Quantitative Thermography for Electric Motor Efficiency Diagnosis Matt Narrol and Warren Stiver School of Engineering University of Guelph Guelph CANADA N1G 2W1 wstiver@uoguelph.ca Abstract Globalclimatechangeisoneofthemost importantchallengesandthreatstoeconomic,social andenvironmentalsustainability..Reducingelectrical powerdemandisanimportantandnecessarystepin lesseningglobalclimatechangeandpreservingour energy resources for future generations. The objective of this work is the development and demonstration of a quantitative thermographic system to rapidly and non-invasively determine in-use electrical motor efficiency. The development has included testing of four motors in a controlled laboratory setting. This setting permitsthecompleteandsteadymeasurementof electricalpowerdraw,mechanicalloadappliedin addition to the thermal imaging. It provides a reliable meanstovalidatethequantitativethermographic system.Thethermographictechniqueprovedtobe reliable for all motors at 60% or more of full load. 1.Introduction. Adequateenergysupplyiscentraltothe currentqualityoflifeinindustrializedcountries.Muchofthecurrentenergysupplyisderivedfrom non-renewableresourcesandthereforeatsomepoint in the future these energy sources will diminish or end. Allformsofenergysupplyresultinsome formofnegativeenvironmentalimpacts.Most notably,fossilfuelconsumptionleadstogenerally diminishedairqualityandgreenhousegasemissions thatcontributetoglobalclimatechange.TheKyoto Accordrepresentsanimportantfirststepbutonlya first step in the reduction of greenhouse gas emissions.Nipperestimateswewillneedtocuttheuseoffossil fuels by 60% to allow CO2 levels to stabilize at twice the pre-industrial level [1]. Topreserveourenergyresourcesforfuture generationsandtopreserveourenvironmentitis essentialthateveryeffortismadetouseenergyas efficiently as possible. Electricmotorsareanintegralpartofa modern society.Approximately 75% of the industrial electricityconsumptiongoestoelectricalmotors[2].Theypowerroboticassemblylines,mixers,pumps, fans,machineshops,andahostofotherdevices.Theyarelocatedinplacesthatusuallyarenot consideredtobemotors,buttheyareinsideair conditioners,compressors,copiersandeven computers.Pumps,using31%ofindustrial electricity,followedbycompressors(18%)andfans (16%)arethelargestusersofelectricityinindustry [2]. Anelectricmotorsenvironmentalimpact derivesfromthesummationofimpactsoverthefive stagesofitslifecycle:pre-manufacturing, manufacturing,transportation,use,anddisposal[3].Over 99.4% of the environmental impact from a motor is attributed to the electricity the motor uses during its operationallifetime[4].Therefore,toreducethe environmentalimpactofamotordrivensystemone mustincreasetheoperatingefficiencyofthesystem, whichdirectlyreducestheelectricalconsumptionof themotordrivensystem.Sevenwayshavebeen identifiedforincreasingtheefficiencyofamotor drivensystem:motorsizing,motorefficiency,repair practices,adjustablespeeddrive,electricalsystem tune up,mechanicaldesign, andmaintenance. Table 1 provides an estimate of the potential savings by each oftheseways.Atotalreductionofbetween20and 50% is possible. Thesavingsfrommotorsize,motor efficiency,adjustablespeeddrivesandimproved mechanical designs are most easily achieved when the motor driven system is installed or overhauled.These make up a possible 35.4% of the potential savings and can be thought of as for new systems.Other savings, from improved repair practices, electrical tune ups and better maintenance are a continual process, and add up to a possible 16.8% of savings.These savings can be achievedbymonitoringasystemandactingwhena diagnostic system indicates it would be beneficial.An improveddiagnosticsystemwouldallowustoknow whenaneworoldsystemneedsworkandwhenan