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64 IEEE Transactions on Power Delivery, Vol. 11, No. 1, January 1996

our Meter Accuracy Under Controlled UnbalancedHarmonic Voltage and Current Conditions

A . Domijan, Jr. , Member,IEEEE. Em br iz-San tander, Member,IEEE

A.Gilani

Flo r ida Pow er A ff i lia tesUniversity of Florida, Dept.of Electr ical Engineering

Gainesvil le ,FL 3261 1

Abstract--- This work presents the results of phase I of theproject on the accuracy of watthour meters when subjected toclosely-duplicated real-world unbalanced harmonic voltage andcurrent conditions. Such real-world conditions involveddifferences in voltage and current magnitudes as well asdifferences in the voltage and current total harmonic distortionlevels of each phase. Tests were performed on a selected sampteof nine three-phase and three single-phase watthour meters.Some results showed that under a particular set of unbalancedwaveforms with harmonic conditions of I > 80 and V >2 , the percentage errors exhibited by these meters ranged from-10.09 to +O.52 .

Keywords: watthour meter, harmonics power quality,unbalance, field m onitoring, testing, waveform reproduction.

I. INTRODUCTION

A . Project Background

There are more harmonic loads appearing on the FloridaPower Corporation (FPC) power system every day,as inmany other electric utility power systems[I]. These loadsinclude a variety of equipment including electronic ballasts,personal computers, laser printers, variable speed motors,variable speed drive heat pumps, etc. The penetration level(quantity) of these loads is a result of: (a) thegrowth ofpower electronics technology [2],(b) the implementationofa national energy strategy[3], and (c) the efforts to improveenergy efficiency and pollution reduction suchas those by theGreen Lights Program[4].

95 WM 039-8 PWRDby t h e IEEE Power Systemments Committee of t h e IEEE Power Engineering Societyf o r p r e s e n t a ti o n a t the 1995 IEEE/PES Winter Meeting,January 29 , t o February 2 , 19 95 , New York, Np. Manu-s c r i p t submitted December 20, 1993; made available f o rp r i n t i n g J a n u a r y 9 , 1995

A paper recommended and approvedInstrumentation & Measure-

G. L a m e rC. Stiles

C. W. Williams, Jr., S enior Member,IEEE

Flor ida Power Corpora t ion3201 34th St ree t Sou th

St. Petersburg, FL 33711

It was thus the concem of FPC and the investigators o seewhat the accuracy was of some of the new watthour meterscurrently available inthe market under controlled harmonicvoltage and current conditions.

B. Project Objective

Florida Power Corporation was specifically interested infinding out if there was a problem with the accuracyofwatthour meters under real-world waveforms. These real-world waveforms impliedtwo main features: (a) the voltageand current magnitudes would be unbalanced, and (b) thevoltage and current waveshapes would have different levelsoftotal harmonic distortion(THD).

C cope

A group of selected three single-phase and nine three-phase meters were to be tested under sinu soidal situations bothat the FPC m eter calibration shop before they left for testingand at the research facility (where all the laboratoryexperiments were conducted) upon arrival. Then these meterswere to be subjected to closely duplicated real-world field-recorded waveforms (with data on harmonic spectra with aTHD limited to 50 'harmonics, per IEEE Std 519-1992)typically found on various loads of the FPC system.

D revious Research

Some of th e early research studies on this area startedoninduction watthour meters about25 years ago, in the late1960s and early 1970s:F. Tschappu [5] in 1968, Hirano andWada [6] in 1969, Auger and Bergerot[7] in 1972, andBagott [SI in 1977, among others. In recent years, Arsenauand Filipski19-111. Additional research has provided resultsthat cover watthour meters, wattmeters and watthour meters,reactive power meters, and definitions and measurements ofpdy pha se apparent power, and power factor among others. Areview on these topics is provided by anIEEE TutorialCourse [121.

0885-8977/96/ 05.00 1995 IEEE

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In the real world, meters are generally not exposed tobalanced conditions, as can be seen inFig. 1. The mon itoringtime for this site was on ly 35 m inutes and yet large statisticalTHD standard deviations of 3.76% to 6.03% for voltage, and20.10 to 32.33% for current were observed. Other sitesshowed variationsas well. This example is used simply toillustrate what is very well known: load and systemimpedance are not fixed, and one can expect the meter to besubjected to these types of variations almost all of the time.

