Phasor Measurement Unit (PMU)

These slides are all about Phasor Measurement Units (PMUs). An introduction to PMU is presented as a preliminary knowledge for the course 'Distribution Generation and Smart Grid'. Your valuable suggestions are welcome.

1. CLASS-4: PHASORMEASUREMENT UNIT
(PMU)
Prof. (Dr.) PravatKumar Rout
Department of EEE
ITER
Siksha‘O’ Anusandhan
(Deemed to be University),
Bhubaneswar, Odisha, India
Course: Distribution Generation and Smart Grid
Swetalina Sarangi
(Research Scholar)
Department of EE
ITER
Siksha‘O’ Anusandhan
(Deemed to be University),
Bhubaneswar, Odisha, India

2. WHATISPHASOR?
Phasor is a quantity with
magnitude and phase (with
respect to a reference) that is used
to represent a sinusoidal signal.
Here the phase or phase angle is
the distance between the signal’s
sinusoidal peak and a specified
reference and is expressed using
an angular measure.
Here, the reference is a fixed point
in time (such as time = 0).
The phasor magnitude is related to the
amplitude of the sinusoidal signal.

3. WHATISPHASOR MEASUREMENT UNIT?
Aphasormeasurement unit(PMU)isadeviceusedtoestimatethe
magnitudeandphaseangleofanelectricalphasorquantity(suchas
voltageorcurrent)intheelectricgridusingacommontimesourcefor
synchronization.
TimesynchronizationisusuallyprovidedbyGPSandallows
synchronizedreal-timemeasurementsofmultipleremotepointsonthegrid.
PMUsarecapableofcapturingsamplesfromawaveforminquick
successionandreconstructingthephasorquantity,madeupofanangle
measurementandamagnitudemeasurement.
Theresultingmeasurementisknownasasynchrophasor.Thesetime
synchronizedmeasurementsareimportantbecauseifthegrid’ssupplyand
demandarenotperfectlymatched,frequencyimbalancescancausestresson
thegrid,whichisapotentialcauseforpoweroutages.

4. CONTINUE...
PMUscanalsobeusedtomeasurethefrequencyinthepower
grid.
AtypicalcommercialPMUcanreportmeasurementswithveryhigh
temporalresolutionintheorderof30-60measurements per
second.Thishelpsengineersinanalyzingdynamiceventsinthegrid
whichisnotpossiblewithtraditionalSCADAmeasurementsthat
generateonemeasurementevery2or4seconds.
Therefore,PMUsequiputilitieswithenhancedmonitoringand
controlcapabilitiesandareconsideredtobeoneofthemost
importantmeasuringdevicesinthefutureofpowersystems.
APMUcanbeadedicateddevice,orthePMUfunctioncanbe
incorporatedintoaprotectiverelayorotherdevice.

5. WHY PMU?
PMUanessentialcomponentofSmartGrids.
ItprovidesSynchrophasordata
ReportsMagnitude,PhaseandFrequencyofanAC
waveform
Makesthegridobservableduetohighreportingrates
Preventiveactionscanbetakensuchasblackouts

6. THEMAINCOMPONENTS OFPMU
Analog Inputs
GPS receiver
Phase locked oscillator
A/D converter
Anti-aliasing filters
Phasor micro-processor
Modem

7. BLOCKDIAGRAM OFPMU

8. ANALOG INPUTS
Currentandpotential
transformers are
employedatsubstationfor
measurementofvoltage
andcurrent.
Theanaloginputstothe
PMUarethevoltages
andcurrentsobtained
from the secondary
windingofpotentialand
currenttransformers.

9. ANTI-ALIASINGFILTERS
Anti-aliasingfilterisananaloglow
passfilterwhichisusedtofilter
outthosecomponentsfromthe
actualsignalwhosefrequencies
aregreaterthanorequaltohalf
ofnyquistratetogetthesampled
waveform.
Nyquistrateisequaltotwicethe
highestfrequencycomponentofinput
analogsignal.
Ifantialiasingfiltersarenotused,
errorwillbeintroducedinthe
estimatedphasor

10. PHASELOCKOSCILLATOR
Phaselockoscillatoralong
withGlobalPositioning
System referencesource
providestheneededhigh
speed synchronized
sampling.
GlobalPositioningSystem
(GPS)isasatellite-based
system for providing
positionandtime.