old system should be replaced or at least how much it is costing in wasted energy. Inthisresearchanddevelopmentprogram, quantitativethermographyhasbeenchosenasa potentialdiagnosticsystem.Quantitative thermographyhastheadvantagesofdirectly measuringtheproductofwasteheatthatishot surfaces,plusitisnon-invasiveandinfraredcameras arebecomingincreasinglycommontoolsatindustrial operationsaspartofpreventativemaintenance programs.The development challenge is to transform thethermalimagesprovidingsurfacetemperatures intowasteheatflowrateswhichisthensufficientto determineefficiency.Thisdevelopmentisbeing conductedintwophases.Thefirstphaseisina controlledlaboratorysettinginwhichtheelectrical motorscanbemonitoredtovalidatethediagnostic.Thesecondphaseisinanuncontrolledindustrial facility.This paper will report on the progress of this first phase. 2. Methodology. Humber Colleges electromechanical lab was usedasthecontrolledsetting.Thelabconsistsofa seriesofsmallelectricmotorsallwithelectrical monitoringequipmentandwithamechanical dynamometer.ThemotorsusedarecomponentsofaLabVolt Computer-assisted 0.2 kW Electromechanical TrainingSystem(#8006).Table2providesthe specifications of the 4 induction motors used.The lab permitsthemotorstoberunatconstantandknown torqueandunderconstantandknownelectrical conditions. AFLIRThermaCAME4thermographic camerawasusedtocapturestillpicturesinthe infrared(IR)region.Thiscamerahasafocalplane arrayinanuncooledmicrobolometercapableof 160x120resolution.Itstemperaturerangeis-20to 250Cwithathermalsensitivityof0.12C[7].Overall,itisacompetitivelypricedcamerathatis commonly used for preventive maintenance. Fourmotorswererunatconstantloaduntil theyreachedthermalsteadystatewiththe surroundings.Steadystatewasjudgedbasedonthe stability of the thermal images.Generally 30 minutes wererequiredtoreachsteadystatefromacoldstart Table 1. Opportunities for increased efficiency within the US [5, 6] Savings MeasureConservative Estimate ofPotential Savings (TWh/yr) Percent of Total Power Used by Motors# Motor Size8.0.7 Motor Efficiency34.3.1 Improved Repair Practices15.1.4 Adjustable Speed Drives75 3006.8 - 27. Electrical Tune-Up14 - 721.3 - 6.5Improved Mechanical Design30 - 502.7 - 4.5Better Maintenance34 - 983.1- 8.9 Total210. - 580.19. - 52. # Based on an estimate of 1100 TWh/yr of total electrical consumption of motors. Table 2: Motor Specifications AC Induction Motorhp 4Pole Synchronous Speed1800rpm Power Supply 3Phase 208V 60Hz Face Area0.0137m2 Housing Area0.0817m2 Coil Area0.0318m2 Pulley Area0.0138m2 Support Cross Sectional Area0.006m2 Conduction Length0.020m Thermal Conductivity79.4W/mK and about 20 minutes from a change in load. A series of thermal images were captured for eachcondition.Theseimagesincludedfrontandtop thermograms.Thelabshousingpreventedimages from all other angles. Eachmotorwasrunforaseriesofdifferent torquestoallowthecreationoftorquevs.efficiency curves for the four motors. Dataanalysisconsistedoftwoparts.The first is the determination of the efficiency based on the electricalandmechanicalmeasurements.Thisis consideredthetrueefficiencyofthemotoratthe specifiedconditions.Equation1providesthe definition of this electrical efficiency. Equation 1 ) 100 () cos( 330) 100 (VINPPelectricalmechanicale= = Thesecondpartofthedataanalysisisthe determinationoftheefficiencybasedontheIR images.Thekeycomponentofthisanalysisisthe determination of the total thermal loss from the motor.This thermal loss is the result of three dominant modes forwasteheattoescapeamotor:conduction, convectionandradiation[8]asdepictedinFigure1.The total thermal loss is the summation of each of the threemodes(Equation2).Thistotalthermallossis thenusedtodeterminethemotorsefficiencyusing