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State EstimationState Estimation

Remote Terminal Unit (Remote Terminal Unit (RTURTU) installed at a substation) installed at a substation door opendoor open

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Plays very important role inPlays very important role in MonitoringMonitoring ofPSofPS

ControlControl ofPSofPS

Security controlSecurity control

Economic DispatchEconomic Dispatch

AimAim ObtainObtain bestbest system state variablessystem state variables to fit ato fit a

scatter of datascatter of data

Scatter of data due toScatter of data due to Imperfect measurementsImperfect measurements Variations in transmission line linear modelsVariations in transmission line linear models

Line charging etcLine charging etc

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Imperfect measurements are due toImperfect measurements are due to Signal noiseSignal noise

Metering accuracyMetering accuracy AA\\ D conversionD conversion

NoisyNoisy datadata areare bestbest modeledmodeled asas randomrandom

variablesvariables

HenceHence estimatingestimating statestate variablesvariables isis basedbased ononstatisticalstatistical criterioncriterion

InIn PS,PS, statestate variablesvariables areare voltagevoltage magnitudesmagnitudes && phasephase anglesangles atat systemsystem

nodesnodes

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HistoryHistory

MajorMajor developmentsdevelopments takentaken placeplace inin aerospaceaerospace

fieldfield inin 2020thth centurycentury

ProblemProblem:: LocationLocation ofof aerospaceaerospace vehiclevehicle(missile,(missile, airplane,airplane, spacespace vehicle)vehicle)

:: EstimationEstimation of itsof its trajectorytrajectory

(Given redundant & imperfect measurements of(Given redundant & imperfect measurements of

position & velocity)position & velocity)

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Definition of State EstimationDefinition of State Estimation

IsIs thethe processprocess ofof assigningassigning aa

valuevalue toto anan unknownunknown systemsystem statestate

variablevariable basedbased onon measurementsmeasurements fromfrom

thatthat systemsystem accordingaccording toto somesome

(statistical)(statistical) criteriacriteria

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State EstimatorsState Estimators

TheyThey areare thethe methodsmethods \\ algorithmsalgorithms,,

developeddeveloped usingusing measurementsmeasurements fromfrom

networknetwork toto calculatecalculate statestate ofof networknetwork

PurposePurpose::

DetectDetect badbad // incorrectincorrect datadata DetectDetect changeschanges inin networknetwork configurationconfiguration

ReplaceReplace faultyfaulty // missingmissing datadata

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Data collection from PSData collection from PS

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?PS State Estimation?PS State Estimation

Problems in monitoring transmission systemProblems in monitoring transmission system

Nature of measurement transducersNature of measurement transducers

Communication problemsCommunication problems in transmitting valuesin transmitting values

back to operations control centreback to operations control centre

Transducers are subject toTransducers are subject to errorserrors

Telemetry equipments experience comm. channelTelemetry equipments experience comm. channel

outout no informationno information of some part of systemof some part of system

These are the reasons for developing PS SEThese are the reasons for developing PS SE

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Principles of State EstimationPrinciples of State Estimation

ConsiderConsider aa DCDC loadload flowflow exampleexample ofof 33--busbus

systemsystem

OnlyOnly informationinformation providedprovided isis byby threethree MWMW

powerpower flowflow metersmeters asas shownshown inin figfig.. meter meter

placementplacement

OnlyOnly TwoTwo ofof thethe metersmeters areare requiredrequired toto

calculatecalculate busbus phasephase angles,angles, loadload &&

generationgeneration valuesvalues fullyfully

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33 -- bus systembus system

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Meter placementMeter placement

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Case 1Case 1

SupposeSuppose metersmeters MM1313 && MM3232 areare usedused

SupposeSuppose MM1313 && MM3232 givegive usus perfectperfect readingsreadings ofof

flowsflows onon theirtheir respectiverespective transmissiontransmission lineslines

MM1313 = 5 MW = 0.05 pu= 5 MW = 0.05 pu

MM3232 = 40 MW = 0.40 pu= 40 MW = 0.40 pu

FlowsFlows onon lineslines 11--33 && 33--22 cancan bebe setset toto metermeter readingsreadings

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puMxf 05.0)(

11331

1313 !!! UU

puMx

f 40.0)(1

322332

32 !!! UU

We knowWe know 33 = 0, s= 0, solve the above equationsolve the above equations

rad02.01 !U rad10.02 !U&&

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Case 2Case 2

All three meter readings have slight errorsAll three meter readings have slight errors

Suppose readings obtained areSuppose readings obtained are

Suppose meters MSuppose meters M1313 & M& M3232 are used as beforeare used as before

puW 62.06212 !!

puMWM 06.0613 !!

puW 37.03732 !!

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Calculate phase anglesCalculate phase angles

This results in system flows as shown in fig.This results in system flows as shown in fig.

Flow on line 1Flow on line 1--2 does not match2 does not match

rad0925.02 !U

rad03 !U

rad024.01 !U

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Flows resulting from use of meters MFlows resulting from use of meters M1313 & M& M3232

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Case 3Case 3

Suppose meters MSuppose meters M1212 & M& M3232 are usedare used

Calculate phase angles & line flowsCalculate phase angles & line flows

This results in system flows as shown in fig.This results in system flows as shown in fig.

Flow on line 1Flow on line 1--3 does not match3 does not match

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Flows resulting from use of meters MFlows resulting from use of meters M1212 & M& M3232

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ConclusionConclusion

AA procedureprocedure isis neededneeded thatthat usesuses

informationinformation availableavailable fromfrom allall metersmeters toto

produceproduce thethe bestbest estimateestimate ofof actualactualangles,angles, lineline flows,flows, busbus loadload && generationsgenerations

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ReferenceReference

AllenAllen JJ..WoodWood andand BruceBruce FF..Woolenberg,Woolenberg,

PowerPower generation,generation, operationoperation andand

control,control, JohnJohn WileyWiley && sonssons IncInc..

GeorgeGeorge LL Kusic,Kusic, ComputerComputer--AidedAided

Power

Power SystemsSystems Analysis,Analysis,

Prentice

Prentice--HallHallofof India,India, PvtPvt.. LtdLtd..

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RTURTU

Provides interface for measurements ofProvides interface for measurements of

voltage, current , power flow, status .. tovoltage, current , power flow, status .. to

be transferred to the central computer viabe transferred to the central computer viatelemetrytelemetry

Also implements commands from the centralAlso implements commands from the centralcomputer to equipmentcomputer to equipment

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