11. A/DCONVERTER
Itconvertstheanalogsignaltothe
digitalsignal.
QuantizationoftheinputinvolvesinADC
thatintroducesasmallamountoferror.
TheoutputofADCisasequenceofdigital
valuesthatconvertacontinuoustimeand
amplitudeanalogsignaltoadiscretetime
anddiscreteamplitudesignal.
Itisthereforerequiredtodefinetherateat
whichnewdigitalvaluesaresampledfrom
theanalogsignal.
Therateofnewvaluesatwhichdigital
valuesaresamplediscalledthesampling
rateoftheconverter.

12. GLOBALPOSITIONING SYSTEM
ThesynchronizedtimeisgivenbyGPSuses
thehighaccuracyclockfromsatellite
technology.
WithoutGPSprovidingthesynchronized
time,itishardtomonitorwholegridatthe
sametime.
TheGPSsatellitesprovideaveryaccurate
timesynchronizationsignal,available,via
anantennainput,throughoutthepower
system.Thismeansthatthatvoltageand
currentrecordingsfromdifferentsubstations
canbedirectlydisplayedonthesametime
axisandinthesamephasordiagram.

13. PROCESSOR
Themicroprocessorcalculatespositive-
sequenceestimatesofallthecurrentand
voltagesignalsusingtheDFTtechniques.
Certainotherestimatesofinterestare
frequencyandrateofchangeoffrequency
measuredlocally,andthesealsoareincluded
intheoutputofthePMU.
Thetimestampiscreatedfromtwoofthe
signalsderivedfromtheGPSreceiver.
Thetime-stampidentifiestheidentityofthe
“universaltimecoordinated(UTC)secondand
theinstantdefiningtheboundaryofoneofthe
powerfrequencyperiods.

14. MODEM
Adevicethatmodulatesananalog
carriersignalandencodesdigital
informationfromthesignalandcan
alsodemodulatethesignaltodecode
thetransmittedinformationfrom
signaliscalledmodem.
Theobjectiveofmodemistoproducea
signalthatcanbetransmittedand
decodedtomakeareplicaofthe
originaldigitaldata.
Modemcanbeusedwithnomeansof
transmittinganalogsignals

15. SYNCHROPHASOR
Asynchrophasorisa
phasor measurement
withrespecttoan
absolutetimereference.
Withthismeasurement
wecandeterminethe
absolute phase
relationshipbetween
phasequantitiesat
differentlocationson
thepowersystem.

17. CONTINUE...Lagging Phase Angles
Leading Phase Angles
Leading Phase Angles
Reference Phase angle (0 Degree)

18. FEATURES OFPMUS
PMUsareMeasures50/60HzACwaveforms(voltageand
current)typicallyatarateof48samplespercycle.
PMUsarethencomputedusingDFT-likealgorithms,andtime
stampedwithaGPS.
TheresultanttimetaggedPMUscanbetransmittedtoalocal
orremotereceiveratratesupto60samplespercycle.

19. APPLICATION OFPMUINPOWER SYSTEM
1.Adaptiverelaying
2.Instabilityprediction
3.Stateestimation
4.Improvedcontrol
5.Faultrecording
6.Disturbancerecording
7.Transmissionandgenerationmodelingverification
8.WideareaProtection
9.Faultlocation

20. Adaptive Relaying
Adaptiverelayingisa
protectionphilosophywhich
permitsandseekstomake
adjustments in various
protectionfunctionsinorderto
makethemmoretunedto
prevailingpower system
conditions

21. Instability prediction
Theinstabilitypredictioncan
beusedtoadaptloadshedding
and/oroutofsteprelays.
Wecanactuallymonitorthe
progressofthetransientinreal
timebythetechniqueof
synchronized phasor
measurements.

22. •Thestateestimatorusesvariousmeasurementsreceivedfrom
differentsubstations,and,throughaniterativenonlinear
estimationprocedure,calculatesthepowersystemstate.
State estimation
•Bymaintainingacontinuousstreamofphasordatafromthe
substationstothecontrolcenter,astatevectorthatcanfollowthe
systemdynamicscanbeconstructed.
•Forthefirsttimeinhistory,synchronizedphasormeasurements
havemadepossiblethedirectobservationofsystem
oscillationsfollowingsystemdisturbances.

