Download - Topic 4 Industrial Power Quality

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Topic4Topic4INDUSTRIALINDUSTRIALPOWERQUALITYPOWERQUALITYBEF44903BEF44903

By:Engr.Dr.Kok BoonChing (JEK2013)

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BEF44903 IndustrialPowerSystems Topic4

OutlinesOutlines4.1MotorStartingStudies

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4.2ApplicationofIndustrialPowerFactorCorrection

4.3HarmonicsTreatmentinIndustrialPowerSystems

4 4 V lt S A l i4.4VoltageSagAnalysis

4.5FlickerAnalysis

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4.1MotorStartingStudies4.1MotorStartingStudiesDirectonDirectonlinestartinglinestarting Whenitisswitchedon,the

motor behaves like a

3

motorbehaveslikeatransformerwithitssecondary,formedbytheverylowresistancerotorcage,inshortcircuit.

Thereisahighinducedcurrentintherotorwhichresultsinacurrentpeakinthemainssupplypp y

Currentonstarting=5to8ratedCurrent

Torqueonstarting(ST)=0.5to1.5ratedtorque(RT)


4.1MotorStartingStudies4.1MotorStartingStudiesStarStardeltastartingdeltastarting Theprincipleistostartthe

motor by connecting the star

4

motorbyconnectingthestarwindingsatmainsvoltage,whichdividesthemotorsratedstarvoltageby3.

Thestartingcurrentpeak(SC)isdividedby3,SC=1.5to2.6RC(RCratedCurrent).

As the starting torque (ST) isAsthestartingtorque(ST)isproportionaltothesquareofthesupplyvoltage,itisalsodividedby3:ST=0.2to0.5RT(RTRatedTorque)

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4.1MotorStartingStudies4.1MotorStartingStudiesResistancestatorstartingResistancestatorstarting Themotorstartsatreduced

voltage because resistors are

5

voltagebecauseresistorsareinsertedinserieswiththewindings.

Whenthespeedstabilises,theresistorsareeliminatedandthemotorisconnecteddirectlytothemains.Thisprocessisusuallycontrolledp ybyatimer.

Thestartingcurrentandtorquevaluesaregenerally:SC=4.5RCST=0.75RT


4.1MotorStartingStudies4.1MotorStartingStudiesAutotransformerstartingAutotransformerstarting Inthefirstplace,the

autotransformerisstar

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connected,thenthemotorisconnectedtothemainsviapartoftheautotransformerwindings.

Thestarconnectionisopenedbeforegoingontofullvoltage.Thisoperationtakesplacewhenthespeedbalancesoutattheendofthefirststep.

The piece of autotransformerThepieceofautotransformerwindinginserieswiththemotorisshortcircuitedandtheautotransformerisswitchedoff.

Thevaluesobtainedare:SC=1.7to4RCST=0.5to0.85RT

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4.1MotorStartingStudies4.1MotorStartingStudiesSlipringmotorstartingSlipringmotorstarting Aslipringmotorcannotbe

started direct on line with its

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starteddirectonlinewithitsrotorwindingsshortcircuited,otherwiseitwouldcauseunacceptablecurrentpeaks.

Resistorsmustthereforebeinsertedintherotorcircuitandthengraduallyshortcircuited.

The current absorbed is moreThecurrentabsorbedismoreorlessproportionaltothetorquesupplied.Forexample,forastartingtorqueequalto2RT,thecurrentpeakisabout2RC.


4.1MotorStartingStudies4.1MotorStartingStudiesSoftstarterstartingSoftstarterstarting Thisisaneffectivestarting

system for starting and

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systemforstartingandstoppingamotorsmoothly.

Controlbycurrentlimitationsetsamaximumcurrent(3to4xRC)duringthestartingstageandlowerstorqueperformance.Thiscontrolisespeciallysuitable forturbomachines (centrifugalturbomachines (centrifugalpumps,fans).

Controlbytorqueadjustmentoptimises torqueperformanceinthestartingprocessandlowersmainsinrushcurrent.Thisissuitedtoconstanttorquemachines.

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4.1MotorStartingStudies4.1MotorStartingStudiesFrequencyconverterstartingFrequencyconverterstarting Thisisaneffectivestarting

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systemtousewheneverspeedmustbecontrolledandadjusted.

