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AppliedPower Quality
AppliedPower Quality
SARATHPERERA
AustralianPowerQualityandReliabilityCentre,UniversityofWollongong, Wollongong,NSW,Australia
SEANELPHICK
AustralianPowerQualityandReliabilityCentre,UniversityofWollongong, Wollongong,NSW,Australia
Elsevier
Radarweg29,POBox211,1000AEAmsterdam,Netherlands TheBoulevard,LangfordLane,Kidlington,OxfordOX51GB,UnitedKingdom 50HampshireStreet,5thFloor,Cambridge,MA02139,UnitedStates
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Notices
Knowledgeandbestpracticeinthisfieldareconstantlychanging.Asnewresearchand experiencebroadenourunderstanding,changesinresearchmethods,professionalpractices,or medicaltreatmentmaybecomenecessary.
Practitionersandresearchersmustalwaysrelyontheirownexperienceandknowledgein evaluatingandusinganyinformation,methods,compounds,orexperimentsdescribedherein. Inusingsuchinformationormethodstheyshouldbemindfuloftheirownsafetyandthe safetyofothers,includingpartiesforwhomtheyhaveaprofessionalresponsibility.
Tothefullestextentofthelaw,neitherthePublishernortheauthors,contributors,oreditors, assumeanyliabilityforanyinjuryand/ordamagetopersonsorpropertyasamatterofproducts liability,negligenceorotherwise,orfromanyuseoroperationofanymethods,products, instructions,orideascontainedinthematerialherein.
ISBN:978-0-323-85467-2
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Contents Acknowledgementsvii
1.Introductiontopowerqualityinmodernpowersystems1
1.1 Introduction1
1.2 Whatispowerquality?3
1.3 Powerqualitymanagementphilosophy11
1.4 Overviewofcontents15 References17
2.Steady-statevoltageinlowvoltagenetworks19
2.1 Introduction19
2.2 Voltagestandards20
2.3 Equipmentresponsetovoltagemagnitude21
2.4 Causesofsteady-statevoltagevariation32
2.5 PrinciplesofvoltageregulationinLVfeeders33
2.6 Techniquesforimprovingvoltageregulation41 References48
3.Impactandmanagementofpowersystemvoltage unbalance49
3.1 Introduction49
3.2 Commonlyuseddefinitions50
3.3 Measurementofvoltageunbalance51
3.4 Impactofvoltageunbalance52
3.5 Managementofvoltageunbalanceinpowersystems54 References68
4.Impactandmanagementofpowersystemharmonics71
4.1 Introduction71
4.2 Definitionofwaveform(harmonic)distortion71
4.3 Measurementandanalysisofharmonicdistortion77
4.4 Sourcesofharmonicdistortion80
4.5 Impactofharmonicdistortion92
4.6 Managementofharmonicdistortioninelectricitysupplynetworks100
4.7 Mitigationofharmonicdistortion126 References128
5.Impactandmanagementofvoltagefluctuations,flickerand rapidvoltagechanges131
5.1 Introduction131
5.2 Effectsofvoltagefluctuations133
5.3 Powerqualityparametersassociatedwithvoltagefluctuations134
5.4 Managementofvoltagefluctuationsandflickerandtheir measurementandnetworkplanninglevels143 References145
6.Impactandmanagementofpowersystemvoltagesags147
6.1 Introduction147
6.2 Definitionofvoltagesags147
6.3 Causesofvoltagesags150
6.4 Empiricalcharacteristicsofvoltagesags151
6.5 Factorsinfluencingvoltagesagseverity153
6.6 Impactofvoltagesags155
6.7 Mitigationofvoltagesags163
6.8 Assessmentandreportingofvoltagesags174 References182
7.Implicationsofequipmentbehaviouronpowerquality185
7.1 Introduction185
7.2 Powerelectronicconverters185
7.3 Motorloads195
7.4 Capacitorbanks197
7.5 Arcingloads207
7.6 Transformers207
7.7 Loadbehaviour215
7.8 Impactofvariationsinsupplyvoltageonapplianceperformance246
7.9 Powerqualitystandardsforequipmentperformance254 References257
8.Powerqualitymonitoring,dataanalysisandreporting259
8.1 Introduction259
8.2 Standardsforpowerqualitymonitoring264
8.3 PQdisturbancesandtheircharacterisation269
8.4 Powerqualityinstruments274
8.5 Transducers282
8.6 Motivationforpowerqualitymonitoring294
8.7 Reportingofpowerqualitydata304 References312
Acknowledgements
IwishtoacknowledgemypastandpresentcolleaguesattheAustralian PowerQualityandReliabilityCentre(APQRC)whohaveinspiredme todelveintothequitefruitfulsubjectofpowerquality.Inparticular, IwishtothankEmeritusProfessorVicGosbellinthatregard.Ihavebeen veryfortunatetohavebrilliantpostgraduatestudentswhowentalong exploratorypathswhichhelpedmetoopennewwaysoflookingatpower qualityphenomenaassociatedwithvoltagefluctuationsandvoltageunbalance.Iwishtoacknowledgethesupportofmycolleaguesfromanumberof CIGREworkinggroupswhohaveacknowledgedtheworkcarriedout atAPQRC.