Literature review on research studies doneso far in thisarea indicated that balanced co nditio ns (i.e., same voltage andcurrent magnitudes and THDs) had been applied to three-phase meters under test. The research wo rk described in thispaper presents results from experiments with meters underunbalanced conditions (i.e., different voltage and currentmagn itudes and THDs for all three phases). These experimentswere performed at the University of FloridaFlorida PowerAffiliates research facility: The Energy, Pow er Qua lity, andPower Electronics Lab which allows for the synchronizedreproduction and measurement of single and three-phasevoltages and curren ts under full computercontrol [131.

11. APPROACH

The approach to this research effort consistedof four majorstages of work as follows: (a) Field Testing and Monitoring,(b) Watthour Meter Selection, (c) Waveform Reproduction,and (d) Watthour Meter Testing.

A. Field Testing and Monitoring

I . Power Monitor Selection. The utility selected aprogrammable power m onitor capableof (a) displaying eightsignals simultaneously, (b) printing phasor diagrams,parameter summary, and FFT analysis, (c) recordingwaveforms information on memory cards, and (d) having thesturdiness for field testing.

2.Field Site Selection. Over 10 field sites were initiallychosen for field testing, an d data was recordedfromeach site.This large data set was compiled and organized by sites. Fig.1 shows data extracted from one of the sites in terms ofvoltage and curren t THDs over time.

6

a

SITE A: 35 minutes12

- P h a s e A - --PhaseB Phase C

I I I I I IT1 T2 T3 T4 T T6 T7

TIME

3. Field Data Evaluation. Three field-test sites (onesingle-phase and two three-phase sites) from FP C's servicearea were selected out of the 10 sites mo nitore d for use in thisproject. The first one was an adjustable-speed-driven heatpump w ith no filtering. This represents a worst case conditionsince the heat pump load would normally be m ixed with otherlinear household loads for most metering applications.However, a homeowner may leave on vacation with virtuallyall loads shut down except the heat pum p. This would resultin the meter seeing the worst case distortion shown in thisexample.

The second site was a pump station which consisted oftwo 150HP 6-pulse adjustable-speed-driven um ps. This is adedicated pump load with n o o ther load on the meter.

The last site was a relatively new(< 3 yrs) office buildingof 168,000ft2 and a 980kW demand with a typical mix oflighting, personal computers, copy machines and other officeequipment.

Fig.2 shows the d uplicated waveforms applied to thesingle-phase meters, and Fig. 3, and4 show the closely-duplicated waveforms that were applied to the three-phasemeters under test. Note in Figs.3 and 4 the differentmagnitudes for voltage and current for phase A,B, and C.Table I shows the percent unbalances for voltage and current

magn itudes, angles, and THDs for the three-phasewaveforms.SINGLE-PHASE HEAT PUMP

20

-15

239.9 rms

-4001 L-20

Fig. 2. Single-phase heat pump voltage and current.

0.00 4.15 8.30 12.45 16.67TIME(msec)

Fig. 1. An example ofV, and I variatio ns.

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Va=122.52 V

I b = 4 7 2 A

Fig. 3. Office building waveforms.

Ia=3.39 A

Fig. 4. Pump station waveforms.

Table I. Percent Unbalances( U).

P Vol tage (rms) Current rm)

Mag. Ang. THD Mag. Ang. THD

Note: S = site #: 2 = ofice building, 3= pump station,P = phase, Mag. = magnitude, Ang. = anglen/a = not applicable.

On the table above, the percen t unbalance for vo ltage, forexample, is equal to the maximum voltage deviation from theaverage divided by the average voltage, with the coefficientmultiplied by 100%. For the office building, the largestpercent unbalances were found on theV and I with18.8% and 27 , respectively. For the pump station, largepercent unbalances were foun d for theV I, and I with32.5 , 28 , and 11.7%, respectively.

B. Watthour Meter Selection

Along with the selectionof field sites, and waveforms,FPC person nel selected 12 watthour meters after consideringseveral new meters in the market.

1. Single Phase Wutthour Meters.Arbitrarily labeled Al,A2, and A3. All three meters were class200 and rated for240 V. Meter A1 is a hyb rid electronic meter. It isaninduction watthour meter with an electronic register.Noinformation was provided by the manufacturer.