Itspurposesinclude: startingwithhighinertialoads, startingwithhighloadsonsupplieswithlowshortcircuitcapacity,

optimisation ofelectricityconsumption adapted to the speedconsumptionadaptedtothespeedof"turbomachines".

Itisasolutionprimarilyusedtoadjustmotorspeed,startingbeingasecondarypurpose.


4.1MotorStartingStudies4.1MotorStartingStudies 10

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4.1MotorStartingStudies4.1MotorStartingStudiesVoltagedrop/dip

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PQduringMotorStarting

InrushcurrentVoltageFlicker

Voltage/CurrentHarmonics


4.1MotorStartingStudies4.1MotorStartingStudiesEXAMPLE4.1:VoltagedropduringmotorstartingA i d t i l t l t

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1MVA11kV/415V%Z=5%X/R=5

ZS =(1.55+j1.66)m

PCC

SupplySystemAn industrial customer plans toconnect a new induction motorto the power supply system asshown in the diagram.

Using the permissible level ofvoltage fluctuations as a

M

ZL =(25+j60)m75kW415VPFStart =0.3KSOC =7kVA/kW

PCCvoltage fluctuations as acriterion, decide whether themotor should be installed.For the planned number of 20starts per hour the voltagechange: Kmax = 3%

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4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFC PowerFactorinSinusoidal Situations

R

13

M MotorLoad(Linear)Vsin (t)

R

)sin()()sin()(

101

101

tItitVtv

rmsrms

avgavgtrue IV

PSP

PF


4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFC Forthepurelysinusoidal case,

P

14

22

)cos(22

11

1111

22

IV

IVQP

PPFPF avgdisptrue

wherePFdisp iscommonlyknownasthedisplacementpowerfactor,andwhere(11)isknownasthepower factor angle

)cos(22

11 powerfactorangle.

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4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFC

7.00EffectofPFonPowerLosses

15

2.00

3.00

4.00

5.00

6.00

Power

Losses

(pu) Displacementpowerfactor

greatlyaffectslosses

0.00

1.00

2.00

1.00 0.90 0.80 0.70 0.60 0.50 0.40

P

PF


4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFC PowerFactorinNonsinusoidal Situations When steady state harmonics are presented the

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Whensteadystateharmonicsarepresented,thevoltagesandcurrentscanberepresentedbyFourierseriesoftheform,

1

0 )sin()(k

kk tkVtv

1

2

1

2

2 kkrms

k

krms V

VV

1

0

1

)sin()(k

kk

k

tkIti

1

2

1

2

11

2 kkrms

k

krms

kk

III

...)cos( 3211

avgavgavgk

kkkrmskrmsavg PPPIVP

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4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFC Totalharmonicdistortion(ordistortionfactor),

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%100%1001

2

2

1

2

2

V

V

V

VTHD k

k

rms

kkrms

V

%100%100 22

2

2

II

THD kk

kkrms

I %00%0011 II rms

I

21 )100/(1 Vrmsrms THDVV 21 )100/(1 Irmsrms THDII


4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFC Truepowerfactor,

1avgP

18

2211 )100/(1)100/(1

1

IVrmsrms

avgtrue

THDTHDIVPF

EXAMPLE4.2Calculatethetruepowerfactorforthefollowingmeasurements:Frequency (Hz) Voltage (V) Current (A)Frequency(Hz) Voltage(V) Current(A)

50 4150 5030150 9.525 1570250 5.840 5010350 1.235 5020

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4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFCEffectofPFtrueonPowerLosses

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3.004.005.006.007.008.00

wer

Losses

(pu)

NonLinearLoad

Linear Load

0.001.002.00

1.00 0.90 0.80 0.70 0.60 0.50 0.40

Pow

PF

LinearLoad


4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFC 20

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4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFC Averagepowerfactorvaluesforthemostcommonlyused

equipmentandappliances

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Why to improve

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Reductionof losses

Reductionofcablesize

Reductioninthecostofelectricity

Whytoimprovethepowerfactor?