Ihavetremendousadmirationofmylong-standingcolleague,Sean Elphick,whohasbeenabackboneofAPQRC.Ialsowishtoacknowledge thesupportandinsightfulknowledgeofmycolleaguesthelateAssociate ProfessorPhilCiufo,AssociateProfessorDuaneRobinson,JasonDavid andGerardDruryofAPQRC.
SarathPerera
Firstly,Iwouldliketothankmycolleagues(pastandpresent)atthe AustralianPowerQualityandReliabilityCentre,specificallyandinnoparticularorder:ProfessorVicGosbell,AssociateProfessorDuaneRobinson, AssociateProfessorPhilCiufo,DrVicSmith,JasonDavid,GerrardDrury andAminRajabi.Ihavebeenfortunateinmycareertohavebeenableto workwithsuchfinementorsandcolleagues.
I’dalsoliketothankmyco-authorProfessorSarathPererawhohasbeen amentortomeforalongperiodoftime.
Finally,Ithankmyfamilywhohavesupportedmethroughtheprocessof compilingthisbookandperhapshavehadtoputupwithafewtoomany weekendsofdadinthestudyworkingonhisbook. SeanElphick
CHAPTER1
Introductiontopowerquality inmodernpowersystems
1.1Introduction
Inindustrialisedcountries,electricitysupplyreliability,asmeasuredbythe frequencyanddurationofelectricitysupplyinterruptions,isnowveryhigh. Whilstreliability,orwhetherornotanylevelofvoltageispresent,may strictlybeconsideredpartoftheumbrellaofdisturbancesincludedinthe broaddefinitionofpowerquality,thefactthatmanagementofreliability iswellunderstoodandthatreliabilityisofahighstandardmeansthatreliabilityandpowerqualityareoftenconsideredtobeseparatetopics.Given theaforementionedhighlevelsofreliability,focushasmovedtootherareas ofpowerqualitywhereimprovementscanbemade.Whilstmanypower qualityconceptshaveexistedformanyyears,inrecenttimestherehavebeen someverysignificantchangestothenatureoftheloadsandgeneratorsthat areconnectingtoelectricitysupplynetworks.Whilstthesenewloadsand generatorsarenotproducinganynewpowerqualitydisturbances,their characteristicsandthemethodsbywhichtheyarebeingintegratedintonetworkshaveresultedinpowerqualitychallengesandcontinuedemphasison theoverallmanagementofpowerqualityfrombothatechnicalandregulatoryperspective.Examplesofrecentpowersystemchangesthatare directlyrelevanttopowerqualityperformanceareasfollows:
•Therehasbeenaproliferationofsmall-scalesolarphotovoltaic(PV)generationbeingintegratedintolowvoltage(LV)networks.Themajority ofthesesystemsareinstalledonhouseholdrooftops.Asanexample, Fig.1.1 showsthetrendoftotalinstalledcapacityofsolarPVinAustralia overthepast20years.Thefigureshowsthattake-upincreasedrapidly from2010onwardandcontinuestoincreaserapidly.Integrationofthese distributedsolarPVgeneratorsintolowvoltageelectricitydistribution networkshasresultedinpowerqualitychallengesrelatedtovoltageregulation,voltageandcurrentunbalanceandtoalesserextentharmonic distortion.
Fig.1.1 TrendofinstalledsolarPVcapacityinAustralia. (DatafromAustralianPV Institute(APVI),SolarMap,FundedbytheAustralianRenewableEnergyAgency, Webpage(LastAccessed7April2021).)
•Solarinvertersand/orassociatedmonitoringsystemsprovideanindicationofnetworkvoltagelevelsandinsomecases,invertersystemsaredisconnectingfromthenetworkduetoovervoltageprotectionsettings. Thishasincreasedconsumerawarenessandvisibilityofnetworkpower qualityandinturnresultedinarequirementforelectricitynetwork operatorstotakeactiontoimprovepowerquality.
•Therehasbeenasignificantincreaseinthenumberoflargerenewable generators.Thesegeneratorspresentpowerqualitymanagementchallengesforthefollowingreasons:
Thelocationoftherenewableenergyresourcesthattheycaptureis ofteninremotelocations,andassuch,thereislimitedtransmission orsubtransmissioninfrastructure.Consequently,manyofthesegeneratorsarebeingconnectedtoweakerpartsofnetworksmaking managementofpowerqualitymoredifficult. Thetechnologiesusedtointegratethesegeneratorswithelectricity transmissionanddistributionnetworkshaveperformanceandcharacteristicsthataredifferenttomoretraditionalloadsandgenerators. Forexample,invertersforlargesolarfarmsmayinjectharmonic orderswhichareatypical.
