Electronic Measurement - Power Factor Meter

This article speaks about electrical power factor and how it can be measured using power factor meter

1. Electrical & Electronic Measurement
Part –XI
Power Factor Meter
ER. FARUK BIN POYEN
[email protected]
AEIE, UIT, BU

2. Contents:
Power Factor
Power Factor Meter
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3. Power Factor:
Powerfactorisdefinedastherationoftheactivepower(P)andvolt-
amperes(VI).
TheactivepoweristherealpowerwhichisassumedinanACcircuit,
whereasthevolt-amperesistheapparentpowerwhichisproducedinthe
circuitwhenthewavesofvoltageandcurrentarenotinphase.
Forsinusoidalwaveform,
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4. Low Power Factor Causes:
Majorreasonforlowpowerfactor(PF)istheinductiveload.
Thecurrentistheinductiveloadlagsbehindthevoltage,andtherefore
PFisalsolagging.
TheinductiveloadsresponsibleforlowPFare3-ɸinductionmotor,
transformer,weldingequipmentandlamps.
DisadvantagesofLowPF:
1.Highercurrentisrequiredbytheequipment.
2.AtlowPF,thecurrentishighgivingrisetocopperlossesinthesystem.
3.Lowerstheefficiencyoftheequipment.
4.Highercurrentproducesalargevoltagedropintheapparatus.
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5. Power Factor Improvement:
TherearethreemainwaysofimprovingPF
1.CapacitorBanks
2.SynchronousCondensers
3.PhaseAdvancers
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6. Power Factor Improvement: Capacitor Bank
Byreducingthephasedifferencebetweenvoltageandcurrent,PFcan
beimproved.
Sincethemajorityoftheloadisinductive,thisrequiressomeamountof
reactivepowerforfunctioning.
Capacitorbankinstalledinparalleltotheloadprovidesthisreactive
power.
Itactsasasourceoflocalreactivepower,andthuslessreactivepower
flowsthroughtheline.
Capacitorbanksreducethephasedifferencebetweenthevoltageandthe
current.
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7. Power Factor Improvement: Synchronous Condenser:
Synchronouscondensersare3phasesynchronousmotorwithnoload
attachedtoitsshaft.
Thesynchronousmotorhasthecharacteristicsofoperatingunderany
powerfactorleading,laggingorunitydependingupontheexcitation.
Forinductiveloads,asynchronouscondenserisconnectedtowardsthe
loadsideandisoverexcited.
Synchronouscondensersmakeitbehavelikeacapacitor.
Itdrawsthelaggingcurrentfromthesupplyorsuppliesthereactive
power.
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8. Power Factor Improvement: Phase Advancers
ThisisanACexcitermainlyusedtoimprovethePFofaninduction
motor.
Theyaremountedontheshaftofthemotorandareconnectedtothe
rotorcircuitofthemotor.
Itimprovesthepowerfactorbyprovidingtheexcitingampereturnsto
producetherequiredfluxatthegivenslipfrequency.
Further,ifampere-turnsincrease,itcanbemadetooperateatleading
powerfactor.
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9. Power Factor Meter:
Thepowerfactormetermeasuresthepowerfactorofatransmission
system.
Thepowerfactoristhecosineoftheanglebetweenthevoltageand
current.
Thepowerfactormeterdeterminesthetypesofloadusingontheline,
anditalsocalculatesthelossesoccuronit.
Thepowerfactorofthetransmissionlineismeasuredbydividingthe
productofvoltageandcurrentwiththepower.Andthevalueofvoltage
currentandpoweriseasilydeterminedbythevoltmeter,ammeterand
wattmeterrespectively.
Thismethodgiveshighaccuracy,butittakestime.
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10. Power Factor Meter:
DirectPFmeasurementintransmissionlines(continuouslychanging
withtime)isfasterbutlessaccurate.
Thepowerfactormeterhasthemovingsystemcalledpointerwhichisin
equilibriumwiththetwoopposingforces.
Thus,thepointerofthepowerfactormeterremainsatthesameposition
whichisoccupiedbyitatthetimeofdisconnection.
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11. Power Factor Meter: Construction
AdynamometertypepowerfactormeterconsistsoftwofixedcoilsFF
connectedinseriescarryingtheloadcurrent(oradefinitefractionofit)
formingthecurrentcircuit,andtwoidenticalmovingcoilsAandB
fixedatthenearlyrightangletoeachotherpivotedonthesamespindle
formingthepressurecircuitasshowninthefigure.
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12. Power Factor Meter: Construction
ThecurrentcoilsFFarewoundwiththickwirewhereaspressurecoilsA
andBarewoundwithfinewire.
Thepressurecoilsfixedonthesamespindle,towhichapointeris
attached,constitutesthemovingsystem.
ThepressurecoilAisconnectedacrossthesupplythroughanon-
