EXPANSION OF TRANSMISSION SYSTEMSEXPANSION OF TRANSMISSION SYSTEMSIN A DEREGULATED ENVIRONMENTIN A DEREGULATED ENVIRONMENT

Yong ZhengYong ZhengSaskatchewan Power CorporationSaskatchewan Power Corporation

N.A.ChowdhuryN.A.ChowdhuryUniversity of SaskatchewanUniversity of Saskatchewan

Regulation:Regulation:

Regulated MonopolyRegulated Monopoly

Deregulation:Deregulation:

Re-structuring of the MarketRe-structuring of the Market

Re-regulationRe-regulation

Unbundling of ServicesUnbundling of Services

CompetitionCompetition

PrivatizationPrivatization

Open accessOpen access

Electrical Industry Regulation and Electrical Industry Regulation and DeregulationDeregulation

GenerationTransmission DistributionRetail Sale

Traditional regulated System Model

Deregulated System Model

Generation Company

Transmission Company Distribution Company

Retailers

Customers Customers

Monopoly FranchiseLimited Benefit Return

Generation & Retailing - DeregulatedTransmission & Distribution - Regulated

GOALS OF DEREGULATIONGOALS OF DEREGULATION

Lower utility ratesLower utility rates Choice of electricity providersChoice of electricity providers Efficient, cost based pricingEfficient, cost based pricing Encouraging renewable energy Encouraging renewable energy

sourcessources Customer specific servicesCustomer specific services

Transmission System CongestionTransmission System Congestion

Transmission system congestion means that one or several transmission lines in the system are overloaded.

G1

G2

Load1

Load2

Line1 Limit: 80MW

Power Flow: 90MW

150MW60MW

0MW

90MW

$20/MW

$40/MW

Transmission System CongestionTransmission System Congestion

The introduction of competition in electric The introduction of competition in electric power market has made power flow power market has made power flow control issues more complex and difficult control issues more complex and difficult than ever before. than ever before.

The scarcity of transmission capacity and The scarcity of transmission capacity and a continued demand for power from less a continued demand for power from less expensive sources lead to transmission expensive sources lead to transmission system congestion.system congestion.

Causes of CongestionCauses of Congestion

Market participants are blind to Market participants are blind to system operating conditions system operating conditions

Generation schedule is determined Generation schedule is determined by competitive marketby competitive market

System operator has no right to System operator has no right to interfere with market-based interfere with market-based generation schedule unless generation schedule unless congestion occurscongestion occurs

Consequences of CongestionConsequences of Congestion

Unsolved congestion will threaten Unsolved congestion will threaten system securitysystem security

Congestion relief will increase system Congestion relief will increase system operating costoperating cost

Congestion will bring extra cost to Congestion will bring extra cost to electrical userselectrical users

Congestion will hinder fair competition Congestion will hinder fair competition between generatorsbetween generators

Ways to Relieve CongestionWays to Relieve Congestion

Generation rescheduleGeneration reschedule

Interruptible load curtailmentInterruptible load curtailment

Transmission system expansionTransmission system expansion

Congestion ReliefCongestion Relief

G1

G2

Load1

Load2

Line1 Limit: 80MW

Power Flow: 80MW

110MW60MW

40MW

90MW

$20/MW

$40/MW

New Added Line

Research ObjectivesResearch Objectives

To develop methods to optimize To develop methods to optimize generation re-schedule when congestion generation re-schedule when congestion happenshappens

To include the effect of short-term power To include the effect of short-term power market on transmission network market on transmission network expansionexpansion

To assess several alternatives to find the To assess several alternatives to find the optimal transmission expansion in case optimal transmission expansion in case of congestionof congestion

Optimization of Generation RescheduleOptimization of Generation Reschedule

Mathematical Model of Optimum Mathematical Model of Optimum Generation Reschedule Generation Reschedule

AC Optimal MethodAC Optimal Method

Mathematical Model for Re-dispatchMathematical Model for Re-dispatch

i= 1

n

Min Ci *PGiObjective Function:Objective Function:

Subject toSubject to PL = 0i= 1

n

PGi

Ci = re-dispatch price submitted by Generator re-dispatch price submitted by Generator ii