Increaseinavailablepower

Reductionofvoltagedrop

oflosses(kW)incables

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4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFCFixedcapacitors Automaticcapacitorbankscto

r?23

Attheterminalsofinductivedevices(motors

andtransformers)

Atbusbars supplyingnumeroussmallmotors

Atthebusbars ofageneralpowerdistribution

board

Attheterminalsofaheavilyloadedfeederve

thep

ower

fac

andinductive

Incaseswherethelevelofloadisreasonably

constant

ycable

How

toim

prov


4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFC(Design)(Design)

IndentifySystemRequirements

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CapacitorSizingConsiderharmonicscondition(capacitorvoltage > system voltage) frequency?

CalculatecompensatedQaccordingtothesystem needs

Totalsystemloading(P&Q) Frequencyandvoltage(system&capacitors) OverallPFandtargetPF

AnalysisforPossiblePQResonanceeffect? Switchingtransient?

voltage>systemvoltage),frequency? systemneeds.

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4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFC(Design)(Design)

1121 QQQC 25

2111 costancostan PFPFP PFDesired

PFOriginal0.85 0.86 0.87 0.88

0.50

0 51

KFactor

0.51

0.52

0.53


4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFC(Design)(Design) Differencesinvoltage/frequencylevelbetweenthesupplysystem andthecapacitor usedwillproducedifferent injected reactive power into the system

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differentinjectedreactivepowerintothesystem. Thefactortobeconsideredisasfollows:

where

2

S

CAPSCAP VVQQ

S

CAPSCAP f

fQQ

where,QCAP =EffectivereactivepowerprovidedbycapacitorQS =EffectivereactivepowerinjectedintosupplysystemVCAP =CapacitorvoltagelevelVS =Supplysystemvoltagelevel

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4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFCEXAMPLE4.3

Incoming

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Incoming3phase,50Hz,400V

M1 M2C1 C2

L1



Component DescriptionM1 8unitsof3phaseinductionmotor,eachoneratedat2kVA,

0.78laggingpowerfactorwith88%efficiency.M2 24unitsofsinglephaseconveyormotor,connectedinbalance

3phasecoordination,eachoneratedat300W,0.82laggingpowerfactorwith78%efficiency.

L1 Lumploads,ratedat10kVAr,0.9laggingpowerfactor.C1 6 steps power factor corrector with the switching arrangementC1 6stepspowerfactorcorrectorwiththeswitchingarrangement

of(1:1:2:2:4:4).Theunitcapacitorusedisratedat525V,2kVAr.

C2 3stepspowerfactorcorrectorwiththeswitchingarrangementof(1:2:3).Theunitcapacitorusedisratedat440V.

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4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFC Analysetheaveragepowerfactorofthisfactorywhenboth

powerfactorcorrectors,C1andC2aredisabled.

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RecommendtheproperkVAr ratingfortheunitcapacitorusedinC2ifthepowerfactorforthegroupmotorcircuit,M1istobecorrectedatleastto0.95lagging.AssumeC2isswitchedtostep3.

AnalyseagaintheaveragepowerfactorforthisfactoryifC1d C2 it h d t t 4 d t 2 ti landC2areswitchedtostep4andstep2,respectively.

IftheC1andC2inFigureareaccidentallyswitchedtoitsmaximumstepsandL1isdisconnectedduetotheshortcircuitevent,predicttheoverallpowerfactorforthisinstallation.


4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFCSomeissuesinPFCapplication:

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Avoidnuisancetripscausebycapacitorswitchingtransients

Currentlimitingfusesat150%to175%ofthecapacitorratedcurrent

Capacitorshouldbedischargetoaresidualvoltageof50V,1minuteafteritisdisconnected

Greaterswitchingtransientswillberesulted if not

Avoidresonanceasitincreasestheheatinganddielectricstresses

Seriesresonancemightcausezerovoltageatsomefrequenciescurrent

Donotsettootightortooloose

Protection

resultedifnotproperlydischarged

CapacitorDischarge

frequencies Parallelresonanceswillamplifyharmonicsatspecificfrequencies

Harmonics

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SeriesSeries

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SeriesSeriesResonanceResonance



ParallelParallel

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ParallelParallelResonanceResonance

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4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFCResonance

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4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFCWhentohavefiltertoeliminatetheharmonics?

