module 2_1.pdf load flow analysis ,PSA-2

Psa-2 module 2 LPF notes .

1. POWER SYSTEM ANALYSIS –2
18EE71
Module-2
Load Flow Studies: Introduction,
Classification of buses.
Power flow equation,
Operating Constraints,
Data for Load flow,
Gauss Seidaliterative method. Illustrative examples.
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2. LOAD FLOW STUDIES
•Loadflowstudiesareimportantinplanninganddesigningfuture
expansionofpowersystems.Thestudygivessteady-statesolutionsofthe
voltagesatallthebuses,foraparticularloadcondition
•importantaspectsofthesystemoperation,suchas:violationofvoltage
magnitudesatthebuses,overloadingoflines,overloadingofgenerators,
stabilitymarginreduction,indicatedbypowerangledifferencesbetween
buseslinkedbyaline,effectofcontingencieslikelinevoltages,the
emergencyshutdownofgenerators,etc.Loadflowstudiesarerequiredfor
decidingtheeconomicoperationofthepowersystem.
•Thesolutionprovidesthevoltagesatvariousbuses,powerflowingin
variouslinesandlinelosses
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3. Information obtained from a load flow
study
•Magnitudeandphaseofbusvoltages,realandreactivepowerflowingin
eachlineandthelinelosses
•Loadflowsolutionalsogivestheinitialconditionsofthesystemwhen
thetransientbehaviourofthesystemistobestudied
•It is essential to decide the best operation of the existing system and for
planning the future expansion of the system
•It is also essential for designing a new power system
Need for load flow study
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4. Work involved in a load flow study or How
a load flow study is performed?
i. Representation of the system by single-line diagram
ii. Determining the impedance diagram using the information in single
line diagram
iii. Formulation of network equations
iv. Solution of network equations
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5. Quantities associated with each bus in a
system
1.Real Power(P)
2.Reactive Power (Q)
3.Magnitude of Voltage (|V|)
4.Phase angle of voltage ()
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6. POWER FLOW EQUATION
Derive the expression for power flow equation used in load flow studies (6m)
•Theanalysisisrestrictedtoabalancedthree-phasepowersystemsothattheanalysiscanbecarriedoutonasingle-phasebasis.Theper-unitquantitiesareusedforallquantities.Thefirststepintheanalysisistheformulationofsuitableequationsforthepowerflowsinthesystem.
•Thepowersystemisalargeinterconnectedsystem,wherevariousbusesareconnectedbytransmissionlines.Atanybus,complexpowerisinjectedintothebusbythegeneratorsandcomplexpoweri_drawnbytheloads.Ofcourse,atanybus,eitheroneofthemmaynotbepresent.(Thepoweristransportedfromonebustoanotherviathetransmissionlines.
18EE71 DR P KASI VISWANATHAN-EEE-DSATM

7. At any bus i, the complex power S; (injected) is defined as
S,=Sgi–Spi
S, = net complex power injected into bus i.
Sgi= complex power injected by the generator at bus i.
Spi= complex power drawn by the load at bus i.
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8. is vector of currents injected at the buses.
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12. CLASSIFICATION OF BUSES
1.Voltage controlled bus
2.Load bus
3.Slack bus
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13. Load bus
•Thesearenon-generatorbuses.Atanyloadbusi,the
•realpowerdemandPp,andthereactivepower
demandOp;arespecified.Theseareknownfromload
forecastsorbymeasurement.Atthesebusesthequantitiestobe
determinedare|Vi)and8,.ThesebusesarealsocalledPObusesor
loadbuses.
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14. Voltage controlled bus
voltagemagnitudecanbeheldconstantataspecifiedvalue,is
calledavoltage-controlledbus.Atthegeneratorbuses,itispossibleto
maintain,theterminalvoltageatthespecifiedvalue,byadjustingthe
excitationofthegenerator.
Further,atthegeneratorbus,theactivepowergenerationcanbe
controlledbyadjustingthemechanicalpowerinput.Hence,ata
generatorbusi,andPGarespecified.ThesebusesarealsocalledPV
buses.Thevariablestobedeterminedare,Qandð,
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15. Slack bus
•voltagemagnitudeandphaseanglearespecified
•activeandreactivepowershavetobedetermined.
•Inanyloadflowstudy,thelossesinthesystemcannotbeknownapriori,
withoutthesolutionofvoltagesatallthebuses.Theslackbus,suppliesthe
differencebetweenthetotalsystemloadpluslossesandthesumofthe
complexpowersattheremainingbuses.Since,theslackbusmustsupplythe
losses,itmusthaveagenerator.Ingeneral,thebusconnectedtolargest
generatingstationisnormallyselectedastheslackbus,sothatduringthe
variationsintheactiveandreactivepowersofthetheloadflowiterations,the
slackbusisasmallpercentageofitscapacity.
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16. CLASSIFICATION OF BUSES
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17. •System Data
•Generator Bus Data
•Load Data
•Transmission Line Data
•Transformer Data
•Shunt Element Data
DATA FOR LOAD FLOW
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18. "Number of buses,
" Number of PV buses.
" Number of loads.
"Number of transmission lines
" Number of transformers. "Number of shunt elements.
The slack bus number.
Voltage magnitude of slack bus (angle is generally taken as 0°).
"Tolerance limit.
"Base MVA.
" Maximum permissible number of iterations.
System Data
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21. OPERATING CONSTRAINTS
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22. OPERATING CONSTRAINTS
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