•Therehasbeenacontinualshiftinthecharacteristicsofconsumerappliancestowardsalldevicesbeingsuppliedbypowerelectronics.Themain reasonforthisshiftisenergyefficiency.Manydeviceswhichincorporate inductionmotors,forexample,airconditioners,washingmachinesand
refrigerators,whichoncemayhavebeendirect-onlinestart,arenow moreandmorelikelytoincludeaninverterastheinterfacebetween thesupplyandthemotor.Inthecaseofairconditioners,itisnowdifficulttofindamodelthatisnotoftheinvertertype.
•Thecharacteristicsoflightingsystemshavecompletelychangedoverthe pastdecade.Inmanycountries,incandescentlamps,whicharealinear loadwithfewpowerqualityimplications,arebeingphasedout.Thisis againforreasonsofenergyefficiency.Inthefirstinstance,incandescent lampswerereplacedwithcompactfluorescentlamps(CFL);however, thesehavebeenreplacedinturnbyLEDlightingsystems.Whilstthere isnoargumentthatCFLsandLEDsuselessenergythanequivalentincandescentlamps,theyareelectronicdeviceswhichdoemitharmonicdistortion.Theseelectroniclightingsystemshavealsobeenobservedtobe moresusceptibletopowerqualitydisturbancesthanincandescentlamps. Inadditiontothechangestoloadsandgeneratorsspecifiedabove,itishighly likelythatthenumberofelectricvehiclesandbatteryenergystoragesystems willincreaseoverthecomingyears.Bothofthesetechnologiesareinterfacedwiththewiderelectricitysupplynetworkthroughelectronicsand assuchhavethepotentialtobothimpactnetworkpowerqualitylevels and/orbesusceptibletopowerqualitydisturbances.Dependingontheir implementation,thesetechnologiesalsohavethepotentialtoimprove powerquality.
1.2Whatispowerquality?
Therearemanydefinitionsforpowerquality.TheInternationalElectrotechnicalCommission(IEC)definespowerqualityas“characteristicsof theelectricityatagivenpointonanelectricalsystem,evaluatedagainsta setofreferencetechnicalparameters” [1] whilsttheInstituteforElectrical andElectronicsEngineers(IEEE)definespowerqualityas“theconcept ofpoweringandgroundingelectronicequipmentinamannerthatissuitable totheoperationofthatequipmentandcompatiblewiththepremisewiring systemandotherconnectedequipment” [2].
Insimpleterms,anydeviationsfromasinusoidalwaveformofnominal voltageandfrequencymaybeconsideredasamanifestationofapowerqualitydisturbance.Powerqualitycoversawiderangeofphenomenathatmay beobservedinpowersystems.Theimpactsofpowerqualityrangefromrelativelybenigntocatastrophic.Bywayofterminology,powerqualityphenomenaareoftencalleddisturbances;however,theIECalsotermspower
qualityphenomenaparameters.Forthepurposesofthisbook,thetermdisturbancehasbeenadopted.
Powerqualitydisturbancescanmanifestineithervoltageorcurrent.In manycases,voltagedisturbancesarearesultoftheinteractionbetweencurrentandnetworkimpedance.Forexample,harmonicvoltagedistortionis causedbytheinteractionbetweenthedistortedcurrentdrawnbynonlinear loadsandnetworkimpedancewhilstvoltagesagsarecausedbytheinteractionbetweenfaultcurrentandnetworkimpedance.Asageneralprinciple, particularlyundertheIECpowerqualitymanagementphilosophy,network operatorsareresponsibleformaintainingacceptablepowerqualitylevelsin voltagewaveformswhilstcustomersareresponsibleformanagingtheir powerqualityemissionsatalevelwherebytheydonothaveanunacceptable impactonvoltage.
1.2.1Mainpowerqualitydisturbances
Thissectionprovidesabriefoverviewofthedefinitionandimpactofthe mainpowerqualitydisturbances.Acomprehensivedefinitionofeachpower qualitydisturbanceisprovidedintheindividualchaptersdedicatedtoeach disturbance.
1.2.1.1Steady-statevoltagevariation
Voltagevariationmaybeconsideredtobethemostbasicofpowerquality disturbances.Thesteady-statevoltagemagnitudeisgenerallyacceptedtobe theroot-mean-square(RMS)valueofthevoltagewaveform.Thisvoltage magnitudewillvaryovertimeduetoarangeoffactorsincludingloadingand networkoperation(e.g.transformertapchangerpositions,connectionor disconnectionofcapacitorbanks).
