1

How the Power Grid Behaves

Tom OverbyeDepartment of Electrical and Computer Engineering

University of Illinois at Urbana-Champaign

2

Presentation Overview

• Goal is to demonstrate operation of large scale power grid.

• Emphasis on the impact of the transmission syste.• Introduce basic power flow concepts through

small system examples.• Finish with simulation of Eastern U.S. System.

3

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-power engineers.

• PowerWorld Simulator can now study systems of just about any size.

4

Eastern Interconnect Operating Areas

T V A

SOUTHERN

AEP

CPLW

AP

JCP&L

PECO

AE

PSE&G

AEC

SMEPA

CEI

CINCIPS

CONS

DECO

CPLE

DLCO

DPL

DUKE

EKPC

IMPA

IP

IPL

KU

NI

NIPS

OE

OVEC

TE

VP

METED

PENELEC

PEPCO

PJM500

BG&E

PP&L

BREC

LGE

SIGE

SIPC

CILCO

CWLP

HE

EEI

EMO

CORNWALL

NYPP

SCE&G

SCPSA

ONT HYDR

DOE

DPL

ENTR

NEPOOL

WPLWEP

WPS

MGE

YADKIN

HARTWELL

SEPA-JST

SEPA-RBR

TAL

JEA

SECCELE

LAFA

SWEP

SWPA

PSOK

GRRD

OKGE

KAMO

WEFA

OMPA

EQ-ERCOT

WERE

NSP

IPW

DPC

MEC

IESC

MPW

NPPD OPPD

SMP

LES

MIPUSTJO

KACY

KACP

ASEC

SPRM

INDN

EMDE

MIDW

Ovals represent operating

areas

Arrows indicate

power flow in MW between

areas

5

Zoomed View of Midwest

CEI

CINCIPS

CONS

DPL

IMPA

IP

IPL

NI

NIPS

OVEC

TE

BRECSIGE

SIPC

CILCO

CWLP

HE

EMO

WPLWEP

6

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.

7

One-line Diagram

• Most power systems are balanced three phase systems.

• A balanced three phase system can be modeled as a single (or one) line.

• One-lines show the major power system components, such as generators, loads, transmission lines.

• Components join together at a bus.

8

Eastern North American High Voltage Transmission Grid

8 2 8 M W2 9 3 M V R2 7 3 M V R8 2 9 M W

2 5 0 M V R1 0 9 3 M W

1 0 9 4 M W2 5 0 M V R

9 M V R3 0 0 M W 9 M V R3 0 0 M W 9 M V R3 0 0 M W

3 0 0 M W 9 M V R3 0 0 M W 9 M V R3 2 0 M W 9 M V R

- 1 1 4 M V R8 9 3 M W

8 9 7 M W- 1 1 0 M V R

- 1 2 7 M V R8 0 1 M W

0 M V R

0 M V R1 1 2 9 M W 1 8 3 M V R

0 M V R

0 M V R

3 4 0 M V R

1 4 3 M V R

2 9 4 M V R

3 4 8 M W 2 6 2 M V R

0 M W 0 M V R

2 8 6 M V R

1 4 5 M V R

2 5 0 M W 4 5 M V R

0 M W 0 M V R

4 5 M V R 2 5 0 M W

0 M V R 0 M W

2 9 4 M V R

- 2 0 2 M V R

- 2 1 0 M V R

1 4 6 M V R

6 7 6 M W 5 0 M V R 6 7 6 M W 5 0 M V R

R i v e r h e a dW i l d w o o d

S h o r e h a m

B r o o k h a v e n

P o r t J e f f e r s o n

H o l b r o o k

H o l t s v i l l e

N o r t h p o r t

P i l g r i mS y o s s e t

B e t h p a g eR u l a n d R d .N e w b r i d g e

L c s t . G r v .

