5/22/2018 aapg2

1/61

How the Power Grid Behaves

Tom Overbye

Department of Electrical and Computer EngineeringUniversity of Illinois at Urbana-Champaign

5/22/2018 aapg2

2/61

Presentation Overview

Goal is to demonstrate operation of large scalepower grid.

Emphasis on the impact of the transmission syste.

Introduce basic power flow concepts throughsmall system examples.

Finish with simulation of Eastern U.S. System.

5/22/2018 aapg2

3/61

PowerWorld Simulator

PowerWorld Simulator is an interactive,Windows based simulation program, originally

designed at University of Illinois for teaching

basics of power system operations to non-powerengineers.

PowerWorld Simulator can now study systems of

just about any size.

5/22/2018 aapg2

4/61

5/22/2018 aapg2

5/61

Zoomed View of Midwest

CEI

CINCIPS

CONS

DPL

IMPA

IP

IPL

NI

NIPS

TE

BRECSIGE

CILCO

CWLP

HE

EMO

5/22/2018 aapg2

6/61

Power System Basics

All power systems have three major components:Generation, Load and Transmission.

Generation: Creates electric power. Load: Consumes electric power. Transmission: Transmits electric power from

generation to load.

5/22/2018 aapg2

7/61

One-line Diagram

Most power systems are balanced three phasesystems.

A balanced three phase system can be modeled asa single (or one) line.

One-lines show the major power systemcomponents, such as generators, loads,

transmission lines. Components join together at a bus.

5/22/2018 aapg2

8/61

Eastern North American High Voltage

Transmission Grid

828MW293MVR273MVR829MW

250MVR1093MW

1094MW250MVR

9MVR300MW9MVR300MW9MVR300MW

300MW9MVR300MW9MVR320MW9MVR

-114MVR893MW

897MW-110MVR

-127MVR801MW

0MVR

0MVR1129MW183MVR

0MVR

0MVR

340MVR

143MVR

294MVR

348MW262MVR

0MW 0MVR

286MVR

145MVR

250MW45MVR

0MW 0MVR

45MVR250MW 0MVR

0MW

294MVR

-202MVR

-210MVR

146MVR

676MW50MVR676MW50MVR

RiverheadWildwood

Shoreham

Brookhaven

PortJefferson

HolbrookHoltsville

Northport

PilgrimSyossetBethpage

RulandRd.NewbridgeLcst.Grv.

