Lecture 4 Power System Operation

Professor Tom OverbyeDepartment of Electrical and

Computer Engineering

ECE 476

POWER SYSTEM ANALYSIS

2

Reading and Homework

• Moving 1st Exam? Oct 11 or 13?• For lectures 4 through 6 please be reading Chapter 4

– we will not be covering sections 4.7, 4.11, and 4.12 in detail though you should still at least skim those sections.

• HW 1 is 2.9, 22, 28, 32, 48; due Thursday 9/8• For Problem 2.32 you need to use the PowerWorld Software. You can

download the software and cases at the below link; get version 15.http://www.powerworld.com/gloversarma.asp

Direct PowerWorld download page is

http://www.powerworld.com/DemoSoftware/GloverSarmaSimdwnldv15.asp

3

State Variation in Electric Rates

4

The Goal: Customer Choice

5

The Result for California in 2000/1

OFF

OFF

6

The California-Enron Effect

Source : http://www.eia.doe.gov/cneaf/electricity/chg_str/regmap.html

RI

AK

electricityrestructuring

delayedrestructuring

no activitysuspended

restructuring

WA

OR

NV

CA

ID

MT

WY

UT

AZ

CO

NM

TX

OK

KS

NE

SD

NDMN

IA

WI

MO

IL IN OH

KY

TN

MS

LA

AL GA

FL

SC

NC

WVA VA

PA

NY

VT ME

MI

NH

MA

CTNJ

DEMD

AR

HI

DC

7

Natural Gas Boom, Bust and Boom

8

August 14th, 2003 Blackout

9

2007 Illinois Electricity Crisis

Two main electric utilities in Illinois are ComEd and Ameren Restructuring law had frozen electricity prices for ten years,

with rate decreases for many. Prices rose on January 1, 2007 as price freeze ended; price

increases were especially high for electric heating customers who had previously enjoyed rates as low as 2.5 cents/kWh

2009 average residential rate (in cents/kWh) is 9.08 in IL, 7.62 IN, 9.38 WI, 7.37 IA, 15.52 NY, 6.60 WA, 13.20 in CA, 9.82 US average

10

The Rise of Renewables

Currentlyabout 4%of our electric capacityis wind

The up/downsin 2001/2 and2003/4 werecaused by expiring tax

credits

11

The Smart Grid

• The term “Smart Grid” dates officially to the 2007 “Energy Independence and Security Act”, Title 13 (“Smart Grid”)• Use of digital information and control techniques• Dynamic grid optimization with cyber-security• Deployment of distributed resources including • Customer participation and smart appliances• Integration of storage including PHEVs• Development of interoperability standards

12

Smart Grid Perceptions

13

In the News: Local Electricity Suppliers

• On Monday (Aug 29) the News-Gazette had a story about alternative electricity suppliers finally entering the Ameren residential market

• For example, BlueStar Energy offers electricity at a fixed price of 5.175 cents/kWh versus Ameren at 5.646 cents/kWh.• There are other rate options as well so consumers need to shop around

for what works best

• You still pay some money to Ameren for the use of the wires, just not for energy

• Check out www.pluginillinois.org

14

In the News: Illinois Smart Grid Bill

• On Monday (Aug 29) legislation to “modernize” the Illinois electric grid was sent to Governor Quinn. He has promised to veto the bill. If vetoed it could be overriden in the fall veto session

• Supporters of the ten year, $3 billion effort, say the savings to consumers due to the installation of smart meters will more than offset the increase in rates.

• Quinn and other argue it gives too much money to ComEd and Ameren.

15

Power System Operations Overview

Goal is to provide an intuitive feel for power system operation

Emphasis will be on the impact of the transmission system

Introduce basic power flow concepts through small system examples

16

Power System Basics

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

Generation: Creates electric power. Load: Consumes electric power. Transmission/Distribution: Transmits electric power

from generation to load. – Lines/transformers operating at voltages above 100 kV are

usually called the transmission system. The transmission system is usually networked.

– Lines/transformers operating at voltages below 100 kV are usually called the distribution system (radial).