0 7 M E R O M 5

K E Y S T O N E

0 1 Y U K O N

C O N E M - G H

J U N I A T A

S U N B U R Y

S U S Q H A N A

W E S C O V L E

A L B U R T I SH O S E N S A K

B R A N C H B G

E L R O Y

W H I T P A I NL I M E R I C K

D E A N SS M I T H B R G

3 M I L E I

R A M A P O 5

H U N T E R T N

C N A S T O N E

P E A C H B T M

K E E N E Y

B R I G H T O N

W C H A P E L

C L V T C L F

C H A L K 5 0 0

B U R C H E S

8 P O S S U M

8 O X

8 C L I F T O N

8 L O U D O N0 8 M D W B R K

8 M O R R S V L

8 M T S T M

8 V A L L E Y

8 D O O M S

8 B A T H C O

8 L E X N G T N

8 N O A N N A8 L D Y S M T H

8 E L M O N T

8 M D L T H A N

8 C H C K A H M

8 C A R S O N8 S E P T A

8 Y A D K I N8 F E N T R E S

8 S U R R Y

8 P E R S O N 8 M A Y O 1

8 P A R K W O D

8 W A K E

8 P L G R D N

8 C U M B E R L

8 R I C H M O N

8 M C G U I R E

8 J O C A S S E

8 B A D C R K

8 O C O N E E

8 N O R C R O S

8 B U L L S L U8 B I G S H A

8 B O W E N

8 K L O N D I K

8 U N I O N C T

8 V I L L A R

8 W A N S L E Y

8 S N P

8 W B N P 1

8 R O A N E

8 B U L L R U

8 V O L U N T E

8 S U L L I V A

8 P H I P P B

0 5 N A G E L

8 W I L S O N

8 M O N T G O M

8 D A V I D S O

8 M A R S H A L

8 S H A W N E E

8 J V I L L E

8 W E A K L E Y

8 J A C K S O N

8 S H E L B Y

8 C O R D O V A

8 F R E E P O R

W M - E H V 8

8 U N I O N

8 T R I N I T Y

8 B F N P8 L I M E S T O

8 B N P 2

8 M A D I S O N 8 B N P 1

8 W I D C R K

8 R A C C O O N

8 F R A N K L I

8 M A U R Y

8 M I L L E R

8 L O W N D E S

8 W P O I N T

M C A D A M 8

8 S . B E S S

8 F A R L E Y

8 S C H E R E R

8 H A T C H 8

8 A N T I O C H

8 C L O V E R

R O C K T A V

C O O P C 3 4 5R O S E T O N

F I S H K I L L

P L T V L L E Y

H U R L E Y 3

L E E D S 3

G I L B 3 4 5

F R A S R 3 4 5

N . S C O T 9 9

A L P S 3 4 5

R E Y N L D 3

E D I C

M A R C Y T 1

M A S S 7 6 5

O A K D L 3 4 5

W A T E R C 3 4 5

S T O L E 3 4 5

L A F A Y T T E

D E W I T T 3

E L B R I D G E

C L A Y

V O L N E Y

S C R I B A

J A P I T Z P9 M I P T 1I N D E P N D C

O S W E G O

P A N N E L L 3R O C H 3 4 5

K I N T I 3 4 5

N I A G 3 4 5

B E C K A

B E C K B

N A N T I C O K

M I D D 8 0 8 6

M I L T O N

T R A F A L H 1T R A F A L H 2

C L A I R V I L

H A W T H O R N

E S S A

B R U J B 5 6 1

B R U J B 5 6 9

B R U J B 5 6 2

L O N G W O O D

B a r r e t t

E . G . C .

V a l l e y S t r e a m

L a k e S u c c e s sR a i n e y

J a m a i c a

G r e e n w o o d

F o x H i l l sF r e s h K i l l sG o e t h a l s

C o g e n T e c hG o w a n u s

F a r r a g u tE 1 5 t h S t .

W 4 9 t h S t .

T r e m o n t

S h o r e R d .

D u n w o o d i eS p r a i n B r o o k

E a s t v i e wP l e a s a n t v i l l e

M i l l w o o d

B u c h a n a n

I n d i a n P o i n t

D v n p t . N KH m p . H a r b o r

V e r n o n

C o r o n a

G r e e l a w nE l w o o d

Figure shows transmission lines at 345 kV or above in Eastern

U.S.

9

Zoomed View of Midwest

1115 MW-185 MVR

600 MW-41 MVR

200 MW 6 MVR

500 MW 25 MVR

05COOK

05GRNTWN

05JEFRSO

05ALLEN

03LEMOYN

05BEATTY

05BENTON

07BLOMNG

05BREED

17BUROAK

05CORRID

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

70%

S L I N E ; BS L I N E ; R

1 7 S H E F L D

1 7 S C H A H F

1 7 D U N A C R

1 7 M C H C T Y

1 7 B A B C O K

1 7 T W R R D

1 7 C H I A V E

B U R N H ; B

B U R N H ; 0 R

1 7 L K G O R G

1 7 M U N S T R

G A C R ; T

1 7 G R N A C RS J O H ; T

1 7 S T J O H N

DAVIS; B

DAVIS; R

BRAID; B

BRAID; R

LASCO; B

LASCO; R

PLANO; BPLANO; R

ELECT; BELECT; R

ZION ; B

ZION ; R

SILVE; RLIBER; R

DRESD; BDRESD; R

LOCKP; BLOCKP; 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

12GHENT06CLIFTY

08BUFTN1

08EBEND

08M.FTHS

08M.FORT 08REDBK1

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; BCHERR; R

53%W A Y N E ; R

? ? ? ? ?