Themagnitudeofthesupplyvoltageisakeyparameterforequipment operation.Ifvoltagemagnitudesaretoolow,equipmentmaynotoperateas intendedoratall.Ifvoltagemagnitudesaretoohigh,equipmentmayexperiencelossoflife,consumeadditionalenergyormayfail.
1.2.1.2Steady-statefrequencyvariation
Frequencyisanotherbasicnetworkoperationparameter.Inlargeinterconnectednetworks,frequencyisgenerallyboundwithintightlimitsandcontrolledthroughcomplexcontrolstrategiesforgenerators.Withtheincrease innonsynchronousgenerationaswellasmovementtowardshighernumbers ofstand-alonepowersupplies,maintenanceofverytightfrequencylimitsis becomingmorechallenging.
Themainimpactofvariationinfrequencyappearstobeimplicationsfor deviceswhichcountzerocrossings.Forthesedevices,variationinfrequency cancauseclockstorunfastorslowdependingonwhetherthefrequencyis aboveorbelowthenominalvalue.
1.2.1.3Unbalance
Unbalance,alsotermedimbalance,isdefinedbytheIECasa“conditionina polyphasesysteminwhichthermsvaluesofthelinevoltages(fundamental component),and/orthephaseanglesbetweenconsecutivelinevoltages,are notallequal”[1]. Fig.1.2 showsavisualisationofunbalance.
Theimpactofunbalanceismainlyonthree-phasedevices.Perhapsthe bestknownimpactisthatofvoltageunbalanceinducingcounter-rotating magneticfieldsininductionmotorsleadingtoadditionalheatingwhich sometimesrequiresderatingofthemotor.Voltageunbalancemayalsocause three-phasedevicestoemitatypicalharmonicdistortion.Inthree-phase supplynetworks,unbalancewillcausecurrenttoflowintheneutralconductor.Insomecases,beforeunbalancewaswellunderstood,thiswasanissueif theneutralconductorwasnotsizedappropriately.However,thisissueis nowwellunderstoodandwiringrulesensurethattheneutralconductor isnowappropriatelysized.
1.2.1.4Harmonicdistortion
Harmonicsaresinusoidalwaveformcomponentswithfrequenciesthatare integermultiplesofthefundamentalfrequency.Whenharmonicsarecombinedwiththefundamentalfrequencytheoutcomeisadistortedwaveform. Harmonicsdistortthevoltageorcurrentwaveformidenticallyforeach cycle.Sometypesofequipment(e.g.powerelectronicconverters)will intrinsicallydrawdistortedcurrentmadeupofharmonics.Theinteraction
Fig.1.2 Visualisationofunbalance.
Fig.1.3 Exampleofwaveformcontainingharmonicdistortion.
betweenthisdistortedcurrentandnetworkimpedanceisthecauseofdistortedvoltagewaveformsandvoltageharmonics. Fig.1.3 showsanexample ofawaveformcontainingharmonicdistortion.
Interharmonicsarewaveformswithfrequencycomponentsthatarenot integermultiplesofthefundamentalfrequencyandoriginatefromdevices suchasstaticfrequencyconverters,cycloconvertersandarcfurnaces.The waveformdistortiontheyproduceisdifferentforeachhalf-cycle.Interharmonicsaregenerallynotofsufficientmagnitudetobeofconcern. Fig.1.4 showsanexampleofawaveformcontaininginterharmonicdistortion.
Theimpactofharmonicdistortioncanbequitewideandvariedand includes
•Additionalheatingandlossesinequipmentandsupplynetworks.
•Interferencewithcontrolandcommunicationsystems.
•Catastrophicfailureofequipment.
Fig.1.4 Exampleofwaveformwithinterharmonicdistortion.
1.2.1.5Voltagefluctuationsandflicker
Voltagefluctuationsandflickerareoftengroupedtogether;however,they arenotequivalent.Voltagefluctuationsarerapidchangesinthemagnitude ofthevoltagewhilstflickerisanongoingmodulationoftheamplitudeofthe voltagewaveformenvelope.Inasimplesense,voltagefluctuationsmaybe thoughtofasthesourceandflickertheoutcome;however,notallvoltage fluctuationsleadtoproblematicflicker.Themainimpactofvoltagefluctuationsinisolationisdimmingoflightsandpotentialtrippingofequipment. Theimpactofvoltagefluctuationsonequipmentlifespanremainsanarea requiringfurtherresearch.Isolatedvoltagefluctuationswillnotcauseflicker; however,ongoingperiodicvoltagefluctuationsarethesourceofflicker.
Ongoingvoltagefluctuationscancauserhythmicchangesintheoutput (flickering)ofsomelightingsystemsandthisisthephenomenaknownas flicker.TheIECdefinesflickeras“impressionofunsteadinessofvisualsensationinducedbyalightstimuluswhoseluminanceorspectraldistribution fluctuateswithtime” [3].Themainimpactofflickerisonhumanswherethe ongoingchangesinlightoutputcancausearangeofdeleterioushealth impacts,rangingfrominabilitytoconcentratethroughtoseizuresinextreme cases. Fig.1.5 showsavisualisationoftheperiodicamplitudemodulationof thevoltagewaveformenvelopethatistherootcauseofflicker.