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Powerfactorcorrection(kvar)isgreaterthan25%ofthe transformer kVA

Harmonicproducingload(e.g.driveload)isgreaterthan40%ofthe transformer kVA

RISK

thetransformerkVA thetransformerkVANoproblemisexpectedifbelow15%

Noproblemisexpectedifbelow25%

kVArZkVA

hrtransforme

rtransforme

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4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFCCAPACITORSWITCHINGTRANSIENTS Capacitor switching transient is a normal system

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Capacitorswitchingtransientisanormalsystemeventthatcanoccurwheneveracapacitorisenergised.

Typically,deenergising acapacitordoesnotcauseasystemtransient.

Thetransientoccursbecauseofthedifferencebetweenthesystemvoltageandthevoltageonthecapacitor.


4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFC Themagnitudeofthetransientwillvarybasedon two variables at the time of the switching.

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ontwovariablesatthetimeoftheswitching.

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4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFC Thesevariablesaretheinitialvoltageonthecapacitor(trappedcharge,usuallyclosetozeroifthe

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capacitorhasbeenallowedtodischarge)andtheinstantaneoussystemvoltageatthetimeoftheswitching.

Thegreaterthedifferencebetweenthesetwovoltages,thegreaterthemagnitudeofthetransient.h ll h h Theworstcasetransientwilloccurwhenthesystemvoltageisatpeakvoltageandthereisatrappedchargeonthecapacitorofpeaksystemvoltageattheoppositepolarity.



LCVVI CStransient

Where,VS :Instantaneoussystemvoltage(V)VC :Instantaneouscapacitorvoltage(V)C:CapacitorvalueinFL:InductancevalueinH

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4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFCBACKTOBACKCAPACITORSWITCHING This situation occurs when a second capacitor is

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Thissituationoccurswhenasecondcapacitorisswitchedoninclose(electrical)proximitytoapreviouslyenergised capacitor.

Inthiscaseahigherfrequencytransientinitiallyoccursasthepreviouslyenergised capacitorsharesitschargewiththenewlyenergizedcapacitor.


4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFC Figurebelowshowstheenergisation ofa50kVAr, 480 V capacitor step with trapped charge

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kVAr,480Vcapacitorstepwithtrappedchargeandwith150kvar ofothercapacitorstepsinservice.

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4.2ApplicationofIndustrialPFC4.2ApplicationofIndustrialPFCMINIMISINGCAPACITORTRANSIENTS There are two basic ways to minimize capacitor

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Therearetwobasicwaystominimizecapacitorswitchingtransients. Switchthecapacitoratapointintimewhenthesystemvoltagematchesthevoltageonthecapacitor,evenifthereisatrappedcharge.I i d i i d i Insertsomeimpedance,resistanceorinductance,inthecircuittominimise thetransient(limitthecapacitorinrushcurrent,thusminimising theresultingvoltageoscillation).


4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystems 42

Fundamental(50Hz) Fifthharmonic(250Hz)Thirdharmonic(150Hz) Resultingwaveform

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4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystems Thisperiodicphenomenon(harmonics)canberepresented by a Fourier series as follows:

44

representedbyaFourierseriesasfollows: nn

nn tnYYty

sin2)(

10

where:

Y = the amplitude of the DC component which is generally

Accordingtostandards,harmonicordersabove40 areneglected.

Y0 =theamplitudeoftheDCcomponent,whichisgenerallyzeroinelectricalpowerdistribution(atsteadystate),Yn =theRMSvalueofthenth harmoniccomponent,n =phaseangleofthenthharmoniccomponentwhent=0.

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4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystemsHarmonicssourcesinindustrialapplications:

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pp Staticconverters(n=kp 1ofcurrentharmonics)

Arcfurnaces Lighting(dischargelampsorfluorescentlampsproducing3rd harmonics)

Variablespeeddrives Weldingmachines


4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystems Oneofthemostcommonharmonicssourcesinindustrial applications is rectifier loads.

46

industrialapplicationsisrectifierloads. TheharmonicloadcurrentdemandsofrectifiersmaybecalculatedfromtherectifierformulastofindI1,thenfindtheoddharmonics(Singlephase)or5,7,11,13th harmonics(sixpulse)

/using1/hrule

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4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystemsExample4.4A 1000 kVA three phase six pulse rectifier serves

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A1000kVA threephasesixpulserectifierservesa2000VDCloadusingthedelayangletoholdtheDCvoltageconstantoverallloadsintherange100kWto250kW.Thesupplytransformerisratedat1100kVA,13.8kV/6900V,x=20%,50Hz.Estimatethefifthandseventhharmoniccurrentsonthehighvoltagesideofthetransformerinthe100kWand250kWoperatingrange.


