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1274 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 50, NO. 2, MARCH/APRIL 2014

Technical and Economical Considerations on SuperHigh-Efficiency Three-Phase Motors

Anbal T. De Almeida, Senior Member, IEEE, Fernando J. T. E. Ferreira, Senior Member, IEEE, andAndr Quintino Duarte

AbstractPremium efficiency motors are now mandatory inNorth America, but new higher efficiency classes are being intro-duced. Motors of IE4 Super-Premium Efficiency Class are alreadyavailable in the market, and a new IE5 Ultra-Premium EfficiencyClass is being considered. Within the IE4 Super-Premium Class,line-start permanent-magnet motors (LSPMs) are a recent en-trance in the industrial motor market. Its steady-state perfor-mance is outstanding, but as in all technologies, there are someassociated issues, both for retrofitting or new applications. TheLSPM efficiency can be measured according to the inputoutput(or direct) method specified in the IEEE 112 or IEC 60034-2-1standards, but if the losses are to be segregated, for example, toallow proper temperature correction, it is important to evaluate ifthe specified test methods can be applied to this sort of machine.Due to the significant promotion and penetration of variable-speeddrives (VSDs) in industrial motor driven systems, the motortolerance and operation limits to such devices are addressed inthis paper. The proposed IEC 60034-2-3 Standard specifies testmethods for determining harmonic losses of VSD-fed motors,supplementing the methods intended for operation on sinusoidalsupply. In this paper, the referred issues will be addressed indetail, and experimental results on the application of the IEC60034-2-1 and IEC 60034-2-3 standards to IE2, IE3, and IE4class motors are presented and discussed, with the focus on theLSPM Super-Premium technology. A comparative technical andeconomical analysis of commercial IE2, IE3, and IE4 class motorsis presented, including an in-field example of replacement of asquirrel-cage induction motor by an LSPM.

Index TermsEfficiency, electric motor standards, IEC60034-30/-2-1/-2-3 standards, line-start permanent magnet (PM)synchronous motors, losses, Super-Premium Class.

I. INTRODUCTION

E LECTRIC motors in industrial applications consumeabout 40% of all the generated electrical energy world-wide. In the European Union (EU), electric motor systems are,by far, the most important type of load in industry, using about70% of the consumed electricity. In the tertiary sector (non-

Manuscript received January 31, 2012; accepted April 15, 2013. Date ofpublication July 10, 2013; date of current version March 17, 2014. Paper 2012-CSC-022, presented at the 2012 IEEE/IAS Industrial and Commercial PowerSystems Technical Conference, Louisville, KY, May 2024, and approved forpublication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by theCodes and Standards Committee of the IEEE Industry Applications Society.

A. T. De Almeida and A. Q. Duarte are with the Institute of Systemsand Robotics, University of Coimbra (ISR-UC), 3004-531 Coimbra, Portugal(e-mail: [email protected]; [email protected]).

F. J. T. E. Ferreira is with the Department of Electrical Engineering, Poly-technic Institute of Coimbra (ISEC-IPC), 3030-199 Coimbra, Portugal, and alsowith the Institute of Systems and Robotics, University of Coimbra (ISR-UC),3004-531 Coimbra, Portugal (e-mail: [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TIA.2013.2272548

residential buildings), although not so relevant, electric motorsystems use about one-third of the consumed electricity. It istheir wide use that makes electric motors particularly attractivefor the application of efficiency improvements. In spite of thewide variety of electric motors available in the market, three-phase squirrel-cage induction motors (SCIMs) are dominant,representing, by far, the largest market share [1][4].

Higher efficiency electric motors can lead to significantreductions in the energy consumption and also reduce theenvironmental impact [1][4]. An important reason for theirwider market acceptance is the harmonized standards, dealingwith motor performance testing, efficiency classification, anddisplay of ratings [5]. Nowadays, as a result of a significanteffort in the last decade to advance the global harmonizationof motor standards, there is a set of active IEC1 InternationalStandards for addressing the performance of industrial electri-cal motors, as it can be seen in Table I [6].

Currently, both IEC 60034-2-1 and IEC 60034-30 standards[7], [8], major milestones in harmonizing motor efficiencytesting, are being updated to address technology developmentsand new motor types. The IEC 60034-2-3 standard [9] is an ad-vanced technical specification undergoing some improvements.

A. IEC 60034-30 Standard

The IEC 60034-30 International Standard has been intro-duced in November 2008 in order to promote a competitiveelectric motor market transformation, by means of globally har-monizing motor energy-efficiency classes. It deals with electricmotors that are rated for sinusoidal power supply. In the firstedition of this standard [8], three normative efficiency classeswere defined, namely, Standard Efficiency (IE1),2 High Effi-ciency (IE2) equivalent to EPAct, and Premium Efficiency (IE3)equivalent to NEMA Premium. In the first edition of the IEC60034-31 Standard [12], published in 2010, a Super-PremiumEfficiency (IE4) Class was defined, intended to be informative,since no sufficient market and technological information wereavailable to allow IE4 standardization and more experiencewith such products was required [4], [8].

The second edition of the IEC 60034-30 Standard is nowbeing prepared, and the IE4 classification will be included init [5], [11]. In Fig. 1, the nominal efficiency limits proposed in

1IECInternational Electrotechnical Committee is a global institutionwhich defines electrical standards for all countries.

2The designation of the energy-efficiency class consists of the letters IE(short for International Energy Efficiency Class), directly followed by anumeral representing the classification.

0093-9994 2013 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

DE ALMEIDA et al.: TECHNICAL AND ECONOMICAL CONSIDERATIONS ON SUPER HIGH-EFFICIENCY MOTORS 1275

TABLE IMAIN IEC MOTOR STEADY-STATE PERFORMANCE STANDARDS [6]

Fig. 1. Nominal efficiency class limits proposed in the second edition of IEC60034-30, for four-pole motors (0.12800-kW power range).

the second edition of the IEC 60034-30 for four-pole motors areshown, for 50 and 60 Hz.