Meter A2 is a d igital electronic watthour meter, and asstated by the manufacturer, it measures electric energy usinga digital sampling technique with a synchrono us sampling andintegrates the samples over time. Only limited informationwas released by the m anufacturer. It has a specified accuracyof *0.1 at full load (FL) with typical linearity of hO.1% atunity power factor(pf). Meter A3 is a solid-state electronicmeter. This is the single-phase versionof Meter B4.

2 Three-phase W utthour Meters.Arbitrarily labeledB1 to

B9. All of the three-phase meters are class 20, except for B5and B9. MetersB 1 andB2 are from the same m anufacturer asA1 andA2. Both are the three-phase versions of A1 and A 2.B1 is a hybrid electronic meter. It is a three-stator indu ctionwatthour meter with an electronic register. No additionalinformation was supplied by the m anufacturer. MeterB2, asA2, is also a digital electronic watthour me ter. Its typeisdescribedas a three-element meter for four wire three-phasewye service. It has a specified accuracy at unity power factor,rated voltage and frequency of O S error for currentsbetween 0.1 and 20 A.

Meter B3 is a solid-state watthour meter that uses a time-division multiplier, whichis a multiplying circuit based on theconcept that the area of an electrical pulse is equal to the

product of pulse width (which is proportional to a inputsignal, say Ex) and pulse height (wh ich is proportional to aninput signal, say Ey).Thus the multiplied output is inproportion to the product ExEy (i.e., instantaneous power),and the impulse train averageis in proportion to the activepower. Its accuracy was not available.

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Meter B4 is a solid-state watthour meter. It is the three-phase version of meter A3. As stated by the m anufacturer, thecurrents and voltages are sensed using specialized currentsensors and resistive voltage dividers, respectively.Multiplication and other calculations are performed using acustom IC, which con sists of a digital signal processor andbuilt-in analog-to-digital converters that sample the voltageand current input signals. The outputs of this custom IC arethen fed to a microcontroller with which the IC has access toan EEPROM where ca libration constants, previously loadedinto the meter at the factory via an optical port, are stored andbecome part of the appropriate multiplications within themetering chip's DSP. It has a specified accuracy of 4 0 . 2+O.Ol(class/I)(1+tanO)] .

Meter B5 is a digital electronic meter that is fullyprogrammable via (a) an IBM PC compatible computer,(b)a handheld programmer, or (c) remotely using a telephonemodem. It has a mother board, a register board with memory(for the program code, for the programm able parameters, andfor data), along with a m odem b oard, among others. It has aspecified accuracy of*(0.09% of reading+ 0.01% of ratedoutput).

Meter B9 is also from the same manufactureras B5, and ithas some of the same boardsas B5, in addition to twomultiplier boards which make up the measuring element ofthe meter. This is a TDM meter whose circuitry employsoperational amplifiers and integrators to measurekilowatthours. It has the same accuracyas B5.

Meter B6 is a TDM electronic meter. It is also fullyprogrammable via anIBM PC compatible and with someboards with a transformer, a measurement, a display/powersupply, and a CPU board which has a custom made IC wh osefunctions are based on time division multiplication. It has aspecified accuracy of *(0.15% maximum error onkWh from

test amps to class rating+ 0.3 from light load to test amps).Meter B7 is a electronic meter; however, no informationwas provided by the manufacturer. Finally, meter B8 is asolid-stateand microprocessor-based electronic meter that usesthe principles of time division multiplier. The secondaryvoltage and current signals from the input transformers aremultiplied to produce signa ls proportional to input w atts.

C Waveform Reproduction and Instrumentation

To match the field recorded waveforms, data from the FFTtables provided by the field power monitor was used alongwith equation1.

s

r 4 = Ah*COS(hOot+ 6 - h*90') 1)h=lwhere A = amplitude of voltage or current

Each equation was entered into, and downloaded fiom, a486 6 6 MHz GPIB con troller into thetwo three-channelhigh-

definition (16-bit) waveform generators, which inturn fed thesignals to a high kVA power amplifier and a three-phasecurrent amplifier. Under sinusoida l conditions, the THD forvoltage was 0.18% and0.2 for current. This add-ondistortion was of n o m ajor concern since the actual signals fed

't o our "reference meter" were measured at the terminals ofthe meter under test.

