmeasures in your plant.2-5

If your facilities have low loadfactors, you must determine theload profile — or load variationby time of day or month — formajor processes or pieces of

power company applies lowerrates to the demand charge on thebill for the duration of the agree-ment. Penalties for nonconfor-mance, however, are high.2-4

Using Billing Data toIdentify OpportunitiesUnderstanding your electricutility bill — knowing how yourdemand meter works and howpower factor penalties are as-sessed — is crucial for the energycoordinator. Energy and demandcosts are controllable, and thebenefits of implementing energyconservation, demand manage-ment, or power factor correctionare directly related to the wayyour facility operates and thestructure of your rate schedule.While power factor correction isnot generally undertaken forenergy conservation reasons(power factor correction doesresult in a reduction in electricalresistance or I R losses within theplant distribution system), it canbe very cost-effective and result insignificant reductions in yourutility bill.

2


equipment within the plant.Compile load data throughconducting periodic measure-ments at a predetermined sam-pling rate or by installing continu-ous metering or data loggingequipment.

Finally, you must be familiar witha host of energy conservation aswell as demand managementapproaches. Demand manage-ment requires that you know howand why tasks are performed atspecific times; you can thendetermine whether any jobs canbe scheduled at a different timewith little or no effect on produc-tion.2-5 You must also understandthe weekly demand profile ineach season to determine whetheropportunities exist to reduce peakdemand or shift load to off-peakperiods.

Demand control measures includeenergy conservation measuresplus equipment scheduling, loadshedding, time clocks and dutycyclers, interlocks, programmablecontrollers, energy managementsystems, adjustable speed drives,and the use of emergency genera-tors to displace large loads duringpeak demand periods.2-5

Checklist for ElectricityCost Savings

✓✓✓✓✓ Compare rate schedulesand use the one bestsuited to your operation.

✓✓✓✓✓ Train operators andmaintenance workers tobe aware of the time ofday for utility on-peakcharges. Run motorsand other electric loadsoff-peak wheneverpossible.

✓✓✓✓✓ Encourage routineenergy-saving practicesand follow recommendedmaintenance procedures.

✓✓✓✓✓ Use sequenced start-ups,and avoid schedulingperiodic equipmenttesting during peakhours.

✓✓✓✓✓ Install capacitors toreduce power factorcharges.

✓✓✓✓✓ Use standby generatorsto reduce peak demand.2-4


ReferencesChapter 2

2-1 A & C Consultants, Inc., “Managing Energy in Local Gov-ernment Facilities,” Washington State Energy Office,WAOENG-87-07, March 1987

2-2 Washington Energy Extension Service, “Under-standing Commercial Electric Bills,” January 1986

2-3 “Energy Accounting,” Electric Ideas ClearinghouseTechnology Update, Bonneville Power Administration,November 1991

2-4 Electric Power Research Institute, “Understanding YourElectric Bill: Cost-Saving Strategies for Industrial andLarge Electric Power Consumers,” BR-104028, 1994.

2-5 “Electrical Demand Control For Industry” Electric IdeasClearinghouse Technology Update, Bonneville PowerAdministration, February 1993

2-6 “Power Factor Correction: A Guide for the PlantEngineer,” Commonwealth Sprague Capacitor, Inc., PF-2000E, October 1991

Industrial Electrical Systems 3-1

Chapter 3

Industrial ElectricalSystems

The plant energy coordinator isthe person who can be mosteffective in increasing electricalenergy efficiency in the plant.However, in order to do so, theenergy coordinator needs somebasic measurement tools and anunderstanding of how inductionmotors relate to the in-plantelectrical distribution system.

The electrical utility deliverspower to the industrial user at aspecified service voltage. A step-down transformer converts theutility voltage to the in-plant

distribution system voltage.Additional transformers may bepresent to reduce the distributionvoltage to a motor’s nominalvoltage, i.e. 480 volts. The utiliza-tion voltage, the voltage value atthe motor leads, is the nominalvoltage less the voltage dropsbetween the points of transforma-tion and end use. The single-linediagram in Figure 3-1 shows theservice voltage, distributionvoltage, and utilization voltagevalues.

Figure 3-1Typical Facility Single-Line Diagram 3-6

Source: Thumann, Albert, P.E., 1991, p.22


The Plant ElectricalDistribution SystemUtilities are concerned withmeeting two principal criteriawhen they supply power to theircustomers. First, the utility strivesto deliver power at a voltage thatis within an acceptable voltagerange. Second, the utility makesefforts to provide polyphase(three phase) power where thephase-to-phase voltage is bal-anced or close to being the samebetween all phases.3-1

Over and Under Voltage

The utility is obligated to deliverpower to the 480V industrialuser’s service entrance in therange from a low of 456V to ahigh of 504V (480 ± 5%). Inpractice, the service voltage isusually maintained within a tightrange. It is common to experiencethe service voltage remaining in arange of 475V to 485V.3-2

Acceptable in-plant distributionsystem delivery voltage values asdefined by IEEE and ANSI stan-dards are summarized in Table 3-1.3-2 When the average of thethree-phase voltages exceeds thevalue ranges in Table 3-1, thesystem is out of compliance. Nofield measurements or analysisshould be undertaken until the

system is brought into compli-ance. Service voltage correctionusually begins by contacting theserving utility.

Figure 3-2 illustrates the relation-ship between system voltage andmotor voltage.

In most northwest industrialfacilities the nominal in-plantvoltage is 480V. Delta type elec-trical systems always refer to “lineto line” voltage values. “Wye”type electrical systems refer to“line to line” and “line to neutral”voltage values. One will fre-quently see a voltage described as277/480. This means that thevoltage from the line-to-neutral is277V and the voltage from line-to-line is 480V.3-1

Usual utilization voltage condi-tions, defined in the NationalElectrical Manufacturers Associa-tion (NEMA) Standards Publica-tion MG 1-1993, Rev. 1, Motors andGenerators, include operationwithin a tolerance of ± 10 percentof a motor’s rated voltage.3-2

The custom by NEMA members isto rate motors at 95.8 percent ofnominal system voltage. Forexample, motors intended for useon 480V systems are rated at 460V(95.8% x 480V) and motors in-tended for use on 240V systemsare rated at 230V (95.8% x 240V).Motors can be allowed to operate

Voltage Definitions

All voltages are phase-to-phase voltage, unless specifi-cally designated otherwise.

■ Service Voltagedescribes the voltagevalue at the pointwhere the utilitydelivers service to theindustrial user.

■ Nominal Voltagedescribes the generalvoltage class thatapplies to the system,i.e., 120V, 240V, 480V.

■ Utilization Voltagedescribes the value ofvoltage at the motorleads.

Nominal Allowable AllowableSystem Voltage Limits % Voltage Range

120V (L - N) ± 5% 114V - 126V

240V (L - L) ± 5% 228V - 252V

480V (L - L) ± 5% 456V - 504V

Table 3-1Acceptable System Voltage Ranges


on voltages as low as 95.6 percentof their specified voltage rating.Thus, a motor rated at 460V canoperate at 440V (460V x 0.956). Aslong as the phase-to-phase volt-ages are balanced, the motor neednot be derated.3-1

If the voltage at the motor feederis increased, the magnetizingcurrent increases. At some point,depending upon design of themotor, saturation of the core ironwill increase and overheating willoccur. At about 10 to 15 percentover voltage both efficiency andpower factor significantly de-crease for standard efficiencymotors while the full-load slipdecreases. The starting current,locked rotor torque, and break-down torque all significantlyincrease with over voltage condi-tions.

If a motor is operated undervoltage, even within the allow-able ten percent limit, the motorwill draw increased current toproduce the torque requirementsimposed by the load. This causesan increase in both stator androtor I2R losses, and overheatingat full-load or service factor

operation. Low voltages can alsoprevent the motor from develop-ing an adequate starting torque.3-2

Voltage Unbalance

A voltage unbalance occurs whenthere are unequal voltages on thelines to a polyphase inductionmotor. This unbalance in phasevoltages causes the line currentsto be out of balance. The unbal-anced currents cause torquepulsations, vibrations, increasedmechanical stress on the motor,and overheating of one andpossibly two of the phase wind-ings. Voltage unbalance has adetrimental effect on motors.Motor efficiency suffers whenmotors are subjected to significantvoltage unbalances. Whenefficiency falls, energy drawn bythe motor dissipates as heat in thecore and in the windings. Usefultorque at the shaft is reduced.

Ultimately, the motor can failfrom insulation breakdown.Figure 3-3 is a derating curvepublished by NEMA. Theamount of derating for a motor isdescribed by the curve as afunction of voltage unbalance.

Figure 3-2Acceptable Voltage Range for Systems and Motors


Unbalance of more than onepercent requires that a motor bederated and may void amanufacturer’s warranty. NEMArecommends against the use ofmotors where the unbalance isgreater than five percent.3-1, 3-2, 3-3

NEMA defines voltage unbalanceas 100 times the maximum devia-tion of the line voltage from theaverage voltage on a three-phasesystem, divided by the averagevoltage (see example below).Most utilities attempt to controlthe service voltage unbalance toless than two percent.

Example 3-1Determining Voltage Unbalance

Voltage unbalance is defined by NEMA as 100 times the maximumdeviation of the utilization voltage from the average voltage on athree-phase system divided by the average voltage.

Unbal = x V -VV

maxdev100Where:

Unbal = Voltage unbalance in %V

maxdev= Line to line phase voltage deviating most

from mean of 3 phasesV = RMS voltage, mean line to line of 3 phases

For example, if the measured line-to-line voltages are 462, 463,and 455 volts, the average is 460 volts. The voltage unbalance is:

(460-455)/460 x 100%=1.1%

Figure 3-3Motor Voltage Unbalance Derating Curve


With a well-designed electricaldistribution system in the plant,the amount of unbalance at theload and motor control centersshould be about the same as thedegree of unbalance at the serviceentrance. When the unbalance issignificantly different at the loadcenters, there is a phase voltagedrop problem between the serviceentrance panel and the loadcenters. The unbalancing prob-lems must be found within theplant and corrected prior torecording motor data.3-1, 3-3

A utility attempts to load indi-vidual phases in a balancedfashion through the process ofalternating single phase loads andother similar practices. An indus-trial user must also exert an effortto balance loads. Analyticaltechniques for balancing loads arestraightforward and are discussedin the Troubleshooting andTuning Your In-Plant DistributionSystem section of this chapter.

A qualified person should takeutilization voltage measurementsat each motor control center orprincipal motor feeder. When autilization voltage unbalance isin excess of one percent, thesystem can benefit from voltagecorrection. The effect of unbal-ance not only distorts potentialenergy savings, but it may causeirreparable damage to equip-ment.3-1, 3-3

Troubleshooting andTuning your In-PlantDistribution SystemMaintenance of in-plant electricaldistribution systems is oftenneglected, with increased costsultimately being paid in the formsof decreased safety (due to in-creased fire hazard), decreasedmotor life, increases in unsched-

uled downtime, and lost produc-tivity.

See the Bonneville Power Admin-istration publication, Keeping theSpark in Your Electrical System: AnIndustrial Electrical DistributionSystem Guidebook, for additionalinformation.

You can improve efficiencythrough eliminating commonproblems such as poor contacts,voltage unbalance, over andunder voltage, low power factor,undersized conductors, andinsulation leakage. 3-4, 3-5 Youshould troubleshoot and correctthe in-plant distribution systembefore taking field data measure-ments.

Begin the electrical distributionsystem tune-up with a search forand correction of poor contacts,since these are most likely toresult in a catastrophic systemfailure and possibly a fire. Cor-rection of poor power factor is thenext step, since this is generallythe source of the greatest utilitycost savings. The system shouldthen be examined for voltageunbalance and over/undervoltage conditions due to theirdetrimental effect on motorperformance and motor life.Finally, survey for insulationleakage and undersized conduc-tors.3-4

Troubleshooting Poor Contacts

The first step in optimizing yourindustrial electrical distributionsystem is to detect and correct anyproblems due to poor connec-tions. High temperatures arecommonly caused by loose anddirty contacts. Such contacts arefound in switches, circuit break-ers, fuse clips, and terminations.These problems are the most costeffective to correct. Poor contactscan be caused by:3-4

Safety Considerations

This guidebook discusses thetype of measurements theelectrician must take. Theguidebook is not meant toinstruct a person on how to bean electrician, nor is it meantto train a person in propersafety techniques. Theguidebook assumes instruc-tions will be followed byqualified electricians who aretrained in safety practicesregarding industrial electricalsystems. Persons who are notproperly qualified in indus-trial electrical techniquesshould not attempt to takeany measurements.


■ Loose cable terminals and busbar connections.

■ Corroded terminals andconnections.

■ Poor crimps or bad solder joints.■ Loose, pitted, worn, or poorly

adjusted contacts in motorcontrollers or circuit breakers.

■ Loose, dirty, or corroded fuseclips or manual disconnectswitches.

Detection should begin witheither infrared thermography or avoltage drop survey of the powerpanels and motor control centers.Advantages of a voltage dropsurvey are that the survey can bedone in-house with existingequipment and that problems canoften be detected before theywould be with infrared thermog-raphy. Voltage drop measure-ments should be taken at a timewhen the plant is heavily loaded. 3-4

During the voltage drop orinfrared survey, the electrician canvisually inspect suspected troubleareas for: 3-4

■ Discoloration of insulation orcontacts.

■ Compromised insulationranging from small cracks tobare conductors.

■ Oxidation of conductormetals.

■ Presence of contaminantssuch as dirt.

■ Mismatched cables in com-mon circuits.

■ Aluminum cables connectedto lugs marked for copperwire.

Voltage Drop Survey

A voltage drop survey can bedone with a simple hand-heldmillivolt-meter. You can use atwo-stage process to quicklyidentify problems without indi-

vidually testing each component.Use extreme caution and wearlineman’s gloves. Voltage dropmeasurements are taken firstfrom the main distributionpanel to the motor controlcenter, then from themotor control center to the motorleads. An example for a typicalmotor circuit is to measure thevoltage drop from the bus bar tothe load side of the motor starter.3-4

Comparing the magnitude ofvoltage drop with other phasessupplying the load can alert theelectrician to poor connections.The electrician can make compo-nent-by-component voltage dropmeasurements on suspect circuitsto isolate and eliminate poorconnections.3-4

Infrared Thermography

Infrared thermography is a quickand reliable method for identify-ing and measuring temperaturesof components operating atunreasonably elevated tempera-tures. High temperatures are astrong indication of both energywastage and pending failure.High resistance connections areself aggravating since they gener-ate high temperatures whichfurther reduce component con-ductivity and increase the operat-ing temperature.3-4

Once the infrared survey iscomplete, the plant electrician canfocus on the located hot spots. Amillivolt meter or milliohmmeteris recommended for measuringthe voltage drop and resistance,respectively, across high tempera-ture connections and connectionsnot shown on the thermographs.These measurements can be usedto determine if the hot spotindicated in the infrared image isdue to a problem with the compo-nent itself or if heat is beingradiated from an adjacent source.3-4


Troubleshooting VoltageUnbalance

Further efforts to optimize yourelectrical distribution systemshould include a survey of loadsto detect and correct voltageunbalances. Unbalances in excessof one percent should be correctedas soon as possible. A voltageunbalance of less than one per-cent is satisfactory.

Figure 3-4 displays motor lossincreases caused by voltageunbalance. Left uncorrected, theincreased losses require motorderating per Figure 3-3. Thefollowing causes of voltageunbalance can be detected bysampling the voltage balance at afew locations:3-4

■ Selection of wrong taps on thedistribution transformer.

■ Presence of a large, single-phase distribution trans-former on a polyphase sys-tem, whether it is under loador not.

■ Asymmetrical (unbalanced)transformer windings deliver-ing different voltages.

■ Faulty operation of automaticequipment for power factorcorrection.

■ Unbalanced three-phase loads(such as lighting or welding).

■ Single-phase loads unevenlydistributed on a polyphasesystem, or a large single-phaseload connected to two con-ductors on a three-phasesystem.

■ Well-intentioned changes,such as improvements in theefficiency of single-phaselighting loads, which inad-vertently bring a previouslybalanced polyphase supplyinto unbalance (possiblywasting more energy thanwas saved).

■ Highly reactive single-phaseloads such as welders.

■ Irregular on/off cycles of largeloads such as arc furnaces ormajor banks of lights.

■ Unbalanced or unstablepolyphase supply from thegrid.

The following problems may bemore critical in nature, resultingin two-phase operation 3-4:

■ An open phase on the pri-mary side of a three-phasetransformer in the distributionsystem.

■ Single phase-to-ground faults.■ Failure or disconnection of

one transformer in a three-phase delta-connected bank.

■ Faults, usually to ground, inthe power transformer.

■ A blown fuse or other opencircuit on one or two phasesof a three-phase bank ofpower-factor correctioncapacitors.

■ Certain kinds of single-phasefailures in adjustable fre-quency drives and othermotor controls.

Figure 3-4Effects of Voltage Unbalance on Motor Losses


The following problems can beisolated to a particular circuit andmay require a load-by-loadsurvey to detect:■ Unequal impedances in

power-supply conductors,capacitors, or distributionwiring.

■ Certain kinds of motor defects.Constant loads can be checked bymeasuring voltage-to-ground oneach phase with a hand-heldvoltmeter. Highly variable loadsmay require simultaneous mea-surement of all three phases withmonitoring over time. Monitor-ing instruments can periodicallymeasure and record the voltage,current, power factor, and totalharmonic distortion on eachphase.

Proper system balancing can bemaintained by:3-4

■ Checking that unloadedtransformer voltage balancedoes not exceed a minimum1.25 percent step per tap.

■ Checking and verifyingelectrical system single-linediagrams to ensure thatsingle-phase loads are evenlydistributed.

■ Regularly monitoring voltageson all phases to verify that aminimal unbalance exists.

■ Installing ground fault indicators.

■ Conducting annual infraredthermographic inspections.

■ Installing sensitive phasevoltage monitors.

Before making changes to yourdistribution system, consider theimpact on the resulting phase-to-phase balance.

Troubleshooting Over and UnderVoltageOver or under voltage conditionscan result from:3-4

■ Incorrect selection of motorsfor the rated voltage. Ex-amples include a 230 voltmotor on a 208 volt circuit.

■ Incorrect transformer tapsettings.

■ Unequal branch line lossesresulting in dissimilar voltagedrops within the system.Often a panel will be suppliedwith a slight over voltage inthe hope of supplying thecorrect voltage to the motorcontrol centers (MCCs).However, voltage drop differ-ences can result in an overvoltage at some MCCs whileothers are under voltage.

A common situation involvingunder voltage occurs in applica-tion of 208-230 volt motors on 208volt systems. Commercial build-ings frequently use 208 volt three-phase power. It is the three phaseline-to-line voltage correspondingto 120 volts line-to-neutral pro-vided for single phase lights andreceptacles. There is no change inmotor wiring connection for thetwo voltages. While 208-230 voltmotors tolerate 208 volts, they areoptimized for the more common230 volts.

208 volts is a nominal systemvoltage; voltage at the motorterminals may even be lower.Additional losses occur when a208-230 volt motor is operated ator below 208 volts. The motorwill exhibit a lower full-loadefficiency, run hotter, slip more,produce less torque, and mayhave a shorter life. It is best tosupply 200 volt motors for use ona 208 volt system, especially ifvoltage at the motor terminalssometimes falls below 208 volts.