Equation3.InthelaboratorysettingthisIRbased efficiency has relied on the measured mechanical load. Equation 2 Equation 3 Determiningeachofthelosstermsreliedon surfacetemperaturesfromtheimagesandclassical heattransferequations.Figures2and3identifythe key temperatures that were obtained from each image.Thetemperaturesarethemotorhousing,themotor face,themotorcoils,thepulleyandthesupporthot andcoldends.TheFLIRcamerassoftwarepermits acquisitionofanaveragetemperatureoveranareaas well as point values. The conduction loss was determined from the temperatures at either end of the support legs and from thephysicalpropertiesofthemotoraccordingto Equation 4. Equation 4 dT T APc h cconduction) ( = The convective loss was determined based on the temperatures of the motor housing, motor face and coils,thephysicalareasofallofthesurfaces accordingtoEquation5.Equation5isasimple convectivemodelwhichiswellsuitedforthe temperaturerangesfoundwithrunningmotorsandis typically used with motors [8]. Equation 5 25 . 1) ( 3s m convectionT T A P = Theradiativelosswasdeterminedbasedon thesamesurfacetemperaturesandtheemissivityof the surfaces according to Equation 6.The emissivities wereobtainedfromFLIRsreferencetableforblack plastic paint and checked against a reference standard. Equation 6 ) (4 4s m radiationT T A P = Theendresultisacalculatedthermalloss termthatreliesonthethermalimagesaloneanda calculated efficiency that relies on the mechanical load on the motor as measured by the dynamometer. Fromthecalculatedefficiencies,the operatingcostofthemotorscanbecalculated.Additionally,thecostdifferentialofoperatingthe givenmotorandareplacementmotorcanbe determined using Equation 7 [2]. Equation 7 =B AEff EffkWh Hr ML HP S100 100* $ * 746 . 0 * * * radiative convective conductive loss thermalP P P P + + =) 100 (_loss thermal mechanicalmechanicalIRP PP+= Theannualsavingscanthenbeusedinanetpresent valuecalculationalongwiththemotorreplacement cost to find the net present value.This will allow it to bedeterminedwhetheritmakeseconomicsenseto replacethemotor.Theefficiencyofthereplacement motor,thecostofthereplacementmotorandthe requiredrateofreturninterestrateareallcritical parametersinthereplaceornotdecision.Ifthenet presentvalueisgreaterthan0thenitmakespurely economicsensetoreplacethemotor.These calculations were performed using Equation 8 [9]. Equation 8 ( )Ci iiS NPVnn+ +=) 1 (1 1 PulleyFaceCoilSupport18.860.9 C204060FLIR Systems Object Parameter ValueEmissivity 0.95Atmospheric Temperature 20.0 CAtmospheric Transmission 0.99Label ValueSupport: Max 40.9 CSupport: Min 39.6 CPulley: Average 33.8 CFace: Average 46.0 CCoil: Average 60.1 C Figure 2. Front view of motor thermograph Conduction Mechanical Power ConvectionRadiation Electrical Power dT T APc h ccond) (.= 25 . 1.) ( 3s m convT T A P = ) (4 4. s m radT T A P = 30 N Pm =Motor Figure 1.Energy transfer modes Housing18.856.0 C2040FLIR Systems Object Parameter ValueEmissivity 0.95Atmospheric Temperature 20.0 CAtmospheric Transmission 0.99Label ValueHousing: Average 48.9 C Figure 3. Top view of motor thermograph 3.Results and Discussion. Thefourmotorsweretestedunderatotalof 28 conditions (Table 3).Full load is 1.3 Nm for these motors.Each thermal calculation is an average from 2 to 4 steady state images. For a standard motor the operating efficiency increasesasloadsincreaseuntilacriticalthresholdis passed, usually close to or greater than full load.This trendwasobservedforboththeactualefficiencyas wellastheefficiencydeterminedbythe thermographicmethod.Theefficienciesareall relativelylowwhichisnotuncommonforsmall, laboratory scale electric motors. There is a good agreement between the actual efficiency and that calculated based on the IR images.Sixof28timestheefficiencycalculatedfromthe