The power amplifier has a specified stabilityof *0.1%,and the current amplifiers have a short-term dc stability of*(0.005% + 200pA) in 10 minutes with constant line, load,and temperature. The maximum available output frequencyof both amplifiers is SkHz, well above the3kHz equired togenerate the highest harmonic (50th) recomm ended by IEEE519-1992. The accuracy of the test system was estimated tobe 99.9% (Le., it had a0.1 uncertainty). Since highaccuracy (

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AnalyzerSCU =Signal Conditioning Unit_ _ _ _ _

j l4 -Channel100 MHz(I)

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I

uara HcquisirionI

4 1

WATT-HOUR METER EXPERIMENT SETUP

Fig. 5. Main block diagram of the power-testing areaof the UFEPA Energy, Power Quality, andPower Electronics Research Laboratory.

Thus it was not d esigned for nonsinusoid al situations, andwhen it was subjected to similar harmo nic conditionsas hosefor meters A I to A3, this standard yielded about the sameregistration errors as those exh ibited by A 1 andA2. Thesepercent registration errors for single-phasemeters indicatetwothings: (1) they confirm previous research studies (e.g.,Baggott [6]), and 2 ) no substantial improvementwas seen onthe harmonic accuracy of these new tested models withrespect to the m eters used four or 20 years ago.

It must be noted that these results are particular for thespecific tested meters under specific waveform conditions;therefore, no statistically valid inferences couldbe maderegarding all or m ost o f the single-phase watthour metersinthe market. An attempt to do that would involve: (a) theincrease of our sampling size (e.g.,10 to 15 single-phasewatthour meters) in our tests, (b) the com pletely randomizedselection of these units, and (c) an increase in the types ofnonsinuso idal wavefo rms to be applied to these meters.

Table III shows the percen t registration errors e xhibitedbythe nine three-phase watthour meters when they weresubjected to the waveforms depicted inFig. 3 and 4.

The three-phase watthour meters were grouped into twocategories. Those that yielded a high registration error(> 4 ),and those with a lower registration error(< 4 ).

Note that the averageVTHD for the pump station andoffice building were not too far apart: 2.852% and 2.576%,respectively. However, the voltage percent unb alance for thepum p station was 6.529 times that of the office building. On .the other hand, the averageITHD for the pump station,94.99%,was 3.5 times higher than the o ffice building'sITHDof 27.0%, but the current percent unbalancewas 12.67 timeshigher than that of the office building.

Given all of th e variables involved (i.e., different voltageand current magnitudes andTHDs for all the phases), it ishard to pin point one of themas he prob able major cause forsuch high percentage registration errors. However, what couldbe said is that a pparently higher current distortion levelsaccompanied by high percen t unbalances will probably yield

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high registration errors. This statement is, of course, notcomplete, and further research is being done by the authors atthe time of this printing to further expand our know ledge onthe m echanics behind these preliminary results.

Table 111. Three-phase Meter Re

Site

B

o Uvc .

141IC

U

B1 (hybrid)B2 (digital)B3 (solid-state)B4 (solid-state)

B5 (digital)B6 (TDM)B7 (electronic)B8 (TDM)B9 (TDM)

Office Building

Mag.

122.5223.44

121.410.85

4.754.724.582.21

THD

2.962.682.09

18.8

4.664.512.9427.0

-5.57-4.76-4.3-3.04

-0.94-0.19-0.18-0.13-0.04

stration Erro rs.

Puml

Mag.

125.40115.83115.205.55

3.395.035.7128.0

tation

THD

3.782.662.1232.5

96.90104.283.88

11.7

8.75-10.09-9.54-7.27

+0.52-2.26-3.24-2.56-0.70

errors may be different.(3) It is thus necessary to classifywaveforms and their impacton meters by not only theTHDbut by the associated FFT spectrum.(4) It is emphasized thatregistration errors might be linked to: (a) the harmonic powerof the test waveforms, (b) the operating principle of the meterunder test, (c) the percent unbalances in the voltage andcurrent magnitudes, and (d) the T HD levels among the phases.

.

IV. FUTURERESEARCH

Phase I1 of this project, which had begun at the time ofthis printing, will make use of a transfer standard with aspecified uncertainty of30 ppm. Calibration instrumentationto be used will be purchased and calibrated by a companywith a highly-reputable primary calibration laboratory whichcurrently hasI S 0 9001 registration and accreditation by theNQA.

V. ACKNOWLEDGEMENTS

The authors wish to express their thanks to: Florida PowerCorporation for funding this project,Mi-. Steve Smirlis andMi-. Bob M atthews from the FPC M eter Department for theirhelp in the setup, calibration and field testing aspects of thisproject, and toh4r Yuexin Y in, graduate research assistant atU.F. for assisting in some of the testing.