Fig.1.5 Visualisationoftheperiodicamplitudemodulationofthevoltagewaveform envelopethatcausesflicker.
1.2.1.6Voltagesags
Avoltagesag,alsoknownasavoltagedip,isashort-termreductionofthe voltagemagnitude.Voltagesagsareidentifiedbythresholdvaluesofvoltage
magnitude.Thereisnoconsistentinternationaldefinitionofthevoltage magnitudeortimeperiodthatdefinesavoltagesag.TheIEEEdefinesa sagas“adecreaseinrmsvoltagetobetween0.1and0.9pufordurationsfrom 0.5cyclesto1min” [4].TheIECismuchlessprescriptivewithrespecttothe magnitudeofvoltageanddurationthatapplytovoltagesags,specifyinga voltagedip(sag)asa“temporaryreductionofthevoltagemagnitudeata pointintheelectricalsystembelowathreshold” [5]. Fig.1.6 showsanexampleofavoltagesag.
Voltagesagsmaywellbethepowerqualitydisturbancewiththegreatest economicimpact.Voltagesagscancauseequipmenttotrip(ceaseoperating).Thistrippingcauseslostproductivityandcanleadtosignificantloss ofproductionandrawmaterialsinindustrialplants.
1.2.1.7Voltageswells
Avoltageswellisashort-termincreaseinthevoltagemagnitude.Insimple terms,voltageswellsmaybethoughtofastheoppositeofvoltagesags.However,measurement,analysisandreportingofvoltageswellsarenotnearlyas welladvancedasthatseenforvoltagesags.Thismaybeduetothefactthat voltageswellsaremuchrarerthanvoltagesagsanddonothavethesame economicimpacts.
Voltageswellsareidentifiedbythresholdvaluesofvoltagemagnitude. Similartothecaseforvoltagesags,thereisnoconsistentinternationaldefinitionofthevoltagemagnitudeortimeperiodthatdefinesavoltageswell. TheIEEEdefinesaswellas“aswellisanincreaseinrmsvoltageabove1.1pu fordurationsfrom0.5cycleto1min” [4].Onceagain,theIECislessprescriptivewithrespecttothemagnitudeofvoltageanddurationthatapplyto voltageswells,specifyingavoltageswellasa“temporaryincreaseofthevoltagemagnitudeatapointintheelectricalsystemaboveathreshold” [5] Fig.1.7 showsanexampleofavoltageswell.
Fig.1.6 Voltagesag.
1.2.1.8Transients
Atransientisaveryshortterm,oftensubcycle,disturbanceintheACwaveformthatisevidencedbyasharp,briefdiscontinuityofthewaveform.Transientsarealsoknownasspikesorsurgesandnormallyareonthelineforonly 1/1000thofasecondorless(lessthan1millisecond).Theycanbefromafew to10,000volts-peakaboveorbelowthevoltagesinewaveordatalinesignal. Theimpactoftransientscanrangefromtrippingofequipmentanddisruptionofcontrolsystemsthroughtocatastrophicfailure.
Therearetwotypesoftransients,namely,oscillatoryorimpulsive.Oscillatorytransientsaregenerallycausedbyenergisationofloadswithcapacitor bankenergisationbeingawell-knowncause.Oscillatorytransientsarecharacterisedbybidirectionalexcursionsinthewaveformfollowedbyoscillation orringing. Fig.1.8 showsanexampleofanoscillatorytransient.
Impulsivetransientsaregenerallycausedbylightning.Thesetransients arecharacterisedbyveryshorttermandoftenverylargeunidirectional excursionsofthewaveform. Fig.1.9 showsanexampleofanimpulsive transient.
Fig.1.7 Voltageswell.
Fig.1.8 Oscillatorytransient.
1.2.1.9Characterisingpowerqualitydisturbances
Whenconsideringmonitoring,analysisandreportingofpowerqualitydisturbancelevels,itiscommontocharacterisepowerqualitydisturbancesas eithercontinuousordiscretephenomena.
Note:TheIECdoesnotusethetermcontinuousdisturbanceinstead adoptingthetermquasisteady-stateparameter;however,thetermcontinuousdisturbanceisusedinthisbook.
Continuousdisturbancesarethosewhicharealwayspresenttosome degree.Discretedisturbancesoccurasisolateddisturbancesoverafewcycles potentiallywithalongintervalbeforetheyarerepeated.Theconceptof ‘steadystate’isnotapplicabletothesedisturbancessince,ifthetermwas tomeananything,itwouldbethattheyareabsent. Table1.1 presents thecontinuousordiscreteclassificationforthemostcommonpowerquality disturbances.