Until 200 volt motors can beprovided, it is recommended thatsystem voltage be tapped at thehigh end of the acceptable rangefor single phase loads and thatdistribution losses are minimized.System voltage can be modified by:■ Adjusting the transformer tap

settings.■ Installing automatic tap-

changing equipment wheresystem loads vary greatlythrough the course of the day.

■ Installing power factor correc-tion capacitors that raise thesystem voltage while correct-ing for power factor.

Troubleshooting Low PowerFactorAnalysis of utility bills will usu-ally reveal if you have a powerfactor problem. Even if the utilitydoes not bill directly for powerfactor, a low power factor canraise your kWh and demandbilling. This is because of realpower wasted in excess trans-former and line losses associatedwith the flow of reactive power.Correcting power factor willreduce the line current and theassociated I2R losses in the entiredistribution system. A compre-hensive discussion of powerfactor including detecting andcorrecting low power factor ispresented in Chapter 8.

Troubleshooting UndersizedConductors

As plants expand, conductorssized for the original load areoften undersized for the newloads they are required to carry.Undersized conductors present anadditional resistive load on thecircuit, similar to a poor connec-tion. The cost of replacing orsupplementing these conductorsis often prohibitive from the

standpoint of energy cost savings.However, the cost may be sub-stantially less when done duringexpansion or retrofit projects.3-4

Troubleshooting InsulationLeakageElectrical insulation leakage canoccur as a result of extremetemperature, abrasion, moistureor chemical contamination, andage.

Resistance is approximatelyhalved for every 10°C tempera-ture increase. Abrasion occursdue to vibration or movementunder magnetic forces such asoccurs with poorly secured endturns in a motor’s winding. Someof the worst chemical contamina-tion is that associated withelectroconductive particles likesalt or coal dust. Moisture oftenintrudes when a motor has longenough off time to completelycool and is in an environmentwith high relative humidity. Evenwithout such harsh threats,insulation testing and trending, atleast annually, is advisable.

Insulation leakage can only bedetected by use of amegohmmeter. It is possible toperform testing at the motorcontrol panel so that cables aretested as well as the motor.Cables are not usually a source ofsignificant leakage unless they arevery old and contaminated, butthey provide easy electrical accessto the motor from the motorcontrol system. Information onperforming insulation testing isprovided in Chapter 9.


3-1 Carroll, Hatch & Associates, Inc., “An ElectricMotor Energy Efficiency Guide and TechnicalReference Manual”, (Draft) June 1994,Bonneville Power Administration, Revision 4,April 1995 (Draft)

3-2 Gilbert A. McCoy and John G. Douglass, “EnergyEfficient Electric Motor Selection Handbook,” U.S.Department of Energy, DOE/GO-10096-290, August1996

3-3 Carroll, Hatch & Associates, Inc., “A Procedure forDeveloping an Energy Efficiency Plan for the Use ofElectric Motors in an Industrial Setting,” (Draft) June1994

3-4 “Electrical Distribution System Tune-Up,” Electric IdeasClearinghouse Technology Update, Bonneville PowerAdministration, January 1995

3-5 Rob Gray, Washington State Energy Office, “Keepingthe Spark in Your Electrical System: An IndustrialElectrical Distribution Maintenance Guidebook,”Funded by Bonneville Power Administration, U.S.Department of Energy, PacifiCorp, Portland GeneralElectric and Tacoma City Light, October 1995

3-6 Albert Thumann, P.E., “Introduction to Efficient Electri-cal Systems Design,” The Fairmont Press, Inc., GA, 1991.

ReferencesChapter 3

Taking Field Measurements 4-1

Field evaluation of motors isessential in making informeddecisions regarding motor selec-tion and use. The amount ofmoney you can save by purchas-ing an energy efficient over astandard motor depends uponmotor size, annual hours of use,load factor, efficiency gain (at theload point), and the servingutility’s charges for electricalenergy and demand.4-1 Fieldmeasurements are necessary toestablish the load imposed uponan existing motor by its drivenequipment and to determinemotor efficiency at its load point.

SafetyConsiderationsSafety is an important consider-ation when using test instru-ments. Plant electricians andequipment operators are hope-fully well trained in safety andguided by company policies forworking close to live circuits andmoving machinery. This guide-book will occasionally recom-mend caution in making certainmeasurements. This is not in-tended to be a replacement forthorough safety training andadherence to company policies.

The absence of a caution state-ment certainly does not mean anaction is inherently safe. Com-pany policies vary dependingupon plant environment, insur-ance requirements, governmentregulations, and management’scommitment to safety. Any actiondescribed in this book which

conflicts with your companysafety procedures, conflicts withyour safety training, createsexposure beyond your normalworkday experience, or simplyseems unsafe, should be omitted!

Particular caution is recom-mended when working withcurrent- or power-recordingdevices. Many of these are eitherassembled from components ordesigned with the expectationthat they will be connected whencircuits are unpowered, then leftalone after they are powered.Some have alligator clips thatrequire fingers to be close toconductors or are hard to connectwhen wearing line worker’sgloves. Some (particularly multi-channel devices intended forresearch-oriented monitoring)have wiring panels that do notseparate 480 volt terminal areasfrom low voltage sensor wires.Others have metal enclosures thatrequire grounding which issometimes challenging in por-table applications. Some haveenclosures which may not besufficient for the environmentalexposure they will experiencewhile deployed. Use of anyrecording device may require thatcontrol panel doors be left open,exposing personnel to dangerunless you mark the area withribbon and signs. Regrettably,most voltage leads are unfused. Ifpossible, leads should be fused,ideally at the clip end. Fusesshould be fast-blow and 1/4 ampor less. Even 1/4 amp can be fatalor cause permanent neurologicaldamage if sustained for severalseconds.

Chapter 4

Taking FieldMeasurements

This guidebookassumes

instructions will be followedby qualified electricians.Persons who are not properlyqualified in industrialelectrical techniques shouldnot attempt to take anymeasurements.


Constructing the MotorList and InventoryDatabase

The energy coordinator shouldprepare a strategy for surveyingand analyzing plant motors.Divide the plant into logical areasand make a list of motors to bereviewed. Motors which aresignificant energy users shouldhead the list. Motors that operatefor extended periods of time andlarger motors should also be onthe list. Conversely, small motorsthat run intermittently should beplaced toward the end of the list.4-2, 4-3

Depending upon size of the plantand complexity of the manufac-turing process, it may be appro-priate to list only motors whichexceed minimum size and operat-ing duration criteria. Each plantwill have to establish appropriatethresholds. Typical selectioncriteria include:

■ Three phase, NEMA Design Bmotors

■ 10 to 600 hp

■ At least 2,000 hours per yearof operation

■ Constant load (not intermit-tent, cyclic or fluctuating)

■ Older and/or rewoundstandard efficiency motors

■ Easy access

■ A readable nameplate

■ Non-specialty motors

Once you have a short list ofmotors, you can collect data oneach motor and use the Motor-Master+ software to determinethe benefits of replacing it with anenergy-efficient unit. (MotorMas-ter+ is discussed in detail in

Chapter 7.) Create an inventorydatabase with a file for eachmotor. Appendix A contains aMotor Nameplate and Field TestData Form, while Appendix Cprovides a Motor Energy SavingsCalculation Form. Examinereplacement alternatives anddevelop a contingent plan ofaction. Then when a motor fails,you can quickly implement thepreferred repair or replacementplan. 4-2, 4-3Include the followinginformation in your inventorydatabase:

� Individual motor identifica-tion and nameplate data

� Full load efficiency, speed,and amperage

� Operating motor voltage,amperage, and power factor

� Speed of motor and drivenequipment while under load

� Annual hours of operation

� Accurate motor load (in kW)

� Motor efficiency at its operat-ing point

� Action to be taken at failure,i.e., repair or replacementspecifications

Acquiring MotorNameplate DataMotor analysis requires thatinformation from the motornameplate be entered into yourinventory database. A typicalmotor nameplate, indicated inFigure 4-1, contains both descrip-tive and performance-based datasuch as full-load efficiency, powerfactor, amperage, and operatingspeed. You can use this informa-tion to determine the load im-posed upon the motor by itsdriven equipment and the motorefficiency at its load point.


Depending upon the motor ageand manufacturer practices, notall of the desired informationappears on every motor name-plate. It is not unusual for powerfactor and efficiency to be miss-ing. When data is not present,you must find the required dataelsewhere. The motor manufac-turer is a logical source.4-2, 4-3

The motor age in years and itsrewind history should also berecorded. Obtain this data fromcompany records or from therecollection of people who haveworked at the plant and can recallmotor histories. Identify thecoupling type, describe the motorload (device being driven), iden-tify load modulation devices suchas throttling valves or inlet damp-ers, and record the driven-equip-ment speed. Lists of load andcoupling types are contained inTables 4-1 and 4-2.

Load-Time Profiles

The energy coordinator needs todetermine the hours per year eachmotor operates. Annual operat-ing hours can be estimated byconstructing a motor operatingprofile. Such a profile, includedin Appendix A—Motor Nameplateand Field Test Data Form, requiresyou to provide input regardingmotor use on various shiftsduring work days, normal week-ends, and holidays.

The nature of the load beingserved by the motor is also impor-tant. Motors coupled to variablespeed drives and operating withlow load factors or that serveintermittent, cyclic, or randomlyacting loads are not cost-effectivecandidates for replacement withenergy efficient units.

Figure 4-1Motor Nameplate


Load ListCentrifugal Fan

Centrifugal Pump

Compressor—screw compressor,reciprocating compressor,centrifugal compressor

Extruder

Conveyer

Crushers/Milling

Blenders/Mixers

Grinder

Machine Tools (Lathes, Sanders)

Crane

Planer

Positive Displacement Pump

ASD1/Centrifugal Fan

ASD1/Centrifugal Pump

ASD1/Compressor

Other

Measuring OperatingValues

In a three-phase power system itis necessary to measure thefollowing at each motor:

■ phase-to-phase voltagebetween all three phases,

■ current values for all threephases,

■ power factor in all threephases, and

■ operating speed of motor anddriven load.

Equipment necessary for thesemeasurements include:

■ voltmeter or multimeter■ clamp-on ammeter■ power factor meter

■ tachometer

Meters should be of adequatequality to read true RMS values.This guidebook proceeds on thebasis that adequate quality metersare being used by the electrician.

When the motor operates at aconstant load, only one set ofmeasurements is necessary.When the motor operates at twoor three distinct load points,measurements are required ateach load because the current andpower factor values vary withchanges in load level. The electri-cian can then determine theweighted average motor load.

A motor that drives a random-acting load presents a difficultmeasurement problem. Theelectrician should take a numberof measurements and estimate thecurrent and power factor that bestrepresent the varying load. Thesevalues are used with the voltageto determine the typical powerrequired by the load.4-1,4-3

Table 4-2

Coupling TypesDirect Shaft

Worm Gear

Helical Gear

Bevel Gear

Roller Chains

Silent Chains

V-Belts

Synchronous Belts

Flat Belts

Other

Table 4-1Typical Motor Load Types

1 Adjustable speed drive


Motor and driven-equipmentspeeds must be measured asclosely as possible, ideally with astrobe tachometer. Motor speed isimportant because a replacementmotor should duplicate theexisting motor speed. Whendriving centrifugal loads (fansand pumps), the motor load ishighly sensitive to operatingspeed. An energy efficient motorusually operates at a slightlyhigher speed than a standardmotor. The higher speed mayresult in an increase in speed-sensitive loads; this can negatesavings due to improved motorefficiency. A speed comparison isnecessary to properly evaluate anenergy-efficient motor conserva-tion opportunity.4-1,4-3

Enter field measurement valuesfor each motor on the MotorNameplate and Field Test Data Form(Appendix A).

Data GatheringApproachesA diagram of a typical three-phase power system serving a“delta” motor load configurationis shown in Figure 4-2. To evalu-ate the motor operation, you needto collect nameplate data plus usea multimeter and analog powerfactor meter to record voltage,amperage, and power factor oneach service phase or leg. Takereadings on all three legs andaverage them. Figure 4-3 indi-cates how measurements aretaken with hand-held instru-ments. It is also useful to use astrobe tachometer to measure thespeed of both the motor and thedriven equipment.

Sensitivity of Motor Load to Operating Speed

For centrifugal loads such as fans or pumps, even a minor changein a motor’s full-load speed translates into a significant change inload and annual energy consumption. Fan or “affinity” lawsindicate that the horsepower loading imposed on a motor bycentrifugal load varies as the third power or cube of its rotationalspeed. In contrast, the quantity of air flow or water deliveredvaries linearly with speed.

Some energy-efficient motors tend to operate with reduced “slip”or at a slightly higher speed than their standard-efficiencycounterparts. This small difference - an average of only 5 to 10RPM for 1800-RPM synchronous speed motors - is significant. Aseemingly-minor 20 RPM increase in a motor’s full-loadrotational speed from 1740 to 1760 RPM can result in a 3.5percent increase in the load placed upon the motor by the rotatingequipment. A 40 RPM increase can boost energy consumption byseven percent, completely offsetting the energy and dollar savingstypically expected from purchase of an energy efficient motor.4-1

To maximize energy savings with cube law loads, be sure to selectan energy-efficient replacement motor that has a full-loadoperating speed that is the same or less than that of your originalmotor. With belt driven equipment, motor speed is not importantif you replace pulleys so that the original rotating equipment speedis maintained.

Figure 4-2Industrial Three-Phase Circuit


Power supplied to the motor canbe measured with a single instru-ment when a “direct reading”meter is available. The directreading meter uses current trans-formers and voltage leads toreliably sense and display powerin watts or kW. Direct readinginstruments are more costly thantypical multimeters. Until re-cently, it was not common fordirect reading meters to be foundin industrial plants. This situa-tion is improving with the avail-ability of digital direct-readingpower meters.4-2, 4-3

Safety Issues in DataGathering� Hand-held instruments are

not recommended for sensingvoltage levels above 600 volts.

� Line-worker’s gloves shouldbe used.

� The unconnected leads ofsome current transducers(CTs) can inflict a dangerouselectrical shock. This is ofsignificance when connectinga CT to a separate readout orrecording device. The woundor conventional CTs haveeither a voltage or currentoutput. The safer (voltageoutput) type is an internally-loaded current transformer,

meaning it has an internalprecision shunt resistorshorting the secondary; theoutput leads are connectedacross the internal shunt so alow voltage output is pro-vided. The current outputtype is merely an unloadedtransformer, so the output is acurrent, requiring a current-sensing device. Alwaysconnect a current output CTto the recording device beforeclosing it around a live con-ductor. Otherwise, danger-ously high voltage will appearacross the open leads.

Voltage MeasurementsUtilization Voltage

Utilization voltage should bechecked first. A convenient placeto take measurements is at amotor starter enclosure. A hand-held voltmeter or multimeter canbe used to measure the phase-to-phase voltages. In a three-phasesystem the electrician shouldmeasure three values, V ab

, V

bc, and

V ca. (See Figure 4-3.) For a 480

volt system, utilization andservice voltage levels should bewithin the range of 456V to 504V(480V ± 5%).

Figure 4-3Instrument Connection Locations


The voltage unbalance should becalculated. The utilization volt-age unbalance should not begreater than one percent. Systemvoltage unbalance and over andunder voltage problems need tobe corrected before valid motoranalyses can take place. Asystem voltage unbalance exceed-ing one percent aggravates motorperformance to the extent thatrecorded data may be meaning-less.

Service Voltage

When the utilization voltageunbalance is greater than onepercent, the electrician mustcheck the voltage values at theservice entrance. Measurementsshould be made at or as close tothe service entrance as possible.This set of measurements allowsthe electrician to determinevoltage balance as delivered bythe utility. If the service voltageunbalance is less than one per-cent, the utilization unbalanceproblem is within the plantdistribution system. It is then theelectrician’s responsibility to findand fix the problem.4-3

Service voltage unbalance greaterthan one percent should bebrought to the attention of thelocal electric utility for correction.Data acquisition techniquesdiscussed in this guidebook areintended for the secondary side ofin-plant distribution systempower transformers. Hand-heldinstruments are not recom-mended for sensing voltage levelsabove 600 volts. 4-2, 4-3

CurrentMeasurementsA hand-held ammeter with aclamp-on CT (current transducer)is convenient and effective formeasuring the line current. It isonly necessary to enclose theconductor within the clamp-ondevice. The current may be readdirectly from the meter. Currentreadings, designated I a

, I b, and I c

should be taken for each phase.Line-worker’s gloves should beused.

Power FactorMeasurementsPower factor should be measuredwith a power factor meter. Mea-sure phase power factor byclamping the current sensingelement on one phase whileattaching voltage leads to theother phases. Take care that theproper voltage lead is used withthe current sensing device.

An alternative to power factormeasurement is power measure-ment. Some instruments canmeasure both. With either poweror power factor known, the othercan be calculated (see Chapter 5,Equation 5-1)

Before a valid motor energysavings analysis can takeplace, you need to correctsystem voltage unbalance andunder voltage problems.


Purchasing Motor TestingInstruments

When shopping for electricaltesting instruments, one caneasily be overwhelmed by thevariety of choices and wide rangeof prices. Three things tend toaffect the price: harmonics han-dling capability, range, andfeatures. To be a smart shopperrequires knowledge of your plantenvironment.

Most manufacturers are wellrepresented in industrial catalogsthat market “instruments”.Many manufacturers also use anextensive chain of independent“local reps”. It is good to getconnected with a local representa-tive. A good local rep can usuallysupply extensive manufacturer’sinformation about a product andmay also represent competingproducts for comparison. Ideally,they will have a good under-standing of the advantages anddisadvantages of each product.

1. Voltage Meters

Hand heldmultimetersusually areused for

measuring AC andDC voltage,current, andresistance.

The upper voltage range shouldnot exceed 600 volts. No attemptshould be made to measurehigher voltages with hand heldinstruments.

Multimeters are used mainly asvoltmeters in an industrial plant.The resistance scales generally donot go low enough for measuringmotor winding resistance, and at

the high resistance scales theyhave insufficient source voltagefor measuring insulation resis-tance. The ampere scales are notdirectly useful for measuringmotor current, but many productlines accommodate a clamp-onAC current transducer as anaccessory. Some manufacturerseven have clamp-on accessoriesthat can be used in conjunctionwith the voltage leads for measur-ing power and or power factor.

2. Current Meters

Clamp-onammeters areabout as com-monplace asmultimeters.Two kinds arein common use.One is a clamp-on currenttransducer thatfeeds an outputsignal to aseparate multi-meter forreading on themilliamp ormilivolt scale.The other is aself-containeddirect clamp-on device. With thelatter, reading the instrument maybe a challenge because it some-times must be thrust deep into abox and oriented at an inconve-nient angle to access a conductor.Many instruments accommodatethis problem with a pivotingdisplay or a hold switch that canlock the display for reading afterthe instrument is removed fromthe conductor. This is an impor-tant feature.

Clamp-on current meters sensecurrent in one of two alternativeways, either by a simple currenttransformer or a Hall-effect


sensor. The latter are less com-mon and more expensive. Bothhave operable iron jaws thatclamp around the conductor,forming an iron ring in whichmagnetic flux is induced by theconductor current. The currenttransformer type has a simplemulti-turn winding around thering to inductively sense thechanging flux. The Hall-effecttype has no winding, but a nar-row gap in the iron ring in whicha sensor is placed. The advantageof the Hall-effect sensor is itsfrequency range. It works for DCand very low frequencies as wellas responding better to higherfrequencies. Current and powermeters intended for use on eitherside of variable frequency drivesoften use Hall-effect currentsensors to handle the severeharmonics and sometimes lowfundamental frequencies.