A comparison (i.e., a series of statements that highlights thesimilarities between two or more items) can not be made inregard to previous research studies because of the followingfour facts: (1) different waveforms may have the same T HD

values but have a completely different shape,( 2 ) the samemeters were not used in the experiments,(3) the samewaveforms were not used in the research studies, and(4) thesame equipment and instrumentation were not used for theexperiments. However, in contrast with previous researchresults, these new fin dings seem to indicate that the individu alelements of the tested meters tend to interact to som e degreeand affect the meter's accuracy negatively.

111. CONCLUSIONS

(1) With four percent unbalances involved for each3-phase case (% Unbalance for voltage magnitude, VTHD,current magnitude, and ITHD), it is hard to pin point--at thistime--one of them as a probable major cause for registrationerrors; further research by the authors is now being cond uctedon this area. ( 2 ) It is conceivable that w hen signals with thesame THD value are applied to these meters, the registration

VI. REFERENCES[l]. A. Domijan,G T eydt, A.P.S. M eliopoulos,S S Venkata,and S. West, "Directions of Research on Electric Power Quality,"IEEE Trans. on Power Delivery, Vol. 8, Nol., Jan. 1993, pp.429-436.

[2]. A. Dom ijan, "Formation of a Strategy for EnergyDevelopment and Utilization with Power Electronic ConversionTechnologies: A Southeast Regional U.S.A. Approach,"IEEETrans. on Energy Conversion, Vol. 7 , No.1, Mar. 1992, pp. 64- 71.

[3]. Energy Information Administration,Energy Consumption andConservation Potential: Supporting Analysis f o r the NationalEnergy Strategy, SR/NES/90-02, 1990.

[4]. R. M. Kwartin, "EPA Green Lights Pollution PreventionThrough Energy Efficiency,"Energy Engineering Journal Vol.89, NO. 2. 1992, pp. 70-79.

[ 5 ] . F. Tschappu, "M ethods for Determining the Effect of M ainsHarmonics on the Accuracy of Electricity Meters,"Achiv fur

Technisches Messen, No. 385, pp. 33-36, Feb. 1968, and No.386, pp. 53-58, Mar. 1968.

[6]. T. Hirano, and H. Wada, "Effects of Waveform Distortion onChara cteristics of Induction W atthour Meters," ElectricalEngineeringin Japan, Vol. 189, No. 4, 1969.

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[7]. M. Auger, and J.L. Bergerot, "Effect of Harmonics on theAccuracy of Induction Watthour Meters,"Electricite de France(ED F) Bulletin de la Direction et Recherches. Series B. ReseauxElectriques. Materials Electriques No. 2, pp. 5-44, 1972.

[8]. A. J. Baggott, "The Effect of Waveshape Distortions on theMeasurement of Energy Tariff Meters," IEE Metering, Apparatusand Tarifs, for Electricity Supply, Conference Publication No.156, pp. 280-284, London, 1977.

[9]. R. Arsenau, and P.S. Filipski, "Application of a Three PhaseNonsinusoidal Calibration System For Testing Energy andDemand Meters Under Simulated Field Conditions,"IEEE Trans.on Power Delivery, Vol. 3, No. 3, Jul. 1988. pp. 874-879.

[lo]. P. S . Filipski, and P. W. Labaj, "Evaluation of ReactivePower Meters in the Presence of High Harmonic Distortion,"IEEE Trans. on Power Delivery, Vol. 7, No. 4, Oct. 1992, pp.1793-1799.

[ l 11. P. S. Filipski, "Polyphase Apparent Power and PowerFactor Under Distorted Waveform Conditions,"IEEE Trans. onPower Delivery, Vol. 6, No. 3, Jul. 1991, pp. 1161-1165.

[121. A. Emanuel, editor, IEEE Tutorial Course,

NonsinusoidalSituations: Effects on the Performance of Me ters and Definitionsof Power, IEEE Cat. No.90EH0327-7-PWR. 1990.

[13]. A. Domijan, and E. Embriz-Santander, "A Novel ElectricPower Laboratory for Power Quality and Energy Studies,"IEEETrans. on Power Systems,Vol. 7, No. 4, Nov. 92 , pp. 1571-1578.

[141. Edison Electric Institute,Handbook fo r Electricity Metering,Ninth Edition, (Washington, DC: 1992), pp. 449-45 1.