W 4 0 7 M ; 9 T

W 4 0 7 K ; 9 T

W 4 0 7 K ; R

L O M B A ; B

L O M B A ; R

E L M H U ; B

E L M H U ; R

I T A S C ; 1 M

D P 4 6 ; B

D P 4 6 ; R

P H 1 1 7 ; R

N B 1 5 9 ; 1 M

N B 1 5 9 ; B

S K 8 8 ; R

S K 8 8 ; B

G O L F ; R

G O L F ; B

L I S L E ; B

L I S L E ; R

J O 2 9 ; B

J O 2 9 ; R

M C C O O ; B

M C C O O ; R

COLLI; R

WILTO;

E FRA; BE FRA; R

BLOOM; R

T A Y L O ; B

T A Y L O ; RC R A W F ; B

C R A W F ; R

B E D F O ; R

B E D F O ; R T

G A R F I ; B

C A L U M ; B

B U R N H ; 4 M

B U R N H ; 1 R

Arrows indicate MW flow on the

lines; piecharts

show percentage loading of

lines

10

Example Three Bus System

Bus 2 Bus 1

Bus 3

200 MW100 MVR

150 MWMW

150 MWMW 35 MVRMVR

114 MVRMVR

100 MW 50 MVR

1.00 pu

-17 MW 3 MVR

17 MW -3 MVR

-33 MW 10 MVR

33 MW-10 MVR

17 MW -5 MVR

-17 MW 5 MVR

1.00 pu

1.00 pu

100 MW 2 MVR

100 MWAGC ONAVR ON

AGC ONAVR ON

Generator

LoadBus

Circuit Breaker

Pie charts show

percentage loading of

lines

11

Generation

• Large plants predominate, with sizes up to about 1500 MW.

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

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

12

Loads

• Can range in size from less than a single watt to 10’s of MW.

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

strong daily, weekly and seasonal cycles.

13

Transmission

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

• P = V I or P/V = I• Losses are I2 R• Less losses at higher voltages, but more costly to

construct and insulate.

14

Transmission and Distribution

• Typical high voltage transmission voltages are 500, 345, 230, 161, 138 and 69 kV.

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

• Lower voltage lines are used for distribution, with a typical voltage of 12.4 kV.

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

15

Other One-line Objects

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

• Pie Charts - Show percentage loading of transmission lines.

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

quantities.

16

Power Balance Constraints

• Power flow refers to how the power is moving through the system.

• At all times the total power flowing into any bus MUST be zero!

• This is know as Kirchhoff’s law. And it can not be repealed or modified.

• Power is lost in the transmission system.

17

Basic Power Control

• Opening a circuit breaker causes the power flow to instantaneously(nearly) change.

• No other way to directly control power flow in a transmission line.

• By changing generation we can indirectly change this flow.

18

Flow Redistribution Following Opening Line Circuit BreakerBus 2 Bus 1

Bus 3

200 MW100 MVR

150 MWMW

150 MWMW 36 MVRMVR

111 MVRMVR

100 MW 50 MVR

1.00 pu

-50 MW 11 MVR

50 MW -9 MVR

0 MW 0 MVR

0 MW 0 MVR

50 MW-14 MVR

-50 MW 16 MVR

1.00 pu

1.00 pu

101 MW 6 MVR

100 MWAGC ONAVR ON

AGC ONAVR ON

Power Balance mustbe satisfied at each bus

No flow onopen line

19

Indirect Control of Line Flow

Bus 2 Bus 1

Bus 3

200 MW100 MVR

150 MWMW

250 MWMW 8 MVRMVR

118 MVRMVR

100 MW 50 MVR

1.00 pu

16 MW -3 MVR

-16 MW 3 MVR

-66 MW 21 MVR

67 MW-19 MVR

83 MW-23 MVR

-82 MW 27 MVR

1.00 pu

1.00 pu

2 MW 30 MVR

100 MWAGC ONAVR ON

OFF AGCAVR ON

Generator MW output changed

Generator change indirectly changes

line flow

20

Transmission Line Limits

• Power flow in transmission line is limited by a number of considerations.