07MEROM5

KEYSTONE

01YUKON

CONEM-GH

JUNIATA

SUNBURY

SUSQHANA

WESCOVLE

ALBURTISHOSENSAK

BRANCHBG

ELROY

WHITPAINLIMERICK

DEANSSMITHBRG

3MILEI

RAMAPO5

HUNTERTN

CNASTONE

PEACHBTMKEENEY

BRIGHTON

WCHAPEL

CLVTCLFCHALK500

BURCHES

8POSSUM

8OX8CLIFTON

8LOUDON08MDWBRK

8MORRSVL

8MTSTM

8VALLEY

8DOOMS

8BATHCO

8LEXNGTN

8NOANNA8LDYSMTH

8ELMONT

8MDLTHAN

8CHCKAHM

8CARSON8SEPTA

8YADKIN8FENTRES

8SURRY

8PERSON8MAYO1

8PARKWOD

8WAKE

8PLGRDN

8CUMBERL

8RICHMON

8MCGUIRE

8JOCASSE

8BADCRK

8OCONEE

8NORCROS8BULLSLU

8BIGSHA

8BOWEN

8KLONDIK

8UNIONCT

8VILLAR

8WANSLEY

8SNP

8WBNP1

8ROANE8BULLRU

8VOLUNTE

8SULLIVA

8PHIPPB

05NAGEL

8WILSON

8MONTGOM

8DAVIDSO

8MARSHAL

8SHAWNEE

8JVILLE

8WEAKLEY

8JACKSON

8SHELBY

8CORDOVA

8FREEPOR

WM-EHV8

8UNION

8TRINITY

8BFNP8LIMESTO

8BNP28MADISON8BNP1

8WIDCRK

8RACCOON

8FRANKLI

8MAURY

8MILLER

8LOWNDES

8WPOINT

MCADAM8

8S.BESS

8FARLEY

8SCHERER

8HATCH8

8ANTIOCH

8CLOVER

ROCKTAV

COOPC345ROSETON

FISHKILL

PLTVLLEY

HURLEY3

LEEDS3

GILB345

FRASR345

N.SCOT99ALPS345

REYNLD3

EDIC

MARCYT1

MASS765

OAKDL345

WATERC345

STOLE345

LAFAYTTE

DEWITT3ELBRIDGE

CLAY

VOLNEYSCRIBA

JAPITZP9MIPT1INDEPNDC

OSWEGO

PANNELL3ROCH345

KINTI345

NIAG345BECKA

BECKB

NANTICOK

MIDD8086

MILTON

TRAFALH1TRAFALH2

CLAIRVIL

HAWTHORN

ESSABRUJB561

BRUJB569

BRUJB562

LONGWOOD

Barrett

E.G.C.

ValleyStream

LakeSuccessRainey

Jamaica

Greenwood

FoxHillsFreshKillsGoethals

CogenTechGowanusFarragut

E15thSt.W49thSt.

TremontShoreRd.

DunwoodieSprainBrook

EastviewPleasantville

Millwood

BuchananIndianPoint

Dvnpt.NKHmp.Harbor

VernonCorona

GreelawnElwood

Figure shows

transmission

lines at 345

kV or abovein Eastern

U.S.

5/22/2018 aapg2

9/61

Zoomed View of Midwest

1115 MW-185 MVR

600 MW-41 MVR

200 MW 6 MVR

500 MW25 MVR

05COOK

05GRNTWN

05JEFRSO

05ALLEN

03LEMOYN

05BEATTY

05BENTON

07BLOMNG

05BREED

17BUROAK

05CORR

03DAV-BE

06DEARBN

05DEQUIN

05DESOTO

05DUMONT

05E LIMA

05EELKHA

19MADRD

05EUGENE

05FALL C

05FOSTOR

16GUION

16HANNA

05HAYDEN

17HIPLE

05HYATT

05JACKSR

05MARQUI

05MARYSV

05OLIVE

06PIERCE

05REYNOL

05ROB PK

05ROBERT

16ROCKVL

05SORENS

17STLWEL

16STOUT

16SUNNYS

05SW LIM

05TANNER

16THOMPS

05TWIN B

07WORTHN

60%

69%

07MEROM5

05KENZIE

SLINE;BSLINE;R

17SHEFLD

17SCHAHF

17DUNACR

17MCHCTY

17BABCOK

17TWRRD

17CHIAVE

BURNH;B

BURNH;0R

17LKGORG

17MUNSTR

GACR;T

17GRNACRSJOH;T

17STJOHN

DAVIS; B

DAVIS; R

BRAID; B

BRAID; R

LASCO; B

LASCO; R

PLANO; B

PLANO; R

ELECT; B

ELECT; R

ZION ; B

ZION ; R

SILVE; R

LIBER; R

DRESD; B

DRESD; R

LOCKP; B

LOCKP; R

GOODI;3B

GOODI;2RGOODI;4B

GOODI;1R

B ISL; R

NELSO; B

H471 ;

TAZEWELL

POWER; B

POWER; R

DUCK CRK

PONTI;

BROKA; T

LATHA; T

KINCA;

08CAYUGA

08CAY CT

BUNSONVLSIDNEY

CASEY

KANSAS

08DRESSR

62%

08WHITST

08NUCOR

?????

?????

08BEDFRD

08ALENJT

08COLMBU

08GWYNN

08OKLND

08GRNBOR

08NOBLSV?????

08WESTWD

17LESBRG

08WALTON

08DEEDSV

05COLNGW

05S.BTLR

56%

05SULLVA

12GHENT

06CLIFTY

08BUFTN1

08EBEND

08M.FTHS

0 8 M. F OR T 0 8 RE D BK 1

08REDBK2

08TERMNL

08SGROVE

08P.UNON

08WODSDL

08TDHNTR

08FOSTER

?????

09CLINTO09NETAP

09KILLEN

09BATH

?????

09GIVENS

08ZIMER

????? 09CARGIL

09URBANA?????

62%

02TANGY

19MAJTC

03BAY SH

02GALION

COFFEEN

PAWNEE

COFFEN N

PANA

RAMSEY

NEOGA

NEWTON

CLINTON

MAROA W MAROA E

OREANA E

RISING

PLANO;

COLLI;

WILTO;

PAD 345

WEMPL; R

WEMPL; B

BYRON; BBYRON; R

CHERR; B

CHERR; R

53%WAYNE;R

?????