Moreover, a new Ultra-Premium Efficiency (IE5) Class hasbeen introduced, which, although not yet defined in detail, is en-visaged for potential products. The levels of the IE5 EfficiencyClass are envisaged to be incorporated into the next edition ofthe IEC 60034-30 standard. The goal is to reduce the lossesof IE5 by some 20% relative to IE4. In Fig. 1, the IE5 limitsassuming 20% loss reduction in the IE4 limits are also drawn.Motor technologies for IE5 are currently not yet well developedand not commercially available.

The second edition of the IEC 60034-30 Standard expandsthe covered product range significantly. The output-powerrange has been expanded, starting at 0.12 kW and ending at800 kW (in the first edition, only the 0.75375-kW power rangewas covered), and two-, four-, six-, and eight-pole induction andpermanent magnet (PM) motors are covered. In fact, as long asthey are designed for sinusoidal voltage, all technical construc-tions of electric motors are covered, and not just three-phaseSCIMs, as in the first edition. The standard is now applicableto both fixed-speed and variable-speed (frequency convertersupplied) motors, but the energy-efficiency classification forboth, as given in it, is related to the losses at the sinusoidalpower supply. Fixed-speed motors covered by this standard maybe used in variable-speed applications (see IEC/TS 60034-25),but in these cases, the actual efficiency of the motor is lowerthan the rated/marked efficiency due to increased losses associ-ated with the harmonic content of the voltages produced by thevariable-speed drive (VSD) (see IEC 60034-2-3 [9]).

The new edition of this standard also includes the following.1) Motors with cooling methods other than IC0Ax, IC1Ax,

IC2Ax, IC3Ax, or IC4Ax (see IEC 60034-6). However,they may not be able to achieve the higher efficiencyclasses.

2) Motors built for a restricted space (high-output design,i.e., frame sizes smaller than usual in national standards)are covered by this standard, but as a result of the smallframe size, they may not be able to achieve the higherefficiency classes.

3) Motors specifically built for operation in explosive en-vironments according to IEC 60079-0 and IEC 61241-1.However, as a result of safety requirements and possibledesign constraints of explosion-proof motors (such asincreased air gap, reduced starting current, and enhancedsealing), which have a negative impact on efficiency,some may not be able to achieve higher efficiency classes.

4) Geared and brake motors, which can incorporate specialshafts and flanges.

Some fixed-speed motors have rated efficiencies below theIE1 limits, and no marking of these motors shall be required(they are commonly designated as IE0 Class).

The rated efficiency and the IE-code shall be durably markedon the motor rating plate (for example, IE2-84.0%).

B. MEPS

The best means to move performance levels of mass-produced pieces of equipment has proven to be minimumenergy-efficiency performance standards (MEPS) [3]. With thenow globally harmonized efficiency classification and testingstandards, it has become easier for legislators to introducemandatory requirements into national law. Currently, over 70%of global electricity use is in countries with electric motorMEPS. From the 13 countries with MEPS, there are three keyregionsboth in terms of motor manufacturing and motor usein industryto influence global market transformation, namely,USA, European Union (EU-27), and China. Their motors use56% of the global motor electricity. In Fig. 2, MEPS evolution


Fig. 2. MEPS evolution in USA, EU-27, and China.

TABLE IIMOTOR TECHNOLOGIES AND THEIR ENERGY-EFFICIENCY POTENTIAL

in these countries is shown, evidencing the late change of policyin Europe, from voluntary to mandatory.

Presently, the leading group of countries with MEPS atIE3/NEMA Premium level (USA, Canada, and Mexico) rep-resents 25% of the global electricity consumption [5].

Table II gives information on the energy-efficiency potentialof various commonly used motor technologies (both line-startand electronic controls).

Not all motor technologies are able to reach all efficiencyclasses, nor can motors for all efficiency classes or ratedpowers be produced or operated in an economically feasibleway. Therefore, when assigning MEPS, regulators are asked toconsider the constraints summarized in Table II.

Motors designed to meet the special requirements of thedriven machine and/or special characteristics of the power net-work supply, beyond the requirements of the IEC 60034 seriesof standards, such as motors for heavy starting duty, special

Fig. 3. Rated efficiency levels for commercial 50-Hz four-pole LSPMs from0.55 to 7.5 kW and IE3-, IE4-, and IE5-Class limits defined in the draft of thesecond edition of IEC 60034-30 Standard [11], [13].

torque stiffness and/or breakdown torque characteristics, largenumber of start/stop cycles, very low rotor inertia, limitedstarting current, and increased tolerances of voltage and/orfrequency, may not be able to achieve higher efficiency classes.

Regarding line-start PM motors (LSPMs), although in [11]they are identified with Difficult for IE4 the Class and Nofor the IE5 Class, if the actual commercially available LSPMsare taken into account, it can be said that they reach IE4 levels(see Fig. 3).

C. IEC 60034-2-3 Standard

The proposed IEC 60034-2-3 Standard [9] specifies testmethods for determining the losses and efficiency of VSD-fed motors, supplementing the methods intended for operationon sinusoidal supply. These losses can be used to compareand rank motors of different designs regarding their efficiencywhen controlled/fed by VSDs integrating two-level voltage-source inverters (VSIs) with pulsewidth modulation (PWM).Such VSDs have, by far, the largest market share (> 90%) in thelow-voltage industrial drive market. In general, when fed froma VSD, the motor losses are higher than during operation on asinusoidal system. The additional losses depend, in part, on theharmonic spectrum of the PWM voltage waveform producedby the VSD. The voltage harmonic magnitude is influenced bycircuitry and control method of the VSD. This standard is aimedto evaluate the additional harmonic motor losses resulting fromnonsinusoidal power supply and, consequently, the efficiencyof the VSD-fed motor.