• Losses (I2 R) can heat up the line, causing it to sag. This gives line an upper thermal limit.

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

21

Overloaded Transmission Line

Bus 2 Bus 1

Bus 3

359 MW179 MVR

150 MWMW

150 MWMW102 MVRMVR

234 MVRMVR

179 MW 90 MVR

1.00 pu

-152 MW 37 MVR

154 MW-24 MVR

-57 MW 18 MVR

58 MW-16 MVR

-87 MW 29 MVR

89 MW-24 MVR

1.00 pu

1.00 pu

343 MW-49 MVR

104% 104%

100 MWAGC ONAVR ON

AGC ONAVR ON

Thermal limit of 150 MVA

22

Interconnected Operation

• Power systems are interconnected across large distances. 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).

23

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 the

flow on its tie-lines.• The flow out of an area is equal to

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

24

Three Bus System Split into Two Areas

Bus 2 Bus 1

Bus 3Home Area Area 2

Scheduled Transactions

214 MW107 MVR

150 MWMW

150 MWMW 41 MVRMVR

124 MVRMVR

107 MW 53 MVR

1.00 pu

-29 MW 6 MVR

29 MW -6 MVR

-35 MW 11 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 ONAVR ON

AGC ONAVR ON

0.0 MWMW Off AGC

Net tie flowis NOT zero

Initially area flow

is not controlled

25

Area Control Error (ACE)

• The area control error mostly the difference between 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 to “chase” the ACE.

26

Home Area ACE

Bus 2 Bus 1

Bus 3Home Area Area 2

Scheduled Transactions

255 MW128 MVR

227 MWMW

150 MWMW 57 MVRMVR

135 MVRMVR

128 MW 64 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 AGCAVR ON

AGC ONAVR ON

0.0 MWMW Off AGC

06:30 AM 06:15 AMTime

-20.0

-10.0

0.0

10.0

20.0

Area

Con

trol E

rror (

MW

)

ACE changes with time

27

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 gets

sufficiently negative they will “pay back” the accumulated energy.

• In extreme cases inadvertent energy is purchased at a negotiated price.

28

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 ACE based upon tie-line flows; then the AGC module sends control signals out to the generators every couple seconds.

29

Three Bus Case on AGC

Bus 2 Bus 1

Bus 3Home Area Area 2

Scheduled Transactions

214 MW107 MVR

150 MWMW

171 MWMW 35 MVRMVR

124 MVRMVR

107 MW 53 MVR

1.00 pu

-22 MW 4 MVR

22 MW -4 MVR

-42 MW 13 MVR

42 MW-12 MVR

22 MW -6 MVR

-22 MW 7 MVR

1.00 pu

1.00 pu

100 MW 2 MVR

100 MWAGC ONAVR ON

AGC ONAVR ON

0.0 MWMW ED

With AGC on, net tie flow is zero, but

individual line flowsare not zero

30

Generator Costs

• There are many fixed and variable costs associated 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 a function of the MW output of the unit.

31

Generator Cost Curves

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

• Fuel-cost curve: Input-output curve scaled by a fuel cost expressed in $ / Mbtu.

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

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

32

Example Generator Fuel-Cost Curve

0 150 300 450 600Generator Power (MW)

0

2500

5000

7500

10000Fu

el-c

ost (

$/hr

)

Current generatoroperating point

Y-axis tells

cost toproduce specified

power (MW) in

$/hr

33

Example Generator Marginal Cost Curve

0 150 300 450 600Generator Power (MW)

0.0

5.0

10.0

15.0

20.0In

crem

enta

l cos

t ($/

MW

H)

Current generatoroperating point

Y-axis tells

marginal cost to

produce one more MWhr in $/MWhr

34

Economic Dispatch

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

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

IC1(PG,1) = IC2(PG,2) = … = ICm(PG,m)

35

Power Transactions

• Power transactions are contracts between areas to do power transactions.

• Contracts can be for any amount of time at any price for any amount of power.