The unconnected leads ofsome CTs can inflict a dangerouselectrical shock. This is of signifi-cance when connecting a CT to aseparate readout or recordingdevice. The wound or conven-tional current transducers (CTs)have either a voltage or currentoutput. The safer (voltage out-put) type is an internally-loadedcurrent transformer, meaning ithas an internal precision shuntresistor shorting the secondary;the output leads are connectedacross the internal shunt so a lowvoltage output is provided. Thecurrent output type is merely anunloaded transformer, so theoutput is a current, requiring acurrent-sensing device. Alwaysconnect a current output CT tothe recording device beforeclosing it around a live conductor.Otherwise, dangerously highvoltage will appear across theopen leads.

Range is particularly importantwith ammeters or current trans-ducers. These generally do notspan the entire range of plantneeds without overloading at thehigh end or providing pooraccuracy at the low end. Also,physical size is a limitation. Itmay be difficult to squeeze largeCTs into a small panel. Likewiseit may be difficult to reach aroundlarge conductors with CTs oflower range, which tend to besmaller. Care must be taken toselect the product or productsthat will span the necessaryrange. Power monitors that use alot of CTs because of unbalancedthree-phase capability or multi-channel monitoring usually useinternally shunted CTs. Often awide range of relatively inexpen-sive CTs can be provided andaccommodated with a minorscaling change to the recorder’sprogram.

3. Tachometers

There are several types oftachometers. Some requiremaking contact with the rotatingmachinery while others do not.Avoid the contact type.

The most common type of non-contact tachometer is the strobetach. Strobe tachs are simplyelectronic strobe lights with anadjustable strobe rate and a veryprecise readout in flashes perminute. Battery-powered unitsare somewhat less common than120-V plug-in models, but formost users the convenience isdefinitely worth the extra cost.


Strobe tachs are very accurate, butsubject to certain operator errorswhich can be reduced withpractice. The operator adjusts thestrobe rate until the rotatingequipment appears to freeze orstop in the light. The rpm of theequipment is hopefully equal tothe strobe rate displayed, but itmight also be an integer multipleof the displayed strobe rate.Rotating equipment with repeat-ing features (like blades on a fan)can also trick the user. Alwayswatch a single feature, like a shaftkeyway, and start at the lowestplausible strobe rate.

Some non-contact tachometers arepassive, i.e., they do not requirethe operator to adjust a stroberate while watching for motion tofreeze. These determine speed bysensing reflected natural light orlight from their own source whichmay be a laser and/or infrared.This can be convenient, butbeware of models that requireyou to stop the machinery andaffix a reflector to the rotatingpart before speed can be read.

4. Power and Power FactorMeters

There are many instrumentsavailable which measure power,power factor, or both. Having theability to directly read powereliminates the need to calculate itas described in chapter 5. Thesimplest instruments have con-nections as shown in figure 4-3.Be sure to choose a model with 3-phase capability; many can beswitched between 3-phase andsingle phase.

The one-CT instrument shown inFigure 4-3 can only be accuratewith balanced voltage and cur-rent. If it is unbalanced, threereadings must be taken with the

Power Quality Considerations

If variable speed drives, induction heaters, or other electronicloads are on the system, voltage harmonics should be expected.Extreme current harmonics are present in circuits feedingthese loads. The purchaser should describe this electricalenvironment to the equipment supplier and determine thecapability of alternative devices to accurately measure such“dirty” power.

At the minimum, devices which sense voltage or current mustoperate on a true RMS principle. Those that do not, will readinaccurately when harmonics are present.

Even knowing an instrument operates on the true RMSprinciple is not completely sufficient because all are limited bythe magnitude and frequency of harmonics they can handle andstill read accurately. One index of this capability is the crestfactor, which is the ratio of peak value to RMS value of a waveform. A perfect sine wave has a crest value of 1.414. TrueRMS instruments should have a crest factor of 3.0 or better.

Unfortunately, crest value alone is not a complete descriptor ofharmonic content. Harmonics caused by most electronic loadscause the current crest factor to be higher and the voltage crestfactor to be lower than sinusoidal. An instrument needs to becapable of measuring accurately across the frequency range ofthe harmonics. The frequency of harmonics is expressed eitherin Hz or the order of harmonic. To convert order to frequency,simply multiply by 60. Most high quality electrical testinginstruments specify the frequency range over which theiraccuracy is maintained.


CT on each phase and the read-ings averaged. Better resultsunder unbalanced conditions canbe obtained using an instrumentwith three CTs. These tend to bemore expensive, especially if theyare configured as a multi-functionpower analyzer.

5. Multi-channel PowerLoggers

Probably the most complicatedinstrument system likely to beused in a plant is a multi-channelpower logger. These are availablein more than one configuration.In packaged units, there is usuallya central module with threevoltage leads and a terminal blockfor two or more trios of CTs. Thecentral module is both a loggerand a transducer; it computespower based upon voltage andthe current from the CTs andrecords the power. All loads mustbe on the same voltage sourcesince there is only one set ofvoltage leads. CTs are marked byphase, so phase identificationmarkings must be present at eachload.

There are numerous variations onthe above configuration. Someproducts consist of a centrallogger with remote power trans-ducers. Interconnections typicallyfollow voltage, current, or pulseconventions used in industrialProgrammable Logic Controller(PLC) systems. Often they can be

equipped with a computer inter-face, phone modems, or radiotransmitters for remote dataretrieval.

6. Motor Analyzers

There are a variety of productsthat are termed motor analyzers.Of special interest are threesubstantial but portable unitswhich have recently appeared onthe market, claiming to computemotor efficiency. These are theMotor Monitor, developed byVectron for the Energy Corpora-tion of New Zealand, the MAS-1000 of Niagara InstrumentCorporation of New York, andMotor-Check, a German productmanufactured by Vogelsang &Benning and marketed in the U.S.

by the A.H. Holden Com-pany of Minnesota.

All have connections to themotor to sense current,voltage and speed. Speedis sensed magnetically oroptically. Certain name-plate information must beentered via keyboard. Thedevices all require windingresistance, which must be


obtained with the motor shutdown; usually the required micro-ohmmeter is built into the tester.All require no-load data whichmust be obtained with the motoruncoupled and running at idle.Fortunately, none require any sortof torque sensor, because it wouldbe nearly impossible to affix onein many field situations.

Industrial Practices

A survey was conducted regard-ing the capability of industrialplant personnel to obtain fieldmeasurements which are used topredict motor performance.

Surveys were sent to 65 industriesin northwest Oregon and south-west Washington. There were 29responses. Every firm had avoltmeter and an ammeter.Twenty-two responded that theircompany had a tachometer. Onlyeight respondents indicated theyhad the ability to measure powerfactor. The survey provides abasis for concluding that mostcompanies estimate motor loadbased solely on speed or currentreadings.4-2, 4-3


ReferencesChapter 4

4-1 Gilbert A. McCoy and John G. Douglass“Energy Efficient Electric Motor SelectionHandbook,” U.S. Department of Energy, DOE/GO-10096-290, August 1996.

4-2 Carroll, Hatch & Associates, Inc., “An Electric MotorEnergy Efficiency Guide and Technical ReferenceManual”, (Draft) June 1994

4-3 Carroll, Hatch & Associates, Inc., “A Procedurefor Developing an Energy Efficiency Plan forthe Use of Electric Motors in an IndustrialSetting,” (Draft), June 1994


Motor Load and Efficiency Estimation Techniques 5-1

To compare operating costs of anexisting motor and a more effi-cient replacement unit, you needto determine operating hours,efficiency improvement values,and load. Part-load is a term usedto describe the actual load servedby the motor as compared to therated full-load capability of themotor. Motor part-loads may beestimated through using inputpower, amperage, or speedmeasurements. Several loadestimation techniques are brieflydiscussed.

Input PowerMeasurementsWhen “direct-read” power mea-surements are available, werecommend using them to esti-mate motor part-load. Withmeasured parameters taken fromhand-held instruments, you canuse Equation 5-1 to calculate thethree-phase input power to theloaded motor.

You can then quantify the motor’spart-load by comparing themeasured input power underload to the power required whenthe motor operates at ratedcapacity. The relationship isshown in Equation 5-3.

Chapter 5

Motor Load andEfficiency EstimationTechniques

Equation 5-1

iP = V x I x PF x 3

1000Where:

Pi = Three phase power in kWV = RMS voltage, mean line to line of 3 phasesI = RMS current, mean of 3 phasesPF = Power factor as a decimal

Equation 5-2

Where:

Pir = Input power at full rated load in kWPor = Nameplate rated horsepowerefl = Efficiency at full rated load

Equation 5-3

Load = PP

x 100%i

i r

Where:

Load = Output power as a % of rated powerPi = Measured three phase power in kWPir = Input power at full rated load in kW

irP P= or x .0 7457

fle


Example 5-1Input Power Calculation

An existing motor is identified as a 40 hp, 1,800 rpm unit with anopen drip-proof enclosure. The motor is 12 years old and hasnot been rewound.The electrician makes the following measurements:Measured Values:V

ab = 467V I a

= 36 amps PF a = 0.75

Vbc= 473V I b = 38 amps PF b = 0.78

Vca = 469V I c = 37 amps PF

c = 0.76

V=(467+473+469)/3=469.7 voltsI=(36+38+37)/3=37 ampsPF=(0.75+0.78+0.76)/3=0.763

Equation 5-1 reveals:

iP = =469.7 x 37 x 0.763x 3 . kw1000

22 97

Line Current MeasurementsThe current load estimation method is recommended when onlyamperage measurements are available. The amperage draw of amotor varies approximately linearly with respect to load, down toabout 50 percent of full load. (See Figure 5-1) Below the 50 percentload point, due to reactive magnetizing current requirements, powerfactor degrades and the amperage curve becomes increasingly non-linear. In the low load region, current measurements are no longer a

Figure 5-1Relationships Between Power, Current, Power Factor and Motor Load


useful indicator of load.Both nameplate full-load and no-load current values apply only atthe rated motor voltage. Thus,root mean square current mea-surements should always becorrected for voltage. If thesupply voltage is below thatindicated on the motor name-plate, the measured amperagevalue is correspondingly higherthan expected under rated condi-tions and must be adjusteddownwards. The converse holdstrue if the supply voltage at themotor terminals is above themotor rating. The equation thatrelates motor load to measuredcurrent values is shown in Equa-tion 5-4.

The Slip MethodThe slip method is recommendedwhen only motor operating speedmeasurements are available. Thesynchronous speed of an induc-tion motor depends on the fre-quency of the power supply andon the number of poles for whichthe motor is wound. The higherthe frequency, the faster a motorruns. The more poles the motorhas, the slower it runs. Table 5-1indicates typical synchronousspeeds.

Equation 5-4

Load = II

x x 100%r

VVr

Where:

Load = Output power as a % of rated power I = RMS current, mean of 3 phasesIr = Nameplate rated currentV = RMS voltage, mean line to line of 3 phasesVr = Nameplate rated voltage

Table 5-1Induction Motor SynchronousSpeeds

Poles 60 Hertz

2 3,6004 1,8006 1,2008 90010 72012 600

The actual speed of the motor isless than its synchronous speedwith the difference between thesynchronous and actual speedreferred to as slip. The amount ofslip present is proportional to theload imposed upon the motor bythe driven equipment. The motorload can be estimated with slipmeasurements as shown inEquation 5-5 and Example 5-2.


Equation 5-5

LoadSlip

sS rSx 100= %

-

Where:

Load = Output power as a % of rated powerSlip = Synchronous speed - Measured speed in RPMSs = Synchronous speed in RPMSr = Nameplate full load speed

Example 5-2: Slip Load Calculation

Given: Synchronous speed in RPM = 1,800Nameplate full load speed = 1,750Measured speed in RPM = 1,770Nameplate rated horsepower = 25 HP

Determine actual output horsepower.

From Equation 5-5

Load1,800 -1,770

1,800 -1,750 x 100 60= %= %

Actual output horsepower would be 60%x25HP=15HP

and may be thought of as insignifi-cant, the slip method relies on thedifference between full-load name-plate and synchronous speeds. Givena 40 rpm “correct” slip, a seeminglyminor 5 rpm disparity causes a 12percent change in calculated load.

Slip also varies inversely withrespect to the motor terminalvoltage squared—and voltage issubject to a separate NEMAtolerance of ± 10 percent at themotor terminals.5-6 A voltagecorrection factor can, of course, beinserted into the slip load equa-tion. The revised slip load, can becalculated as shown in Equation5-6.5-3

The speed/slip method of deter-mining motor part-load has beenfavored due to its simplicity andsafety advantages. Most motorsare constructed such that the shaftis accessible to a tachometer or astrobe light.

The accuracy of the slip methodis, however, limited by multiplefactors. The largest uncertaintyrelates to the 20 percent tolerancethat NEMA allows manufacturersin their reporting of nameplatefull-load speed.

Given this broad tolerance, manufac-turers generally round their reportedfull-load speed values to somemultiple of 5 rpm. While 5 rpm is buta small percent of the full-load speed


An advantage of using the current-based load estimation technique isthat NEMA MG1-12.47 allows atolerance of only 10 percent whenreporting nameplate full-load current.In addition, motor terminal voltagesonly affect current to the first power,while slip varies with the square ofthe voltage. 5-6

While the voltage-compensatedslip method is attractive for itssimplicity, its precision should notbe overestimated. The slipmethod is generally not recom-mended for determining motorloads in the field.

Variable Load LevelsWhen the load is variable, youmust determine the average loadimposed upon the motor. Thatcan be accomplished throughlong-term monitoring of the inputpower. If there are two loadlevels (for instance a water supplypump motor that operates con-tinuously but against two differ-ent static heads), both motorloads can be measured. Deter-mine the weighted average loadby timing each motor load period.When many load levels exist, youmust monitor loads over a periodof time and estimate the weightedaverage load level.

Equation 5-6

Where:

Load = Output power as a % of rated powerSlip = Synchronous speed - Measured speed in RPMSs = Synchronous speed in RPMSr = Nameplate full load speedV = RMS voltage, mean line to line of 3 phasesVr = Nameplate rated voltage

Table 5-2Characteristics of Motor Loads

Description of Motor Use Type of Load

Centrifugal Supply Air Fan Motor Constant, but will change slightly withoutside air temperature.

Conveyor with Continuous and Constant Constant Load

Boiler Feed Water Pump Motor, Starts/stops. Constant while on.“On-Off” Control

Hydraulic Power Unit Motor, Two levels of different but constant“On and Bypass” Control values.

Air Compressor Motor with Two levels of different but constant“Load/Unload” Control values.

Air Compressor Motor with Random load.“Inlet Valve” Control

When loads fluctuate randomly,hand-held instruments provide only aglimpse of the overall load profile.To obtain valid data in random loadsituations you need to use recordingmeters with integrating capabilities.Examples of various load types aregiven in Table 5-2.5-2, 5-3


Determining MotorEfficiency

The NEMA definition of energyefficiency is the ratio of its usefulpower output to its total powerinput and is usually expressed inpercentage as shown in Equation5-7.

By definition, a motor of a givenrated horsepower is expected todeliver that quantity of power ina mechanical form at the motorshaft.5-4, 5-5

Figure 5-2 is a graphical depic-tion of the process of convertingelectrical energy to mechanicalenergy. Motor losses are thedifference between the input andoutput power. Once the motorefficiency has been determinedand the input power is known,you can calculate output power.

NEMA design A, B, and E motors upto 500 hp in size are required to havea full-load efficiency value (selectedfrom a table of nominal efficiencies)stamped on the nameplate. Mostanalyses of motor energy conserva-tion savings assume that the existingmotor is operating at its nameplateefficiency. This assumption isreasonable above the 50 percent loadpoint as motor efficiencies generallypeak at around 3/4 load with perfor-mance at 50 percent load almostidentical to that at full-load. Largerhorsepower motors exhibit a rela-tively flat efficiency curve down to25 percent of full-load.

Figure 5-2Depiction of Motor Losses

Equation 5-7

e = 0.7457 xP x LoadP

or

iWhere:

e = Efficiency as operated in %Por = Nameplate rated horsepowerLoad = Output power as a % of rated powerPi = Three phase power in kW


It is more difficult to determine theefficiency of a motor that has been inservice a long time. It is not uncom-mon for the nameplate on the motorto be lost or painted over. In thatcase, it is almost impossible to locateefficiency information. Also, if themotor has been rewound, there is aprobability that the motor efficiencyhas dropped slightly.

When nameplate efficiency is missingor unreadable, you must determinethe efficiency value at the operatingload point for the motor. If available,record significant nameplate data andcontact the motor manufacturer.With the style, type, and serialnumber, the manufacturer canidentify approximately when themotor was manufactured. Often themanufacturer will have historicalrecords and can supply nominalefficiency values as a function ofload for a family of motors.5-4, 5-4

When the manufacturer cannotprovide motor efficiency values,you may use estimates fromAppendix B. Appendix B con-tains nominal efficiency values atfull, 75, 50, and 25 percent loadfor typical standard-efficiencymotors of various sizes and withsynchronous speeds of 900, 1200,1800, and 3600 rpm. Appendix Bis derived from the MotorMaster+database and indicates “industryaverage” full and part-loadperformance for all standard-efficiency motors currently on themarket. 5-5

Three steps are used to estimateefficiency and load. First, usepower, amperage or slip measure-ments to identify the load im-posed on the operating motor.Second, obtain a motor part-loadefficiency value consistent withthe approximated load eitherfrom the manufacturer or by interpo-lating from the data supplied in

Appendix B. Finally, derive a revisedload estimate using both the powermeasurement at the motor terminalsand the part-load efficiency value asshown in Equation 5-8.

For rewound motors, you shouldmake an adjustment to the effi-ciency values in Appendix B.Tests of rewound motors showthat rewound motor efficiency isless than that of the original motor.To reflect the typical rewind losses,you should generally subtract twopoints from your standard motorefficiency on smaller motors (<40 hp)and subtract one point for largermotors. Shops with the bestquality-control practices canoften rewind with no significantefficiency degradation.

Equation 5-8

Load = P x eP x 0.7457

i

or

Where:

Load = Output power as a % of rated powerPi = Three phase power in kWe = Efficiency as operated in %Por = Nameplate rated horsepower


Computerized Load andEfficiency EstimationTechniques

The Oak Ridge National Labora-tory has developed ORMEL96(Oak Ridge Motor Efficiency andLoad, 1996), a computer programwhich uses an equivalent circuitmethod to estimate the load andefficiency of an in-service motor.Only nameplate data and ameasurement of rotor speed arerequired to compute both themotor efficiency and load factor.Dynamometer tests have shown thatthe method produces efficiencyestimates that average within ± 3percentage points of actual. Thisaccuracy is valid for motor loadsranging from 25 to 100 percent ofrated capacity.5-7 The programallows the user to enter optionalmeasured data, such as statorresistance, to improve accuracy ofthe efficiency estimate.

Motor efficiency estimation methodsand devices were evaluated at theMotor Systems Resource Facility atOregon State University in 1997.Efficiencies calculated by threemotor analyzers and several algo-rithms and computer programs werecompared to dynamometer deter-mined efficiencies on five motorsunder numerous operating conditions.The three analyzers and one analyti-cal method performed well. Errorswere less than three percent for allmotors and less than one percent fornewer motors in good condition on abalanced power suply. These meth-ods were also demonstrated in thefield but were not embraced becauseof the labor-intensive necessity touncouple the mtors and perform a no-load run. The analytical methodavoids an expensive tester, but stillrequires a wattmeter with goodaccuracy at very low power factor.