Thephilosophyformanagement,monitoringandanalysisofcontinuous anddiscretedisturbancesisverydifferent,andassuch,eachdisturbanceclassificationneedstobeaddressedindividually.
Table1.1 Continuousanddiscretedisturbanceclassification.
Continuousdisturbances(present everycycle)
Voltagevariation Unbalance Harmonicdistortion
Voltagefluctuations/flicker
Discretedisturbances(presentinasmall fractionofcycles)
Sag/interruption Swell Transient
Fig.1.9 Impulsivetransient.
1.3Powerqualityman agementphilosophy
Theoverallaimsofmanagingpowerqualitydisturbancelevelswithinelectricitysupplynetworksareasfollows:
•Toensureasafeandsecureelectricitysupply.
•Toensurethatallequipmentconnectedtotheelectricitynetworkoperatesasexpected.
•Tofullyutilisetheabsorptioncapacityoftheelectricitynetworkensuringtheoptimumeconomicoutcomesforconsumersandnetwork operators.
Managementofpowerqualitylevelsinelectricitynetworkstoensure thatalloftheearliermentionedobjectivesaremetisachievedthrougha combinationofequipmentdesignguidelinesalongwithmeasuresundertakentolimitthemagnitudeofdisturbancespresentinelectricity.Inmost cases,therearestandardsand/orregulationsthatspecifythemethodsthat networkoperatorsshouldusetoimplementapowerqualitymanagement philosophy.
Intermsofequipmentdesigntherearestandardswhichdefineacompatibilitylevel.TheIECdefinescompatibilitylevelas“thespecifiedelectromagneticdisturbancelevelusedasareferencelevelforco-ordinationin thesettingofemissionandimmunitylimits.”Thecompatibilitylevelis effectivelythehighestlevelofanydisturbancethatshouldbepresentin theelectricitysupplynetwork.Equipmentmanufacturersusethecompatibilityleveltodesignequipmentsuchthattheequipmentimmunitylevelis greaterthanthecompatibilitylevel,thusensuringthatequipmentshould operateasexpectedforanypowerqualitydisturbancelevellikelytobepresentinthesupplyvoltage.
Oncecompatibilitylevelshavebeenestablishedelectricitynetwork planningmethodologiesmustbeimplementedtoensurethatpowerquality disturbancemagnitudespresentinelectricitynetworksdonotexceedthe compatibilitylevel.Therearetwoaspectstothisplanningmethodology:
1. Specificationofplanninglevels—TheIECdefinesplanninglevelas “levelofaparticulardisturbanceinaparticularenvironment,adopted asareferencevalueforthelimitstobesetfortheemissionsfromthe installationsinaparticularsystem,inordertoco-ordinatethoselimits withallthelimitsadoptedforequipmentandinstallationsintendedto beconnectedtothepowersupplysystem.”Theplanningleveleffectivelyidentifiesthemaximumdisturbancemagnitudethatshouldbepresentataparticularlocation.
2. Allocationofemissionlevelstolargeloads—Emissionlevelisdefinedby theIECas“levelofagivenelectromagneticdisturbanceemittedfroma particulardevice,equipment,systemordisturbinginstallationasawhole, assessedandmeasuredinaspecifiedmanner.”Forlargeinstallationsconnectingtomediumvoltagenetworksandabove,itistypicaltoundertake anemissionallocationprocessinordertolimittheoverallcontributionthat anyparticularinstallation(loadorgenerator)maymaketooverallpower qualitydisturbancelevelsthroughtheirpowerqualityemissions.Forlow voltagenetworks,thepowerqualityemissionsofequipmentandinstallationsaregenerallycontrolledthroughstandardswhichlimitthemagnitude ofemissionfromindividualpiecesofequipmentanditislesscommon foremissionallocationstobeprovidedforlowvoltageinstallations.
Basedonthephilosophiesdescribedbefore, Fig.1.10 providesvisualisation oftheprocessforimplementingapowerqualitymanagementphilosophy.
Fig.1.11 providesvisualisationoftheoverallpowerqualitymanagement philosophy,thatis,howcompatibilitylevels,planninglevelsandequipment immunityworktogetherinordertoensureappropriatepowerquality outcomesforallstakeholders.Networkdisturbancelevelsareduetothe
Fig.1.10 Flowchartforimplementationofapowerqualitymanagementphilosophy.
Fig.1.11
Fig.1.12 Visualisationofoverlappingresponsibilitiesfornetworkoperators,equipment suppliersandinstallationsforpowerqualitymanagement.
cumulativeimpactofallequipmentconnectedtothenetworkwhilstequipmentimmunitylevelsaredeterminedthroughtypetesting.