The fundamental losses in electric motors can be segregatedinto five different components: 1) iron/core; 2) friction andwindage losses (both varying with motor speed); 3) rotorwinding/cage (I2R) losses; 4) stator winding (I2R) losses; and5) additional/stray load losses. The first two loss componentsare approximately load independent. The last three loss com-ponents are load dependent. Harmonic losses are produced inthe motor by the nonsinusoidal voltage and current waveformsgenerated by the VSD and are in addition to the previouslyreferred fundamental losses.


It is not the purpose of this standard to define test proceduresfor power drive systems or for VSDs alone. The methodspresented in the standard are intended for VSD-fed SCIMs.However, the application to other ac or dc motors supplied byVSDs is not excluded.

In VSDs, there are several settings/parameters that can bechanged by the user and influence the motor losses, such asswitching frequency, amplitude modulation index, U/f relation(in the case of scalar control), magnetizing current, energysaving options, etc.

In the IEC 60034-2-3 Standard, for all test methods, thereference VSD should be parameterized according to the speci-fication of the standard, or if an individual combination of VSDand motor is to be tested, the VSD should be parameterized forthe specific application. The reference VSD should be seen as avoltage source independent of the load current, set at the ratedvoltage and fundamental frequency of the motor under test.

The reference conditions are as follows [9]: 1) VSD witha two-level VSI; 2) no motor current feedback control acti-vated; 3) no additional components other than sensors shallbe installed between the reference VSD and the motor;4) fundamental VSD output voltage equal to motor rated volt-age (however, the input voltage of the reference VSD shall beset to a value that allows rated motor voltage to be appliedand to avoid overmodulation); 5) fundamental motor frequencyequal to rated motor frequency; 6) switching frequency of 4 kHzfor rated output powers up to 90 kW and 2 kHz for outputpowers above 90 kW (in this scope, the switching frequencyis the real number of pulses per second as can be determinedby a frequency counter at the output PWM); 7) the PWM pat-tern shall be symmetric three-phase modulation with linearityextension or its equivalent in space vector PWM (SVPWM)technique.

The standard fixes most of such variables, but even so, thereare some particular aspects that are difficult to fulfill, such asthe avoidance of overmodulation operation. For example, if atypical VSD, integrating a three-phase diode rectifier at theinput and a two-level VSI with PWM at the output, is fed at400 V and is set to produce 400-V fundamental line-to-linevoltage at the output (fundamental voltage amplitude at theVSD output equal to the motor rated voltage), it will operateslightly in the nonlinear or overmodulated region, even if thethird harmonic injection or SVPWM techniques are used toextend the linear region. Therefore, in order to guarantee theoperation in the linear region, in most VSDs, it is necessary toincrease the voltage at the input to a value slightly higher thanthat to be produced at the output (e.g., if a VSD with an inputdiode rectifier is used, an autotransformer can be used to adjustthe input voltage), yet if the VSD input voltage is increased, thePWM pulse peak values also increase, leading to higher high-order harmonics. This fact should be taken into account.

The PWM pattern and, consequently, the additional har-monic motor losses also change considerably with the outputfundamental frequency (or speed of the motor). Therefore, thisstandard defines procedures for rated fundamental frequencyand rated motor speed. It should be possible to use a similarprocedure at different speeds in order to obtain the respectiveadditional harmonic motor losses.

The nonlinear modulation region avoidance is to exclude/attenuate the low-order harmonic influence, such as the 5th-,7th-, 11th-, and 13th-order harmonics. However, since VSDscan operate large periods of the operating cycle with a funda-mental output voltage and frequency equal or near to that of thegrid (with the possibility of slightly overlapping the overmod-ulation mode), the specification of two operating modes shouldbe includedat rated voltage and frequency with and withoutVSD input voltage adjustment.

Considering the harmonics involved in VSDs feeding acmotors and their contribution to the motor losses, the measuringequipment has to be selected according to the range of relevantfrequencies with sufficient accuracy. The instrumentation formeasuring electrical quantities shall meet the requirements ofIEC 60034-2-1 at 50- or 60-Hz fundamental frequency andshould have a bandwidth from 5 Hz to a frequency of at least tentimes the PWM carrier frequency (triangular wave frequency).For a 4-kHz switching frequency, the bandwidth of the poweranalyzer should be from 5 to 40 000 Hz. The instrumentationfor measuring torque and speed at the motor output should alsomeet the requirements of IEC 60034-2-1.

The sequence of tests is as follows: 1) determination of no-load losses with sinusoidal power supply of rated frequencyand rated voltage according to IEC 60034-2-1; 2) determinationof no-load losses, but with VSD power supply, similar to IEC60034-2-1. The difference between the no-load losses with a si-nusoidal power supply and operation with VSD is the additionalharmonic motor losses. The additional harmonic motor lossesshall be added to the fundamental motor losses as determinedwith a sinusoidal power supply according to IEC 60034-2-1in order to obtain the motor efficiency under frequency VSDoperation. For larger motors, the determination of the additionalharmonic losses caused by VSD operation based on calcula-tions is an alternative procedure. This calculation has to bebased on the real pulse patterns of the VSD and the frequency-dependent equivalent circuit parameters of the electric motor.

It should be referred that only the no-load losses are evalu-ated because it is commonly assumed that, as long as the PWMpattern is constant, the additional harmonic losses are practi-cally independent of motor load. However, the experimentalresults show that these losses can actually depend on load (seeSection II-C). Thus, at least, a test at no load and a test at fullload should be performed.