inductiveresistantandpressurecoilBisconnectedacrossthesupply
throughhighlyinductivechokecoilofinductanceL.
ThevalueofresistanceRandinductanceLaresochosenthatforthe
mainsupplyfrequency,thecurrentinthetwopressurecoilsAandBis
thesame.
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13. Power Factor Meter: Construction
Thusthefieldsproducedbythetwocoilsareofthesamestrength.The
fieldproducedbythecoilBlagsbehindthefieldproducedbythecoilA
slightlylessthan90°becauseofresistanceofthecoil.
AccordinglywhilefixingthecoilBtheplaneofthiscoilisdisplaced
fromtheplaneofthecoilAbytheelectricalanglewhichisslightlyless
than90°.
Howeverwhilediscussingtheaction(working)oftheinstrumentitwill
beassumedthatthephasedifferencebetweenthetwocurrentsflowing
throughthecoilsAandBis90°andsameistheanglebetweenthe
planesofthecoils.
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14. Power Factor Meter: Working Principle
ThebasicworkingprincipleofPFmeterissimilartothatof
dynamometertypewattmeteri.e.whenthefieldproducedbymoving
systemtriestocomeinlinewiththefieldproducedbythefixedcoil,
deflectingtorqueisexertedonthemovingsystemwhichdeflectsthe
pointerattachedtoit(themovingsystem).
PFmeterisanindicatinginstrumentandnocontrollingtorqueis
providedinthisinstrument.Thecurrentsarebeingledintothemoving
coilsAandBbyfineligamentswhichexertnocontrol.
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15. Power Factor Meter: Working Principle
Whentheinstrumentisconnectedtotheloadcircuit,currentflows
throughthefixedcoilsFFandMovingcoilsAandB,fluxissetbythe
fixedcoilsandmovingcoils.
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16. Power Factor Meter: Output Conditions
Bythealignmentoftwofields,torqueisdevelopedi.e.theresultant
fieldproducedbythemovingcoilstriestocomeinlinewiththefield
producedbythefixedcoilsandtorqueisdevelopedtillbothofthem
comeinlinewitheachother.Therearethreeextremeconditionsin
whichthisinstrumentisconnectedinthecircuit.
1.Whenpowerfactorofthecircuitisunity:
2.Whenpowerfactorofthecircuitiszerolagging:
3.Whenpowerfactorofthecircuitiszeroleading:
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17. Power Factor Meter: Condition 1
Whenpowerfactorofthecircuitisunity:Inthiscase,currentisin
phasewithcircuitvoltage.ThecurrentflowingthroughpotentialcoilA
isinphasewiththevoltagewhichisalsoinphasewiththecurrent
flowingthroughcurrentcoilFF.
Atthesametime,thecurrentflowingthroughpotentialcoilBlags
behindvoltageaswellasthecurrentflowingthroughcurrentcoilFFby
90°.ThuspressurecoilAwillexperienceaturningmomentsoitsplane
willcomeinpositionaparalleltotheplaneofthecurrentcoilFF.
ThetorqueactingonthepressurecoilBiszero.Thus,thepointer
indicatesunitypowerfactoronthescale.
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18. Power Factor Meter: Condition 2
Whenpowerfactorofthecircuitiszerolagging:Inthiscase,current
lagsbehindthecircuitvoltageby90°.Therefore,thecurrentflowing
throughpressurecoilBwillbeinphasewiththecurrentincurrentcoils
FF,bothbeinglaggingbehindthecircuitvoltageby90°.
ThecurrentflowingthroughpressurecoilAwillleadthecurrentin
currentcoilFFby90°.Thusaturningmomentactsonthepressurecoil
BandbringsitsplaneparalleltotheplaneofcurrentcoilFFandpointer
indicateszeropowerfactorlagging.
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19. Power Factor Meter: Condition 3
Whenpowerfactorofthecircuitiszeroleading:Inthiscasecurrent
leadsthecircuitvoltageby90o.Therefore,thecurrentflowingthrough
pressurecoilAlagsthecurrentincurrentcoilFFby90°andthecurrent
flowingthroughpressurecoilBlagsthecurrentincurrentcoilFFby
180°.
Thusfieldproducedbythemovingsystemisjustreversedtothatinthe
case(2).ThusanoppositeturningmomentactsonthepressurecoilB
andbringsitsplaneparalleltotheplaneofcurrentcoilFFandpointer
indicateszeropowerfactorleading.
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20. Power Factor Meter: Types
Thepowerfactormeterisoftwotypes.Theyare
1.Electrodynamometer
a)SinglePhaseElectrodynamometer
b)ThreePhasesElectrodynamometer
2.MovingIronTypeMeter
a)RotatingIronMagneticField
b)NumberofAlternatingField
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21. References:
https://circuitglobe.com/power-factor-meter.html
https://www.electrical4u.com/power-factor-meters-electrodynamometer-
type-power-factor-meter/
https://www.yourelectricalguide.com/2017/01/power-factor-meter.html
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