Inorderfortheentirepowerqualitymanagementphilosophytobe effective,aholisticapproachmustbeadoptedwhichlinkscompatibility levelswithplanninglevelsandtheemissionallocationstrategy.Eachofthese aspectsmustbewellunderstoodbythekeystakeholders,namely,thenetworkoperator,equipmentsuppliersandinstallations. Fig.1.12 provides visualisationoftheoverlappingresponsibilitiesrequiredforeffectivemanagementofpowerquality.
1.3.1Powerqualitystandards
Whilstbespokepowerqualitymanagementphilosophyandstandardsexist forindividualcountriesandevenindividualorganisations,thepredominant powerqualitymanagementmethodologyandstandardsusedoradoptedin mostlocationsareeitherthoseproducedbytheIECortheIEEE.
1.3.1.1IECstandards
TheIEChasahighlystructuredsuiteofpowerqualitystandardsforpower qualitywhicharecontainedwithintheumbrellaofElectromagneticCompatibility(EMC)andspecificallythe61000series.TheIEC61000seriesof standardsispublishedinseparatepartsaccordingtothefollowingstructure:
1. General:fundamentalprinciples,definitions
2. Environment:descriptionandclassificationoftheelectromagneticenvironment,compatibilitylevels
3. Limits:emissionandimmunitylimits
4. Testingandmeasurementtechniques:e.g.forassessingequipment immunityandforassessingdisturbancelevels
5. Installationandmitigationguidelines
6. Genericstandards:generalproceduresfortestingequipment
7. Miscellaneous
Thenomenclatureforthe61000seriesofIECstandardsis61000.Part Number.StandardNumber.Forexample,instrumentationstandardsare thereforenumberedintheformIEC61000.4.xwhilstlimitsfornetwork operators,installationsandequipmentarenumberedIEC61000.3.x. Whilstthecatch-alltermstandardsareoftenappliedtoIECdocuments, theIECactuallyhasthreetiersofdocumentasfollows:
•InternationalStandard(IS)—Aninternationalstandardisadocument thathasbeendevelopedthroughtheconsensusofexpertsfrommany countriesandisapprovedandpublishedbyagloballyrecognisedbody. Itcomprisesrules,guidelines,processesorcharacteristicsthatallowusers toachievethesameoutcometimeandtimeagain.
•TechnicalSpecification(TS)—Atechnicalspecificationapproachesan internationalstandardintermsofdetailandcompletenessbuthasnot yetpassedthroughallapprovalstages,eitherbecauseconsensushas notbeenreachedorbecausestandardisationisseentobepremature.
•TechnicalReports(TR)—Technicalreportsfocusonaparticularsubjectandcontain,forexample,data,measurementtechniques,test approaches,casestudies,methodologiesandothertypesofinformation thatareusefulforstandardsdevelopersandotheraudiences.Theyare nevernormative.Technicalreportstypicallyhavenotachievedtheconsensusrequiredforpublicationasaninternationalstandard.
1.3.1.2IEEEstandards
TheIEEEhasasomewhatlessstructuredapproachtostandardisationthan theIEC.IEEEstandardsalsotendtoincludemuchmore‘tutorial’orinformativetypeinformationthanIECstandards.TheIEEEstandardformanagementofharmonicsisIEEEStd519“IEEERecommendedPractices andRequirementsforHarmonicControlinElectricalPowerSystems.” IEEEStd1159is“IEEERecommendedPracticeforMonitoringElectric PowerQuality”providesrecommendationsformonitoringofpower quality.
IEEEcolourbookseriesalsoprovideusefulguidanceformanagementof powerquality,especiallythefollowing:
•IEEEStd142-2007“IEEERecommendedPracticeforGroundingof IndustrialandCommercialPowerSystems,”alsoknownasthe GreenBook.
•IEEEStd1100-2005“IEEERecommendedPracticeforPoweringand GroundingSensitiveElectronicEquipment,”alsoknownasthe EmeraldBook.
•IEEEStd446-1995“IEEERecommendedPracticeforEmergencyand StandbySystemsforIndustrialandCommercialApplications,”also knownastheOrangeBook.
1.4Overviewofcontents
Thisbookhasbeenwrittentospecificallyassistpractitionersworkingin powerquality;however,arangeofindividualsworkingintheelectricalsupplyindustrymayfindaspectsofthebookuseful.Thebookisdesignedto assistreaderstohaveabetterunderstandingofpowerqualityandtoexplain andsimplifycomplexaspectsoftheirjobs.Thecontentpresentedhasbeen collatedtoprovideaone-stopguidetobroadmanagementofpowerquality fromequipmentbehaviourthroughtonetworkoperationandplanning. Evaluationoftheperformanceandtrendsinmodernequipmentareprovided.Whererelevant,comprehensiveguidanceonthestandardsapplicable tomanagementofpowerqualityisalsoprovided.Thetheoreticalmaterial presentedinthebookissupportedbythelatestresearchaswellaslaboratory andfieldmeasurementsofequipmentandnetworkdata.Thebookmayalso beusefulinassistingwiththedesignofpowerqualityallocation,monitoring andassessmentsystems.Thisbookisorganisedasfollows:
1.4.1 Chapter2:Steady-statevoltageinlowvoltagenetworks
Thischapterdiscussestherelevanceofmanagingsteady-statevoltagemagnitudesinlowvoltagenetworks.Thechapterdetailstheimpactoftheproliferationofsmall-scalerenewableenergydevicesonvoltageandthe strategiesthatcanbeusedtomanagevoltageregulation.Thechapteralso examinestheimpactofsupplyvoltageonequipmentperformance,includingfindingsrelatedtolossofequipmentlife.