Moreover, to avoid errors associated with the operating con-ditions (fundamental voltage and ambient temperature for theno-load test and, additionally, motor load if the load test isperformed), the authors suggest that the harmonic losses canbe estimated during the VSD supply test by subtracting thefundamental no-load losses from the total no-load losses. Thismethod has been applied in the experimental tests (the modernpower analyzers allow to segregate the fundamental componentof the measured total active power; see Section II-C), and atno load, the difference between the additional harmonic lossescalculated according to the IEC 60034-2-3 (ensuring very simi-lar fundamental voltage supply and ambient temperature for thesinusoidal and PWM supply tests) and to the proposed methodis very reduced at no load. However, at full load, significantdifferences were obtained, which, in part, can be explained


by the differences in the motor load for both sinusoidal andPWM supply tests. Therefore, the proposed method seems to bevalid, and it has the advantage of avoiding the error associatedto the possible fundamental voltage and ambient temperaturedifferences that can exist when performing different tests.

This standard defines the reference VSD and test methods tocheck its conformity. However, the specifications are confusingor complex to apply using commercial VSDs. For example,to check if the linearity extension is correctly applied, thereference signal shall be measured through a low-pass filterapplied to the output voltage of the VSD in the minus dc link tothe output phase terminal, which is not a simple task to perform.

Maybe a more simple procedure should be used, suitableto be applied in commercial VSDs, based exclusively on theoutput PWM voltage waveform since it is possible to iden-tify overmodulation operation by analyzing the output PWMpulses/waveform, and for a specified output fundamental volt-age level and switching frequency in scalar mode, the inputvoltage of the VSD should be properly adjusted in order toavoid merged PWM pulses in the center of each semicycle.The authors applied this strategy to three 7.5-kW four-polemotors of different efficiency classes, using an autotransformerto increase the VSD (with scalar control) input voltage up toa value leading to a nonovermodulated PWM. The results arepresented in Section II-B.

Moreover, the standard also specifies that the ac mains sourceearthing system shall be a star-grounded TN-earthing system.A protective bonding shall be connected to the VSD and to themotor under test. A shielded cable shall connect the referenceVSD to the motor. The cable length shall be less than 10 m.

For VSDs with voltage ratings above 1 kV, the standard statesthat a reference VSD cannot be specified. Such motors andVSDs can only be tested as a complete power drive systembecause the pulse pattern of frequency VSDs for higher outputpowers is too different between manufactures and very differentbetween no load and rated load.

D. IEC 60034-2-1 Standard

The revision of the testing method IEC 60034-2-1 is under-way (publication planned for 2013/2014) [10] in order to makethe efficiency results more accurate and repeatable [14]. In therevision of the testing standard, the results of the IEC RoundRobin test campaign that was conducted with a total of 194tests on 75 motors in 17 test laboratories situated in 11 countriesare being taken into account [5], [15]. The testing methods willchange from the older concept of low uncertainty that wasnever to be quantified to the more MEPS-oriented philosophyof the preferred method that every laboratory has to use in apredetermined sequence of procedures.

Regarding LSPMs, due to their performance superiority, itis expectable that the respective market share increases in thefuture [17]. Thus, the applicability of the IEC 60034-2-1 to thissort of motors has to be properly analyzed. As far as the authorsknow, it is only possible to apply the inputoutput (or direct)method, without loss segregation [17]. Therefore, the ambienttemperature correction can only be made for the stator winding(I2R) losses [17]. The other losses are not easy to segregate.

Fig. 4. (a) Efficiency and power factor for a commercial 3-kW four-poleLSPM. (b) Loss segregation for a commercial 3-kW four-pole LSPM [17].

For that purpose, tests used to conventional synchronous andinduction motors should be complementarily used. However,some of the tests used in conventional synchronous motors can-not be applied to LSPMs due to the impossibility of regulatingthe excitation (which is fixed by the PMs). An alternative tocontrol the induced electromotive force in LSPMs is varyingspeed, but proper compensation of the frequency has to be donein the calculations. In [17], an attempt to segregate the lossesof a 3-kW four-pole LSPM was made, using the inputoutputmethod. In Fig. 4(a) and (b), the resulting efficiency and losssegregation, as a function of motor load, are presented.

The constant losses are easy to identify/quantify, being equalto the minimum power obtained when varying the appliedvoltage at no load, as shown in Fig. 5(a). The mechanical plusiron losses can then be obtained by subtracting the no-loadstator winding I2R losses. However, the mechanical losses arenot easy to segregate since the method used in SCIMs cannot bedirectly applied, as it can be seen in Fig. 3(b). An attempt hasbeen made to identify the flatter zone of the curve to draw atangent line to intersect the power axis to obtain the mechanicallosses. However, it is obvious that it is not possible to clearlyidentify that flatter zone.

An alternative to quantify the mechanical losses in a SCIM isto disconnect it from supply and mechanically drive it at ratedspeed and measure the shaft torque with a high-precision torquesensorin these conditions, the measured mechanical powercorresponds to the mechanical losses. However, in the case of


Fig. 5. (a) Experimental no-load active power as a function of voltage [17].(b) Experimental no-load active power as a function of voltage squared.

LSPMs, this is not possible because there is a braking torquedue to the PMs.

The additional load losses can be calculated using differentapproaches. In the approach used, it was assumed that theyinclude the reaction iron losses, the rotor losses (at rated speed,mainly due to magnetomotive-force spatial harmonic effect inthe auxiliary cage), and other stray losses. Alternatively, thereaction iron losses can be considered equal to the differencebetween the remaining losses (total losses minus stator I2R andconstant losses) and the additional losses obtained by propor-tionality to the square of the current, taking the nominal point asreference. In Fig. 6, the additional load losses obtained by losssubtraction [as presented in Fig. 4(b)] and by proportionality tothe square of the armature current, taking the nominal point asreference, are presented [17].