Recently at least two manufacturersof motor current-signature predictivemaintenance analyzers have intro-duced products that advertise capa-bility for determining efficiency. Themanufacturers claim that this isaccomplished without necessity foruncoupling. Connecting throughexisting potential transducers andcurrent transducers allows testing onmedium voltage motors.


5-1 J. D. Kueck, J.R. Gray, R. C. Driver and J. S. Hsu,“Assessment of Available Methods for EvaluatingIn-Service Motor Efficiency,” Oak Ridge NationalLaboratory, (Draft) January 1996

5-2 “MChEff: A Computer Program for In-Service Estimation ofMotor Efficiency and Load Using the ORNL NameplateEquivalent Circuit Method,” Oak Ridge National Laboratory;August 1995

5-3 Gilbert A. McCoy and John G. Douglass, “Energy EfficientElectric Motor Selection Handbook,” U.S. Department ofEnergy, DOE/GO-10096-290, August 1996.

5-4 Carroll, Hatch & Associates, Inc., “An Electric Motor EnergyEfficiency Guide and Technical Reference Manual” (Draft)June 1994

5-5 Carroll, Hatch & Associates, Inc., “A Procedure forDeveloping an Energy Efficiency Plan for the Use of ElectricMotors in an Industrial Setting,” (Draft) June 1994

5-6 Richard L. Nailen, “Finding True Power Output Isn’tEasy,” Electrical Apparatus, February 1994

5-7 P. J. Otaduy, “ORMEL96 (Oak Ridge Motor Efficiency andLoad, 1996) User’s Guide,” Oak Ridge National Laboratory,March 1996

5-8 Annette von Jouanne, Alan Wallace, Johnny Douglass,Craig Wohlgemuth, and Gary Wainwright, “A LaboratoryAssessment on In-Service Motor Efficiency TestingMethods” submitted for publication at the IEEE-InternationalElectric Machines and Drives Conference Milwaukee, WI,May 1997

ReferencesChapter 5


Energy, Demand, and Dollar Savings Analysis 6-1

This chapter illustrates how to usefield measurements to determinedemand reductions, energy sav-ings, and the simple payback oninvestment in a new or replace-ment energy efficient motor.

Calculating Annual Energyand Demand SavingsTo determine the annual dollarsavings from the purchase of anenergy efficient motor, you firstneed to estimate the annual energysavings. Energy efficient motorsrequire fewer input kilowatts toprovide the same output as astandard-efficiency motor. Thedifference in efficiency betweenthe energy-efficient motor and acomparable standard motor deter-mines the demand or kilowattsavings. For two similar motorsoperating at the same load, but

having different efficiencies,Equation 6-1 is used to calculatethe kW reduction.6-3 The kWsavings are the demand reduction.The annual energy savings arethen calculated as shown inEquation 6-2.

Equations 6-1 through 6-3 applyto motors operating at a specifiedconstant load. For varying loads,you can apply the energy savingsequation to each portion of thecycle where the load is relativelyconstant for an appreciable periodof time. The total energy savingsis then the sum of the savings foreach load period. The equationsare not applicable to motorsoperating with pulsating or randomloads or for loads that cycle atrapidly repeating intervals.

Chapter 6

Energy, Demand,and Dollar SavingsAnalysis

Equation 6-1

Where:

kWsaved = Savings from efficiency improvement in kWPor = Nameplate rated horsepowerLoad = Output power as a % of rated powerestd = Efficiency of a standard motor as operated in %eEE = Efficiency of an energy efficient motor as

operated in %


You can now use the demand savings and annual energy savings alongwith utility rate schedule information to estimate your annual reduc-tion in operating costs. This calculation of total annual cost savings isshown in Equation 6-3. Be sure to apply any seasonal and decliningblock energy charges.

Equation 6-2

kWh kW x hourssavings saved= Where:

kWhsavings = Annual electric energy saved in kWh

kWsaved = Savings from efficiency improvement in kW

hours = Annual operating hours

Equation 6-3

Where:

$savings = Total annual dollar savings

kWsaved = Savings from efficiency improvement in kW

$demand = Monthly demand dollar charge

kWhsavings = Annual electric energy saved in kWh

$energy = Dollar charge per tailblock kWh

Assessing EconomicFeasibilityBecause of better design andhigher quality materials, premiumefficiency motors typically cost15 to 30 percent more than theirenergy efficient counterparts. Inmany situations (new motorpurchase, repair, or motorreplacement) you quickly recoverthis price premium throughenergy cost savings. To deter-mine the economic feasibility ofinstalling premium efficiencymotors, examine the total annualenergy savings in relation to theprice premium. Appendix Ccontains a Motor Energy SavingsCalculation Form.

Most industrial plant managersrequire that, based on a simplepayback analysis, investments berecovered through energy savingswithin one to three years. Thesimple payback is defined as theperiod of time required for thesavings from an investment toequal the initial or incrementalcost of the investment. For initialmotor purchases or replacementof burned-out and rewindablemotors, the simple paybackperiod for the extra investment inan premium efficiency motor isthe ratio of the price premium(less any available utility rebate)to the total annual electricaldollar savings. This calculation isshown in Equation 6-4.


Equation 6-4

PB$$

$premium

savings

rebate=

−

Where:


$premium = Price premium for premium efficiency motor compared toenergy efficient

$rebate = Utility rebate for premium efficiency motor


For replacements of operational motors, the simple payback is theratio of the full cost of purchasing and installing a new premium orenergy efficient motor relative to the total annual electrical savings.This calculation is shown in Equation 6-5.Equation 6-5

PB$ $$$

new

savings

inst rebate=+ −

Where:


$new = New motor cost

$inst = Installation cost

$rebate = Utility rebate for premium efficiency motor



Example:

The following analysis for replacing a 100 hp TEFC motor oper-ating at 75 percent of full rated load illustrates how to use Equa-tions 6-1 through 6-4. The analysis determines the cost-effective-ness of purchasing a replacement premium efficiency motorhaving a 3/4-load efficiency of 95.7% instead of an energy effi-cient motor.

Kilowatts saved:From Equation 6-1

This is the amount of power conserved by the energy efficientmotor during each hour of use. Multiply this by the number ofoperating hours at the indicated load to obtain annual energysavings.Energy saved:

From Equation 6-2kWh 0 74 x8000 5 936savings = . = ,

Assuming utility energy and demand charges of $0.04/kWh and$5.00 per kW per month:

From Equation 6-3

In this example, installing an premium efficiency motor reducesthe utility billing by $576 per year. The simple payback for theincremental cost associated with a premium efficiency motorpurchase is the ratio of the price premium or incremental cost tothe total annual cost savings.Assuming a price premium of $900, the simple payback oninvestment is:

From Equation 6-4

PB900 0

2823 2 yrs= =

-$$

$ .

The additional investment required to buy an energy efficientmotor is recovered within 1.6 years. Premium efficient motors canoften rapidly pay for themselves through reduced energy con-sumption. After this initial payback period, the annual savings willcontinue to be reflected in lower operating costs and will add toyour firm’s profits.


ReferencesChapter 6

6-1 Gilbert A. McCoy and John G. Douglass, “EnergyEfficient Electric Motor Selection Handbook,” U.S.Department of Energy, DOE/GO-10096-290,August 1996.


Motor Improvement Planning 7-1

A company should plan ahead sothat it can make timely decisionson energy-efficient motor replace-ments. Take the following plan-ning steps for each motor in theplant that meets minimum sizerequirements:� Accurately determine motor

load in kW.� Accurately establish the power

factor for each motor at load.� Establish the existing motor

efficiency.� Determine annual operating

hours.� If the motor is under 50%

loaded, consider replacementwith a smaller motor eitherfrom company inventory orfrom new stock. If a newmotor alternative is preferred,compare an energy-efficientwith a standard-efficiencyunit.

� If the existing motor were tofail, analyze the use of arewound motor against use ofa new standard and a newenergy-efficient motor.

� Recommend the most cost-effective alternative.

� Obtain prior approval to usethe “best” approach.

� Establish an action plan to becarried out once the “trigger-ing event” takes place.

If the analysis indicates a simplepayback period or other eco-nomic performance value that

meets your company guidelines,a change may be warranted rightaway. Most of the time the “trig-gering event” is that the existingmotor must be replaced. Byplanning ahead, you can executethe plan on short notice andacquire the best available motor foryour particular need.

Energy Efficient AlternativesAfter you determine the load,operating hours, and efficiency ofeach existing motor, you are readyto develop an action plan. Thereare a number of alternatives toconsider and analyze. There aretwo principal types of situationsencountered. One set of analysesis based on the event of existingmotor failure, while the second setof analyses assumes no failure ofthe existing motor. The alternativesare:

� Upon Failure of ExistingMotor� Repair the motor.� Replace motor with a new

standard motor.� Replace motor with a new

energy-efficient motor.

� Without Existing MotorFailure� The motor can be left to

operate just as it is.� The motor can be replaced

immediately with a higherefficiency motor.

Chapter 7

MotorImprovementPlanning


With either situation, the alternativescan include downsizing if the existingmotor is oversized. MotorMaster+allows for side-by-side comparisonof annual energy costs due tooperation of motors of differenthorsepower.

Upon Failure AlternativesWhen a motor fails, there are twoalternatives.

Repair the Motor

The least capital cost approach isgenerally to repair the failed motor.This often means rewinding of thestator in addition to mechanicalrepairs such as bearing replacement.The motor must be out of serviceduring repair.

For a major rebuild to be justified,the original stator and rotor must bein serviceable or reasonably-repair-able condition. Repair of significantrotor or stator core damage isgenerally only cost effective onlarger motors.

Replace with a New Motor

When replacement is chosen, it isoften cost effective to select a newpremium efficiency motor. Excep-tions can occur if there is an existingstandard motor in inventory and/orannual operating hours are very low.

When a previously rewound stan-dard efficiency motor fails, theopportunity to replace it with anenergy efficient model can tip thescale from repair to replacement.Replacing the motor with anotherstandard efficiency motor is usuallynot cost effective unless annualoperating hours are very low orelectricity is very inexpensive.

The economic analysis for decidingwhether to repair or replace a failedmotor is straight-forward. The “do

MotorMaster+: Motor Energy Management Software

The Bonneville Power Administration and the U.S. Department ofEnergy Motor Challenge Program have supported the development ofMotorMaster+, an energy efficient motor selection and energy-manage-ment tool.

MotorMaster+ software supports industrial energy managementactivities by providing:

� The ability to select the “best” available new or replacementmotor through accessing an internal database of price andperformance information for over 27,000 1-to-2000 hp industrialmotors;

� A plant motor inventory module where motor nameplate data,operating information and field measurements are linked toutility, facility, and process information;

� Capability to automatically estimate in-place motor load andefficiency;

� The ability to scan for motors which operate under abnormal orsub-optimum power supply conditions;

� Descriptor search capability to assist you in targeting energy-intensive systems and replacing inefficient motors;

� Inventory management functions including maintenance logs andspare tracking;

� Analysis features for rapidly determining the annual energy,demand and dollar savings resulting from selecting and using anenergy-efficient motor in a new purchase or retrofit application;

� The ability to analyze “batches” or selected populations ofinventory for motor rewind, downsizing, or replacement ofoperable standard with energy-efficient motors;

� Energy accounting features including utility billing, plant pro-duction and energy conservation and greenhouse gas emissionreduction summary reports;

� Life cycle costing capability, including the ability to compute theafter-tax return on investment in an energy-efficient product.

Call the Motor Challenge Information Clearinghouse (800) 862-2086to obtain information on motors and motor-driven equipment, fortechnical consultation, and for your copy of MotorMaster+.


nothing” alternative doesn’t exist.The least capital cost alternative,repairing the failed motor, becomesthe base case. The biggest challengeis estimating the cost of the motorrepair and its prospective efficiencyafter repair.

The principal difference in all of thealternatives is the amount of energythat will be used to satisfy motorlosses. The logic used to evaluatethe alternatives will seek to identifythe operating cost for each alterna-tive. It is then possible to compareboth the incremental cost of thealternative and also the operatingcost reduction associated with thealternative.

Energy consumed in motor losses iscomputed in terms of kilowatt-hours

(kWh). The difference in operatingcost is readily computed uponexamining the utility rate schedule.

In the following example (Table 7-1), MotorMaster+ identified a newpremium efficiency motor. Thesoftware determined comparativeperformance values based on anenergy cost of $.04/kWh and amonthly demand charge of $2/kW.You can also calculate these valueswith the equations provided inChapter 6. The comparison ofalternatives, provided in Table 7-1,indicates an attractive 1.0 yearsimple payback on the investment ina premium efficiency replacementmotor. The failed motor could eitherbe rewound and retained as a spare,junked, or sold for its salvage value.

Table 7-1Motor Repair Versus Replace Analysis

Motor Size 40 40 40 hp

Load 75 75 75 %

Nominal Efficiency 88.5 88.5 94.5 %

Motor Rewind Loss - 2.0 - %

Operating Hours 6,000 6,000 6,000 Hours

Cost (Repair/Purchase) - $880 $1,764 $

Premium efficiency motor rebate - - $300 $

Annual Energy Use 151,729 155,237 142,095 kWh/Year

Annual Energy Cost $6,069 $6,209 $5,684 $/Year

Demand Charge $607 $621 $568 $/Year

Savings compared to repair Savings

Energy 13,142 kWh/Year

Energy Value $525 $/Year

Demand 2.2 kW

Demand Cost $53 $/Year

Total Saved $578 $/Year

Simple Payback 1.0 Years

OriginalStandard

Efficiency Motor

RepairMotor

NewPremiumEfficiency

MotorUnits


Additional alternatives may beconsidered. There could be asuitable surplus or repaired motorin inventory, which would avoid thenew motor purchase price. Asdiscussed earlier in this chapter,either an inventory motor or a newmotor could be a smaller size. TheMotorMaster+ “Compare”routine will compare motors ofdifferent horsepowers. It will evenadjust the output power for partload operating speed differenceswhen “cube law” loads (e.g.,centrifugal pumps or fans) aredriven.

You must weigh several factors inmaking a good decision. Theseinclude:

1. Cost of the proposed replace-ment motor

2. Efficiency of proposed motor3. Downtime cost for each

alternative (if different)4. Cost to repair the existing

motor5. Efficiency of the existing

motor after repair6. Availability of a utility rebateItems 1 and 2 are available fromMotorMaster+, the motor manu-facturer, or distributor. Item 3 maybe equal for each alternative.Generally it is quicker to repairlarge or special motors, but dis-tributors usually have standard andenergy-efficient non-specialtysmaller size motors in stock. Items4 and 5 are the most difficult toquantify.In the motor comparison windowof MotorMaster+ a default costof repairing an existing motor isprovided, but it can be overwritten.Indeed, it usually needs to beoverwritten because there is toomuch variation in motor repair costto rely on the default number forinvestment decisions. Repair cost

varies with the extent of damage,geographical location, overtimerequirements, and type of statorimpregnation. Moreover, repairsare usually provided by other thanmanufacturers’ shops, so there isnot an annual update of repaircosts in the MotorMaster+database. Two sources of betterinformation on repair cost exist.Users can maintain their own costdatabase from records of recentrepairs. Users can also subscribe toan annually-updated motor repaircost guide. Vaughens’ Price Pub-lishing Inc. produces a priceestimator that is widely used.7-1

Determining an “appropriate”rewind efficiency loss is somewhatlike projecting how many pointsthe home team will score when youdon’t know who they are playing.The default efficiency loss inMotorMaster+ is merely intendedto be central to a plausible range ofzero to about five percent. Therehave not been enough before/afterstudies done to establish a statisti-cally-valid mean efficiency reduc-tion. In most cases there will be anefficiency loss between 0.5 percentand two percent. A two percentreduction is a reasonable estimatefor motors under 40 hp rewound ina shop with unknown qualitypractices, while 0.5 percent is areasonable estimate for motorsover 40 hp rewound in a good shopwith a well-run quality manage-ment program.7-2

Motors can be rewound with noefficiency loss whatsoever. Effi-ciency degradation followingrewind is caused either by aspectsof the original failure that cannoteconomically be completely re-paired, or by errors or shortcutsoccurring in the repair. Either way,selecting a shop with a soundquality management system is thebest precaution. Electrical Appara-tus Service Association (EASA)


supports their members with aquality management program calledEASA-Q. Member shops canparticipate at various levels. Fornon-EASA shops, look for evi-dence of a quality managementprogram based upon ISO 9000.

Without an Existing MotorFailureLeave the Present Situation AsIs

An energy coordinator has anumber of demands on his or hertime. It may be that the benefit ofreducing motor losses is not a highpriority when compared to otherduties competing for the limitedtime available. The immediate costof keeping a working standardmotor is zero. Savings may simplyaccrue too slowly to justify invest-ment in a new more efficientmotor. Each plant is different anddecisions concerning relativeimportance of projects are best leftto those responsible for operationof the plant.

Replace Operating Motor with aNew Energy-Efficient Motor

An energy efficient replacementmotor can always be found in thesame frame size and with compa-rable starting torque and lockedrotor current as the existing motor.The average energy efficient motorturns at a fraction of a percenthigher speed than its standardcounterpart. In many centrifugalpump and fan applications, thischaracteristic will increase flow andenergy consumption. This candiminish expected savings. Fortu-nately, full load speed varies amongenergy-efficient motors and amodel can usually be found toclosely match the speed of all butthe slowest standard efficiencymotors.

Table 7-2 illustrates the benefits ofreplacing an existing standardefficiency motor with an energy-efficient unit. Again, the newmotor price and performanceinformation is extracted fromMotorMaster+. The softwaredetermined comparative perfor-mance values based on an energycost of $.04/kWh and a monthlydemand charge of $2/kW.

The 6.8 year simple payback in thisexample is longer than the criteriaused by most industry decisionmakers. Replacing a workingmotor is usually not cost effective.Payback, however, is very sensitiveto individual circumstances. Anoperating time of 8,000 hours or autility rebate would reduce thepayback period, and a higherdemand or energy cost wouldreduce it even further.

Other factors can contribute to adecision to replace a workingmotor. You may be nearing ascheduled downtime for a processline, and age or predictive mainte-nance trends may portend troublefrom an existing motor. It may bevery wise to replace the motorrather than risk an unscheduledshutdown of a process line. SeeChapter 9 for more information onpredictive maintenance.

Motor ResizingHistorically, the plant electrician isresponsible for keeping motors ingood operation. It was, and still is,common for part of a manufactur-ing plant to be down because of asingle electric motor failure. Underthese circumstances, the plantelectrician works quickly to replacethe failed unit so there is minimaldisruption to the plant operatingschedule. The best way to mini-mize downtime is to have a re-placement motor on hand, ready to


install. However, it is too costly tohave a spare for every motor in theplant. Thus, when the proper sizereplacement is not in inventory, theelectrician typically places the nextlarger motor available into service.

The intention is to have the failedmotor rebuilt and then put backinto service when time permits.However, there is rarely enoughtime to replace a temporary work-ing motor, so the motor that isreturned from the repair shop goesinto inventory, waiting for anothermotor to fail. In this way, the sizeof motors at many industrialfacilities grows over time.

The power delivered by a motor isdetermined by the interactionbetween the motor and the load.