PGi = active power variation of Generator active power variation of Generator ii

PL = change in transmission losschange in transmission loss

n = number of generators number of generators

AC Optimal MethodAC Optimal Method Based on AC power flow methodBased on AC power flow method

Linearized relationship between power Linearized relationship between power flow variation and generation variation flow variation and generation variation

Linearized relationship between Linearized relationship between transmission loss variation and transmission loss variation and generation variationgeneration variation

Takes transmission loss into accountTakes transmission loss into account

90MW

60M

W

G5(90MW)

T3

G4(0MW)

G1(45MW)

T1

G2(45MW)

T2

90MW(T3)

90MW(T1+T2)

G3

1 2

3 45

6

A System with Three TransactionsA System with Three Transactions

45 MW 0 MW MW

50

-30

70

-40

20

Price($/MWh) Price($/MWh) Price($/MWh)

G1 & G2 G4 G5

90

Reloading BidsReloading Bids

Active power flows before and after re-dispatchActive power flows before and after re-dispatch

Line Line No.No.

From From

ToTo Initial FlowInitial Flow

(MW)(MW)Flow After Re-Flow After Re-dispatch (MW) dispatch (MW)

111 1

22 29.45 29.45 29.6229.62

221 1

33 104.05104.05 89.6089.60

331 1

55 - 88.49- 88.49 -73.95-73.95

442 2

33 74.2974.29 59.4559.45

553 3

44 92.0692.06 61.3061.30

663 3

66 92.0692.06 92.0792.07

The increased cost due to the re-dispatch The increased cost due to the re-dispatch is $954.384/hr. is $954.384/hr.

Load function can be expressed as:Load function can be expressed as:P(t) = Q0 + Q(t) + Q(r); t = 1, 2, 3, ……, 24

Q0 andand Q(t) are non-price responsive partsare non-price responsive parts

Q(r) is the price responsive partis the price responsive part

Load ModelLoad Model

Benefit Function can be expressed as:Benefit Function can be expressed as:B(PGi) = F(PGi) + M(PGi)

Bidding ModelBidding Model

Cost function:Cost function: F(PGi) = PGi2 + PGi +

Profit function:Profit function: M(PGi) = k* PGi

Bidding price function:Bidding price function:H(PGi) = B(PGi)/PGi = 2PGi + + k

n

iGiit PBB

1

Total generating cost as seen by the ISOTotal generating cost as seen by the ISO

rQtQQrn

iii

0

1

Market Clearing Price, r can be found by Market Clearing Price, r can be found by solvingsolving

Actual bidding price curve

Linear bidding price function

$/MWh

Pmin Pmax MW

Bidding Price CurveBidding Price Curve

Transmission System ExpansionTransmission System Expansion

Expanding transmission system is more Expanding transmission system is more economic if congestion fee is higher than the economic if congestion fee is higher than the investment cost of building new transmission investment cost of building new transmission line.line.

Future short-term power market should be Future short-term power market should be considered when planning transmission considered when planning transmission system expansion.system expansion.

Different expansion options should be Different expansion options should be assessed when selecting the most acceptable assessed when selecting the most acceptable expansion scheme.expansion scheme.

Steps involved in transmission Steps involved in transmission system expansion planningsystem expansion planning

Forecast short-term market generation schedule Forecast short-term market generation schedule on the basis of typical load curves and bidding on the basis of typical load curves and bidding price functions.price functions.

Combine the predicted short-term generation Combine the predicted short-term generation schedule with long-term generation schedule to schedule with long-term generation schedule to evaluate system power flow distribution and evaluate system power flow distribution and congestion fee.congestion fee.

Select new lines that can relieve congestion with Select new lines that can relieve congestion with investment cost less than congestion fee.investment cost less than congestion fee.

Summary and ConclusionsSummary and Conclusions Deregulation makes power flow control more Deregulation makes power flow control more

complicatedcomplicated

Market-driven generation schedule results in Market-driven generation schedule results in transmission system congestiontransmission system congestion

Congestion will threaten system security and must Congestion will threaten system security and must be relieved be relieved

Generation reschedule will increase system Generation reschedule will increase system operating costoperating cost

Expansion of transmission becomes economic if Expansion of transmission becomes economic if the investment cost of building new transmission the investment cost of building new transmission facilities is less than the congestion fee. facilities is less than the congestion fee.

Question?