17

Simulation of the Eastern Interconnect

Bloomington

Peoria

RockfordWaukegan

Zi on

Pl easant

Des Pl ai nes

El mhurst

I t asca

Tol l w ay

W407 ( Fermi )

Cherry Val ley

Wempleton

Paddock

Cl inton

Powerton

Ipava

D uck Creek

Brai dw ood

Shefi eld

Chiave

Munster

El ect r i c Junct i on

Pl ano

La Sal le

Lombard

Li sle

Col l ins

D resden

Lockport

East Frankfort

Goodings Grove

Tazwel l

Lake George

D unacr

Green Acres

Schahfer

Tower Rd

Babcock

Prai ri e

Racine

Michi gan Ci ty

El wood

Gulon

Sti l lwel l

O l i ve

Sycamore

Bondurant

Motezuma

Arnold

Se Pol k

H azel ton

Burr Oak

Pl ai sades

Benton Harbor

RN TOUL J

PERKN SRD

CH AMP ECH AMP W

LEVER RD

RISIN G

CH AMP TP

MAHOMET

WEED MAN

N LEROY

PAXTON E

RANTOUL

GIBSON C

GIBSONCP

H OOPESTN

VERMILON

TILTN EC

BUNSONVL

W TILTON

VERML 1

VERMILON

GILMAN

WATSEKA 17GOD LN D

CLTN TAP

CLT RT54

S CLN TN

R FAL; R

1346A TP

H OLLAND

MACOMB WH AMLTNAM

H AVAN A

IPAVA

CANTON

CUBA

KICKAPOO

MASON

H AVAN A SMASON CY

TAZEWELL

H ALLOCK

ED WARD S3

CAT MOSSFARGO

KEYSTONE

E PEORIA

RSW EAST

CAT SUB2

H INES

PION EERC

RAD N OR

CAT TAP

CAT MAP

CAT SUB1

EASTERNBURLIN 1G

MACOMBN E

N IOTA

N IOTA

BRLGTN 5

SB 18 5

E MOLIN E

SB 43 5

SB 112 5

KPECKTP5

SO.SUB 5

SB 85 5

SB 31T 5

SB 28 5

SB 17 5

SB 49 5

SB 53 5

SB 47 5SB 48 5

SB A 5

SB 70 5

SB 79 5

SB 88 5

SB 71 5

BVR CH 65 BVR CH 5 ALBAN Y 5

YORK 5

SAVAN NA5

GALEN A 5

8TH ST.5

LORE 5

SO .GVW.5

SALEM N5

ALBAN Y 6

GARD E;

H 71 ;BTH 71 ; B

H 71 ; R

R FAL; B

N ELSO; R

N ELSO;RT

STERL; B

D IXON;BT

MECCORD 3

CORD O;

LEECO;BP

MARYL; B

MEND O; T

STILL;RT

B427 ;1T

LANCA; R

PECAT; B

FREEP;

ELERO;BT ELERO;RT

LENA ; RLENA ; B

H 440 ;RT

H 440 ; R

STEWA; B

H 445 ;3B

Roscoe

Pi erpont

S PEC; R

FORD A; R

H arlem

Sand Park

N WT 138

BLK 138

ROR 138

JAN 138

ALB 138

N OM 138

D AR 138

H LM 138

POT 138 MRE 138

COR 138 D IK 138

BCH 138

Sabrooke

Bl awkhawk

Al pine

E. Rockford

Charles

Belvidere

B465

Marengo

WIB 138

WBT 138 ELK 138

N LG 138

N LK GV T

SGR CK5

BRLGTN 1

BRLGTN 2

SGR CK4

UN IVRSTY

UN IV NEU

WHTWTR5

WHTWTR4

WHTWTR3

SUN 138

VIK 138

LBT 138

TICH IGN PARIS WE

ALBERS-2

Green Lake

Sand Ridge

Chicago H eights

Burnham

Lansing

F-575

F-503Gl enwood

Bl oomPark ForestMatteson

Country Cl ub H i l l s

Woodhi l lU. Park

Bl ue Island

Wi lmington

Wi l ton Center

Frankfort

N Len

Brigg

D owners Groove

N Aurora

Hanover

Bart l et t

Church

Addi son

NordiG l endal e

Romeo

Wayne

Wi l l Co.