An AC motor turns at a speeddetermined by the AC frequencyand its design (i.e. number ofmagnetic poles). This speed isabsolutely exact in synchronousmotors and only varies (with torqueloading) by a few percent in induc-tion motors. In essence, the motordetermines at what speed the loadwill run. Any load (pump, fan,conveyor, etc.) has a characteristictorque demand, i.e. for any runningspeed, it resists with a certaintorque. This relationship is thetorque-speed curve. So, whenmotor and load are coupled to-gether, the motor dictates therunning speed and the load dictatesthe torque required.

Power delivered by the motor isproportional to speed times torque.

Table 7-2Existing Motor Replacement Analysis

Motor Size 40 40 hp

Load 75 75 %

Nominal Efficiency 90.4 94.4 %

Operating Hours 6,000 6,000 Hours

Motor Cost - $1,764 $

Installation Cost - $105 $

Annual Energy Use 148,507 142,246 kWh/Year

Annual Energy Cost $5,940 $5,690 $

Demand Charge $594 $569 $/Year

Savings Savings

Energy 6,261 kWh/Year

Energy Cost $250 $/Year

Demand 1.0 kW

Demand Cost $25 $/Year

Total Saved $275 $/Year

Simple Payback 6.8 Years

OriginalStandard Efficiency Motor

NewEnergy- Efficient Motor

Units


This leads to some interesting andcounter-intuitive results. Supposean 1800 rpm 50 hp motor delivers50 hp to a certain load. If it isreplaced by an 1800 rpm 100 hpmotor, it will still deliver only 50 hpto the load. The load is obliviousto the potential power of a motor,and only responds by requiring acertain torque commensurate withits driven speed.

This requires rethinking the mean-ing of rated horsepower. Ratedhorsepower is neither the horse-power that is invariably deliverednor the maximum horsepower thatcan be delivered. It is the nominalhorsepower for which the manu-facturer publishes “full load”parameters such as efficiency,current, amps, maximum tempera-ture rise, etc. If a certain loadresists with a lower torque at motornameplate speed, the motor willoblige, delivering the lower torqueand less than rated power. If aload requires more than themotor’s rated torque to operate atthe motor’s nameplate rpm, themotor will attempt to deliver morethan its rated torque and horse-power.

There is, of course, a limit tooverloading. Small or brief over-loads will be accommodatedsuccessfully, albeit with a decreasein efficiency and an increase inoperating temperature. Withgreater or longer overloads, motorlifetime is sharply reduced. Withstill greater overloads, the motorwill not start and accelerate torunning speed, and it will eitherburn out or trip circuit protectors.

Downsizing can be a money saverfor two reasons:� When purchasing replacement

motors, smaller motors tend tocost less.

� An underloaded motor oper-ates less efficiently and withlower power factor than amotor loaded at 75 to 100percent of rated power.

Power factor begins to drop offfairly rapidly as load is reduced, butthere has been some tendency tooverstate the drop in efficiency atpart load. Motor efficiency curvesvary by horsepower and model, butmost peak near 75 percent load andstill provide near nameplate effi-ciency at half load. Below halfload, efficiency begins to drop offdramatically. Performance curvesfor two typical motors are pre-sented in Figure 7-1. When com-paring an existing motor to adownsized replacement, be sure touse the appropriate part loadefficiency for each motor. Sincelarger motors exhibit higher effi-ciency over their load range, it iscommon to find a larger motor’shalf load efficiency to be greaterthan the full load efficiency of areplacement motor rated at halfthe power output.

The first step in consideringdownsizing is to determine loadingon the existing motor using meth-ods discussed in Chapter 5. Forvariable loading, be sure to makethis determination when the motoris operating at its highest load. Asa rule of thumb, it is best not todownsize to where the replacementmotor is more than 75 percentloaded. This rule can be exceededwhen you are certain of the maxi-mum loading.

Even with the same number ofpoles, motors vary slightly in fullload speed. This is an importantconsideration in resizing becausethe torque of some loads is verysensitive to rpm. The most notableexamples are fans and pumpswhich are working primarily against


flow friction (as opposed to a highstatic discharge head). In theseapplications, a one percent reduc-tion in speed produces a onepercent reduction in flow, but athree percent reduction in shaftpower.

An example will be valuable inappreciating the concept ofdownsizing motors. Table 7-3 is ananalysis of downsizing a lightlyloaded, existing 75 hp motor. Acareful check of motor load by theelectrician reveals that the maxi-mum (peak) load encountered is 30hp. The peak load is short induration (one hour per day). Thepotential replacement motor (40hp, energy-efficient) is forecast tooperate at 75% load. The valuesfor efficiency and power factorhave been selected to reflect theload. You will develop data of thisnature as you follow the motoranalysis procedures described inChapter 5.In the example shown in Table 7-3,installation of a replacement motoris expected to result in a reducedelectrical demand of 1.7 kW. Thevalue of energy savings will depend

Figure 7-1Motor Performance at Part Load

on the number of hours the motoris operated and the cost of electri-cal energy. If the load in thisexample were a continuously-operated conveyor with constantloading, the value of energy saved(at $0.04 per kWh) would bealmost $600 per year (8,760 hr/yr x1.7 kW x $0.04/kWh). A newmotor costs about $1,500. Theexisting motor would likely be agood candidate motor fordownsizing.

The decision to change out theexisting motor is also influenced byone or more of the following:

� Length of service life inpresent motor

� Operating hours

� Availability of a smaller motorin company inventory

� An inducement or incentivefrom the local utility

� The ability of the energycoordinator to analyze thesituation and propose aneconomically-sound change


Existing Motor 75 hp

Replacement Motor 40 hp

Table 7-3Motor Downsizing Example

1 Load Imposed on Motor 40.0% 75.0% %

2 Average Volts - V 476.0 476.0 Volts

3 Average Current - I 44.2 33.9 Amps

4 Power Factor - pf at load point 69.9% 85.0% %

5 Input power - Pin 25.5 23.8 kW

6 Motor Efficiency - ∈ at load point 87.9% 94.1% %

7 Output Power - Pout 22.4 22.4 kW

8 Motor Losses (Pin - Pout) 3.1 1.4 kW

9 Power Savings 0 1.7 kW

Units

The skilled electrician will alsonotice that with the smaller, en-ergy-efficient motor the requiredpower output is being delivered,while at the same time the currentto the motor has been reduced byabout 25%. Current reductionsdecrease the I2R (line) lossesthroughout the distribution systemand allow load centers to servemore load without exceedingcapacity.


ConclusionA motor systems management planhas many benefits. The history ofmaintenance actions, load levels,and operating environment isimportant information when amotor goes to the repair shop.

Another very important planningbenefit is that you know in advancewhat action to take with eachmotor (either immediately, upon afailure, or during scheduled down-time). An example of this infor-mation is presented in Figure 7-2.This can be accompanied byindividual recommendations forreplacement motors, simplepaybacks computed on an indi-vidual motor basis, or by a compre-hensive life-cycle-cost analysis forbatch actions on multiple motors.

Figure 7-2Motor Efficiency Improvement Action Plan


7-1 “Vaughen’s Complete Price Guide for MotorRepairs & New Motors,” 1995, Vaughen’s PricePublishing Co. Inc., Pittsburgh, PA

7-2 Vince Schueler and Johnny Douglass,“Quality ElectricMotor Repair: A Guidebook for Electric Utilities,” 1995,Bonneville Power Administration, Portland, OR

References

Chapter 7


Power Factor Correction 8-1

The Concept of PowerFactorPower factor is a measure of howeffectively electrical power isbeing used. A high power factor(approaching unity) indicatesefficient use of the electricaldistribution system while a lowpower factor indicates poor use ofthe system.8-1

Many loads in industrial electricaldistribution systems are inductive.Examples include motors, trans-formers, fluorescent lightingballasts, and induction furnaces.8-1

The line current drawn by aninductive load consists of twocomponents: magnetizingcurrent and power-producingcurrent.

The magnetizing current is thecurrent required to sustain theelectro-magnetic flux or fieldstrength in the machine. Thiscomponent of current creates

reactive power that is measuredin kilovolt-amperes reactive(kVAR). Reactive power doesn’tdo useful “work,” but circulatesbetween the generator and theload. It places a heavier drain onthe power source, as well as on thepower source’s distribution system.

The real (working) power-produc-ing current is the current thatreacts with the magnetic flux toproduce the mechanical output ofthe motor.8-2,8-3 Real power ismeasured in kilowatts (kW) andcan be read on a wattmeter. Real(working) power and reactivepower together make up apparentpower. Apparent power is mea-sured in kilovolt-amperes (kVA).8-1

Power factor is the ratio of realpower to apparent power. Todetermine power factor (PF),divide real power (kW) by appar-ent power (kVA). In a sinusoidalsystem, the result is also referredto as the cosine 0.

Chapter 8

Power FactorCorrection

Equation 8-1

Where:


Pi = Three phase power in kW

PApparent = Apparent power in kVA

PF = P

Pcosine i

Apparent= θ


Power Factor PenaltiesWhen a utility serves an indus-trial plant that has poor powerfactor, the utility must supplyhigher current levels to serve agiven load. In a situation wherereal power demand (kW) at twoplants is the same, but one planthas an 85 percent power factorwhile the other has a 70 percentpower factor, the utility mustprovide 21 percent more currentto the second plant to meet thatsame demand. Conductors andtransformers serving the secondplant would need 21 percentmore carrying capacity than thoseprovided to the first plant.Additionally, resistance losses(I2R) in the distribution conduc-tors would be 46 percent greaterin the second plant.8-2, 8-3

A utility is paid primarily on thebasis of energy consumed andpeak demand supplied. Withouta power factor billing element,the utility would receive no moreincome from the second plantthan from the first. As a meansof compensation for the burdenof supplying extra current,utilities typically establish a“power factor penalty” in theirrate schedules. A minimumpower factor value is established,usually 95 percent. When thecustomer’s power factor dropsbelow the minimum value, theutility collects “low powerfactor” revenue. As shown in the“Benefits of Power FactorCorrection” section of thischapter, the lower the actualpower factor, the greater thepenalty.8-2,8-3

PReactive =PApparentx sine 0

Pi=PApparent x PF

Pi=PApparent x cosine 0

Terminology■■■■■ Apparent PowerThis value is determined bymultiplying the current timesvoltage. In a three-phase circuit,multiply the average phase-to-phase voltage, times the averageline current, times the squareroot of 3 divided by 1,000.The units are kilovolt-amperes(kVA).

ApparentPVxIx= 3

1000

■■■■■ Reactive PowerThis term describes the magne-tizing requirements of anelectric circuit containinginductive loads. The value ofmagnetizing power is deter-mined by multiplying theApparent Power by the sine ofthe phase angle, 0, between thevoltage and the current. Unitsare kilovolt-amperes reactive(kVAR).

■■■■■ Real PowerThis term is what electriciansdeal with in plant loads.Previous references in thisguidebook to “power” have allmeant real power. Real poweris related to Apparent Power bythe cosine of the phase angle, 0,between voltage and current.Units are kilowatts (kW).

Another way to visualize powerfactor and demonstrate the rela-tionship between kW, kVAR andkVA, is the right “power” triangleillustrated in Figure 8-1. Thehypotenuse of the triangle repre-sents the apparent power (kVA)which is simply the system voltagemultiplied by the amperage timesthe square root of three (for athree-phase system) divided by1,000. The right side of thetriangle represents the reactivepower (kVAR). The base of thetriangle represents the real orworking power, measured in kW.The angle between the kW andkVA legs of the triangle is thephase angle 0.8-4

Figure 8-1The Power Triangle

Example:If a sawmill was operating at1,000 kW and the apparent powerconsumed was 1,250 kVA, youwould divide 1,000 by 1,250 tocome up with a power factor of0.80. The phase angle is arc cosine0.80 or 36.8 degrees.

Power factor is also referred to asleading or lagging. In the caseof the magnetizing current, thepower factor is lagging, in that thecurrent follows the voltage wave-form. The amount of lag is theelectrical phase angle between thevoltage and the current. Powerfactor is equal to the cosine of thephase angle between the voltageand current waveforms.


Power FactorImprovementSome strategies for improving yourpower factor are:

■ Use the highest-speedmotor that an applicationcan accommodate.Two-pole (nominal 3600 rpm)motors have the highest powerfactors; power factor decreasesas the number of poles in-creases.8-5

■ Size motors as close aspossible to the horsepowerdemands of the load.A lightly loaded motor requireslittle real power. A heavilyloaded motor requires morereal power. Since the reactivepower is almost constant, theratio of real power to reactivepower varies with inductionmotor load, and ranges fromabout 10 percent at no load toas high as 85 percent or moreat full load.8-2,8-3,8-5 (See Figure8-2) An oversized motor,therefore, draws more reactivecurrent at light load than doesa smaller motor at full load.Low power factor results whenmotors are operated at less

than full-load. This oftenoccurs in cyclic processes(such as circular saws, ballmills, conveyors, compressors,grinders, extruders, or punchpresses) where motors aresized for the heaviest load. Inthese applications, powerfactor varies from moment tomoment. Examples of situa-tions where low power factors(from 30 percent to 50 per-cent) occur include a surfacegrinder performing a light cut,an unloaded air compressor,and a circular saw spinningwithout cutting.8-1 The indus-tries shown in Table 8-1typically exhibit low powerfactors and do not fully utilizethe incoming current suppliedby the electrical utility.8-1,8-6

■ Add power factor correctioncapacitors to your in-plantdistribution system.Power capacitors serve asleading reactive current gen-erators and counter the laggingreactive current in the system.By providing reactive current,they reduce the total amountof current your system mustdraw from the utility.8-1

The Bonneville Power Adminis-tration has produced the Indus-trial Power Factor AnalysisGuidebook. Software designedfor the Microsoft© Windows™operating environment is availableto make the power factor correc-tion process as simple as possible.The Guidebook addresses thefollowing topics: ■ How to tell if your plant

could benefit from capacitors. ■ How to select capacitor

schemes to eliminate powerfactor penalties and minimizelosses.

■ How to perform detailed plantsurveys to collect sufficientdata to determine where to putcapacitors.

■ Why the power system must bebuilt with extra capacity tosupply power.

■ How reactive power contrib-utes to additional losses.

■ How capacitors, synchronousmachines, and static (adap-tive) power compensatorscorrect for power factor.

■ When to use switched andfixed capacitors.

■ How and when capacitorscontribute to harmonicdistortion problems and howto predict this.

■ How capacitors can fall preyto harmonics and switchingtransients and what to doabout it.

The Guidebook ($25) andSoftware ($395) are availablefrom Bonneville Power Adminis-tration. Send check to AccountingOperations, Mailstop FRO,BPA, P.O. Box 6040, PortlandOR 97228.

Figure 8-2Power Factor as a Function of Motor Load


motors throughout an industrial

Industry Uncorrected Power FactorSaw mills 45% - 60%

Plastics (extruders) 55% - 70%

Machine shops 40% - 65%

Plating, textiles, chemicals,breweries

65% - 75%

Foundries 50% - 80%

Chemicals 65% - 75%

Textiles 65% - 75%

Arc welding 35% - 60%

Cement Works 78% - 80%

Printing 55% - 70%

Table 8-1Industries That Typically Exhibit Low Power Factor

Sizing and Locating PowerFactor CorrectionCapacitorsOnce you decide that your facilitycan benefit from power factorcorrection, you need to choose theoptimum type, size, number, andstrategic locations for capacitors inyour plant. The unit for ratingpower factor capacitors is thekVAR, equal to 1,000 volt-am-peres of reactive power. ThekVAR rating signifies how muchreactive power a capacitor willprovide.8-1

The value of individual motorreactive power is cumulativetoward the overall plant reactivepower. Therefore, when youimprove the power factor of asingle motor, you are reducing theplant’s reactive power require-ment.

The greatest power factor correc-tion benefits are derived when youplace capacitors at the source ofreactive currents. It is thus com-mon to distribute capacitors on

plant.8-6,8-7 This is a good strategywhen capacitors must be switchedto follow a changing load. If yourplant has many large motors, 25 hpand above, it is usually economicalto install one capacitor per motorand switch the capacitor andmotor together.8-1

Switched capacitors don’t requireseparate switch control equipmentwhen they are located on the loadside of motor contactors. Thus,capacitors installed on the largermotors are nearly as economical asfixed banks installed at motorcontrol centers. When someswitching is required, the mosteconomical method is to install abase amount of fixed capacitorsthat are always energized, with theremainder on the larger motors andswitched when the motors areenergized. Observe load patternsin order to determine good candi-date motors to receive capacitors.

If your plant contains many smallmotors (in the 1/2 to 10 hp sizerange), it may be more economicalto group the motors and placesingle capacitors or banks ofcapacitors at, or near, the motor


control centers. If capacitors aredistributed for loss reduction andalso need to be switched, you caninstall an automatic power factorcontroller in a motor controlcenter; this provides automaticcompensation and may be moreeconomical than capacitors oneach of the small motors fed fromthat control center.8-6 Often thebest solution for plants with largeand small motors is to specify bothtypes of capacitor installations.8-1,8-6

Sometimes, only an isolatedtrouble spot requires power factorcorrection. This may be the caseif your plant operates weldingmachines, induction heaters, or D-C drives.8-1 Facilities with verylarge loads typically benefit from acombination of individual load,group load, and banks of fixed andautomatically-switched capacitorunits.

Advantages of individual capaci-tors at the load include8-1:

� Complete control. Capacitorsdon’t cause problems on theline during light load condi-tions.

� No need for separate switch-ing. The motor always oper-ates with its capacitor.

� Improved motor performancedue to reduced voltage drops.

� Motors and capacitors can beeasily relocated together.

� Easier to select the rightcapacitor for the load.

� Reduced line losses.

� Increased system capacity.The advantages of bank installa-tions at the feeder or service entryare8-1:� Lower cost per kVAR.

� Lower installation costs.

� Total plant power factorimproves which reduces oreliminates utility power factorpenalty charges.

� Total kVAR may be reduced,as all capacitors are on-lineeven when some motors areswitched off.

� Automatic switching ensuresthe exact amount of powerfactor correction and elimi-nates overcapacitance andresulting overvoltages.

If your facility operates at aconstant load around-the-clock,fixed capacitors are the bestsolution. If load is variable suchas eight-hour shifts five days aweek, you’ll require switched unitsto decrease capacitance duringtimes of reduced load.8-1

If your feeders or transformers areoverloaded, or if you wish to addadditional load to already loadedlines, you should apply powerfactor correction at the load. Ifyour facility has excess current-carrying capacity, you can installcapacitor banks at main feeders.