W407M;9T

W407K;9T

W407K;R

LOMBA;B

LOMBA;R

ELMHU;B

ELMHU;R

ITASC;1M

DP46;B

DP46;R

PH117;R

NB159;1M

NB159;B

SK88;R

SK88;B

GOLF;R

GOLF;B

LISLE;B

LISLE;R

JO29;B

JO29;R

MCCOO;B

MCCOO;R

COLLI; R

WILTO;

E FRA; B

E FRA; R

BLOOM; R

TAYLO;B

TAYLO;RCRAWF;B

CRAWF;R

BEDFO;R

BEDFO;RT

GARFI;B

CALUM;B

BURNH;4M

BURNH;1R

Arrows

indicate MW

flow on the

lines;

piecharts

show

percentage

loading of

lines

5/22/2018 aapg2

10/61

Example Three Bus System

Bus 2 Bus 1

Bus 3

200 MW

100 MVR

150 MWMW

150 MWMW

35 MVRMVR

114 MVRMVR

100 MW50 MVR

1.00 pu

-17 MW 3 MVR

17 MW-3 MVR

-33 MW10 MVR

33 MW

-10 MVR17 MW-5 MVR

-17 MW

5 MVR

1.00 pu

1.00 pu

100 MW

2 MVR

100 MWAGC ON

AVR ON

AGC ON

AVR ON

Generator

LoadBus

Circuit Breaker

Pie charts

show

percentage

loading of

lines

5/22/2018 aapg2

11/61

Generation

Large plants predominate, with sizes up to about1500 MW.

Coal is most common source, followed by hydro,nuclear and gas.

Gas is now most economical. Generated at about 20 kV.

5/22/2018 aapg2

12/61

Loads

Can range in size from less than a single watt to10s of MW.

Loads are usually aggregated. The aggregate load changes with time, with

strong daily, weekly and seasonal cycles.

5/22/2018 aapg2

13/61

Transmission

Goal is to move electric power from generation toload with as low of losses and cost as possible.

P = V I or P/V = I Losses are I2R Less losses at higher voltages, but more costly to

construct and insulate.

5/22/2018 aapg2

14/61

Transmission and Distribution

Typical high voltage transmission voltages are500, 345, 230, 161, 138 and 69 kV.

Transmission tends to be a grid system, so eachbus is supplied from two or more directions.

Lower voltage lines are used for distribution, witha typical voltage of 12.4 kV.

Distribution systems tend to be radial. Transformers are used to change the voltage.

5/22/2018 aapg2

15/61

Other One-line Objects

Circuit Breakers - Used to open/close devices; redis closed, green is open.

Pie Charts - Show percentage loading oftransmission lines.

Up/down arrows - Used to control devices. Values - Show current values for different

quantities.

5/22/2018 aapg2

16/61

Power Balance Constraints

Power flow refers to how the power is movingthrough the system.

At all times the total power flowing into any busMUST be zero!

This is know as Kirchhoffs law. And it can notbe repealed or modified.

Power is lost in the transmission system.

5/22/2018 aapg2

17/61

Basic Power Control

Opening a circuit breaker causes the power flowto instantaneously(nearly) change.

No other way to directly control power flow in atransmission line.

By changing generation we can indirectly changethis flow.

5/22/2018 aapg2

18/61

Flow Redistribution Following Opening

Line Circuit Breaker

Bus 2 Bus 1

Bus 3

200 MW

100 MVR

150 MWMW

150 MWMW

36 MVRMVR

111 MVRMVR

100 MW50 MVR

1.00 pu

-50 MW11 MVR

50 MW-9 MVR

0 MW 0 MVR

0 MW

0 MVR50 MW-14 MVR

-50 MW

16 MVR

1.00 pu

1.00 pu

101 MW

6 MVR

100 MWAGC ON

AVR ON

AGC ON

AVR ONPower Balance must

be satisfied at each bus

No flow on

open line

5/22/2018 aapg2

19/61

Indirect Control of Line Flow

Bus 2 Bus 1

Bus 3

200 MW

100 MVR

150 MWMW

250 MWMW

8 MVRMVR

118 MVRMVR

100 MW50 MVR

1.00 pu

16 MW-3 MVR

-16 MW 3 MVR

-66 MW21 MVR

67 MW

-19 MVR83 MW-23 MVR

-82 MW

27 MVR

1.00 pu

1.00 pu

2 MW

30 MVR

100 MWAGC ON

AVR ON

OFF AGC

AVR ONGenerator MWoutput changed

Generator change

indirectly changes

line flow

5/22/2018 aapg2

20/61

Transmission Line Limits

Power flow in transmission line is limited by anumber of considerations.