• Scheduled power transactions are implemented by modifying the area ACE:

ACE = Pactual,tie-flow - Psched

36

Implementation of 100 MW Transaction

Bus 2 Bus 1

Bus 3Home Area Area 2

Scheduled Transactions

340 MW170 MVR

150 MWMW

466 MWMW 9 MVRMVR

232 MVRMVR

170 MW 85 MVR

1.00 pu

-31 MW 6 MVR

31 MW -6 MVR

-159 MW 55 MVR

163 MW-41 MVR

133 MW-35 MVR

-130 MW 44 MVR

1.00 pu

1.00 pu

1 MW 38 MVR112%

112%100 MW

AGC ONAVR ON

AGC ONAVR ON

100.0 MWMW ED

Net tie flow isnow 100 MW from

left to right Scheduled Transaction

Overloaded line

37

Security Constrained ED

• Transmission constraints often limit system economics.

• Such limits required a constrained dispatch in order to maintain system security.

• In three bus case the generation at bus 3 must be constrained to avoid overloading the line from bus 2 to bus 3.

38

Security Constrained Dispatch

Bus 2 Bus 1

Bus 3Home Area Area 2

Scheduled Transactions

340 MW170 MVR

177 MWMW

439 MWMW 15 MVRMVR

223 MVRMVR

170 MW 85 MVR

1.00 pu

-22 MW 4 MVR

22 MW -4 MVR

-142 MW 49 MVR

145 MW-37 MVR

124 MW-33 MVR

-122 MW 41 MVR

1.00 pu

1.00 pu

-0 MW 37 MVR100%

100%100 MW

OFF AGCAVR ON

AGC ONAVR ON

100.0 MWMW ED

Net tie flow isstill 100 MW from

left to right

Gens 2 &3changed to

removeoverload

39

Multi-Area Operation

• The electrons are not concerned with area boundaries. 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 “parallel path” or “loop flows.”

40

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 MW 30 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 MW 20 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 $/MWH 4189 $/MWH

Case Hourly Cost 16933 $/MWH

Area “Top”has 5 buses

Area “Left” has one bus Area “Right” has one bus

ACE foreach area

is zero

41

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

42

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

Losseswent up

from7.09 MW

100 MW Scheduled Transfer from Left to Right

43

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 MW 30 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 MW 52 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 $/MWH 5943 $/MWH

Case Hourly Cost 16654 $/MWH

Transfer also

overloadsline in Top

44

Transmission Service

• FERC Order No. 888 requires utilities provide non-discriminatory open transmission access through tariffs of general applicability.

• FERC Order No. 889 requires transmission providers set up OASIS (Open Access Same-Time Information System) to show available transmission.

45

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.

46

Eastern Interconnect Example

T V A

SOUTHERN

AEP

CPLW

AP

JCP&L

PECO

AE

PSE&G

AEC

CEI

CINCIPS

CONS

DECO

CPLE

DLCO

DPL

DUKE

EKPC

IMPA

IP

IPL

KU

NI

NIPS

OE

OVEC

TE

VP

METED

PENELEC

PEPCO

PJM500

BG&E

PP&L

BREC

LGE

SIGE

SIPC

CILCO

CWLP

HE

EEI

EMO

CORNWALL

NYPP

SCE&G

SCPSA

ONT HYDR

DOE

DPL

ENTR

NEPOOL

WPLWEP

WPS

MGE

YADKIN

HARTWELL

SEPA-JST

SEPA-RBR

SWEP

SWPA

PSOK

GRRD

KAMO

NSP

IPW

DPC

MEC

IESC

MPW

OPPD

SMP

MIPUSTJO

KACY

KACP

ASEC

SPRM

INDN

EMDE

Arrows indicate

the basecase

flow between

areas

47

Power Transfer Distribution Factors (PTDFs)

• PTDFs are used to show how a particular transaction will affect the system.

• Power transfers through the system according to the impedances of the lines, without respect to ownership.

• All transmission players in network could be impacted, to a greater or lesser extent.

