lecture 23 trans

8/13/2019 Lecture 23 Trans

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PowerTransferCapabilityLimits

DrMSRMurty

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Transfercapability Themaximumpowerthatcanbetransferred

iscalled

the

transfercapability.

Forproperoperationofthepowersystem

and

to

gain

the

benefits

of

the

bulk

power

transfers,thetransfercapabilitiesmustbe

calculatedandthepowersystemplannedand

operatedso

that

the

power

transfers

do

not

exceedthetransfercapability.

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TransferCapability:

Terminology

TotalTransferCapability(TTC):Theamountof

electricpower

that

can

be

moved

or

transferredreliablyfromoneareatoanother

areaoftheinterconnectedtransmission

systemsby

way

of

all

transmission

lines

(or

paths)betweenthoseareasunderspecified

system

conditions.

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TotalTransfer

Capability

(TTC)

TTC=ETC+ATC+CBM+TRM

Where

ETC= ExistingTransmissionCommitments

ATC

=AvailableTransfer

Capability

CBM=CapacityBenefitMargin

TRM=Transmission

Reliability

Margin

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FCITC:FirstContingencyIncrementalTransfer

Capability(FCITC)

is

the

Available

Transfer

Capability(ATC),afterCapacityBenefit

Margin(CBM)

TRM:TransmissionReliabilityMargin

ETC:ExistingTransmissionCommitments

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Flowpaths

between

areas

Flowsalongtheprimarypathand

Flowsoccur

along

the

parallel

path

due

to

physicalconditions

Restrictionon

the

amount

of

power

transfer

canoccurduetoanypath

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Transferlimits

Keyconsiderationsinevaluatingtransferlimits

are:

thermalloading

voltageproblem,

or

angularstability

Theconditionsbywhichatransferlevelis

acceptableor

not

are

defined

by

the

reliability

criteria.

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Transferlimits

Thelimitmaybereachedduring

normalconditions

inthetransientperiodfollowinga

disturbanceor

following

acontingency

such

as

lossofaline.

Typically,therewillbeonelimitingcondition

definedby

the

type

of

disturbance,

the

type

of

limit(thermal,voltageorstability)andthe

loadinganddispatchstate.10/16/2010 8


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Transferlimits

Transferlimitsareafunctionoftheoperating

state:

theloadlevel

generationdispatch

thestatusoftransmissionelements(e.g.,

undermaintenanceoroffline).

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Transferlimits

Hourlytransferlimitsexperiencedbythe

operatingpower

system,

and

plannedtransfercapabilityasstudiedby

transmissionplanners.

Thecalculationoftransferlimitsmay

sometimesbeconstrainedbytheactual

capabilityto

monitor

specific

parameters

of

thepowersystem.

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Firstcontingencyincremental

transfercapability(FCITC)

FCITCistheamountofelectricpower,

incrementalabove

normal

base

power

transfer,thatcanbetransferredoverthe

interconnectedtransmissionsystemsina

reliablemannerbasedonvariousconditions.1)Withnormal(precontingency)operating

procedures,all

facility

loads

are

within

normal

ratingsandallvoltagearewithinnormal

limits.

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FCITC

2)Theelectricsystemsarecapableofremaining

stablefollowing

any

single

contingency.

3)Afterthedynamicpowerswingssubside

followingasinglecontingency,alltransmission

facilityloadingsarewithinemergencyratings

andallvoltagesarewithinemergencylimits.