On the basis of the arguments and experimental resultspresented in [17], it can be concluded that the simplest and mostaccurate method to determine the full-load efficiency of LSPMsis the direct method at thermal equilibrium with temperaturecorrection of the stator/armature winding losses. These lossescan be obtained by simply correcting the measured winding re-sistance immediately after a load test at a given ambient temper-ature to the 25 C reference ambient temperature. Nevertheless,the impact is expected to be relatively low in the final efficiencyvalue (variation less than 0.15 p.p.) if the ambient temperatureis in the 1535 C range. Therefore, for that temperature range,

Fig. 6. Additional load losses obtained by loss subtraction and by propor-tionality to the square of the armature current, taking the nominal point asreference [17].

it is reasonable to neglect the temperature correction process inthe stator winding losses.

II. TECHNICAL AND ECONOMICAL CONSIDERATIONS ONCOMMERCIAL SUPER-PREMIUM LSPMs

The informative limits in the IEC 60034-31 Standard for theIE4-Class (Super Premium) three-phase motors are a result ofa first approach, taking into account the motor manufacturerlimitations. However, as previously referred, the LSPMs arebeing introduced in the market and can exceed those proposedIE4 Super-Premium limits, respecting the standard frame sizes.The same applies to PM motors controlled by VSDs.

Since only the line-start IE4-Class technology does not re-quire a VSD in the low-power-range market,3 a significantincrease in the LSPM market share in the next decade isexpected.

As demonstrated in [4], with SCIM technology and respect-ing the standard frame sizes, it seems unlikely to achieve IE4Super-Premium limits in the power range under 7.5 kW, asdefined in the first edition of IEC 60034-31. In Fig. 3, theefficiency of 0.557.5-kW commercial LSPMs is shown. It canbe concluded that, for the 0.55-, 1.5-, and 3-kW rated powers,the IE4 limits defined in the second edition of IEC 60034-30 arenot achieved. However, according to the limits defined in thefirst edition of that standard (which is still active), the LSPMsunder consideration are formally of IE4 class, with exceptionfor the 0.55-kW motor, since this rated power is not covered bythis edition.

In the early stages of LSPM development, one of the maininitial drawbacks was the starting torque, particularly in loadscombining high starting torque and high inertia. Presently,commercial LSPMs can have a maximum allowable load inertialimited to 30 times the motor inertia, which is enough formost industrial loads. The commercial four-pole LSPMs in the0.557.5-kW power range have a starting torque 2.2 to 3.8 timeshigher than the nominal torque.

3In the end of 2012, a large motor manufacturer introduced in the marketIE4-Class SCIM models in the 5.5355-kW range for two and four poles andin the 3315 kW for six poles.


TABLE IIIMAIN CHARACTERISTICS OF COMMERCIAL IE2-, IE3-, AND IE4-CLASS

7.5-kW FOUR-POLE MOTORS [17]

It is worth noting that the starting kick of LSPMs is quiteviolent, which can accelerate the mechanical wear of the motorand load bearings and/or gears (if any). This can be particularlycritical in application with frequent start/stop cycles. The useof belts can help in reducing this impact. This is not an issue inVSD-fed LSPMs.

Considering the price of IE2-Class SCIMs as reference, theIE3-Class SCIMs and IE4-Class LSPMs have a price 1.11.3and 2.23.8 times higher, respectively.

A. Comparative Economical Analysis

As an example, for comparison purposes, three 7.5-kW four-pole commercial motors with different efficiency classes fromone of the largest motor manufacturers are now considered,whose main characteristics are presented in Table III. Theprices with a typical 40% discount for the IE2 SCIM, IE3SCIM, and IE4 LSPM models are 328 C, 378 C, and 764 C,respectively. The efficiency gain of the IE4 LSPM with respectto the IE2 and IE3 SCIMs is 4.1 and 1.4 p.p., respectively [18].

Since the speed of LSPMs is higher than that of SCIMs, itis important to take that fact into account in the economicalevaluation of such options. For example, considering a typicalindustrial centrifugal fan, in which the shaft power input isproportional to the cube of the angular speed, the expecteddifference in the speed and in the shaft power input for the threedifferent class motors is presented in Table IV. Since June 16,2011, the IE1-Class motors in 0.75375 kW are out of the EUmarket, but the stock of such motors will be operating for atleast a decade more. Therefore, it makes sense to consider themin the following analysis.

Due to the expected slip decrease, in order to avoid over-loading IE3 or IE4 motors when replacing an IE2 motor, the

latter has to be slightly oversized. In the case of fans and pumps(without static pressure), for a proper IE2 motor replacementby an IE3 motor, the first should have 98% load, and for aproper IE2 replacement by an IE4 motor, the first should have91% load.

Moreover, in pumps and fans, if the installed IE2-Class motoris operating very close to full load, the energy savings can benegative (i.e., instead of a decrease in the consumed energy,there is an increase). In the example given (see Table IV), thereis a 4.9% energy consumption increase when replacing theIE2-Class SCIM by an IE4-Class LSPM, which demonstrateshow the direct replacing can be a wrong option in some cases,particularly if the additional flow (proportional to the speed) isnot actually required by the process.