23. The role of state estimation in power system operationContingency
Analysis
Security
Enhancement
Dynamic Security
Analysis
Optimal Power
Flow
Other
Applications
State
Estimation
Other
Data
Network
Model
SCADA
PDC
PMU PMUPMU

24. • Power system control elements use local feedback to achieve the control
objective.
Improved control
•ThePMUwasnecessarytocapturedataduringthestaged
testingandaccuratelydisplaythisdataandprovide
comparisonstothesystemmodel.
•The shown figure shows a typical example of one of the output
plots from the PMU data

26. •Theycancaptureanddisplayactual60/50Hzwaveformand
magnitudedataonindividualchannelsduringpowersystemfault
conditions.
Fault Recording

27. •Lossofgeneration,lossofload,orlossofmajortransmissionlines
mayleadtoapowersystemdisturbance,possiblyaffecting
customersandpowersystemoperations.
Disturbance Recording

28. •Computerizedpowersystemmodelingandstudiesarenowthe
normalandacceptedwaysofensuringthatpowersystem
parametershavebeenreviewedbeforelargecapitalexpenditures
onmajorsystemchanges.
Transmission and Generation
Modeling Verification
•Inyearspast,actualverificationofcomputermodelsvia
fieldtestswouldhavebeeneitherimpracticalorevenimpossible
•ThePMUclassofmonitoringequipmentcannowprovidethe
fieldverificationrequired.

29. •Theshownfigurecomparesaremotesubstation500kVbus
voltagecapturedbythePMUtothestabilityprogramresults
Continue …
Positive sequence voltage phasor on a 500 kvbus vs computer model
simulation of switching test

30. TheintroductionofthePhasorMeasurementUnit(PMU)has
greatlyimprovedtheobservabilityofthepowersystem
dynamics.BasedonPMUs,differentkindsofwidearea
protection,emergencycontrolandoptimizationsystemscanbe
designed
WIDE–AREAPROTECTION

31. Multilayered wide area protection architecture

32. Afaultlocationalgorithmbasedonsynchronizedsampling.Atime
domainmodelofatransmissionlineisusedasabasisforthe
algorithmdevelopment.Samplesofvoltagesandcurrentsatthe
endsofatransmissionlinearetakensimultaneously
(synchronized)andusedtocalculatefaultlocation.
Fault Location
Phasormeasurementunitsareinstalledatbothendsofthe
transmissionline.Thethreephasevoltagesandthreephasecurrents
aremeasuredbyPMUslocatedatbothendsoflinesimultaneously

33. Apuresinusoidquantitygivenby??????�=??????
??????cos(??????�+??????)andits
phasorrepresentation??????= Τ??????
??????2??????
????????????
= Τ??????
??????2??????��??????+����??????
areillustratedinFigure.Theaimofphasorestimationtechnique
isjusttoacquirethephasorrepresentation.
Samplesofwaveformdataarecollectedoveradatawindowwhich
isnormallyoneperiodofthefundamentalfrequencyofthepower
system.Inearlydaysasamplingrateof12timesacycle(720Hz
forthe60Hzsystem)wascommonlyused.Muchhighersampling
ratesarecurrentlyusedincommercialPMUs.
Phasor MeasuremnetTechniques

34.  RMSt tx
RMS
Imaginary Axis
Real Axis
(a) (b) A sinusoid and its representation as a phasor

35. COMPARISON
Digital measurement
60 samples per cycle
(resolution)
Dynamic (Observability)
Wide area monitoring
Phasorangle
measurement: Yes
SCADA PMU
Analogue measurement
2-4 samples per cycle
(resolution)
Steady state
(Observability)
Local monitoring
Phasorangle
measurement: No

36. REFERENCES
Phadke,A.G.,&Thorp,J.S.(2006,October).Historyand
applicationsofphasormeasurements.In2006IEEEPESPower
SystemsConferenceandExposition(pp.331-335).IEEE.
Tholomier,D.,Kang,H.,&Cvorovic,B.(2009,March).Phasor
measurementunits:Functionalityandapplications.In2009
PowerSystemsConference(pp.1-12).IEEE.
Phadke,A.G.,&Tianshu,B.I.(2018).Phasormeasurement
units,WAMS,andtheirapplicationsinprotectionandcontrolof
powersystems.JournalofModernPowerSystemsandClean
Energy,6(4),619-629.

37. QUESTIONS
How does a Phasor Measurement Unit (PMU) work?
Whatare the main components of PMU? Explain
briefly with PMU Block Diagram.
What is use of PMU in Smart Grid?
Explain the application of PMU in power system.
What is synchrophasor?
What is phasor measurement techniques?