48

PTDFs for Transfer from Wisconsin Electric to TVA

T V A

SOUTHERN

20%

AEP

CPLW

AP

PECO

CEI

CINCIPS

CONS

DECO

CPLE

DLCO

DPL

DUKE

EKPC

IMPA

IP

IPL

KU

NI

NIPS

OE

OVEC

TE

VP

METED

PENELEC

PEPCO

PJM500

BG&E

PP&L

BREC

LGE

SIGE

SIPC

CILCO

CWLP

HE

EEI

EMO

CORNWALL

NYPP

SCE&G

SCPSA

ONT HYDR

DOE

ENTR

25%

7%

10%

6% 7% 8%

9%

9%

8%

7%

16% 39%

6%

19%

5% 6%

13%

WPLWEP

WPS

MGE

7%

7%

11%

55% 22%

10%

55% 54%

YADKIN

HARTWELL

SEPA-JST

SEPA-RBR

SWPA

PSOK

GRRD

OKGE

KAMO

6%

WEFA

OMPA

WERE

NSP

19%

IPW

DPC

8%

10%

MEC

IESC

MPW

9%

8%

7% 8%

NPPD OPPD

7%

SMP

LES

MIPUSTJO

6%

KACY

KACP

11% 8%

ASEC 13%

11%SPRM

INDN

EMDE

MIDW

Piecharts indicate

percentage of transfer that will

flow between specified

areas

49

PTDF for Transfer from WE to TVA

CINCIPS

CONS

DECO

DPL

IP

IPL

NI

NIPS

TE

CILCO

CWLP

8%

7%

16% 39%

6%

13%

WPLWEP

WPS

MGE

7%

7%

55% 22%

10%

55% 54%

NSP

19%

IPW

DPC

8%

10%

MEC

IESC

MPW

9%

8%

7% 8%

OPPD

7%

SMP

MIPUSTJO

100% of transfer leaves

Wisconsin Electric (WE)

50

PTDFs for Transfer from WE to TVA

TVA

SOUTHERN

20%

CPLW

DUKE

EKPC

KU

BREC

LGE

SIGE

SIPC

EEI

SCE&GSCPSA

DOE

25%

10%

6% 7% 8% 19%

11%

YADKIN

HARTWELL

SEPA-JST

SEPA-RBR

About 100% of transfer

arrives at TVA

But flow does NOT

follow contract

path

51

Contingencies

• Contingencies are the unexpected loss of a significant device, such as a transmission line or a generator.

• No power system can survive a large number of contingencies.

• First contingency refers to loss of any one device.• Contingencies can have major impact on Power

Transfer Distribution Factors (PTDFs).

52

Available Transfer Capability

• Determines the amount of transmission capability available 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.

53

Reactive Power

• Reactive power is supplied by–generators–capacitors– transmission lines– loads

• Reactive power is consumed by– loads– transmission lines and transformers (very high losses

54

Reactive Power

• Reactive power doesn’t travel well - must be supplied locally.

• Reactive must also satisfy Kirchhoff’s law - total reactive power into a bus MUST be zero.

55

Reactive Power Example

Bus 2 Bus 1

Bus 3

359 MW179 MVR

150 MWMW

150 MWMW102 MVRMVR

234 MVRMVR

179 MW 90 MVR

1.00 pu

-152 MW 37 MVR

154 MW-24 MVR

-57 MW 18 MVR

58 MW-16 MVR

-87 MW 29 MVR

89 MW-24 MVR

1.00 pu

1.00 pu

343 MW-49 MVR

104% 104%

100 MWAGC ONAVR ON

AGC ONAVR ON

Reactive power

must also sum to zero at

each bus

Note reactive

line losses are about 13 Mvar

56

Voltage Magnitude

• Power systems must supply electric power within a narrow voltage range, typically with 5% of a nominal value.

• For example, wall outlet should supply 120 volts, with an acceptable range from 114 to 126 volts.

• Voltage regulation is a vital part of system operations.

57

Reactive Power and Voltage

• Reactive power and voltage magnitude are tightly coupled.

• Greater reactive demand decreases the bus voltage, while reactive generation increases the bus voltage.

58

Voltage Regulation

• A number of different types of devices participate in 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 specified range.

59

Five Bus Reactive Power Example

Bus 3Bus 4

Bus 5

200 MW100 MVR

405 MWMW 96 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 ONAVR ON

79 MVRMVR

0.982 pu

0.995 pu

100 MWMW 0 MVRMVR

3 L

-40 MW 24 MVR

100 MW 10 MVR

Voltage magnitude

is controlled

bycapacitor

LTC Transformer

is controlling

load voltage

60

Voltage Control

• Voltage control is necessary to keep system voltages within an acceptable range.

• Because reactive power does not travel well, it would be difficult for it to be supplied by a third party.

• It is very difficult to assign reactive power and voltage control to particular transactions.

61

Conclusion

• Talk has provided brief overview of how power grid operates.

• Educational Version of PowerWorld Simulator, capable of solving systems with up to 12 buses, can be downloaded for free atwww.powerworld.com

• 60,000 bus commercial version is also available.