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TransferCapability

Analysis:

Steps

1. EstablishaSecure,solvedbasecase

With

no

power

transfer

lineflows,busvoltageswithinoperating

limits2.Specifyatransferincludingsourceandsink

assumptions

Bus

A

(source

of

power

)to

Bus

B

(sink)

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TransferCapability

Analysis:

Steps

3.Establishasolvedtransferlimitedcaseanda

bindingsecurity

limit

Transferincreasedtoalimitonlineflow,

voltagemagnitude,voltagecollapseetc.,

4.CalculateTransfermargin

Differencebetweenthetransferatbase

caseand

limiting

case

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TransferCapability

Calculation

Amountoftransfer:AScalarparameterthat

canbe

varied

in

the

model

Transferexpressedintermsofbusinjections

Continuation

process:

Series

of

power

system

solutionssolvedandtestedforlimits

Transfercapability:Amountoftransferfrom

thebase

case

transfer

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ContinuationModel

Aseriesofloadflowcalculationsforincreasing

amountsof

transfers

or

by

more

elaborate

highperformancenumericalmethods.

Powersystemnonlinearity,operatoractions,

controlssuchastapchanges,andgenerator

limitsarealsobeincluded

Usefultransfer

capabilities

can

also

be

obtainedwithsimplerpowersystemmodels

suchastheDCloadflowapproximation.

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TransferLimitAnalysis(TLA)

modulein

PSS/E

AvailableTransferCapability(ATC)calculation

Transferlimits

due

to

thermal

and

voltage

relatedavailabilitycriteria

Parametric

analysis:

Series

of

Power

Flows

till

limitingcondition

PVCurveanalyticalengine:Tofindboth

thermaland

voltage

constrained

transfers

Probabilistictransferlimits

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ACbased

transfer

limits

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Low voltage transfer limit: As transfer is increased voltage decreases at

some bus near transfer path and reaches low voltage criterion

With further increase Voltage collapses at a point called voltage collapse

transfer limit


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PVCurve

or

Knee

of

curve

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PV Curve from a series of AC

power flows from a low transfer

level increasing in steps

Voltage collapse studied separately

Using Non- Divergent power flow method

For buses relatively remote from transfer path

All of the curves will not have a low voltage

transfer limit.

However, all of the curves have the

same voltage collapse transfer limit.


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PV

Curve

analysis

Monitorsvoltageatallbusesornodeswithin

amonitored

sub

system

which

may

include

busesonthetransferpathaswellasthosein

thereceivingandsendingareas.

Appliesitsnondivergentpowerflowalgorithmtoidentifythetransferlevelat

which

voltage

collapse

occurs.

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PV

Curve

analysis

contd.,

Optionsforadjustingtransfers:

loadchange

generationredispatchaccordingto

participation

factors

and generationredispatchaccordingtoeconomic

basis.

Usesan

adaptive

step

size

to

minimize

the

numberofpowerflowevaluationpointswhile

maintainingresolutiononthePVcurves10/16/2010 22


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ThermalTransfer

Limit

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Monitoring of flow on a selected branch

Thermal rating specified

Is reached at Overload tr. limit

Linearized

DC power flow method

used to generate tableof tr limits


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ThermalTransfer

Limit

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Linearized

DC power flow methodused to generate table

of tr limits

Linear approximation methods:1. Distribution factors method

2. Interpolation method


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Transferlimit

monitoring

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Each line has its own thermal limit

Constraining thermal limit: Line which reaches its

Thermal rating at the lowest transfer level


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UncertaintiesinTransferlimits:

deterministiccalculation

Generationdispatchandinthemannerwhich

init

changes

as

transfers

increase

Demandorloadwithrespecttoboththetotal

andthedistributionbysubstation

Theuncertaintyintransfersincreasingtothe

levelswhichhavelimitingconditions

Theimpact

of

forced

outages

in

the

transmissionsystem

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Probabilitymethod

Exposurefunctiontorepresenttheprobabilityof

occurrence

of

agiven

load,

dispatch

and

transferlevel

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Cumulativeprobability:

Example

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Cumulative probability of overloads as

function of transfer

At transfers below 440 MW: Zero possibility

Above 580 : 100 % probability


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Summary Themaximumpowerthatcanbetransferred

iscalled

the

transfercapability.

Limitscanbeduetothermalloading,voltage

problem,orstability

Methodsofanalysis:PVCurveanalysis,

probabilisticmethods

Seriesof

Power

flow

calculations

are

required

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lecture 23 trans

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