Figure 8-3Locating Capacitors on Motor Circuits


Three options, indicated in Figure8-3, exist for installing capacitorsat the motor:8-1

Location A — motor side ofoverload relay

■ New motor installations inwhich overloads can be sizedin accordance with reducedcurrent draw

■ Existing motors when nooverload change is required

Location B — between the starterand overload relay

■ Existing motors when place-ment at A would allow over-load current to surpass code

Location C — line side of starter

■ Motors that are jogged,plugged, reversed

■ Multi-speed motors■ Starters with open transition

and starters that disconnect/reconnect capacitor duringcycle

■ Motors that start frequently■ Motor loads with high inertia

NEMA B C DCode Before 1955 U-Frame T-FramePoles 2 4 6 8 10 12 2 4 6 8 10 12 2 4 6 8 10 12 4-6 8 6 Wound

RPM 3600 1800 1200 900 720 600 3600 1800 1200 900 720 600 3600 1800 1200 900 720 60018001200

900 1200 Rotor

HP=3

1.5 1.5 1.5 2 2.5 3.5 1 1 1 2 1.5 1.5 2.5 3 3 4

5 2 2 2 3 4 4.5 1 2 2 2 2 2.5 3 4 4 57.5 2.5 2.5 3 4 5.5 6 1 2 4 4 2.5 3 4 5 5 610 3 3 3.5 5 6.5 7.5 2 2 4 5 5 5 4 4 5 6 7.5 815 4 4 5 6.5 8 9.5 4 4 4 5 5 5 5 5 6 7.5 8 10 5 5 5 5.520 5 5 6.5 7.5 9 12 4 5 5 5 10 10 6 6 7.5 9 10 12 5 6 6 725 6 6 7.5 9 11 14 5 5 5 5 10 10 7.5 7.5 8 10 12 18 6 6 6 730 7 7 9 10 12 16 5 5 5 10 10 10 8 8 10 14 15 23 7.5 9 10 1140 9 9 11 12 15 20 5 10 10 10 10 15 12 13 16 18 23 25 10 12 12 1350 12 11 13 15 19 24 5 10 10 15 15 20 15 18 20 23 24 30 12 15 15 1860 14 14 15 18 22 27 10 10 10 15 20 25 18 21 23 26 30 35 18 18 18 2075 17 16 18 21 26 33 15 15 15 20 25 30 20 23 25 28 33 40 19 23 23 25100 22 21 25 27 33 40 15 20 25 25 40 45 23 30 30 35 40 45 27 27 30 33125 27 26 30 33 40 48 20 25 30 30 45 45 25 36 35 42 45 50 35 38 38 40150 33 30 35 38 48 53 25 30 30 40 45 50 30 42 40 53 53 60 38 45 45 50200 40 38 43 48 60 65 35 40 60 55 55 60 35 50 50 65 68 90 45 60 60 65250 50 45 53 58 70 78 40 40 60 80 60 100 40 60 63 82 88 100 54 70 70 75300 58 53 60 65 80 88 45 45 80 80 80 120 45 68 70 100 100 120 65 90 75 85350 65 60 68 75 88 95 60 70 80 80 50 75 90 120 120 135400 70 65 75 85 95 105 60 80 80 160 75 80 100 130 140 150450 75 68 80 93 100 110 70 100 80 90 120 140 160 160500 78 73 83 98 108 115 70 100 120 150 160 180 180

Table 8-2Sizing Guide for Capacitors on Individual MotorskVAR to correct typical motor to 0.95 PF; motor and capacitor switched as single unit. (ANSI/NEMA MGI - 1978)

Sizing Capacitors forIndividual Motor andEntire Plant LoadsCapacitors which are installedacross the motor terminals andswitched with the motor shouldnot be sized larger than theamount of kVAR necessary toraise the motor no-load powerfactor to 100 percent.8-5 Use Table8-2 to size capacitors for indi-vidual motor loads. Look up thetype of motor frame, synchronousspeed (RPM), and horsepower.The table indicates the kVARnecessary to correct the powerfactor to 95 percent.8-1,8-6

If you know the total plant load(kW), your present power factor,and the power factor you intend toachieve, use Table 8-3 to identifythe required capacitance.8-1 Thistable is useful for sizing banks ofcapacitors which may be locatedat motor control centers, feeders,branch circuits, or the plantservice entrance.


Table 8-3Multipliers to Determine Capacitor Kilovars Required for Power Factor Correction

Instructions: 1. Find the present power factor in column 1. 2. Read across to optimum power factor column. 3. Multiply that number by kW demand.Example: If your plant consumed 410 kW, was currently operating at 73% power factor and you wanted to correct power factor to 95%, you would:

1. Find 0.73 in column 1. 2. Read across to 0.95 column. 3. Multiply 0.607 by 410 = 249 (round to 250). 4. You need 250 kVAR to bring your plant to 95% power factor. If you don’t know the existing power factor level of your plant, you will have to calculate it before using this table. To calculate existing power factor: kW divided by kVA = Power Factor

ORIGINALPOWERFACTOR

C orrected P ower F actor0.80 0.81 0.82 0.83 0.84 0.85 0.86 0.87 0.88 0.89 0.90 0.91 0.92 0.93 0.94 0.95 0.96

0.50 0.982 1.008 1.034 1.060 1.086 1.112 1.139 1.165 1.192 1.220 1.248 1.276 1.306 1.337 1.369 1.403 1.4400.51 0.937 0.962 0.989 1.015 1.041 1.067 1.094 1.120 1.147 1.175 1.203 1.231 1.261 1.292 1.324 1.358 1.3950.52 0.893 0.919 0.945 0.971 0.997 1.023 1.050 1.076 1.103 1.131 1.159 1.187 1.217 1.248 1.280 1.314 1.3510.53 0.850 0.876 0.902 0.928 0.954 0.980 1.007 1.033 1.060 1.088 1.116 1.144 1.174 1.205 1.237 1.271 1.3080.54 0.809 0.835 0.861 0.887 0.913 0.939 0.966 0.992 1.019 1.047 1.075 1.103 1.133 1.164 1.196 1.230 1.2670.55 0.769 0.795 0.821 0.847 0.873 0.899 0.926 0.952 0.979 1.007 1.035 1.063 1.093 1.124 1.156 1.190 1.2270.56 0.730 0.756 0.782 0.808 0.834 0.860 0.887 0.913 0.940 0.968 0.996 1.024 1.054 1.085 1.117 1.151 1.1880.57 0.692 0.718 0.744 0.770 0.796 0.822 0.849 0.875 0.902 0.930 0.958 0.986 1.016 1.047 1.079 1.113 1.1500.58 0.655 0.681 0.707 0.733 0.759 0.785 0.812 0.838 0.865 0.893 0.921 0.949 0.979 1.010 1.042 1.076 1.1130.59 0.619 0.645 0.671 0.697 0.723 0.749 0.776 0.802 0.829 0.857 0.885 0.913 0.943 0.974 1.006 1.040 1.0770.60 0.583 0.609 0.635 0.661 0.687 0.713 0.740 0.766 0.793 0.821 0.849 0.877 0.907 0.938 0.970 1.004 1.0410.61 0.549 0.575 0.601 0.627 0.653 0.679 0.706 0.732 0.759 0.787 0.815 0.843 0.873 0.904 0.936 0.970 1.0070.62 0.516 0.542 0.568 0.594 0.620 0.646 0.673 0.699 0.726 0.754 0.782 0.810 0.840 0.871 0.903 0.937 0.9740.63 0.483 0.509 0.535 0.561 0.587 0.613 0.640 0.666 0.693 0.721 0.749 0.777 0.807 0.838 0.870 0.904 0.9410.64 0.451 0.474 0.503 0.529 0.555 0.581 0.608 0.634 0.661 0.689 0.717 0.745 0.775 0.806 0.838 0.872 0.9090.65 0.419 0.445 0.471 0.497 0.523 0.549 0.576 0.602 0.629 0.657 0.685 0.713 0.743 0.774 0.806 0.840 0.8770.66 0.388 0.414 0.440 0.466 0.492 0.518 0.545 0.571 0.598 0.626 0.654 0.682 0.712 0.743 0.775 0.809 0.8460.67 0.358 0.384 0.410 0.436 0.462 0.488 0.515 0.541 0.568 0.596 0.624 0.652 0.682 0.713 0.745 0.779 0.8160.68 0.328 0.354 0.380 0.406 0.432 0.458 0.485 0.511 0.538 0.566 0.594 0.622 0.652 0.683 0.715 0.749 0.7860.69 0.299 0.325 0.351 0.377 0.403 0.429 0.456 0.482 0.509 0.537 0.565 0.593 0.623 0.654 0.686 0.720 0.7570.70 0.270 0.296 0.322 0.348 0.374 0.400 0.427 0.453 0.480 0.508 0.536 0.564 0.594 0.625 0.657 0.691 0.7280.71 0.242 0.268 0.294 0.320 0.346 0.372 0.399 0.425 0.452 0.480 0.508 0.536 0.566 0.597 0.629 0.663 0.7000.72 0.214 0.240 0.266 0.292 0.318 0.344 0.371 0.397 0.424 0.452 0.480 0.508 0.538 0.569 0.601 0.635 0.6720.73 0.186 0.212 0.238 0.264 0.290 0.316 0.343 0.369 0.396 0.424 0.452 0.480 0.510 0.541 0.573 0.607 0.6440.74 0.159 0.185 0.211 0.237 0.263 0.289 0.316 0.342 0.369 0.397 0.425 0.453 0.483 0.514 0.546 0.580 0.6170.75 0.132 0.158 0.184 0.210 0.236 0.262 0.289 0.315 0.342 0.370 0.398 0.426 0.456 0.487 0.519 0.553 0.5900.76 0.105 0.131 0.157 0.183 0.209 0.235 0.262 0.288 0.315 0.343 0.371 0.399 0.429 0.460 0.492 0.526 0.5630.77 0.079 0.105 0.131 0.157 0.183 0.209 0.236 0.262 0.289 0.317 0.345 0.373 0.403 0.434 0.466 0.500 0.5370.78 0.052 0.078 0.104 0.130 0.156 0.182 0.209 0.235 0.262 0.290 0.318 0.346 0.376 0.407 0.439 0.473 0.5100.79 0.026 0.052 0.078 0.104 0.130 0.156 0.183 0.209 0.236 0.264 0.292 0.320 0.350 0.381 0.413 0.447 0.4840.80 0.000 0.026 0.052 0.078 0.104 0.130 0.157 0.183 0.210 0.238 0.266 0.294 0.324 0.355 0.387 0.421 0.4580.81 0.000 0.026 0.052 0.078 0.104 0.131 0.157 0.184 0.212 0.240 0.268 0.298 0.329 0.361 0.395 0.4320.82 0.000 0.026 0.052 0.078 0.105 0.131 0.158 0.186 0.214 0.242 0.272 0.303 0.335 0.369 0.4060.83 0.000 0.026 0.052 0.079 0.105 0.132 0.160 0.188 0.216 0.246 0.277 0.309 0.343 0.3800.84 0.000 0.026 0.053 0.079 0.106 0.134 0.162 0.190 0.220 0.251 0.283 0.317 0.3540.85 0.000 0.027 0.053 0.080 0.108 0.136 0.164 0.194 0.225 0.257 0.291 0.3280.86 0.000 0.026 0.053 0.081 0.109 0.137 0.167 0.198 0.230 0.264 0.3010.87 0.000 0.027 0.055 0.083 0.111 0.141 0.172 0.204 0.238 0.2750.88 0.000 0.028 0.056 0.084 0.114 0.145 0.177 0.211 0.2480.89 0.000 0.028 0.056 0.086 0.117 0.149 0.183 0.2200.90 0.000 0.028 0.058 0.089 0.121 0.155 0.1920.91 0.000 0.030 0.061 0.093 0.127 0.1640.92 0.000 0.031 0.063 0.097 0.1340.93 0.000 0.032 0.066 0.1030.94 0.000 0.034 0.0710.95 0.000 0.0370.96 0.0000.970.980.99

0.99 1.01.589 1.7321.544 1.6871.500 1.6431.457 1.6001.416 1.5591.376 1.5191.337 1.4801.299 1.4421.262 1.4051.226 1.3691.190 1.3331.156 1.2991.123 1.2661.090 1.2331.068 1.2011.026 1.1690.995 1.1380.965 1.1080.935 1.0780.906 1.0490.877 1.0200.849 0.9920.821 0.9640.793 0.9360.766 0.9090.739 0.8820.712 0.8550.685 0.8290.659 0.8020.633 0.7760.609 0.7500.581 0.7240.555 0.6980.529 0.6720.503 0.6460.477 0.620.0450 0.5930.424 0.5670.397 0.5400.369 0.5120.341 0.4840.313 0.4560.283 0.4260.252 0.3950.220 0.3630.186 0.3290.149 0.2920.108 0.2510.060 0.2030.000 0.143

0.000


The power triangle in Figure 8-4indicates the demands on a plantdistribution system before andafter adding capacitors to improvepower factor. By increasing thepower factor from 70 percent to95 percent, the apparent power isreduced from 1,420 kVA to 1,050kVA, a reduction of 26 percent.

Benefits of Power FactorCorrectionThe cost-effectiveness of powerfactor correction depends uponsuch variables as utility powerfactor penalties, the need foradditional system capacity, energyand demand cost, hours of facilityoperation, distribution system wiresizes, and the distance betweenthe motor and the electricalmeter.8-8 As shown in the follow-ing examples, it is critical tounderstand your utility’s ratestructure in order to assess thebenefits or reduction in utilitybilling due to power factor correc-tion.8-1

Figure 8-4Apparent Power Requirements Before and After Adding Power FactorCorrection Capacitors

70% PFBefore


Example 8-1

Utility Rate Schedule: The utility measures and bills based upon totalcurrent used (working plus reactive current) at $3.50/kVA Demand.

Plant Conditions: Assume a constant 4,600 kVA demand with an 80percent power factor. Correct to 95 percent power factor.

Billing Before Power Billing After Power Factor Corrected to 95%Factor Correction

4,600 kVA x $3.50 =$16,100/month demand demand 1 1kW PF= kVA x

= =4,600 x 0.8 3,680

demand 2kVA = =3 6800 95

3 873,.

,

kVAdemand 1 = kVA demand before PF correction

kVAdemand 2 = kVA demand after PF correction

kWdemand = Electric demand in kW

PF1 = Original power factor

PF2 = Power factor after correction

Corrected Billing3,873 kVA x $3.50 = $13,555/month

Savings are ($16,100-$13,555) x 12 months = $30,540/year

Up to $61,000 could be spent on power factor correction equipment if plant manage-ment would support a two-year simple payback on investment.8-9

Where:

demand 2demandkVA kW

PF=

2


Example 8-2

Utility Rate Schedule: In this scenario, the utility charges according to kWdemand ($4.50/kW) and includes a surcharge or adjustment for low powerfactor. The following formula shows a billing adjustment based upon adesired 95 percent power factor.

billedkW = dem andkW xPF

0 95.

Where:

kWbilled = Adjusted or billable demand

kWdemand = Measured electric demand in kW


The multiplier applies to power factors up to 0.95.

Plant Conditions: For our sample facility, the original demand is4,600 kVA x 0.80 or 3,680 kW.

Billing Before Power Billing After Power Factor Correction Factor Corrected to 95%

3,680 kW x 0.950.80

= 4,370 × $4.50 = 3,680 × $4.50= $19,665/month or $235,980/year = $16,560/month or $198,720/year

Savings are $37,260/year

Additional Benefits ofPower Factor CorrectionThe “Industrial Electrical Distri-bution Systems Guidebook”contains worksheets for calculat-ing the benefits of correctingindividual motor and total plantpower factor.8-10

Power factor correction capacitorsincrease system current-carryingcapacity, reduce voltage drops, anddecrease distribution systemresistance (I2R) losses.8-1 Increas-ing the power factor from 75percent to 95 percent results in a21 percent lower current when

serving the same kW load.Through adding power factorcorrection capacitors to yoursystem, you can add additional kWload without increasing linecurrents, wire size, transformersize, or facility kVA charges. Byincluding power factor correctioncapacitors in new construction orfacility expansions, you can reduceproject costs through decreasingthe sizes of transformers, cables,busses, and switches.8-1 In prac-tice, however, ampacity ratings area function of full-load equipmentvalues; therefore, size reductionsmay be precluded by electricalcodes.


Poor power factor contributes topower losses in the in-plant distri-bution system. Calculate thepower loss by squaring the linecurrent and multiplying by thecircuit resistance (I2R). Generally,distribution system losses are small— a typical industrial plant willsuffer only a 2 percent loss in thecables if the cables are loaded tofull capacity.8-6 Reductions inlosses (upstream of the powerfactor correction capacitor loca-tions) are calculated by the rela-tionship shown in Equation 8-2:8-1

Excessive current draws due tolow power factors also causeexcessive system voltage drops.Operating motor-driven equip-ment under low voltage conditionsresults in efficiency decreases,motor overheating, and subse-quent diminished motor life. Byadding power factor correctioncapacitors, you can restore operat-ing voltage to proper designconditions.

Power Factor CorrectionCostsThe average installed cost ofcapacitors on a 480-volt system isabout $30 per kVAR. Automaticpower factor controllers orcapacitors with harmonic filterscost more. These features aretypically associated with capaci-tors exceeding 100 kVAR. Asingle, large capacitor bank has alower installed cost than multiplesmall installations scatteredthroughout the plant. The costper kVAR for small capacitors onmotors is substantially higher dueto labor and materials costs. Thecost for large banks is lower on aper kVAR basis because of theeconomy of scale. The installedcost per kVAR of capacitance isalso lower at higher voltages. Athigher voltage levels (2400V andup) unit costs are generally about$6 - $12 per kVAR installed.8-6

Suppliers of capacitors are listedin Appendix D.

Equation 8-2

Where:

% reduction = Percent reduction in distribution losses

PF1 = Original power factor

PF2 = Power factor after correction


Avoiding HarmonicResonances WhenInstalling CapacitorsApproximately twenty percent ofindustrial plants that install andoperate capacitors must paycareful attention to the creation ofsteady state harmonic resonances.8-

6 The resonant frequency createdwith a capacitor and systeminductance is calculated by Equa-tion 8-3. As shown in the equa-tion, the square root of the shortcircuit MVA divided by the capaci-tor MVAR indicates the resultantharmonic for the system understudy.8-11

Equation 8-3

If the resonant frequency is nearto an odd harmonic, considerreducing capacitor MVA to bringthe system out of tune with thatharmonic. This is particularlyimportant if you have a knownsource of these harmonics. Forexample, adjustable speed drivescan be a significant source of 5thand 7th harmonics.

Resonant conditions near the 3rd,5th, 7th, 11th, and 13th harmonicare usually the most troublesome.8-

11 Harmonics cause additionalnoise on the line and generateheat. This heat can cause failureof capacitors or transformers.Consult with your capacitorsupplier or a specialist in harmonicmitigation. Many vendors offerharmonic analysis services andwill assist you to properly selectand install power factor correctionequipment. Appendix D containsa list of manufacturers of powerfactor correction capacitors.

Short circuit MVA repre-sents system impedance. Itis the current (in millionsof amperes) that would bedrawn by a short circuit,multiplied by the no-loadvoltage of the system at thepoint of interest. In reality,circuit protectors wouldblow before shor t circuitcurrent could stabilize, so itis defined by linearlyextrapolating the volts-per-amp system voltage drop,at moderate load, down tozero system volts.

Example 8-3

Consider a case where a 1200 kVAR capacitor is to be installed on a12.47 kV system at a location where the three phase short circuitcurrent is 2800 amps.

shortcircuitMVA 2800 amps x 12.47 kV x 31,000,000

= = 60 5.

capacitorMVAR f1200 kVAR 1000 = 1.2 MVAR and h = 60.51.2

= = 71.


8-1 “Power Factor Correction: A Guide for the Plant Engineer,”Commonwealth Sprague Capacitor, Inc., PF-2000E, Octo-ber 1991

8-2 Carroll, Hatch & Associates, Inc., “An ElectricMotor Energy Efficiency Guide and TechnicalReference Manual,” (Draft) June 1994.

8-3 Carroll, Hatch & Associates, Inc., “A Procedure for Develop-ing an Energy Efficiency Plan for the Use of Electric Motorsin an Industrial Setting,” (Draft), June 1994.

8-4 “Reducing Power Factor Cost,” Electric Ideas ClearinghouseTechnology Update, Bonneville Power Administration, April1991.

8-5 Edward Ader and William Finley, Compensating for Low PowerFactor, Plant Engineering, June 17, 1993.