Losses (I2R) can heat up the line, causing it tosag. This gives line an upper thermal limit.

Thermal limits depend upon ambient conditions.Many utilities use winter/summer limits.

5/22/2018 aapg2

21/61

Overloaded Transmission Line

Bus 2 Bus 1

Bus 3

359 MW

179 MVR

150 MWMW

150 MWMW

102 MVRMVR

234 MVRMVR

179 MW90 MVR

1.00 pu

-152 MW37 MVR

154 MW-24 MVR

-57 MW18 MVR

58 MW

-16 MVR-87 MW29 MVR

89 MW

-24 MVR

1.00 pu

1.00 pu

343 MW

-49 MVR

104% 104%

100 MWAGC ON

AVR ON

AGC ON

AVR ON

Thermal limit

of 150 MVA

5/22/2018 aapg2

22/61

Interconnected Operation

Power systems are interconnected across largedistances. For example most of North American

east of the Rockies is one system, with most of

Texas and Quebec being major exceptions Individual utilities only own and operate a small

portion of the system, which is referred to an

operating area (or an area).

5/22/2018 aapg2

23/61

Operating Areas

Areas constitute a structure imposed on grid. Transmission lines that join two areas are known

as tie-lines.

The net power out of an area is the sum of theflow on its tie-lines.

The flow out of an area is equal to

total gen - total load - total losses = tie-flow

5/22/2018 aapg2

24/61

Three Bus System Split into Two Areas

Bus 2 Bus 1

Bus 3Home Area

Area 2

Scheduled Transactions

214 MW

107 MVR

150 MWMW

150 MWMW

41 MVRMVR

124 MVRMVR

107 MW53 MVR

1.00 pu

-29 MW 6 MVR

29 MW-6 MVR

-35 MW11 MVR

35 MW

-10 MVR 8 MW-2 MVR

-8 MW

2 MVR

1.00 pu

1.00 pu

121 MW

-3 MVR

100 MWAGC ON

AVR ON

AGC ON

AVR ON

0.0 MWMW

Off AGC

Net tie flow

is NOT zero

Initially

area flow

is not

controlled

5/22/2018 aapg2

25/61

Area Control Error (ACE)

The area control error mostly the differencebetween the actual flow out of area, and

scheduled flow.

ACE also includes a frequency component. Ideally the ACE should always be zero. Because the load is constantly changing, each

utility must constantly change its generation tochase the ACE.

5/22/2018 aapg2

26/61

Home Area ACE

Bus 2 Bus 1

Bus 3Home Area

Area 2

Scheduled Transactions

255 MW

128 MVR

227 MWMW

150 MWMW

57 MVRMVR

135 MVRMVR

128 MW64 MVR

1.00 pu

-12 MW 2 MVR

12 MW-2 MVR

-17 MW 5 MVR

17 MW

-5 MVR 6 MW-2 MVR

-6 MW

2 MVR

1.00 pu

1.00 pu

106 MW

-1 MVR

100 MWOFF AGC

AVR ON

AGC ON

AVR ON

0.0 MWMW

Off AGC

06:30 AM 06:15 AMTime

-20.0

-10.0

0.0

10.0

20.0

AreaControlError(M

W)

ACE changes with time

5/22/2018 aapg2

27/61

Inadvertent Interchange

ACE can never be held exactly at zero. Integrating the ACE gives the inadvertent

interchange, expressed in MWh.

Utilities keep track of this value. If it getssufficiently negative they will pay back the

accumulated energy.

In extreme cases inadvertent energy is purchasedat a negotiated price.

5/22/2018 aapg2

28/61

Automatic Generation Control

Most utilities use automatic generation control(AGC) to automatically change their generation to

keep their ACE close to zero.

Usually the utility control center calculates ACEbased upon tie-line flows; then the AGC module

sends control signals out to the generators every

couple seconds.