1.4.2 Chapter3:Impactandmanagementofpowersystem
voltageunbalance
Thischapterdiscussesvoltageunbalanceincludingitscausesandeffects includingimpactonequipmentbehaviour.Thechaptercontainsoutcomes ofthelatestresearchintotheimpactofunbalanceoninductionmotorperformance.Thechapteralsoprovidessomedetailsoftheeconomicimpactof voltageunbalanceonconsumers.
1.4.3Chapter4:Impactandmanagementofpowersystem harmonics
Thischapterdescribespowersystemharmonicsincludingtheircauses(with thefocusbeingonmodernequipment)andeffectsincludingimpacton equipmentbehaviour.Thechapteralsoprovidesanin-depthexplanation ofthecomplexIECguidelineswhichareusedformanagementofharmonics,includingapplicationofthestandardstolargerenewableenergy generators(currentlyatopicofmuchconjecture).Thelimitationsassociated withtheexistingapproachesusedtostudyharmoniccomplianceinnetworksarealsoaddressed.
Thischapteralsoexaminesthetopicalsubjectofhigh-frequencyharmonicemissionsfromsmall-scalerenewablegenerators.
1.4.4Chapter5:Impactandmanagementofpowersystem voltagefluctuations,flickerandrapidvoltagechanges
Thischapterdetailsthecausesandeffectsofvoltagefluctuations,flickerand rapidvoltagechanges,includingimpactonequipmentbehaviour.The chapteralsoexaminestheIECguidelinesthatareapplicabletovoltagefluctuationsandflicker,includingexplanationandsimplificationoftheemission allocationforflickerandrapidvoltagechanges.
1.4.5 Chapter6:Impactandmanagementofpowersystem voltagesags
Thischapterexaminesthecausesandimpactsofvoltagesags,includingthe economicimpactofvoltagesagsonconsumers.Modernmethodsoflimiting andmanagingvoltagesagbehaviourarealsoexamined.
1.4.6 Chapter7:Implicationsofequipmentbehaviouron powerquality
Thischapterinvestigatesthebehaviourofmodernequipmentasitpertains topowerquality.Inthepastdecadetherehavebeensignificantchangesto theoperatingcharacteristicsofdevicesconnectedtoelectricitydistribution systems.Majorchangesincludethemovementtohighefficiencylighting loads(i.e.LEDlamps),themovetowardspowerelectronicfrontendson mosthouseholdappliances(e.g.washingmachinesandrefrigerators)and theproliferationofrenewableenergytechnologiesatbothsmallandlarge scale.Thechapterwillhighlightthemajordifferencesbetweenperformance
ofmodernequipmentcomparedtotraditionalconceptswithrespectto equipmentperformance.
1.4.7
Chapter8:Powerqualitymonitoring,dataanalysis andreporting
Thischapterfocusesonpowerqualitymonitoring,dataanalysisandreporting.Methodologiesforbothreactive(i.e.inresponsetocomplaintsorfaults) andproactive(i.e.continuousmonitoringtoestablishbaselineperformance) willbediscussed.Topicsdiscussedinthechapterinclude
•RationaleforPQmonitoring.
•PQmonitoringinstruments.
•Analysisandreportingmethodologiesincludingindices.
•Standardsforpowerqualitymonitoring.
•Transducersforpowerqualitymonitoring.
References
[1]IEC,IEC60050,InternationalElectrotechnicalVocabulary(IEV),1990.
[2]IEEE,IEEE100™,TheAuthoritativeDictionaryofIEEEStandardsTerms,seventhed., 2000.
[3] IEC,Electromagneticcompatibility(EMC)—Part3-7:Limits—Assessmentofemission limitsfortheconnectionoffluctuatinginstallationstoMV,HVandEHVpowersystems, IECTR61000-3-7,2008.
[4] IEEERecommendedPracticeforMonitoringElectricPowerQuality,IEEEStd 1159-2019(RevisionofIEEEStd1159-2009),2019,pp.1–98.
[5] IEC,ElectromagneticCompatibility(EMC)—Part4-30:TestingandMeasurement Techniques—PowerQualityMeasurementMethods,2008.