8-6 “Industrial Power Factor Analysis Guidebook,” BonnevillePower Administration, DOE/BP-42892-1, April 1995.

8-7 Portland General Energy Systems, “Power Quality forElectrical Contractors: Application Guide, Volume 7:Recommended Practices,” Electric Power Research Institute,December 1994.

8-8 Power Factor Correction Equals Big Savings, Georgia TechResearch Institute, Conserver, March 1991.

8-9 Fred L. Montgomery, The Dollars and Sense of Power FactorCorrection, AIPE Facilities Management, Operations &Engineering, September/October 1989.

8-10 Rob Gray, Washington State Energy Office, “Keeping theSpark in Your Electrical System: An Industrial ElectricalDistribution Systems Guidebook,” Funded by the BonnevillePower Administration, U.S. Department of Energy,Pacificorp, Portland General Electric and Tacoma City Light,October 1995.

8-11 PSI Energy, Avoiding Steady-State Harmonic Resonances WhenInstalling Capacitors, Power Clinic Tech Tip, Issue Number 7.

ReferencesChapter 8


Preventative and Predictive Maintenance 9-1

Everyone knows that mainte-nance is good. The traditionalpurpose has been two-fold: keepequipment from failing prema-turely and keep equipmentcalibrated for optimum perfor-mance. Both of these objectivescan be thought of as preventativemaintenance. A two-year FactoryMutual study reveals that effec-tive preventative maintenanceprograms could have preventedmore than half the losses associ-ated with electrical equipmentfailure. It also showed that well-maintained motors dramaticallyimprove a facility’s overall effi-ciency.9-1

More recently, attention has beendirected at predictive mainte-nance. Predictive maintenancerefers to scheduled testing andmeasurement, and trending of theresults over time. Proper analysisof the results can predict animpending failure so that neces-sary repair, cleaning, or alignmentcan be scheduled before a costlycatastrophe occurs.

A good maintenance programcontains elements of both predic-tive and preventative mainte-nance (PPM). Both involvescheduled actions to the motorsand controls as well as recordkeeping. Depending upon yoursituation, it may be efficient tomerge the two activities. How-ever, depending upon the organi-zation of your maintenance staff,and the service intervals youselect, it may be beneficial to

separate the tasks on some basisother than predictive versuspreventative.

Mechanical tasks like lubricationand cleaning might require adifferent schedule and differenttradespeople than electrical tasks.Vibration and acoustic testingcould fit in either category. Sometasks like infra-red scanning ordry ice cleaning could require anoutside contractor operating onyet another schedule. You mustdesign a system to fit your uniquesituation. This chapter willdiscuss key elements of any goodplan but it can not dictate details.

To have an effective maintenanceplan, all four of the followingmust be executed well:

� Identify responsiblepersonnelPersonnel must be designatedfor the necessary activities.Best results follow when staffbuy in to the concept of PPM.This is most likely to occurwhen they are given thenecessary training and tools,and they participate in devel-oping the maintenance plan.

� Establish a scheduleEstablishing a schedule is aniterative process. It is oftennecessary to prescribe some-what frequent intervals atfirst, then experiment withlengthening the intervals.Some activities can actually beharmful if performed toofrequently (e.g. high voltageinsulation testing and bearing

Chapter 9

Preventative andPredictiveMaintenancePlanning


greasing). If you observe thatcertain test results progressuniformly, you can establish adefinite and often longerinterval. If bearings survivewell at a given lubricationinterval, you can experimentwith a longer lubricationinterval. Revise, but do notabandon the schedule.

� Keep recordsRecord keeping can be donein a number of different ways.Using printed cards or datasheets is the oldest methodand may be sufficient. Thereare certain advantages togoing “high tech” with alaptop computer or specialelectronic recording device fordata entry. One advantage isthat analysis routines can beset up to graph trends with-out a second “handling” ofpenciled forms by a data entryoperator. The costliest ap-proach involves special testinstruments that connectelectrically and actually entermeasured data into computerfiles. Certain actions likerecording lubrication andcleaning are not amenable tosuch devices. New productsthat bring maintenance intothe “information age” areevolving rapidly. Keepabreast of these develop-ments.

� Analyze resultsTesting and record keepingare only as good as the follow-up analysis. There are varioussoftware tools to help.Spreadsheets and databaseprograms are useful forstoring and manipulating dataand especially for graphingtrends. A third category ofsoftware, the statistical pack-age, is often overlooked but

may be the best of all. Thereare certain special applica-tions software packages thatare tailored to this type ofrecord keeping and analysis.MotorMaster + contains anexcellent motor inventorymodule that is dedicated tokeeping track of motor perfor-mance trends and calculatingthe most cost effective alterna-tives when motors fail orbecome obsolete.

The following sections covermajor categories and make recom-mendations on servicing andtesting. Some of the recommen-dations may seem too costly to bejustifiable for small inexpensivemotors. If so, omit them, butremember to consider the totalcost of an untimely motor failure.The unscheduled downtime andloss of materials in process can farexceed the cost of the motor.

CleaningA clean motor is more than just apretty motor. Avoid too manythick coats of paint or dirt build-ups which can foul heat transfersurfaces. Why is dirt bad? Dirt isa very general word that canmean many things: dust, corro-sive buildups, sugary syrups fromfood processing, electro-conduc-tive contaminants like salt depos-its or coal dust. It can damage amotor in three ways. It can attackthe electrical insulation by abra-sion or absorption into the insula-tion. It can contaminate lubri-cants and destroy bearings.

A clean motor runs cooler. Dirtbuilds up on the fan-cooled motorinlet openings and fan blades.This reduces the flow of air andincreases the motor operatingtemperature. Dirt on the surfaceof the motor reduces heat transfer


by convection and radiation. Thisis especially critical for totallyenclosed motors since all thecooling takes place on the outsidesurface. Heavily loaded motorsare especially vulnerable tooverheating, so they have littletolerance for dirt.

Surface dirt can be removed byvarious means, depending uponits composition. Compressed air(30 psi maximum), vacuumcleaning and direct wipe downwith rags or brushes are usuallyused. There has been a recentintroduction of dry ice “sand”blasting. This is usually done by aspecial contractor. The dry ice isless abrasive than mineral depos-its, is non-electro-conductive, andleaves no residue other than theremoved dirt.

Dirt inside the motor is moredifficult to remove. It is best tokeep it from getting inside. Atotally enclosed motor helps inthis regard, but fine dust caninvade and destroy even anexplosion-proof motor. Somelarger motors can be providedwith a filter in the ventilation airpassages to keep out dirt. Keep-ing moisture out can decrease theattachment of dirt inside themotor and reduce the electricalconductivity of some contami-nants. This will reduce thefrequency with which the motormust be disassembled for clean-ing.

LubricationMany small or integral horse-power motors have factory-sealedbearings that do not require re-lubrication. All others requirelubrication. Unfortunately,lubrication can be more art thanscience.

Motor manufacturers’ recommen-dations should be followedinitially. Eventually, with someexperimentation and analysis ofwell-kept records, you maydiscover that a different type oflubricant or lubrication interval isbetter. It is good to compareexperience with others in yoursame industry because the operat-ing environment has a great effectupon re-lubrication requirements.Consult with your motor repairshop. By inspecting bearings andanalyzing failures, the repairermay be able to tell if you are usingthe wrong lubricants, lubricationmethods, or intervals.

Typical lubrication intervals varyfrom less than three months (forlarger motors subject to vibration,severe bearing loads, or hightemperature) to five years forintegral horsepower motors withintermediate use. Motors usedseasonally should be lubricatedannually before the season ofuse.9-2

One cannot merely be conserva-tive and over-lubricate. There aremany ways that improper lubrica-tion shortens bearing life. Re-lubrication with a different greasecan cause bearing failure whentwo incompatible greases mix.Grease consists of an oil in sometype of constituent to give it bodyor thickness so that it doesn’t runout of the bearing. Mixinggreases with incompatible con-stituents can cause the compo-nents of the mixed grease toseparate or harden. Table 9-1 is aguide to compatibility of greasebases.9-3

Adding too much grease orgreasing too frequently can forcegrease past the bearing shield orseal into the motor, resulting inwinding damage. Merely having

Some of these recommendationsmay seem too costly to bejustifiable for small inexpensivemotors. If so, omit them. Butremember to consider the totalcost of an untimely motorfailure.


too much grease in the bearingitself can prevent proper flow ofthe grease around the rollers.Sometimes bearing failures due toover-lubrication are interpreted asinsufficient lubrication andintervals are made even shorter.

Perhaps the worst problem withgreasing is introduction of con-taminants. Contamination occurswhen strict cleanliness standardsare not followed in grease storageand application. It may be wise tobuy grease in more expensiveindividual cartridges rather thanlarge quantities that are subject tocontamination when refillinggrease guns. Take special carewith grease fittings. Clean thefitting before filling and keep thegrease gun nozzle covered whennot injecting grease.

When selecting oil or grease,begin with the motor manufactur-ers’ recommendations. However,these sometimes are quite general

or have allowed unexplainedbearing failures. In this case,review alternative lubricantspecifications and select a typecompatible with the knowncontaminants in your operatingenvironment. For severe situa-tions, a synthetic lubricant may bebest. Consult with lubricantvendors, the motor manufacturer,and your repair shop. Lubricantsvary in their tolerance to tempera-ture, water, salt or acids.

Finally, remember to completelyremove old lubricant beforetrying a different one. If this isimpossible, relubricate soon afterintroduction of a new lubricant. Ifthere is a plug under a greaselubricated bearing, remove thiswhen first greasing with a newgrease to encourage flushing ofthe old. Some authorities recom-mend running the motor forabout an hour with the plug outto help flush the old grease. TheElectrical Apparatus Service

Table 9-1Grease Compatibility


Association recommends remov-ing the plug for all regreasing topurge the bearing of excessgrease.9-4 The advisability of thispractice depends upon the geom-etry of the bearing cavities andtype of seal/shield. Again,consult the manufacturer orrepairer.

Mountings, Couplings,and AlignmentMounting is not really a mainte-nance issue, but if it is inadequate,it can result in serious mainte-nance problems. The entirestructure must be rigid with a flatcoplanar surface for the fourmounting legs. The same appliesto the structure for mounting theload. Both motor and load struc-ture must be rigidly bound to thefloor or a common structure.Failure to provide a solid mount-ing can lead to vibration ordeflection which leads to bearingfailure.

Vertical motors can be even moredemanding than horizontalmotors because the mountingcircle constitutes a small foot-print for a large mass cantileveredabove. Pliancy in the mountingstructure can exacerbate lowfrequency vibration to whichvertical motors are vulnerable.Always check hold-down bolts/dowels at every maintenanceinterval and do a visual check forcracks or other failures of themounting system.

Coupling alignment is oftenpromoted for energy efficiency.Energy loss in couplings is some-times overstated, but properalignment is always important tobearing and coupling life. Aslight misalignment can dramati-cally increase the lateral load onbearings. It can also shorten the

life of the coupling. One sourceattributes 45% to 80% of bearingand seal failures to misalign-ment.9-5

Alignment means that thecenterline of the motor and loadshaft coincide. If they are parallel,but do not coincide, this is parallelmisalignment. If the centerlinesare not parallel but they intersectinside the coupling, this is angularmisalignment. It is certainlypossible to have misalignment inboth respects.

Misalignment is usually the resultof errors in installation. Howevermisalignment sometimes devel-ops after installation. This canoccur if the mounting structure isnot completely rigid, if vibrationor impact causes something toslip, or if dirty or bent shims wereoriginally used. Alignmentshould be checked soon afterinstallation and less frequentlyafter that if there are no condi-tions likely to cause misalign-ment. If there is evidence ofmisalignment, such as vibration,warm bearings or couplings,unusual noise, or rubber crumbsunder the coupling, check align-ment.

Most users align couplings with adial indicator. To check forangular misalignment, mount theindicator on one shaft and contactthe other coupling flange with theplunger parallel to the shaft. Tocheck for parallel misalignment,arrange the plunger radial to theflange. Rotate the shafts throughat least 180° and ideally 360°,checking for runout.For misalignment in the horizon-tal plane, loosen motor mountingbolts and reposition the motor.For any misalignment in thevertical plane, shims must beadded or removed. Angular


vertical misalignment requiresunequal application of shimsbetween shaft end and oppositeend feet. Apply shims so that themotor rests with equal weight onboth diagonal pairs of feet (i.e.,there is no rocking of the motorbefore tightening bolts). Shimsand the work area around motorfeet must be completely clean.Discard any shims that are bent orscuffed. Always make a finalalignment check after the mount-ing bolts are torqued.

Alignment is not easy. Manyfrustrating trial and error cycles ofposition and remeasure can berequired. There are computerdevices and software available tohelp in choosing shim size andpositioning, but nothing makes itcompletely easy. In recent years,laser alignment devices havebecome the rage. They are accu-rate and easy to use, particularlywhere long extensions would berequired to mount dial indicators.The laser devices simplify attach-ment, eliminate the problem ofcompliance of dial indicatormounting arms, and are usuallyassociated with (or directlyconnected to) computer devicesthat prescribe the adjustmentsnecessary at all four legs.

Belt drives are entirely differentfrom couplings, but they havetheir own needs for vigilant care.The most important thing is tocontrol their tension. If belts aretoo loose, they tend to vibrate,wear rapidly, and waste energythough slippage. If they are tootight, they will also wear exces-sively and can dramaticallyshorten bearing life thoughexcessive lateral loading.

Belt drives require parallel align-ment between motor and loadshaft and require drive and

driven pulleys to be in the sameplane. You can usually checkboth of these conditions with agood straight edge. Once aligned,with a rigid base, alignment tendsto hold constant much better thanbelt tension.

When belts appear worn orrequire over-tensioning to pre-vent slip, they should be replaced.Always replace multiple V-belts atthe same time with a matched set.Re-check new V-belt tensionseveral times until they completetheir break-in stretching (usuallywithin the first 48 operatinghours).

Consider replacing V-belts withsynchronous belts (sometimescalled cog belts) to eliminate sliploss. However, before doing so,determine whether slip is neces-sary in your application to protectthe motor and load from jam-ming. Slip is sometimes requiredin systems that perform crushingor pumping of fluids with en-trained solids. Operators some-times rely upon the horriblescreech to alert them that a jamhas occurred.

Operating ConditionsMotor operating conditions affectefficiency and reliability. Recordoperating conditions at regularintervals. This will ensure thatthey are within tolerances for themotor. Also, trending theseconditions can allow early detec-tion of problems developing inthe motor, load, or power distri-bution system.

Operating speed and voltage, andcurrent on all three phases shouldbe recorded. Also record powerand power factor; these can bothbe determined by using either apower factor meter or power

By trending a motor’s operatingconditions over time, you maydetect problems that aredeveloping in the motor, load, orpower distribution system.


meter. Refer to Chapter 4 forinformation on selecting appro-priate test instruments for thesemeasurements. For belt driveapplications, also record speed ofthe load; it can be compared tomotor speed over time to detectchanges in slippage.

A significant change in voltage isnot likely to be caused by themotor, but it affects the way themotor performs. Figure 9-1 showshow various full load perfor-mance parameters tend to changewith a departure from nameplatevoltage. At part load the changesin power factor and efficiency areworse with overvoltage, but onlyslight at undervoltage.

A change in current is usuallyassociated with a change in shaftload. However, other factors canbe involved such as a change involtage as discussed above. Referto Equation 5-4 to correct loadestimates for a voltage change.An increase in current after motorrepair may signal degradationfrom the failure and repair, suchas turning down the rotor diam-eter to clean up a rub. This willbe accompanied by an increasedpower factor and lower efficiency.It is best to determine shaft loadchange by determining inputpower with a power meter orcombining a power factor readingwith voltage and current readingsusing Equation 5-1. Outputpower still needs to be adjusted

Figure 9-1

Effect of Voltage Variation on Induction Motor Performance Characteristics


for efficiency differences whichare associated with voltagechange as indicated in Figure 9-1.

When power changes, it usuallymeans something is changing inthe load. With a centrifugalpump, a reduction in power maymean damage to an impeller.Inspect for variations in fluid flowand discharge pressure. With beltdrives, a reduction in power maymean a slipping belt. With fansand blowers, a reduction inpower generally signals cloggingof filters or obstruction of ductwork. Since motor speed onlyvaries by a couple of percent fromidle to full load, load changes areassociated with changes in torqueby the load. Understand howyour load torque requirementvaries with operating conditions.Power changes can then be usedto detect load problems.

It is very important to note phasebalance because unbalance candramatically reduce motor effi-ciency and life. Check both volt-age and current balance. A slightvoltage unbalance can cause alarger motor current unbalance.

It is important not to mistake thissituation for a motor problem. Ifthere is a large current unbalancewith little or no voltage unbal-ance, the motor may be at fault. Adelta wound motor will still drawsome current from all phases evenwith an open circuit in one phasewinding. Take the motor off lineand perform a winding resistancecheck. Aim for zero voltageunbalance. Unbalance over 2% iscause for immediate action.

With any of the measured condi-tions, do not assume the condi-tion has progressively changedover time. Many conditionsassociated with the load or powersupply vary during the day, evenminute to minute. These can bepicked up with a recording loggerleft in place for several hours ordays. Often the patterns immedi-ately hint at an explanation whichmay even be normal behavior.Other times, certain fluctuationsremain an unsolved mystery.

An excellent tracking tool formanaging your motor inventoryand keeping track of powersupply and loading conditions isthe MotorMaster+ software.

Equation 9-1

02

01

2 x 2

1 x 1

PP

ePeP

=

Where:

Po2 = Corrected output power

Po1 = Output power before correction

e2 = Corrected efficiency

e1 = Efficiency before correction

P2 = Corrected input power

P1 = Input power before correction


Consult the Motor ChallengeInformation Clearinghouse at(800) 862-2086 for availability ofthis product.

Thermal, Vibration andAcoustic TestsCertain non-electrical tests canreveal problems that either resultfrom or cause motor componentsto deteriorate.

ThermalThermal testing is a good indica-tor. It is not possible to measuresurface temperature of a motoronly once and infer its efficiencyor general health. However, overtime, increases in temperaturewhich cannot be explained byother observed factors oftensignal problems.

Use a good contact thermometerat maintenance intervals. (Main-tenance personnel can sometimesget early warning of a developingproblem by cautiously touchingthe middle of the motor andbearing locations daily.) Measuretemperature after the motor hasbeen running long enough fortemperature to stabilize. Agreater increase in temperature atthe bearing location than in themiddle of the motor suggests abearing problem. Verify adequatelubrication and schedule a bear-ing change soon. If it is a smallmotor on a non-critical applica-tion, it is sometimes sufficient toobtain a spare and wait.

A temperature increase awayfrom the bearings is usuallyassociated with something exter-nal to the motor that can harm themotor. Check for:

� An increase in loading,

� Obstruction of cooling airflow,

� Under-voltage,

� Development of a voltageunbalance condition,

� Line harmonics,

� Recent multiple starts, plug-ging, or jogging.

In variable speed drive poweredmotors, low speed without adramatic torque reduction cancause overheating. Check withthe drive and motor manufac-turer regarding minimum safespeed for the torque loading.

Some larger motors have tem-perature sensors built right intothe stator slots. This makesrecording and trending tempera-ture easy. When rewinding largeor critical motors that do not havetemperature sensors, considerhaving the sensors installed. Notonly can they allow trending, theycan be connected to protectionequipment that sounds an alarmor shuts down the motor whentemperature limits are exceeded.