VII. BIOGRAPHIES

Alexander Domiian, Jr. obtained his B.S.E.E. degree at theUniv. of Miami, M.E. degree from the Rensselaer Polytechnic

Institute, Troy, N.Y., and the Ph.D. from the University ofTexas at Arlington (UTA). Dr. Domijan has also been aPostdoctoral Fellow with the Energy Systems Research Centerat UTA, and an engineer with theG.E. Co. Advance De-velopment Engineering, Pittsfield, Mass., and a consultant withFlorida Power Corporation, St. Petersburg, FL . He joine d theelectrical engineering faculty of the University of Florida in1987, and is also Director of the Florida Power Affiliates andis the founder of the Power Electronics Consortium. He is amember of several IEEE societies, the American Society forEngineering Education, Eta Kappa Nu, and is an AmericanElectronics Association Fellow.

Ernesto Embriz-Santander was born in yexico Gity, in1960. He received the A S . in Industrial Electronics (highhonors), 'and A.A. (high honors) degrees from Santa Fe

Community Collegein 1983 and 1984; and the B.S.E.E.,M.S.E.E., and Engineer degrees from the Univ. of Florida, in1988, 1991, and 1994 respectively. He has held numerousscholarships and awards, among them: from the MexicanNational Council for Science and Technology (1981-83),NACM E (1983-88), the nationally prestigious 1992ASHRAE/ASHAE Homer Adams Award for his work in

power quality, and life-time membership into the Florida Pow eAffiliates. He began his engineering career in 1979 working foGuillette Co. He then served as office chief of CEGPCSA'sbranch office in Mexico City until he moved to Gainesville, FLFrom 1989 to 1994, he has been a Teaching and ResearchAssociate for the Florida Power Affiliates at U.F., where he isalso the Manager of the Energy, Power Quality and PowerElectronic Systems Lab. He is a registered ProfessionalElectronics Technician with the Department of Public Educationof Mexico, and a member of IEEE, IAS, and the PowerEngineering Society.

Asif Jah Gilani was born in Nalanda, India in 1965. He receivedhis B.S.E.E. from the Bihar Institute of Technology, Sindri, Indiain 1988. After graduating he worked as a testing andcommissioning engineer with the Steel Authority of IndiaLimited. Since 1992 he has been a teaching and research for theFPA at U.F. Presently, he is completing h is Master program an dwill be pursuing his Ph.D. in electrical engineering. His researchinterests arein the areas of metering and instrumentation, motordrives, power electronics and power quality.

Gene Lamer was born in Boston, MA in 19 43. He is presentlya Meter Consultant with the Metering Department of FloridaPower Corporation, St. Petersburg, FL. He has served as theChairman of the Southeastern Electric Exchange Metering andDistribution Services Device Committee. He is an active memberof the Southeastern Electricity Metering Association, oftenchairing sessions and lectures in the annual me tering short courseand conference nowin Orlando, Florida. His technical interestsare in the metering and transformer areas.

Christopher Stiles was born in St. Petersburg, Florida. He wasthe Manager of the Meter Department of Florida PowerCorporation, St. Petersburg, FL. Mr. Stiles is a member of EEIand is involved with the Southeastern Electricity MeteringAssociation in forming the annual metering short course andconference.

Charles W. Williams Jr., P.E., obtained his B.S.E.E degree

from U.F.in

1971. He began work with Florida PowerCorporationin June 1971 as an associate engine erin distributionengineering. Mr. Williams has held several positionsindistribution engineering during his 21 year career with FPC,including District Engineer. Mr. Williams present position isPrincipal Engineer, Distribution Engineering, St. Petersburg, FL.His responsibilities include distribution transformers, lightningarresters, R&D projects, and other special studies such asharmonic effects on the distribution system, and lightningresearch. Mr. Williams is a registered Professional Engineer inthe state of Florida since 1975. As a Senior Mem ber of the IEEE ,Mr. Williams is a member of the IEEE Transform ers C omm ittee,and is the past Chairman of working group 3.3.11 of the IEEESurge Protective Devices Committee (Continuous revisionstoC62. Metal Oxide Arresters). He is past Chairman of theOverhead Distribution Committee of the Southeastern Electric

Exchange and an EL& P delegate to the ANSI C57.12.2 workinggroup on distribution transformers.