Considering now that the motors are fed by a VSD, the speedcan be set to exactly the same value. If the VSD efficiency is thesame (for example, 97%), the energy savings will be much moresignificant, and the estimated payback time is 0.5 and 2.8 yearsfor the IE3- and IE4-Class motors under consideration (7.5 kWand four poles), respectively, assuming 5840 h/year of operationand 0.07 C/kWh, as can be seen in Table V. This paybacktime is very attractive (lower than three years). Although theLSPMs have a much longer payback than that for the IE3-Class SCIM when replacing an IE2-Class SCIM, the life-cyclecost will be lower. For example, neglecting the possible statorrewinding and bearing replacement costs, during a 15-year pe-riod, the estimated energy savings value is 1458 C and 2295 Cfor the IE3-Class SCIM and IE4-Class LSPM, which, duringthat period, is equivalent to approximately 29 and 5 times theirextra initial cost (or price difference, with respect to IE2-ClassSCIM), respectively. In that 15-year period, these motors willconsume an amount of energy with a value equivalent to nearly137 and 67 times their price (with 40% discount), respectively.Considering that the IE2 SCIM needs to be rewound/repaired,the rewinding plus bearing replacement price is 175 C (46%of the price of a new IE3), the original motor efficiency ismaintained after repair, and the payback time for the additionalcost associated with the decision of replacing the damaged IE2motor by a new IE3 or IE4 motor, instead of rewinding it, wouldbe 2.1 and 3.8 years, respectively, which is still very attractive,particularly for the IE3 motor. Considering a damaged IE1motor, if the user decides to replace it, instead of repairing it,the payback time for the additional investment in a new IE3 orIE4 motor, would be 1.1 and 2.5 years, respectively, being anattractive option for both cases.

It is important noting that, although LSPMs are design forline-start VSD-less operation, they have the possibility of di-rectly replacing SCIMs fed by low-cost VSDs, which, in somecases, is not possible for conventional permanent magnet syn-chronous motors, since they require special closed-loop controlstrategies in VSD, with rotor position sensing or estimation.This is another potential advantage of LSPMs, even for newapplications, since cheaper VSDs can be used.

B. In-Field Experience With IE4-Class LSPMs

As an example of retrofitting, an IE0-Class Equivalent5.5-kW four-pole SCIM driving a fan in an industrial facility,


TABLE IVESTIMATED SHAFT POWER FOR DIFFERENT LOADS DRIVEN BY 7.5-kW FOUR-POLE MOTORS OF IE1, IE2, IE3, AND IE4 CLASSES WITHOUT VSD [17]

TABLE VESTIMATED ENERGY SAVINGS AND PAYBACK TIME FOR IE3- ANDIE4-CLASS 7.5-kW FOUR-POLE MOTORS, ASSUMING CONSTANT

OUTPUT POWER [17]

was replaced by an IE4-Class LSPM (see Fig. 7). The resultsare presented in Table VI.

Note that the original motor was oversized (load lower than57%), and therefore, a 4-kW LSPM would be enough for thisapplication, but the user decided to maintain the rated power.Moreover, since the new 5.5-kW LSPM has a load lower than60%, it can benefit in terms of efficiency and power factor fromvoltage regulation.

Considering 5840 h/year of operation and 0.07 C/kWh, a250-W power reduction leads to 102.2 C of annual savings. It

Fig. 7. Photos of the replaced and replacing motors: (a) Brand A, 132S, IP55,Cl. F, 5.5 kW, 380420 V, 11.5 A, 1450 r/min, PF = 0.83, Eff. = 83.2%(IE0/EFF3 Class). (b) Brand B, 132S, IP55, Cl. F, 5.5 kW, 380420 V, 9.34 A,1500 r/min, PF = 0.93, Eff. = 92.5% (IE4 Class). (a) IE0-Class SCIM.(b) IE4-Class LSPM.

TABLE VISUMMARY OF THE MOTOR PERFORMANCE FOR THE SCIM AND LSPM

should be noted that, although the rated efficiency of the newLSPM is quite higher than that of the replaced SCIM, the sav-ings are moderate due to the speed increase and, as a result, thepower required by the centrifugal fan increased significantly,leading to the increase of the input active/real power, reducingthe consumption reduction potential associated with the motor


Fig. 8. Motor losses. (Top) No-load total losses. (Center) No-load harmoniclosses calculated according to two different methods (Method 1: HarmonicLosses = Total Losses Fundamental Losses; Method 2: Harmonic Losses =Grid-fed Motor Losses VSD-fed Motor Losses). (Bottom) Harmonic lossesat full load calculated according to Method 1. VSD supply tests, accordingto the IEC 60034-2-3 Standard test conditions (two-level VSI with 4-kHzswitching frequency).

efficiency gain. If the additional air flux, which is proportionalto the fan angular speed, was useful to the process, this shouldbe considered as a benefit from the perspective of useful power.If a VSD is installed, the speed increase issue can be overcomebecause the speed can be adjusted to the original value. Fromanother perspective, without a VSD, if an ON/OFF control isused as a function of a reference temperature dependent on thefan air flux, the extra flux can lead to the reduction of the motoroperating time, reducing the energy consumption.

Fig. 9. Experimental efficiency, power factor, and winding head temperaturefor IE2, IE3, and IE4 motors, as a function of load, at 400 V and 50 Hz.

In short, the installation of the IE4-Class LSPM, even withthe 6% increase of the power required by the fan due to the2% increase in the speed (14721500 r/min), led to a 6.6%decrease in the motor input active power, to a 22% reduction inthe apparent power, and to a 20% increase in the power factor.Those results led to a fair energy saving and, additionally, to areduction in the power cables and transformer load and losses.In applications already equipped with a VSD, the savings canbe much higher since the speed and voltage can be adjusted toany specific value.

C. Laboratory Experimental Results

In this scope, tests were made using three 7.5-kW motorsfrom the same manufacturerone High-Efficiency IE2, onePremium Efficiency IE3, and one Super-Premium EfficiencyIE4. In Fig. 8, the motor total and harmonic losses at no load,with grid and VSD supply, measured according the conditionsspecified in the IEC 60034-2-3 Standard, are shown. The no-load and full-load harmonic losses for VSD supply, calculatedby subtracting the fundamental component value to the totalvalue of the input active power, are also presented.

On the basis of the experimental results, it seems that, on theone hand, the LSPM has less immunity to PWM supply at noload but, on the other hand, it has higher immunity to the PWMsupply at full load. In fact, the harmonic losses at full load aredifferent from that at no loadfor the IE2 and IE3 motors, theyincrease with the load, but for the IE4 motor, they decrease.