electricalmeanswashigher.Additionallywhenthe electricalresultswerehighertheywereonlyslightly higher,anaverageof2.3percentagepointswitha maximumdifferenceof4.7percentagepoints.When theefficiencywashigherforthethermographic methodtheaveragedifferencewas7.7percentage pointswithamaximumoverestimateofefficiencyof 25.6 percentage points. Figure4showsthethermalbasedefficiency versustheelectricalbasedefficiencyfortheaveraged steady state thermographs.It is evident that the cluster ofresultsallshowgoodagreementbetweenthetwo measures of efficiency.The agreement deteriorates at lowerefficienciesandattheselowerefficienciesthe IR image efficiency is biased high. Figure 5 presents the data as a function of the percentage of full load.The ordinate is the percentage errorassociatedwiththethermographicefficiency measurement.TheIRtechniqueisclearlysuccessful for all cases with a motor operating at more than 60% full load.At these loads, the maximum overestimation was7.2percentandtheaveragedifferencewasonly 5.1percent.Overall,theerrorrangeisfrom-171%underestimatedto7.2%overestimated.Also,allthe caseswithanerrorofworsethan-30%werefor motors with loads of 40% or less.Theincreasederrorforthelowloadcase shouldbeexpected,inthethermalcalculationsthe mechanicalpowerisrelativelysmall,15%,compared tothethermallylostpower.Whentakingratiosof numbers as such, it tends to magnify any slight error. Table 3. Summary of Motor Efficiency Results Efficiency (%) Motor Applied Load(% of full)Actual IR Calculated 1614.123.8 6158.565.0 7060.867.5 7463.565.2 7864.465.2 10666.465.0 13463.859.6 21930.842.0 7860.262.6 7959.661.7 8360.263.6 8860.960.1 10961.860.0 11758.860.5 34046.060.5 4749.860.4 5550.564.2 6253.559.7 6555.360.7 6957.067.4 8758.062.1 4915.040.6 2836.955.0 8764.171.0 9267.869.0 9769.068.3 10163.471.3 12765.260.5 Figure 4. Efficiency Calculation Comparison Figure 5.Error in IR based technique vs. Load Forthehigherloadedcasesthemechanical powerisaround60%ofthepower,andcomparing numbers that are more similar any slight inaccuracy is not magnified. Figure6illustratesthedistributionofenergy flowforoneofthefourmotors.Theseresultsare representativeofallfourmotors.Forhigherload conditions,electricityconversiontomechanical energyis60to70%efficient.Theremainingenergyisconvertedintoheat.Around7%oftheenergyis expelledfromthemotorbyradiation,7%by convection and 18% by conduction. Forhigherloadconditions,approximately 15%oftheheatlossisthrougheachofradiationand naturalconvection,andtheremaining70%islost through Figure 6. Electrical Energy Distribution (Motor #1) conduction.In an industrial setting this distribution of heat loss is not expected to prevail.The metal support forthelaboratorymotorsenhancedconduction considerably.Industrialmotorswillrunhotterand thustheradiativetermwillbemoresignificantand industrialmotorsareoftencooledthroughforced convection which increases the convective term.Theultimateassessmentofthisdiagnostic techniqueisnottheaccuracyoftheefficiencybut moreimportantlyonwhetherthedecisionsmade based on the diagnostic are correct.The key decision is whether to replace a given operating motor.Table 4 presentstheresultsoftheNetPresentValue(NPV) calculationsasonebasisformakingsuchadecision.Itisrecognizedthattherearemanyothereconomic modelsthatcouldbeused.NPVisusedheresimply forillustrationpurposes.Itwasassumedthatthe replacementmotorwouldoperateatanefficiencyof 72%, the replacement cost was $130, the required rate ofreturninterestwas15%,andtheprojecttermwas 10 years.These calculations neglect installation costs and possible tax complexities. The decision of whether to replace the motor ornotisbasedonwhethertheNPVispositiveor negative.For14outof21conditionstheIRimage technique makes the same recommendation as the true efficiencydata.Allofthedisagreementscorrespond totheIRimagetechniquerecommendingnot replacingthemotor,thatismissinganopportunity.Allofthesemissedopportunitieswerewithmotors running underloaded. Anon-invasiveandquicktechniqueto identify two-thirds of the inefficient electric motors in industrywouldbeaconsiderablebenefittoindustry and society. 