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Discussion

A. E. Em anuel (Worcester Polytechnic Institute) The results of this study should causea great dealof concern to prod ucers as well as t o large users o f electric energyAn errorof 1% on thekWh meter that m onitors the electric energy on a SOMVA electnc arcfurnace with a0 125 load factor, translatesn $50,00O/year unfairly distributedEstimating that 3% of the total 3000BkWhused yearly in USA flows throug h largenonlinear loads and assuming again1% error, results that900 MkWh are wronglyaccounted

Undoubtedly the authors tried to usea correct testing pro tocol and traceable standardinstrumentation,however, when one compares the new results w th previously publisheddatawll find quite a large discrepancy The results thatI would like to see clarified firsthave values associated w th Fig 3 and reported in Table I11 The meter B3 for example, atime-dinsion unit, has an error of m ore than4 at a modest voltage distortionVTHD 35th).

2. The results associated withFig. 3 and reported in TableI11for B3 and the other m eters are correct and valid exclusively(a) for the meters specifically used for the research, and (b)for specific waveform conditions with their own particularrms magnitudes, thd levels, specific harmonics, and specificharmonic phase shifts.A comparison (i.e., a series ofstatements hat highlights the sim ilarities between two or m oreitems) can not be m ade in regard to previous research studiesbecause of the four facts listed below Table111

3 . Providing detailsof calibration was out of the scope of thispaper; however, the authors recommend the followingreference for an excellent source on calibration.Calibration:Philosophy in Practice, Second Edition, by Fluke Corporation,

995.

4. A crucial item that can make a difference in the accuracyare the current and voltage transformers, andso do: (a) theaccuracy of the calibration instrumentation used for the

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calibration of the system, (b) the accuracy of the analog-to-digital converters and their vertical and horizontal resolution,and (c) the form ulas used to comp ute the variable of interest[see for example,L.S. Czamecki, "Comparison of PowerDefinitions for Circuits with Nonsinusoidal Waveforms,"IEEE Tutorial Course. Nonsinusoidal Situations: Esfectson

the Performance of Meters and Definitions of Power, IEEE1990, pp. 43-50].

5. The discusser sug gests that, "it %rillbe a great service to theengineering community if the authors can repeat themeasurements published by Filipski and Arsenau and comp arethe results." The au thors would like to sugg est that it will bea great service to the engineering community if otherinvestigators can repeat the measurements published by theauthors or conduct similar experimnets and compare theresults. Research work is dependent upon time and funding.

6 . The fact that the discusser generalized hisown"impression" as to include "all types ofWh meters" is

inappropriate, since as the authors specified in the paper onpage 5, 2n d paragraph: I... these results are particular for thespecific tested meters under specific waveform conditions:therefore, no statistically valid inferences cou ld be m aderegarding all or most of the watthour metersin the m arket."

7. Tne results presented in the paper are clearly stated and notleft in limbo. Rather, additional work is called forinperforming sensitivity studies. This additional research isbeing done by the authors in the next phase of the project.

With regard to the comments made by Dr.Y

Baghzouz, we respond as follows:

We agree with Dr. Bagh zouz thatour paper is the only articleso far that deals with meter's accuracy under unbalanceconditions(rms and thd levels).

We also agree with the statement that, "Finding that nearlyhalf the meters are off by over 3% is alarming and calls formore testing " We are presently doing additional research,which involves more testing, as part of phaseI1 of thisproject.

Responding t o each item:

1. Yes, that field power monitor was used in the field;however, the data was compared in the lab against thosemeasurements taken with o ur laboratory instrumentation.

interpret correctly because either they reach the u pper limit ofan A/D converter or somewhere in the electronic circuit anamplifier is driven to its limit; [thus some signal truncationmay occur under specific circumstances]I'

3 . Figs. 3 and 4 include the scaling factors (PT and C T ratios)

provided by Florida Power Corporation for meter testing.

4. On item(4): Adapted from IEEE Standard 112-1984, "Thepercent voltage [current or thd level] unbalance equals100times the maximum voltage [current or thd level] deviationfrom the averag e voltage [current or thd level] divided by theaverage voltage [current or thd level].

The corrected sentence on page 5 should read: "The averagecurrent THD for the pump station, 94.99%) was 23.5 timeshigher than the office building'sITHD of 4.03 , . . . ' I

Manuscript received April 17, 1995.

2. An explanation provided by one of the manufacturers statesthe following: "highly distorted waveforms such as this one[Fig. 21 often havea very high crest factor. Electronic metershave some limit to the maximum current magnitude they can