5/22/2018 aapg2

29/61

Three Bus Case on AGC

Bus 2 Bus 1

Bus 3Home Area

Area 2

Scheduled Transactions

214 MW

107 MVR

150 MWMW

171 MWMW

35 MVRMVR

124 MVRMVR

107 MW53 MVR

1.00 pu

-22 MW 4 MVR

22 MW-4 MVR

-42 MW13 MVR

42 MW

-12 MVR22 MW-6 MVR

-22 MW

7 MVR

1.00 pu

1.00 pu

100 MW

2 MVR

100 MWAGC ON

AVR ON

AGC ON

AVR ON

0.0 MWMW

ED

With AGC on, net

tie flow is zero, butindividual line flows

are not zero

5/22/2018 aapg2

30/61

Generator Costs

There are many fixed and variable costsassociated with power system operation.

Generation is major variable cost. For some types of units (such as hydro and

nuclear) it is difficult to quantify.

For thermal units it is much easier. There are four

major curves, each expressing a quantity as afunction of the MW output of the unit.

5/22/2018 aapg2

31/61

Generator Cost Curves

Input-output (IO) curve: Shows relationshipbetween MW output and energy input in Mbtu/hr.

Fuel-cost curve: Input-output curve scaled by afuel cost expressed in $ / Mbtu.

Heat-rate curve: shows relationship between MWoutput and energy input (Mbtu / MWhr).

Incremental (marginal) cost curve shows the costto produce the next MWhr.

5/22/2018 aapg2

32/61

Example Generator Fuel-Cost Curve

0 150 300 450 600Generator Power (MW)

0

2500

5000

7500

10000

Fuel-cost($/hr)

Current generator

operating point

Y-axis

tells

cost to

produce

specifiedpower

(MW) in

$/hr

5/22/2018 aapg2

33/61

Example Generator Marginal Cost

Curve

0 150 300 450 600Generator Power (MW)

0.0

5.0

10.0

15.0

20.0

Incrementalcost($/MWH)

Current generator

operating point

Y-axis

tells

marginal

cost toproduce

one more

MWhr in

$/MWhr

5/22/2018 aapg2

34/61

Economic Dispatch

Economic dispatch (ED) determines the least costdispatch of generation for an area.

For a lossless system, the ED occurs when all thegenerators have equal marginal costs.

IC1(PG,1) = IC2(PG,2) = = ICm(PG,m)

5/22/2018 aapg2

35/61

Power Transactions

Power transactions are contracts between areas todo power transactions.

Contracts can be for any amount of time at anyprice for any amount of power.

Scheduled power transactions are implemented bymodifying the area ACE:

ACE = Pactual,tie-flow- Psched

5/22/2018 aapg2

36/61

Implementation of 100 MW Transaction

Bus 2 Bus 1

Bus 3Home Area

Area 2

Scheduled Transactions

340 MW

170 MVR

150 MWMW

466 MWMW 9 MVRMVR

232 MVRMVR

170 MW85 MVR

1.00 pu

-31 MW 6 MVR

31 MW-6 MVR

-159 MW55 MVR

163 MW

-41 MVR133 MW-35 MVR

-130 MW

44 MVR

1.00 pu

1.00 pu

1 MW

38 MVR112%

112%

100 MWAGC ON

AVR ON

AGC ONAVR ON

100.0 MWMW ED

Net tie flow is

now 100 MW fromleft to right

Scheduled Transaction

Overloaded

line

5/22/2018 aapg2

37/61

Security Constrained ED

Transmission constraints often limit systemeconomics.

Such limits required a constrained dispatch inorder to maintain system security.

In three bus case the generation at bus 3 must beconstrained to avoid overloading the line from bus

2 to bus 3.

5/22/2018 aapg2

38/61

Security Constrained Dispatch

Bus 2 Bus 1

Bus 3Home Area

Area 2

Scheduled Transactions

340 MW

170 MVR

177 MWMW

439 MWMW15 MVRMVR

223 MVRMVR

170 MW85 MVR

1.00 pu

-22 MW 4 MVR

22 MW-4 MVR

-142 MW49 MVR

145 MW

-37 MVR124 MW-33 MVR

-122 MW

41 MVR

1.00 pu

1.00 pu

-0 MW

37 MVR100%

100%

100 MWOFF AGC

AVR ON

AGC ONAVR ON

100.0 MWMW ED

Net tie flow is

still 100 MW from

left to right

Gens 2 &3

changed to

remove

overload

5/22/2018 aapg2

39/61

Multi-Area Operation

The electrons are not concerned with areaboundaries. Actual power flows through the

entire network according to impedance of the

transmission lines. If Areas have direct interconnections, then they

can directly transact up their tie-line capacity.