4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystemsSolution:Find transformer reactance

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Findtransformerreactance, 28.43

1100)6900( 22

kVAV

SVX LLbase

656.828.432.0SS XL3)(23 S ILVV

)2

cos(

22)cos()cos(

)cos(

disp

LL

dcS

dcS

LLdc

PF

VIL

IVV

SixpulseRectifierFormula

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4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystems At250kW,

49

003.71

2000250656.83cos6900232000

kW

22cos)cos(

LL

dcS

VIL

216.0)2/cos(042.13

)6900(2)2000/250)(656.8(2)003.71cos()003.71cos(

dispPF

kW


4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystems

kVAkWPFPS 1157

2160250

50

AII

AVSI

PF

PLL

disp

68.951

405.483

216.0

15

)(1

AII 92.671

17

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4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystems At100kW,

51

990.74

2000100656.83cos6900232000

kW

22cos)cos(

LL

dcS

VIL

2149.0)2/cos(206.5

)6900(2)2000/100)(656.8(2)990.74cos()990.74cos(

dispPF

kW



kVAkWPFPS 33.465

21490100

52

AII

AVSI

PF

PLL

disp

89.351

468.193

2149.0

15

)(1

AII 78.2715

17

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Summary

53

4

6

8

10

12

Harm

onic

Value(

A)

0

2

I5(250kW) I7(250kW) I5(100kW) I7(100kW)

Curren

t

HarmonicOrderbyApplicationPower



INSTANTANEOUS LONGTERM

CONSEQUENCESOFHARMONICS54

INSTANTANEOUSEFFECTS

Disturbcontrollers

LONGTERMEFFECTS

Additionalheatingoninductiveloads/equipment

Additionalerrorsininductiondiskelectricity

meters

Disturbprotectivedevices

Vibrationsandnoise

Interferenceoncommunicationandcontrol

circuits

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4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystemsSomesymptomscausedbyharmonics:

Voltagenotching

55

Erraticelectronicequipmentoperation Computerand/orPLClockups Overheating(motors,cables,transformers,neutrals) Motorvibrations Audiblenoiseintransformersandrotatingmachines Nuisancecircuitbreakeroperation Timingordigitalclockerrors Electricalfires Voltage/generatorregulatormalfunctioning


4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystemsCompatibilitylevelsforvoltagetolerance,voltageunbalanceandpowerfrequencyvariations

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4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystemsHarmonicStandardforIndustrialNetworks IEC6100024:2002Oddharmonicsnonmultipleofthree

57


4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystemsHarmonicStandardforIndustrialNetworks IEC6100024:2002Oddharmonicsmultipleofthree

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4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystemsHarmonicStandardforIndustrialNetworks IEC6100024:2002Evenharmonics

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4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystemsCompatibilitylevelsfortotalharmonicdistortion

60

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4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystemsHarmonicmitigationmethods:Passive filter (or tuned filter)

61

Passivefilter(ortunedfilter)ActivefilterMultipulse transformerHarmonicsmitigationtransformer



Passivefilter

62

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4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystems TunedFilter

Xf 1

63

LCXX

ffh

L

Cnn

00

1

CC Q

kVX2

CLXXX /XR n CLXXX CLn /Q

R n

22 /)(

/)(

hXhXRhZ

hXhXjRhZ

CLF

CLF


4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystemsEXAMPLE4.5A series filter is tuned to the 11th harmonic

64

Aseriesfilteristunedtothe11th harmonic.GivenXC =405Ohm.Calculatethefilterelements.Takethequalityfactor(Q)as50.

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4.3HarmonicsTreatmentin4.3HarmonicsTreatmentinIndustrialPowerSystemsIndustrialPowerSystemsEXAMPLE4.6What is the tuning order and the quality factor

65

Whatisthetuningorderandthequalityfactorfora36kVseriestunedfilterwithXC =544.5Ohms,XL =4.5OhmsandR=0.825Ohms?