0.0000.2000.4000.6000.8000.0 0.2 0.4 0.6 0.8Efficiency Electrical Based CalculationEfficiency Thermal Based Calculation0.0020.0040.0060.0080.00100.00120.00% Load% of Electrical Energy% Unaccounted% Mechanical% Conduction% Radiation% Convection9 28 879297100127-100.0-80.0-60.0-40.0-20.00.020.00 50 100 150% of Full Load Torque % Difference(e-t)/e4.Conclusions. Thequantitativethermographicmethodhas provenaccurateforlaboratorymotorsthatare loaded in excess of 60% of full load Thethermographicmethodoffersanoninvasive motor efficiency test Thismethodshouldeasilyrecognizemotorthat arerunningsubstantiallybelowtheexpected efficiency Financialmodelingillustratesthepotentialto identifytwo-thirdsoftheinefficientmotorsin operation

5.Nomenclature. P = Power (W) A = Surface area of the motor (m2) Tm = Temperature of the motor (K) Ts = Temperature of the surroundings (K) Th = Hot Temperature of the support (C) Tc = Cold Temperature of the support (C) = Emissivity = Boltzman constant= Thermal Conductivity (W/mK) Ac = Contact Area (m2) d = Conduction distance (m) N = Rotations per minute (RPM) = Torque (Nm) e = Electrical Efficiency (%)t = Efficiency (%) based on IR images = Phase angle S = Savings / year HP = Motor Horse Power ML = Motor LoadHr = Operating hours per year $kWh = Cost per kWh EffA = Motor Efficiency of Motor A EffB = Motor Efficiency of Motor B NPV= Net Present Value i= required interest rate n=term of project 6.Acknowledgements Financialsupportforthisworkhasbeen providedbytheNSERCChairsinEnvironmental DesignEngineeringprogramandbyMcNeil Consumer Healthcare.A scholarship for MN has been providedbyMaterialsandManufacturingOntario (an Ontario Centre of Excellence). WewouldliketothankDr.T.Sharmafor providingaccesstoHumberCollegeselectrical machines laboratory. 7.References. [1]Nipper, Simon, Energy Is Now Part of the Big Picture, Facilities Management, November, 2000 pp. 14-15. [2] Bonnette, Austin H., Understanding the Changing Requierments and Opportunities for Improvement of Operating Efficiency of AC Motors, IEEE Transactions on Industry Applications, 1993, pp. 600-610. [3]Graedel, Thomas, E., Streamlined Life-Cycle Assessment, Prentice Hall, New Jersey, 1998. [4]Rennie, Ian, Improving Motor Efficiency for a Better Environment, ABB Review, 2000, pp. 20-27. [5] Bonnette, Austin H., An Overview of How AC Induction Motor Performance Has Been Affected Table 4. Summary of Net Present Values for Motor ReplacementNPV($) Motor Applied Load(% of full)ActualIR Calculated 161138-37 70112-63 7456-21 7843-15 1063325 134173234 27815834 7917752 8317522 88164109 109195166 117339167 36227650 6524341 69213-63 8726061 48770-113 92-22-75 97-52-58 101118-116 127102185 Assumptions: EffA= 72%, C=$130, n=10 yr, i=15% by the October 24, 1997 Implementation of the Energy Policy Act of 1992, IEEE Transactions on Industry Applications, 2000, pp. 242-256. [6]Moreira, Julio C., Simple Efficiency Maximizer for an Adjustable Frequency Induction Motor Drive, IEEE Transactions on Industry Applications, 1991, pp. 940-946. [7] FLIR, ThermaCAM E4 Operators Manual, FLIR Systems, Danderyd, Sweden, 2004. [8] Wildi, Theodore, Electrical Machines, Drives, and Power Systems,Prentice Hall, NJ, 2002. [9]Riggs, James L., Rentz, William F., Kahl, Alfred L., and West, Thomas M., Engineering Economics, McGraw-Hill Ryerson Limited, Toronto, 1986.