Flow through other areas is known as parallelpath or loop flows.

5/22/2018 aapg2

40/61

Seven Bus, Thee Area Case One-line

Top Area Cost

Left Area Cost Right Area Cost

1

2

3 4

5

6 7

106 MWMW

168 MWMW

200 MWMW 201 MWMW

110 MW

40 MVR

80 MW30 MVR

130 MW

40 MVR

40 MW

20 MVR

1.00 pu

1.01 pu

1.04 pu1.04 pu

1.04 pu

0.99 pu1.05 pu

62 MW

-61 MW

44 MW -42 MW -31 MW 31 MW

38 MW

-37 MW

79 MW -77 MW

-32 MW

32 MW

-14 MW

-39 MW

40 MW-20 MW20 MW

40 MW

-40 MW

94 MWMW

200 MW 0 MVR

200 MW 0 MVR

20 MW -20 MW

AGC ON

AGC ON

AGC ON

AGC ON

AGC ON

8029 $/MWH

4715 $/MWH4189 $/MWH

Case Hourly Cost

16933 $/MWH

Area

Top

has 5

buses

Area Left has one bus Area Right has one bus

ACE for

each area

is zero

5/22/2018 aapg2

41/61

Seven Bus Case: Area View

Area Losses

Area Losses Area Losses

Top

Left Right

-40.1 MW 0.0 MWMW

0.0 MWMW

0.0 MWMW

40.1 MW

40.1 MW

7.09 MW

0.33 MW 0.65 MW

Actual

flow

between

areas

Scheduled

flow

between

areas

5/22/2018 aapg2

42/61

Seven Bus Case with 100 MW Transfer

Area Losses

Area Losses Area Losses

Top

Left Right

-4.8 MW 0.0 MWMW

100.0 MWMW

0.0 MWMW

104.8 MW

4.8 MW

9.45 MW

0.00 MW 4.34 MW

Losses

went up

from

7.09MW

100 MW Scheduled Transfer from Left to Right

5/22/2018 aapg2

43/61

Seven Bus Case One-line

Top Area Cost

Left Area Cost Right Area Cost

1

2

3 4

5

6 7

106 MWMW

167 MWMW

300 MWMW 104 MWMW

110 MW

40 MVR

80 MW30 MVR

130 MW

40 MVR

40 MW

20 MVR

1.00 pu

1.01 pu

1.04 pu1.04 pu

1.04 pu

0.99 pu1.05 pu

106%

60 MW

-60 MW

45 MW -44 MW -27 MW 27 MW

40 MW

-39 MW

106 MW -102 MW

-35 MW

36 MW

-24 MW

-4 MW

5 MW-50 MW52 MW

5 MW

-5 MW

97 MWMW

200 MW 0 MVR 200 MW 0 MVR

52 MW -50 MW

AGC ON

AGC ON

AGC ON

AGC ON

AGC ON

8069 $/MWH

2642 $/MWH5943 $/MWH

Case Hourly Cost

16654 $/MWH

Transfer

also

overloads

line in Top

5/22/2018 aapg2

44/61

Transmission Service

FERC Order No. 888 requires utilities providenon-discriminatory open transmission access

through tariffs of general applicability.

FERC Order No. 889 requires transmissionproviders set up OASIS (Open Access Same-

Time Information System) to show available

transmission.

5/22/2018 aapg2

45/61

Transmission Service

If areas (or pools) are not directly interconnected,they must first obtain a contiguous contract

path.

This is NOT a physical requirement. Utilities on the contract path are compensated for

wheeling the power.

5/22/2018 aapg2

46/61

Power Transfer Distribution Factors

5/22/2018 aapg2

47/61

Power Transfer Distribution Factors

(PTDFs)

PTDFs are used to show how a particulartransaction will affect the system.

Power transfers through the system according tothe impedances of the lines, without respect toownership.

All transmission players in network could be

impacted, to a greater or lesser extent.