Jol i et

D umont 345 D umont 765

Kenzie Creek

JackSr

Cook - 345 kV

Cook - 765 kV

Twin Branch

BAIN 4

SOMERS

ST RITA

BIG BEND

MUKWON GO

N ED 138

N ED 161

LAN 138

EEN 138

CASVILL5TRK RIV5D UND EE 5

LIBERTY5

ASBURY 5

CN TRGRV5

JULIAN 5

MQOKETA5

E CALMS5

GR MN D 5

D EWITT 5

SBHYC5

SUB 77 5

SB 74 5SB 90 5

SB 78 5D AVN PRT5

SB 76 5

SB 58 5

SB 52 5

SB 89 5

IPSCO 5

IPSCO 3

D ENMARK5

N EWPORT5

H WY61 5

WEST 5

9 SUB 5

H ENRYCO5

VIELE 5

TRIVERS5

CARBID E5

TRIPP

Kenda

MPWSPLIT

WYOMIN G5

MT VERN5

BERTRAM5

H AZL S 5

BLKHAWK5

ED WARD S1

JEFF 5

WAPELLO5

APANOSE5

AD AIR

H ILLSIE5

PCI 5

BEVERLY5

FAIRFAX5

H ILLS 5PARNEL 5POWESHK5

BEACON 5

EIC 5

BRD GPRT5

LUCAS 5

CRLRID G5

SB PIC 5

SB J IC 5

SB EIC 5

SB YIC 5

SB GIC 5

SB UIC 5

WASH BRN 5

UN IONTP5

EL FARM5

D R EN G 5

WTWEST 5

D RFN D RY5

MID PORT5

6 ST 5

VINTON 5

H IAWATA5

D YSART 5

TRAER 5

D R N E 5

LUND QST5

D RCOMP 5

H AMPTON 5

FRANKLN5BUTLER 5

M-TOWN 5

REASN OR5

N EWTON 5

JASPER 5

TIMBRCK5

McCook

Covert

93%B

MVA105%

B

MVA

18

Small PowerWorld Simulator Case

Bus 2 Bus 1

Bus 3Home Area

204 MW

102 MVR

150 MW

150 MW 37 MVR

116 MVR

102 MW 51 MVR

1.00 PU

-20 MW 4 MVR

20 MW -4 MVR

-34 MW 10 MVR

34 MW-10 MVR

14 MW -4 MVR

-14 MW

4 MVR

1.00 PU

1.00 PU

106 MW 0 MVR

100 MWAGC ONAVR ON

AGC ONAVR ON

Load withgreenarrows indicatingamountof MWflow

Usedto controloutput ofgenerator

Direction of arrow is used to indicatedirection of real power (MW) flow

Note thepower balance ateach bus

19

Power Balance Constraints

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

At all times in the simulation 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.

20

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.

21

Transmission Line Limits

Power flow in transmission line is limited by heating considerations.

Losses (I2 R) can heat up the line, causing it to sag. Each line has a limit; Simulator does not allow you

to continually exceed this limit. Many utilities use winter/summer limits.

22

Overloaded Transmission Line

23

Interconnected Operation

Power systems are interconnected across large distances. For example most of North America 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).

24

Operating Areas

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

25

Area Control Error (ACE)

The area control error is the difference between the actual flow out of an area, and the scheduled flow.

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

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.

27

Three Bus Case on AGC

Bus 2 Bus 1

Bus 3Home Area

266 MW

133 MVR

150 MW

250 MW 34 MVR

166 MVR

133 MW 67 MVR

1.00 PU

-40 MW 8 MVR

40 MW -8 MVR

-77 MW 25 MVR

78 MW-21 MVR

39 MW-11 MVR

-39 MW

12 MVR

1.00 PU

1.00 PU

101 MW 5 MVR

100 MWAGC ONAVR ON

AGC ONAVR ON

Net tie flow is close to zero

Generationis automaticallychanged to matchchange in load

28

Generator Costs

There are many fixed and variable costs associated with power system operation.

The major variable cost is associated with generation. Cost to generate a MWh can vary widely. For some types of units (such as hydro and nuclear) it

is difficult to quantify. For thermal units it is much easier. These costs will

be discussed later in the course.