VibrationA change in vibration oftensignals a bearing problem. It canalso signal other problems like aload imbalance, bent shaft, rotordamage, coupling misalignment,increase or change in line har-monics, or even voltage unbal-ance.

Many instruments are available tomeasure vibration. They varyfrom very sophisticated equip-ment that reads vibration andprints frequency profiles tosimple hand-held gadgets with arow of resonating reeds.

Increased vibration at multiples ofline frequency often signalselectrical problems like harmon-ics. Vibration at 120 Hz can beindicative of phase unbalance.Vibrations at low multiples ofactual rpm suggest mechanical


imbalance within the motor orload, or failure of some part of themounting. Bearing problems areusually high frequency vibrationsthat may not be exact multiples ofeither line frequency or rpm.Instrument manufacturers usuallyprovide analysis documentationthat assists in diagnosing causesof certain vibration changes.

Acoustic

Audible vibration can often alertexperienced personnel to prob-lems. The most common of theseare bearing problems. Electronicultrasonic listening equipmentcan sometimes detect certainbearing problems like pittingfrom arcing or the occurrence ofarcing in the windings.

Electrical TestsCertain electrical tests should beperiodically performed on themotor and motor circuit. Testsperformed on the motor generallydetect insulation problems. Testsperformed on the distributionsystem frequently detect looseconnections in the motor circuit,and can also detect windingerrors in the motor.

Insulation resistance testing is themost important predictive motorelectrical test. There are a numberof special insulation resistancetests that can reveal degradationin insulation. Some can be usedto trend degradation and foreseeimpending failures so a motor canbe pulled for a clean and bake.This can avoid a costly or irrepa-rable failure. These tests areknown variously as AC or DCHigh Potential (Hi-Pot) test, surgecomparison testing, polarizationindex (P-I) test, etc. The methodsare too involved for completedescription here, but numerous

materials are available to guide intheir application.9-8, 9-9, 9-10, 9-11, 9-12, 9-13

The motor circuit needs mainte-nance and inspection, too. Fusesdegrade and develop high resis-tance. Connections become loosebecause of thermal cycling andcreep. Aluminum componentsare particularly vulnerable tocreep, the tendency to deformslowly over time with stress.Contacts become burned andworn so they “make” with highresistance or fail to “make”simultaneously. At annual main-tenance intervals tighten connec-tions with a torque wrench. Then,check connections and contactswith a micro-ohmmeter. Trendthe results to reveal changes. It isdifficult to give guidelines onacceptable resistance because ofthe tremendous difference incurrent between motors of differ-ent power and voltage. Some-times it helps to determine rea-sonableness by converting theresistance values to watts lost orvoltage drop. This is easily donewith the Ohm’s law equations.(See Equation 9-2.)

It is inconvenient and time con-suming to de-energize circuits toperform circuit troubleshootingmaintenance. Some peoplesupplement this with infraredthermography. Smaller firmsoften contract for this service.Equipment varies from smallhand-held non-contact thermom-eters to devices that give colorimages of equipment with thecolors correlated to temperature.This technology can identifytrouble spots quickly withouthaving to de-energize circuits.Various ANSI, IEEE, and NEMAstandards give guidance on limitsof temperature rise and ultimatetemperatures for various electricalsystem components.


Motor circuit analysis is growingin popularity. This service is oftenoffered by private contractors.The process usually consists ofconnecting proprietary testequipment to the circuit at themotor control panel. The equip-ment generally energizes thecircuit with some sort of lowpower signal or pulsing, followedby an analysis of the circuitresponse with a computerizeddetector. Circuit resistance in-cluding motor winding resistanceis determined. Sources of induc-tance and capacitance are mea-sured and asymmetries detected.

A very comprehensive guidebookon maintaining distributionsystem health and symmetry isKeeping the Spark in Your ElectricalSystem: An Industrial ElectricalDistribution Maintenance Guide-book.9-7 It covers all aspects of theelectrical distribution systemincluding methods of testing anddiagnosis, cost of uncorrectedproblems, and maintenanceissues.

Storage and TransportMotors can fail sitting on theshelf. Indeed, they can have ashorter life unpowered thancontinuously running. Lubricantcan drain away from bearingsurfaces and expose them to airand moisture. Even a tiny rust pitfrom such exposure can begin aprogressive failure when themotor is put into service. Highhumidity is also an enemy to thewinding insulation. Most insula-tion will absorb moisture from theair to a degree that significantlyreduces dielectric strength. Vibra-tions can damage ball and rollerbearings when the shaft is notturning. This is most commonwhen motors are installed in highvibration equipment and subjectto long periods not running, but itsometimes happens in transporta-tion and storage areas subject tovibration.

Several things are necessary toreduce the stress of storage. Ifmotors are connected, theyshould be started and run up to

Equation 9-2

j jV I x R=

j j2P I x R=

Where:

VJ = RMS voltage across a junction

IJ = RMS current through a junction

R = Resistance in ohms

PJ = Power dissipated in a junction in watts


temperature at least monthly;weekly is better in high relativehumidity areas. For motors instorage, rotate the shaft at leastmonthly to reposition the bear-ings and distribute the lubricant.

Humidity control is imperative instorage areas. During coldweather, this can usually beaccomplished by heating thestorage area. If there are nosources of moisture (people,coffee makers, rain leaks, etc.), a15°F rise above outdoor tempera-ture will bring relative humidityunder 70%, no matter how humidit is outside. During moderate tohot weather, dehumidification orair conditioning may be neces-sary. Some motors can beequipped with internal heaters bythe manufacturer or when beingrewound. These can be con-nected to keep the windings 10-20°F warmer than ambient whenthe motor is not running. Whenheaters are not installed, themotor can be connected to a lowvoltage DC power supply so thatthe windings serve as a lowpower heater. The power supplyneeds to be either current regu-lated or provided at a voltagedetermined by winding resis-tance. Consult your motor re-pairer for recommendations on apower supply. If a motor is to beput into service after prolongedstorage in less than ideal condi-tions, warm it for a day or morebefore powering it.

Before shipping a motor, block theshaft to prevent axial and radialmovement. If it is oil lubricated,drain the oil and tag the reservoiras empty.


9-1 “Quality Partnering: A Guide to Maximizing YourElectromechanical Systems,” Electrical ApparatusService Association, St. Louis, MO

9-2 Todd Litman, “Efficient Electric Motor Systems,” TheFairmont Press, Inc., 1995, Lilburn, GA

9-3 “Incompatibility of Greases,” NSK Techtalk Vol. 01, No.02, April 1992, Technical Tip-Sheet of the NSK Corpora-tion

9-4 “How to Get the Most From Your Electric Motors,”Electrical Apparatus Service Association, St. Louis, MO

9-5 Richard L. Nailen, “Managing Motors,” Barks Publica-tions Inc., 1991, Chicago, IL

9-6 “Electrical Engineering Pocket Handbook,” ElectricalApparatus Service Association, 1993, St. Louis, MO

9-7 Rob Gray, Washington State Energy Office, “Keep-ing the Spark in Your Electrical Distribution System:An Industrial Electrical Distribution MaintenanceGuidebook,” Bonneville Power Administration,United States Department of Energy, PacifiCorp,Portland General Electric, Tacoma Public Utilities,October 1995.

9-8 “EASA Standards for the Repair of Electrical Appara-tus,” The Electrical Apparatus Service Association, St.Louis, MO

9-9 Institute of Electrical and Electronics Engineers, “IEEEStd. 43-1974(R1991) IEEE Recommended Practice forTesting Insulation Resistance of Rotating Machinery.”(ANSI)

9-10 Institute of Electrical and Electronics Engineers, “IEEEStd. 95-1977 (R1991) IEEE Recommended Practice forInsulation Testing of Large AC Rotating Machinery withHigh Direct Voltage.” (ANSI)

ReferencesChapter 9


9-11 National Electric Manufacturers Association, “NEMAStd. MG 1-1993 (R3): Motors and Generators.” Virginia,1995.

9-12 Howard W. Penrose, “Field Testing Electric Motors forInverter Application,” Transactions: Electrical Manu-facturing & Coil Winding ’96, Electrical Manufacturing& Coil Winding Association, Inc.

9-13 David E. Schump, “Predict Motor Failure with Insula-tion Testing,” Plant Engineering, September 1996

Motor Nameplate and Field Test Data Form A-1

Appendix AMotor Nameplate and Field Test Data Form

Employee Name ________________________

Company ______________________________

Date ___________________________________

Facility/Location ________________________

Department _____________________________

Process ________________________________

General Data

Serving Electrical Utility _________________

Energy Rate ($/kWh) ________________

Monthly Demand Charge ($/kW/mo.) _____

Application _____________________________ Type of equipment that motor drives

Coupling Type __________________________

Motor Type (Design A,B,C,D _____________AC,DC, etc.)

Motor Purchase Date / Age ______________

Rewound _______________ �� Yes �� No

Motor Nameplate Data

1. Manufacturer ________________________

2. Motor ID Number ____________________

3. Model _______________________________

4. Serial Number _______________________

5. NEMA Design Type __________________

6. Size (hp) ____________________________

7. Enclosure Type ______________________

8. Synchronous Speed (RPM) ___________

9. Full Load Speed (RPM) _______________

10. Voltage Rating ______________________

11. Frame Designation __________________

12. Full Load Amperage _________________

13. Full Load Power Factor (%) __________

14. Full Load Efficiency (%) ______________

15. Service Factor Rating ________________

16. Temperature Rise ___________________

17. Insulation Class _____________________

18. kVA Code ___________________________

Motor Operating Profile

Weekdays Wknd/HolidayDays/Year Days/Year

Hours 1st Shift ________ ________Per 2nd Shift ________ ________Day 3rd Shift ________ ________

Annual Operating Time ______ hours/year

Type of load (Place an “X” by the mostappropriate type)

____ 1. Load is quite steady, motor “On” during shift

____ 2. Load starts, stops, but is constant when “On”

____ 3. Load starts, stops, and fluctuates when “On”

Answer the following only if #2 or #3 abovewas selected: % of time load is “on” ____%

Answer the following only if #3 was selected: Estimate average load as a % of motor size____%

Measured Data

Supply Voltage By Voltmeter

Line- Vab ________to- Vbc ________ Vavg ______Line Vca ________

Input Amps By Ampmeter

Aa __________Ab __________ Aavg ______Ac __________

Power Factor (PF) _______________________

Input Power (kW)________________________ If available. Otherwise equal to:

V A PF 3 / 1000avg avgx x x

Motor Operating Speed _________________ By Tachometer

Driven Equipment Operating Speed ______

A-2 Energy Management for Motor-Driven Systems

Average Efficiencies for Standard Efficiency Motors at Various Load Points B-1

Efficiencies for 900 rpm, Standard Efficiency Motors

Load Level In PercentMotor ODP TEFCSize 100 % 75% 50% 25% 100% 75% 50% 25%

10 87.2 87.6 86.3 78.3 86.8 87.6 86.8 77.315 87.8 88.8 88.2 79.6 87.5 88.7 88.1 79.120 88.2 89.2 88.0 81.8 89.2 89.9 89.2 82.625 88.6 89.2 88.0 83.0 89.7 90.3 89.1 78.630 89.9 90.7 90.2 84.5 89.6 90.5 86.5 84.140 91.0 91.8 91.7 86.2 90.5 91.4 85.5 85.050 90.8 91.9 91.1 87.1 90.2 91.0 90.2 84.975 91.7 92.4 92.1 86.5 91.6 91.8 91.0 87.0

100 92.2 92.2 91.8 85.8 92.4 92.5 92.0 83.6125 92.9 92.3 91.7 86.9 93.0 93.1 92.1 87.9150 93.3 93.1 92.6 89.5 93.0 93.4 92.5 NA200 92.8 93.5 93.1 NA 93.7 94.1 93.4 NA250 93.1 93.5 93.0 NA 91.7 94.8 94.5 NA300 93.1 93.7 92.9 92.7 94.4 94.2 93.7 NA



10 87.3 86.9 85.7 78.5 87.1 87.7 86.4 80.315 87.4 87.5 86.8 80.8 88.2 88.1 87.3 80.720 88.5 89.2 88.8 84.1 89.1 89.7 89.4 82.825 89.4 89.7 89.3 85.0 89.8 90.5 89.8 83.530 89.2 90.1 89.8 87.6 90.1 91.3 90.7 84.640 90.1 90.4 90.0 85.8 90.3 90.1 89.3 85.350 90.7 91.2 90.9 86.9 91.6 92.0 91.5 86.775 92.0 92.5 92.3 88.6 91.9 91.6 91.0 87.2

100 92.3 92.7 92.2 87.4 92.8 92.7 91.9 86.5125 92.6 92.9 92.8 87.9 93.0 93.0 92.6 88.7150 93.1 93.3 92.9 89.7 93.3 93.8 93.4 91.1200 94.1 94.6 93.5 91.5 94.0 94.3 93.6 NA250 93.5 94.4 94.0 91.9 94.6 94.5 94.0 NA300 93.8 94.4 94.3 92.9 94.7 94.8 94.0 NA

Appendix BAverage Efficiencies for Standard Efficiency

Motors at Various Load Points

B-2 Energy Management for Motor-Driven Systems



10 86.3 86.8 85.9 80.0 87.0 88.4 87.7 80.015 88.0 89.0 88.5 82.6 88.2 89.3 88.4 80.720 88.6 89.2 88.9 83.3 89.6 90.8 90.0 83.425 89.5 90.6 90.0 86.6 90.0 90.9 90.3 83.430 89.7 91.0 90.9 87.3 90.6 91.6 91.0 85.640 90.1 90.0 89.0 86.3 90.7 90.5 89.2 84.250 90.4 90.8 90.3 88.1 91.6 91.8 91.1 86.375 91.7 92.4 92.0 87.7 92.2 92.5 91.3 87.1

100 92.2 92.8 92.3 89.2 92.3 92.1 91.4 85.5125 92.8 93.2 92.7 90.7 92.6 92.3 91.3 84.0150 93.3 93.3 93.0 89.2 93.3 93.1 92.2 86.7200 93.4 93.8 93.3 90.7 94.2 94.0 93.1 87.8250 93.9 94.4 94.0 92.6 93.8 94.2 93.5 89.4300 94.0 94.5 94.2 93.4 94.5 94.4 93.3 89.9



10 86.3 87.7 86.4 79.2 86.1 87.2 85.7 77.815 87.9 88.0 87.3 82.8 86.8 87.8 85.9 79.520 89.1 89.5 88.7 85.2 87.8 89.6 88.3 79.725 89.0 89.9 89.1 84.4 88.6 89.6 87.9 79.330 89.2 89.3 88.3 84.8 89.2 90.0 88.7 81.040 90.0 90.4 89.9 86.9 89.0 88.4 86.8 79.750 90.1 90.3 88.7 85.8 89.3 89.2 87.3 82.075 90.7 91.0 90.1 85.7 91.2 90.5 88.7 82.5

100 91.9 92.1 91.5 89.0 91.2 90.4 89.3 83.8125 91.6 91.8 91.1 88.8 91.7 90.8 89.2 82.6150 92.0 92.3 92.0 89.2 92.3 91.7 90.1 85.6200 93.0 93.0 92.1 87.9 92.8 92.2 90.5 84.9250 92.7 93.1 92.4 87.1 92.7 92.5 91.2 90.3300 93.9 94.3 93.8 90.4 93.2 92.8 91.1 89.9

Motor Energy Savings Calculation Form C-1

Employee Name ______________________

Company ____________________________

Date ________________________________

Facility/Location ______________________

Department __________________________

Process ______________________________

Motor Nameplate & Operating Information

Manufacturer ________________________

Motor ID Number______________________

Size (hp) ____________________________

Enclosure Type ______________________

Synchronous Speed (RPM) _____________

Full Load Speed (RPM)_________________

Full Load Amperage ___________________

Full Load Power Factor (%) _____________

Full Load Efficiency (%) ________________

Utility Rates

Energy Rate ($/kWh) __________________

Monthly Demand Charge ($/kW/mo.) _____

Annual Operating Hours (hrs/yr.) ________

Annual Energy Use and Cost

Input Power (kW) _____________________

Annual Energy Use ___________________Input Power x Annual Operating Hours

Annual Energy Cost ___________________Annual Energy Use x Energy Rate

Annual DemandCost __________________Input Power x Monthly Demand Charge x 12

Total Annual Cost ____________________Annual Energy Cost + Annual Demand Cost

Motor Load and Efficiency Determination

Load ___________________________________Input Power(kW) / [ Motor Size(hp) x 0.746 / Efficiency atFull Load ]

Motor Efficiency at Operating Load ________(Interpolate from Appendix B)

Energy Savings and Value

kW saved ___________________________Input Power - [ Load x hp x 0.746 / Efficiency ofReplacement Motor at Load Point ]

kWh saved ___________________________kW saved x Annual Operating Hours

Total Annual Savings

Total Annual Savings $ __________________(kW saved x 12 x Monthly Demand Charge) + (kWh savedx Energy Rate)

Economic Justification

Cost for Replacement Motor ______________(or Incremental Cost for New Motor)

Simple Payback (years) ___________________( Cost for Replacement Motor + Installation Charge - UtilityRebate ) / Total Annual Savings

Appendix CMotor Energy Savings Calculation Form

C-2 Energy Management for Motor-Driven Systems

Power Factor Correction Capacitor Suppliers D-1

ASC Industries Inc./Power Distribution Group8967 Pleasantwood Avenue NWNorth Canton, OH 44720-0523Phone: (216) 499-1210

ASEA Brown boveri Inc./ABB Power T & D Co., Inc.630 Sentry ParkBlue Bell, PA 19422Phone: (215) 834-7400

Aerovox Inc.370 Faunce Corner RoadNorth Dartmouth, MA 02747Phone: (508) 995-8000

Brush Fuses Inc.800 Regency DriveGlendale Heights, IL 60139-2286Phone: (708) 894-2221

Commonwealth SpragueCapacitor, Inc.Brown StreetNorth Adams, MA 01247Phone: (413) 664-4466

Delta Start Inc.3550 Mayflower DrivePO Box 10429Lynchburg, VA 24506-0429Phone: (800) 368-3017

General Electric CompanyIndustry Sales and ServicesDivision1 River RoadSchenectady, NY 12345Phone: (518) 385-2211

Graybar Electric Company, Inc.34 North Meramec AvenuePO Box 7231St. Louis, MO 63172-9910Phone: (314) 727-3900

North American CapacitorCompany7545 Rockville RoadPO Box 1284Indianapolis, IN 46206Phone: (317) 273-0090

Plastic Capacitors, Inc.2623 N. Pulaski RoadChicago, IL 60639Phone: (312) 489-2229

Ronk Electrical Industries, Inc.PO Box 160Nokomis, Il 62075-0160Phone: (217) 563-8333

Appendix DPower Factor Correction Capacitor Suppliers

D-2 Energy Management for Motor-Driven Systems

FOR ADDITIONAL INFORMATION, PLEASE CONTACT:

The OIT Information ClearinghousePhone: (800) 862-2086Fax: (360) 586-8303

Please send any comments,questions, or suggestions [email protected]

Visit our home page atwww.oit.doe.gov.

Office of Industrial TechnologiesEnergy Efficiencyand Renewable EnergyU.S. Department of EnergyWashington, DC 20585

DOE/MC-10021Reprinted February 2000

Cover Art 11/7/03 9:56 AM Page 1

Documents

Energy Management for Motor-Driven Systemsiv Energy Management for Motor-Driven Systems Throughout this guidebook we identify sources of additional informa-tion, such as MotorMaster+