Activefilter

66

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Multipulse transformer

68

Multipulse transformer

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Harmonicsmitigationtransformer

69



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4.4VoltageSagAnalysis4.4VoltageSagAnalysis 71


4.4VoltageSagAnalysis4.4VoltageSagAnalysisIEEEStd.11591995/MSIEC61000

72

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4.4VoltageSagAnalysis4.4VoltageSagAnalysis Maincausesofvoltagesagsinindustrialpowersystems:

73

systems: Faults inthesystem,includinglightningstrike Transformerenergising Heavyloadswitching,mainlylargemotor (>300HP)

Typesofvoltagesags: Sudden SinglePhaseSags PhasetoPhaseSags ThreephaseSags

QEXAMPLEStartinglargemotorsorbyelectricalfaultsinsidethefacility


4.4VoltageSagAnalysis4.4VoltageSagAnalysisSinglePhaseSags The most common voltage sags over 70% are single

74

Themostcommonvoltagesags,over70%,aresinglephaseeventswhicharetypicallyduetoaphasetogroundfaultoccurringsomewhereonthesystem.Thisphasetogroundfaultappearsasasinglephasevoltagesagonotherfeedersfromthesamesubstation Typical causes are lightning strikes treesubstation.Typicalcausesarelightningstrikes,treebranches,animalcontactetc.Itiscommontoseesinglephasevoltagesagsto30%ofnominalvoltageorevenlowerinindustrialplants.

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4.4VoltageSagAnalysis4.4VoltageSagAnalysisPhasetoPhaseSags 2 Phase phase to phase sags may be caused by

75

2Phase,phasetophasesagsmaybecausedbytreebranches,adverseweather,animalsorvehiclecollisionwithutilitypoles.Thetwophasevoltagesagwilltypicallyappearonotherfeedersfromthesamesubstation.


4.4VoltageSagAnalysis4.4VoltageSagAnalysisThreephaseSags Symmetrical3phasesagsaccountforlessthan20%

76

y p gofallsageventsandarecausedeitherbyswitchingortrippingofa3phasecircuitbreaker,switchorrecloser whichwillcreatea3phasevoltagesagonotherlinesfedfromthesamesubstation.3phasesagswillalsobecausedbystartinglargemotors butthis type of event typically causes voltage sags tothistypeofeventtypicallycausesvoltagesagstoapproximately80%ofnominalvoltageandareusuallyconfinedtoanindustrialplantoritsimmediateneighbours.

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4.4VoltageSagAnalysis4.4VoltageSagAnalysis

Metering systems? Motor quality? Speed

77

Meteringsystems?Monitoringsystems?Accuracyproblems?

Motorquality?Speedvariation?Motordrives

effects?

EFFECTSOFVOLTAGESAGS

ControlSystem?PLC?Electronicprocesscontrols?Sensors?Computercontrols?

VSD?

Industrialprocesses?Manufacturingstoppage?

Restartproduction?


4.4VoltageSagAnalysis4.4VoltageSagAnalysis Thedipmagnitudeduringafaultisdependenton two impedances, the source impedance, ZS

78

ontwoimpedances,thesourceimpedance, ZSandtheimpedancetothefault,ZF

EZZ

ZVFS

FPCC

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4.4VoltageSagAnalysis4.4VoltageSagAnalysis Industrialcustomerswhohaveinvestedheavilyin production equipment which is susceptible to

79

inproductionequipmentwhichissusceptibletovoltagesagsmusttakeresponsibilityfortheirownsolutionstovoltagesagsorlosesomebenefitfromtheirinvestment.

ReplacementofcomponentsorVoltagesagsareafactoflifetheycannotreadilybeeliminatedfromregularutilitysystems.

devices,whichareespeciallysensitive,withlessvoltagesensitivesubstitutesorinstallationofsomeformofprotectionagainstvoltagesags.


4.4VoltageSagAnalysis4.4VoltageSagAnalysisIdentifytheProblem

MeasuretheProblem

ChooseaSolution

80

EquipmentIdentification

Whichequipmentissusceptibletounplannedstoppages?