Regarding the performance as a function of load, for fixedfrequency, the IE4 Super-Premium LSPM has a quite higherpower factor in whole load range, and the efficiency is higherthan that of the IE3 SCIM motor, from full load down to60% load. Below that value, the LSPM becomes lower. Thestator winding heads of the drive end (hottest points in thewinding) has a much lower temperature rise and lower variationwith the load, as it can be seen in Figs. 9 and 10. The coilhead temperature was measured by contact with a precisiontemperature sensor. The input current is much lower for theLSPM (see Fig. 11).

In variable-speed applications, the torque derating to main-tain the steady-state full-load temperature is, in practice, similar


Fig. 10. Drive-end winding head temperature rise evolution for IE2, IE3, andIE4 motors after starting at full load, at 400 V and 50 Hz.

Fig. 11. Experimental input current as a function of load, for IE2, IE3, andIE4 motors, at 400 V and 50 Hz.

Fig. 12. Experimental load, torque, and efficiency for IE2, IE3, and IE4motors, maintaining constant drive-side winding head temperature equal to thenominal value (at 400 V, 50 Hz, and full load). Scalar control with U1/f1 = 8.Ambient temperature between 25 and 30 C.

for the three tested motors, and the efficiency decrease withthe speed decrease is lower for LSPM, as it can be seenin Fig. 12. In fact, the LSPM efficiency is higher in allspeed ranges below the rated speed, which is an importantadvantage.

Fig. 13. Experimental torque, efficiency, winding head temperature rise, andvoltage fundamental component for IE3 and IE4 SCIMs, maximizing efficiencyin each load point for 50-Hz frequency. Ambient temperature between 21 and25 C. Motor fed by a two-level VSI with a 4-kHz switching frequency PWM.

Fig. 14. (a) Efficiency as a function of load for different voltage levels, for acommercial 3-kW four-pole LSPM [17]. (b) Power factor as a function of loadfor different voltage levels, for a commercial 3-kW four-pole LSPM [17].

In Fig. 13, the experimental results for the IE3 and IE4 mo-tors fed by the same VSD (two-level VSI with 4-kHz switchingfrequency), at 50 Hz, with the fundamental component of thevoltage regulated in order to maximize the motor efficiency, canbe seen. This figure shows that, with proper voltage regulation,as a function of the motor load, the efficiencies of both IE3 and


IE4 motors become very close. This is still valid for differentfundamental frequencies. In VSD-fed motors, this conclusionis in favor of IE3 SCIMs since they are cheaper than IE4LSPMs. However, to guarantee the efficiency maximization, theVSD should incorporate optimum magnetizing flux searchingmethods or pretested U1/f1 relations with more than two pointsproperly adapted to the load mechanical characteristic. Thevoltage reduction to maximize the efficiency for lower loadsin the SCIM is higher than that for the LSPM, demonstratingthat the commonly used U1/f1 relations are not valid for thelatter.

In Fig. 14, the LSPM steady-state performance dependenceon load and voltage can be seen, demonstrating that suchmotors can benefit significantly in terms of efficiency and powerfactor from the voltage regulation or, alternatively, windingconnection change (e.g., delta to star for light loads) whendirectly fed from the grid and having variable load or permanentlight load. For example, in a motor operating at 50% load, thesimple change from delta to star connection (equivalent to avoltage reduction from 400 to 231 V), 2- and 36-p.p. gainscan be obtained in the efficiency and power factor, respectively.Better results can be obtained if continuous voltage regulationis provided as a function of the motor actual load.

As demonstrated before, this aspect is also important formotors fed by VSDs, in which, if low-cost scalar controlis used, it is necessary to define a proper voltagefrequencyrelation/curve that maximizes the motor efficiency.

III. CONCLUSION

Growing environmental concerns and high energy costsmake more and more important to look at life-cycle costs ofnonstandard technologies. PM motors prove to be significantlymore efficient than SCIMs, in the low-power range (15 kW).Therefore, even in applications that were exclusively limited toSCIMs, they can now profit from the advantages of PM motors.Regarding single-speed applications, with direct mains oper-ation, the SCIM still has some cost advantage, although newdevelopments in LSPMs make them a cost-effective alternativeon a life-cycle basis.

Since the energy-savings potential associated with Super-Premium IE4-Class motors is large and the technology toachieve such efficiency levels is already available to be pro-duced in large scale, it makes sense to promote such motors, bymeans of suitable incentives, particularly in the smallmediumpower ranges.

Taking into account that LSPMs are already available inthe market, it can be said that the efficiency limits of Super-Premium IE4 Class were already achieved. The starting torqueof those motors is similar to that of SCIMs.

Although the price of LSPMs is about 2.238 times higherthan that of equivalent IE2-Class SCIMs, when considering thetwo options for a new application operating more than 6000 h/year, the payback time for the additional investment in theLSPMs is expected to be less than three years, which is anattractive solution from an economic point of view.

If permanently oversized or having variable load, as SCIMs,LSPMs can also benefit in terms of efficiency and power

factor from the voltage regulation or, alternatively, windingconnection mode change (e.g., delta to star).

It seems that the simplest and accurate method to determinethe full-load efficiency of LSPMs is the direct inputoutputmethod at thermal equilibrium with ambient temperature cor-rection of the stator/armature winding losses. Regarding theadditional harmonic losses when motors are supplied by VSDs,it was found that, at full load, they are lower in LSPMs (inrespect to those in SCIMs), thus providing additional savings insuch operating conditions. However, at no load, the harmoniclosses seem to be higher in LSPMs.

Finally, it should be mentioned that, in most cases, energy-efficiency optimizations will have to focus on improved overallsystem efficiency, including the individual component effi-ciency, such as motor, VSD, filters, cables, mechanical trans-mission/coupling, and load/application.