5/22/2018 aapg2

48/61

5/22/2018 aapg2

49/61

PTDF for Transfer from WE to TVA

CINCIPS

CONS

DECO

DPL

IP

IPL

NI

NIPS

TE

CILCO

CWLP

8%

7%

16% 39%

13%

WPL

WEP

WPS

MGE

7%

7%

55%22%

10%

55%54%

NSP

19%

IPW

DPC

8%

10%

MEC

IESC

MPW

9%

8%

7%

8%

7%

SMP

100% of

transfer

leavesWisconsin

Electric

(WE)

5/22/2018 aapg2

50/61

PTDFs for Transfer from WE to TVA

TVA

SOUTHERN

20%

CPLW

DUKE

EKPC

KU

LGE

SIPC

I

SCE&G

DOE

25%

10%

6% 7% 8%19%

11%

YADKI

HARTWELL

SEPA-JST

-

About

100% of

transfer

arrives at

TVA

But flow

does NOT

follow

contract

path

5/22/2018 aapg2

51/61

Contingencies

Contingencies are the unexpected loss of asignificant device, such as a transmission line or a

generator.

No power system can survive a large number ofcontingencies.

First contingency refers to loss of any one device.

Contingencies can have major impact on PowerTransfer Distribution Factors (PTDFs).

5/22/2018 aapg2

52/61

Available Transfer Capability

Determines the amount of transmission capabilityavailable to transfer power from point A to point

B without causing any overloads in basecase and

first contingencies. Depends upon assumed system loading,

transmission configuration and existing

transactions.

R i P

5/22/2018 aapg2

53/61

Reactive Power

Reactive power is supplied bygeneratorscapacitors

transmission linesloads

Reactive power is consumed by

loadstransmission lines and transformers (very high losses

R ti P

5/22/2018 aapg2

54/61

Reactive Power

Reactive power doesnt travel well - must besupplied locally.

Reactive must also satisfy Kirchhoffs law - total

reactive power into a bus MUST be zero.

R ti P E l

5/22/2018 aapg2

55/61

Reactive Power Example

Bus 2 Bus 1

Bus 3

359 MW

179 MVR

150 MWMW

150 MWMW

102 MVRMVR

234 MVRMVR

179 MW90 MVR

1.00 pu

-152 MW37 MVR

154 MW-24 MVR

-57 MW18 MVR

58 MW

-16 MVR-87 MW29 MVR

89 MW

-24 MVR

1.00 pu

1.00 pu

343 MW

-49 MVR

104% 104%

100 MWAGC ON

AVR ON

AGC ON

AVR ON

Reactive

power

must also

sum tozero at

each bus

Note

reactive

line losses

are about13 Mvar

V lt M it d

5/22/2018 aapg2

56/61

Voltage Magnitude

Power systems must supply electric power withina narrow voltage range, typically with 5% of a

nominal value.

For example, wall outlet should supply120 volts, with an acceptable range from 114 to

126 volts.

Voltage regulation is a vital part of systemoperations.

R ti P d V lt

5/22/2018 aapg2

57/61

Reactive Power and Voltage

Reactive power and voltage magnitude are tightlycoupled.

Greater reactive demand decreases the bus

voltage, while reactive generation increases thebus voltage.

V lt R l ti

5/22/2018 aapg2

58/61

Voltage Regulation

A number of different types of devices participatein system voltage regulation

generators: reactive power output is automatically

changed to keep terminal voltage within range.capacitors: switched either manually or automatically

to keep the voltage within a range.

Load-tap-changing (LTC) transformers: vary their off-

nominal tap ratio to keep a voltage within a specifiedrange.

Five Bus Reactive Power Example

5/22/2018 aapg2

59/61

Five Bus Reactive Power Example

Bus 3Bus 4

Bus 5

200 MW

100 MVR

MWMW

MVRMVR

100 MWMW

50 MVRMVR

1.000 pu

143 MW

5 MVR

-60 MW

5 MVR

61 MW

-2 MVR

1.00 pu

0.994 pu

100 MW

12 MVR

100 MWAGC ON

AVR ON

79 MVRMVR

0.982 pu

0.995 pu

100 MWMW

0 MVRMVR

3 L

-40 MW

24 MVR

100 MW

10 MVR

Voltagemagnitude

is

controlled

by

capacitor

LTC

Transformer

is

controlling

load voltage

Voltage Control

5/22/2018 aapg2

60/61

Voltage Control

Voltage control is necessary to keep systemvoltages within an acceptable range.

Because reactive power does not travel well, it

would be difficult for it to be supplied by a thirdparty.

It is very difficult to assign reactive power andvoltage control to particular transactions.

Conclusion

5/22/2018 aapg2

61/61

Conclusion

Talk has provided brief overview of how powergrid operates.

Educational Version of PowerWorld Simulator,

capable of solving systems with up to 12 buses,can be downloaded for free at

www.powerworld.com

60,000 bus commercial version is also available.