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Nirmal-Kumar C Nair

Department of Electrical Engineering

Texas A&M University

EPPE Power Seminar SeriesMay 3, 2001


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PRESENTATION INDEX

De-Regulation

Electric Markets

Transaction Based Power Flow

Conventional Power Flow Analysis

Transaction Based Voltage Margin Allocation


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POWER SYSTEM DE-REGULATION (RESTRUCTING)

GENCO

TRANSCO

DISCO

Tie Lines

GENCO

TRANSCO

DISCO

GENCO

DISCO

GENCO

DISCO

GENCO

TRANSCO

DISCO

Deregulation or Restructuring denotes breaking up of the

Vertically Integrated Utility(VIU) structure into Competitive

Market Entities.


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RESTRUCTURED ELECTRICAL INDUSTRY


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ENTITIES RESULTING FROM DE-REGULATION

SO

GENCO TRANSCO DISCO

SO is the Power System Operator and the Power Market

Operator, which may include other entities depending on the

market structure. SO, is independent of the other entities


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An Integrated Electricity Market

Power Commodity Markets

Real-time Balancing Markets (RBM)

Transmission Capacity Markets

Power Exchange Market (PX)

Bilateral Contract Market (BCM/SC)

Ancillary Service Market (ASM)

New types of transmission directives.

(ISO, ISA, RTO)

Long-term capacity access charge (LCC)

Fixed transmission rights (FTRs)

To perform a security-constrained ED function

To re-dispatch bilateral contracts

RESTRUCTURED COMPETITIVE ELECTRICITYMARKET


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Power Commodity Market Components

A Power Exchange (PX) establishes an auction market where energyoffers/bids by the generators/consumers are matched anonymously based onvolume and prices. The PX may operate a forward (a day-ahead) market as wellas an hour-ahead spot market separately.

A Bilateral Contractis defined as the right to inject a certain amount ofpower at a delivery point iand remove it at another receipt point jat aspecified price Pij.

BCM/SC market shields for pro-conservative market agents against risk ofhedging of electricity price in the central spot market (PX) due to variousstrategic bids/offers.

The Ancillary Service Market is responsible for procuring spinning reserve,non-spinning reserve, AGC, replacement reserves, voltage support and blackstart, to secure stable operation of the system.


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Transmission Capacity Market Components

Within the context of Transmission Open Access (TOA) philosophy, thetransmission entities continue to evolve towards new types of directives like

For-Profit TRANSCO

Non-Profit Independent System Operator (ISO)

Independent Scheduling Administrator (ISA)

Regional Transmission Operator (RTO)

The Capacity Connection Charge (LCC), or power fee, is a long-term (sayone year) charge per MW of connected capacity as a portion of thetransmission tariff package.

The capacity charge could be same for all users connected to ISO, or can berelated to the geographical location or based on other market designs relatedto congestion.

Firm Transmission Rightis defined as A financial contract that entitles theholder to a stream of revenues (or charges) based on the reserved level andhourly LMP difference across the specified transmission paths.FTR protects transmission customers from increased cost due to transmissioncongestion on the condition that energy trades are consistent with firmreservation.


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REAL-TIME BALANCING MARKET

The Real-time Balancing Market is a real-time energy balancingmarket performed by the ISO to revise the preferred schedules whenthere is any imbalance or transmission congestion.

In the RBM, both generators and consumers in the PX can submit

their incremental or decremental energy offers and bids to theISO, who will select the least cost resources to meet the balancingrequirements or to eliminate the congestion on a real-time basis.

In the RBM, the ISO also can curtail the bilateral contracts whose

sensitivity to the violated constraints is high, or call for newbilateral transactions resulting in a negative power flow effect onthe congested lines.


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MARKET COORDINATION MODELS

SO

BUYER SELLER

SO

BUYER

SELLER

C

O

N

T

R

A

C

T

Bid

Transaction

Bid

Transaction

Approve/

Disapprove

Submit

POOLCO OPCO

POOLCO

OPCO

VIU

Regulation

Market Force

ISO

SC PX

SO


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ikkiikkiikkiDiGi

kiikkiikki

ik

DiGi

bgVVPQ

bgVVPP

)]cos()sin([||||

)]sin()cos([|||| 1

Here all N buses fall into 3 categories: PQ bus, PV bus and

one single slack bus .

Since power flow equation is in term of angle difference, areference angle is assigned to the slack bus in advance,

whereas generation of the slack bus is left open to account

for imbalance between the total generation and load in the

system.