REFERENCES[1] Improving the Penetration of Energy-Efficient Motors and Drives, Univ.

Coimbra, Coimbra, Portugal, 2000.[2] A. De Almeida, F. Ferreira, J. Fong, and P. Fonseca, EuP Lot 11 motors,

ecodesign assessment of energy using products- Final report for the Euro-pean Commission, Brussels, Belgium, ISR-Univ. of Coimbra, Coimbra,Portugal, Feb. 2008.

[3] A. De Almeida, F. Ferreira, J. Fong, and B. Conrad, Electric motorecodesign and global market transformation, in Proc. IEEE/IAS I&CPSTech. Conf., Clearwater Beach, FL, USA, May 48, 2008, pp. 19.

[4] A. De Almeida, F. J. T. E. Ferreira, and J. Fong, Standards for efficiencyof electric motors, IEEE Ind. Appl. Mag., vol. 17, no. 1, pp. 1219,Jan./Feb. 2011.

[5] C. Brunner, P. Waide, and M. Jakob, Harmonized standards for motorsand systems-global progress report and outlook, in Proc. 7th EEMODS,Alexandria, VA, USA, 2011, pp. 444456.

[6] International Electrotechnical Commission (IEC) Webstore, Nov. 2011.[Online]. Available: http://webstore.iec.ch/

[7] Ed. 1: Rotating Electrical MachinesPart 2-1: Standard Method forDetermining Losses and Efficiency from Tests (Excluding Machines forTraction Vehicles), IEC Std.60034-2-1, 2007.

[8] Ed. 1: Rotating Electrical MachinesPart 30: Efficiency Classes ofSingle-Speed, Three-Phase, Cage-Induction Motors (IE-Code), IEC Std.60034-30, 2008.

[9] Ed.1, Draft, 2/1626/CDV, Rotating Electrical MachinesPart 2-3: Spe-cific Test Methods for Determining Losses and Efficiency of Converter-FedAC Motors, IEC Std. 60034-2-3, Apr. 2011.

[10] Ed. 2, Committee Draft for Vote, 2/1687/CDV: Rotating ElectricalMachinesPart 2-1: Standard Method for Determining Losses and Ef-ficiency from Tests (Excluding Machines for Traction Vehicles), IEC Std.60034-2-1, Jan. 2013.

[11] Ed. 2, Draft, Nov. 2011, WG31/2CD: Rotating Electrical MachinesPart30: Efficiency Classes of Single-Speed, Three-Phase, Cage-Induction Mo-tors (IE-Code), IEC Std. 600-34-30, Nov. 2011.

[12] Ed. 1: Rotating Electrical MachinesPart 31: Selection of Energy-Efficient Motors Including Variable Speed ApplicationsApplicationGuide, IEC/TS Std. 60034-31, 2010.

[13] WEG motor catalogue, WQuattroSuper Premium Efficiency Motor2011.

[14] A. Baghurst, P. Pierre Angers, and M. Doppelbauer, A standard algorithmfor the calculation of induction motor efficiency based on InternationalStandard IEC 60034-2-1, in Proc. 7th EEMODS, Alexandria, VA, USA,2011, pp. 470488.

[15] A. Mhle, The Round-Robin-Test for the improvement of IEC 60034-2-1,in Proc. 7th EEMODS, Alexandria, VA, USA, 2011, pp. 290300.

[16] M. Patra, Standardization for ASD, in Proc. 7th EEMODS, Alexandria,VA, USA, 2011, pp. 525537.

[17] F. Ferreira and A. De Almeida, Technical and economical consid-erations on line-start PM motors including the applicability of theIEC60034-2-1 standard, in Proc. 7th EEMODS, Alexandria, VA, USA,2011, pp. 275289.

[18] WEGeuro, Commercial Dept., Maia, Portugal, 2011.


Anbal T. De Almeida (SM03) received thePh.D. degree in electrical engineering from ImperialCollege, University of London, London, U.K.

He is currently a Professor with the Departmentof Electrical Engineering and Computers, Univer-sity of Coimbra, Coimbra, Portugal. He is also aConsultant of the European Commission FrameworkProgrammes, UNDP and UNIDO. He is the coauthorof six books on energy efficiency and industrialautomation and more than 200 papers published ininternational journals and conference proceedings

and presented at meetings. He has coordinated six European projects dealingwith energy-efficient technologies. He has also participated as a consultanton several international projects to promote energy efficiency in developingcountries.

Prof. de Almeida was a recipient of the Best Paper Award at the 2001IEEE Industry Applications Society Industrial and Commercial Power SystemsTechnical Conference.

Fernando J. T. E. Ferreira (SM09) received thePh.D. degree in electrical engineering from the Uni-versity of Coimbra, Coimbra, Portugal, in 2009.

He is currently with the Department of Electri-cal Engineering, Polytechnic Institute of Coimbra(ISEC-IPC), Coimbra, Portugal, as a Professor. Since1998, he has also been a Researcher with the Instituteof Systems and Robotics, University of Coimbra(ISR-UC), Coimbra, and has participated in sev-eral European projects dealing with electric motortechnologies.

Dr. Ferreira was a recipient of the Best Paper Award at the 2001 IEEE/Industry Applications Society Industrial and Commercial Power Systems Tech-nical Conference and of the Best Poster Presentation Award (for the technicalcompetence displayed in the poster presentation) at the 2010 InternationalConference on Electrical Machines.

Andr Quintino Duarte received the Licentiate andM.Sc. degrees in electrical engineering from theUniversity of Coimbra, Coimbra, Portugal, in 2012.

He is currently a Researcher with the Institute ofSystems and Robotics, University of Coimbra, wherehe has been working on electric motor efficiency,automation, and data acquisition systems for groundsource heat pumps in the FP7 GroundMed projectsince 2011.

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