29

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)

30

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

31

100 MW Transaction

Bus 2 Bus 1

Bus 3Home Area

Scheduled Transactions

225 MW

113 MVR

150 MW

291 MW 8 MVR

138 MVR

113 MW 56 MVR

1.00 PU

8 MW -2 MVR

-8 MW 2 MVR

-84 MW 27 MVR

85 MW-23 MVR

93 MW-25 MVR

-92 MW

30 MVR

1.00 PU

1.00 PU

0 MW 32 MVR

100 MWAGC ONAVR ON

AGC ONAVR ON

100.0 MW

Scheduled100 MWTransaction from Left to Right

Net tie-lineflow is now100 MW

32

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.

33

Security Constrained Dispatch

Bus 2 Bus 1

Bus 3Home Area

Scheduled Transactions

357 MW

179 MVR

194 MW

448 MW 19 MVR

232 MVR

179 MW 89 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 MWOFF AGCAVR ON

AGC ONAVR ON

100.0 MW

Dispatch is no longer optimal due to need to keep line from bus 2 to bus 3 from overloading

34

Multi-Area Operation

If Areas have direct interconnections, then they may directly transact up to the capacity of their tie-lines.

Actual power flows through the entire network according to the impedance of the transmission lines.

Flow through other areas is known as “parallel path” or “loop flows.”

35

Seven Bus Case: One-line

Top Area Cost

Left Area Cost Right Area Cost

1

2

3 4

5

6 7

106 MW

168 MW

200 MW 201 MW

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 MW

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

System hasthree areas

Area lefthas onebus

Area right has onebus

Area tophas fivebuses

36

Seven Bus Case: Area View

System has40 MW of“Loop Flow”

Actualflowbetweenareas

Loop flow can result in higher losses

Area Losses

Area Losses Area Losses

Top

Left Right

-40.1 MW

0.0 MW

0.0 MW

0.0 MW

40.1 MW

40.1 MW

7.09 MW

0.33 MW 0.65 MW

Scheduledflow

37

Seven Bus - Loop Flow?

Area Losses

Area Losses Area Losses

Top

Left Right

-4.8 MW

0.0 MW

100.0 MW

0.0 MW

104.8 MW

4.8 MW

9.44 MW

-0.00 MW 4.34 MW

100 MW Transactionbetween Left and Right

Transaction has actually decreasedthe loop flow

Note thatTop’s Losses haveincreasedfrom 7.09MW to9.44 MW

38

Pricing Electricity

Cost to supply electricity to bus is called the locational marginal price (LMP)

Presently some electric makets post LMPs on the web In an ideal electricity market with no transmission

limitations the LMPs are equal Transmission constraints can segment a market, resulting

in differing LMP Determination of LMPs requires the solution on an

Optimal Power Flow (OPF)

39

3 BUS LMPS - OVERLOAD IGNORED

Bus 2 Bus 1

Bus 3

Total Cost

0 MW

0 MW

180 MWMW

10.00 $/MWh

60 MW 60 MW

60 MW

60 MW120 MW

120 MW

10.00 $/MWh

10.00 $/MWh

180 MW120%

120%

0 MWMW

1800 $/hr

Line from Bus 1 to Bus 3 is over-loaded; all buses have same marginal cost

Gen 1’scostis $10per MWh

Gen 2’scostis $12per MWh

40

LINE OVERLOAD ENFORCED

Bus 2 Bus 1

Bus 3

Total Cost

60 MW

0 MW

180 MWMW

12.00 $/MWh

20 MW 20 MW

80 MW

80 MW100 MW

100 MW

10.00 $/MWh

14.01 $/MWh

120 MW 80% 100%

80% 100%

0 MWMW

1921 $/hr

Line from 1 to 3 is no longer overloaded, but nowthe marginal cost of electricity at 3 is $14 / MWh

41

MISO and PJM

MISO and PJM arethe reliabilitycoordinatorscovering theelectric gridin Illinois. ComEd is inPJM, and Ameren is inMISO.

42

MISO ACE Chart from Aug 31, 2011

https://www.midwestiso.org/MarketsOperations/RealTimeMarketData/Pages/ACEChart.aspx

43

MISO LMPs 8/31/11 at 11:05 AM

www.midwestmarket.org