),( V

THE CONVENTIONAL POWER

FLOW ANALYSIS


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Provides reference angle

Accounts for energy imbalance

Makes N power flow equations a consistent set

Causes dependency of the PF solution on the slack

bus when specified real power of N bus is inconsistent.

Difficulty in determining loss responsibility for

individual generators/loads/transactions.

Causes PF sensitivity factors being slack bus

dependent.

NECESSITY

NECESSITY & PROBLEMS WITH

CLASSICAL SLACK BUS

PROBLEMS


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KEY TO TBPF FORMULATION

Nodal power balance equations (a) vs. nodal

current balance equations (b).

...3,2,1)cossin()(

)sincos()(

i

bgVQQ

bgVPP

ijijijijijiDiGi

ij

ijijijijiDiGi

(b)

(a)

i

i

j

n

j

n,nn,

,n,

n

eV

.

eV

y.y

...

y.y

I

.

I1

1

1111

*

i

j

iii IeVjQPi

Can we build a bridge between certain real power

and particular nodal current ?


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R/X ratio and branch angle difference are small.

Strongly Coupling relation betweenP and .

Strongly Coupling relation between Q and V.

Strongly Coupling relations between and, and between and V, provided nodalphase angle is small enough (say | max|< /9).

)Re(busI)Im( busI

SOME GENERAL FACTS

Note that PandQare coupled withIthrough associated

phase angle and voltage magnitude, thus it is impossibleto find the exact contribution ofP onI.Fortunately,transmission grids hold several characteristics like:


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APPROXIMATIONS LEADING TO TBPF

Exact expression Piin terms of nodal current is

We make the following approximation according

to the discussed basic facts:

The aggregated reactive power of the system takes

care the remaining current components, includingall Im(Ii) terms and residual errors of Im(Ii), which

are

)Im(sin)Re(cos iiiiiii IVIVP

ii

ii

V

PI

cos)Re( , assuming Vi sini Im(Ii) is small.

ii

ii

V

PI

cos)Re(


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Main Features of The TBPF Analysis

Decompose complex AC power flows directly intotransaction components, in the light of Physical Laws.

Evaluate interaction quantities of different energytransactions on particular power flows and losses

Show effect of reactive power scheduling on reactiveloss and transmission losses.

Assure satisfactory decomposition accuracy when

realistic network conditions are satisfied. Sustain a simple and fast computation procedure.


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Transaction loss evaluations

Parallel flow evaluation and compensation

Conducting FTR purchase/sale and settlement

Congestion Management

Reactive power support charge for energy delivery

Responsibility settlement of voltage stability

TBPF APPLICATION SCOPES


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VOLTAGE STABILITY INDICATOR

G

L

GGGL

LGLL

G

L

G

L

V

I

YK

FZ

V

I

HI

V

2

jjj

j

j

VY

S

L

jcorrjj SSS

jiLi

j

i

i

jj

ji

jcorr V

V

S

Z

ZS )(

jj

jj

Z

Y

1

[I bus] = [Y bus] * [E bus]


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TRANSACTION BASED VOLTAGE

MARGIN ALLOCATION (TB-VMA)


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TB-VMA Application Scope

Responsibility Settlement of Voltage Security

Node-wise Voltage Stability Margin UtilizationEvaluation

Evolve Transaction Based Pricing Mechanism forVoltage Security

A Tool to confirm whether a Transaction could be

committed from voltage security margin viewpoint

A Tool to decide which transaction if curtailed givesmaximum effect in case of potential voltage collapse

situation


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CONCLUSION

A Transaction Based Voltage Margin Assessmentprocedure has been formulated

The TB-VMA is able to evaluate voltage securitymargin utilization on a node wise basis with respectto individual transactions

TB-VMA has been effectively demonstrated using acomposite market model containing both PoolCotype and Point-To-Point type transactions


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REFERENCES Hongming Zhang,Transactions-based power flow analysis and its

application s to a competitive power market Ph.D dissertation

submitted to Texas A&M University, June 2001

P Kessel, H Glavitsch,Estimating the voltage stability of a powersystem, IEEE Trans on Power Delivery, vol. PWRD-1, No.3, July 1986,pp. 346-354.

G M Huang, N C Nair,An OPF based algorithm to evaluate loadcurtailment incorporating voltage stability margin criterion,

Conference Proceeding of NAPS 2001, TX, October 2001.

G M Huang, N C Nair,Voltage stability constrained load curtailment

procedure to evaluate power system reliability measures, ProcIEEE/PES Winter Meeting Jan 2002, NewYork.

G M Huang, N C Nair,Incorporating TCSC into the Voltage StabilityConstrained OPF Formulation submitted to the IEEE/PES Summer

Meeting, Jun 2002.


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