IdentifytheVoltageSags

Determine the

InstallMetering Installationofanelectronicmeterwithwaveformcapturecapability

RecordUnplannedProductionStoppages

Calculatethetypeofvoltagesagcorrectionofexpectedfuturevoltagesagevents

CorrecttheproblembychangingsomeDeterminethe

frequency,depthanddurationofthevoltagesags

pp g MeterCostvs.CostofUnplannedProductionStoppage

sensitivecomponents

IdentifythesizeoftheloadtobeprotectedinkVAanditssupplyvoltage

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4.4VoltageSagAnalysis4.4VoltageSagAnalysis Somepossiblevoltagesagscorrectionmethods:

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FerroresonantTransformer

UninterruptiblePowerSupply

(UPS)

FlywheelandMotor

Generator(MG)

DynamicVoltage

Restorer(DVR)StaticVar

Compensator(SVC)

SagProofingTransformers


4.4VoltageSagAnalysis4.4VoltageSagAnalysisFerroresonant Transformer Also known as a constant voltage transformer (CVT), is a

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Alsoknownasaconstantvoltagetransformer(CVT),isatransformerthatoperatesinthesaturationregionofthetransformerBHcurve.

Voltagesagsdownto30%retainedvoltagecanbemitigatedusingthistechnique.

Ferroresonant transformersareavailableinsizesuptoaround25kVAkVA.

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4.4VoltageSagAnalysis4.4VoltageSagAnalysisUninterruptiblePowerSupply(UPS) UPS mitigate voltage sags by supplying the load using stored

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UPSmitigatevoltagesagsbysupplyingtheloadusingstoredenergy.

Upondetectionofavoltagesag,theloadistransferredfromthemainssupplytotheUPS.

BlockDiagramofanofflineUPS BlockDiagramofanonlineUPS


4.4VoltageSagAnalysis4.4VoltageSagAnalysisFlywheelandMotorGenerator(MG) Flywheel systems use the energy stored in the inertia of a rotating

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Flywheelsystemsusetheenergystoredintheinertiaofarotatingflywheeltomitigatevoltagesags.

Theflywheelisacceleratedtoaveryhighspeedandwhenavoltagesagoccurs,therotationalenergyofthedeceleratingflywheelisutilised tosupplytheload.

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4.4VoltageSagAnalysis4.4VoltageSagAnalysisDynamicVoltageRestorer(DVR) DVRinjectsvoltageintothesystemin

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ordertobringthevoltagebackuptothelevelrequiredbytheloadduringvoltagesag.

Injectionofvoltageisachievedbyaswitchingsystemcoupledwithatransformerwhichisconnectedinserieswith the loadwiththeload.

ThedifferencebetweenaDVRwithstorageandaUPSisthattheDVRonlysuppliesthepartofthewaveformthathasbeenreducedduetothevoltagesag,notthewholewaveform.


4.4VoltageSagAnalysis4.4VoltageSagAnalysisStaticVar Compensator(SVC) A SVC is a shunt connected power electronics based device

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ASVCisashuntconnectedpowerelectronicsbaseddevicewhichworksbyinjectingreactivecurrentintotheload,therebysupportingthevoltageandmitigatingthevoltagesag.

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4.4VoltageSagAnalysis4.4VoltageSagAnalysisSagProofingTransformers Also known as voltage sag

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Alsoknownasvoltagesagcompensators,arebasicallyamultiwindingtransformerconnectedinserieswiththeload.

Effectiveforvoltagesagstoapproximately40%retainedvoltage.g

Onlyavailableforrelativelysmallloadsofuptoapproximately5kVA.


4.5FlickerAnalysis4.5FlickerAnalysis Flickerisdefinedasthevariationintheluminosityproducedinalightsourcebecauseoffluctuationsin

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p gthesupplyvoltage.

Themainsourcesofflickerarelargeandfastloadvariationsindustrialloads,suchaselectricarcfurnaces,motors,rollingmills,mashwelders electric welders and electric boilerswelders,electricwelders,andelectricboilers.

Thevoltageflickerischaracterised byvariationofvoltagemagnitudeintherangeof10%ofnominalvoltageandwithfrequencies between0.2to30Hz.

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4.5FlickerAnalysis4.5FlickerAnalysis Rectangularfluctuationatafrequencyof8.8Hzandanamplitude

V=0.4V(i.e.,V/V=40%),whichmodulatesamainssignalof50 H d li d V 1 V

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50HzandamplitudeV=1V.


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