1

Stability Issues in Entergy SystemStability Issues in Entergy System

Sharma KolluriSharma KolluriSujit MandalSujit Mandal

Entergy Services, Inc.Entergy Services, Inc.

TVA/NERCTVA/NERC Stability WorkshopStability Workshop

Chattanooga, TN Chattanooga, TN

May 24, 2007May 24, 2007

2

Presentation Outline

• Background on Entergy

• Criteria

• Stability Problems

• Summary

• Issues/Concerns

3

• Over 15,500 miles of transmission lines in four states

• 1,450 transmission substations

• 2.6 million customers

• 40,400 MW of interconnected generating plant capability

• Of which, 13,670 MW is uncommitted capacity

• 22,000 MW of Entergy native load plus additional 3,500 MW of wholesale & network service customer load

Entergy’s Transmission System

4

Mississippi Co. area

Ouachita Parish area

Beaumont/ Lake Charles

New Orleans

Baton Rouge

Union Co. (Panda)

Hot Springs

Lonoke Co. (Wrightsville)

Pine Bluff

Freeport

Panola Co.

Choctaw Co.

Attala Co.

Hinds Co.Warren Co.

BogalusaTenaska

North ARCentral

Amite SouthWOTAB

As of April 2007

New Generation(EWG or QF) with

Filed IOAsSince 1998

Operational

Under Construction/On Hold

5

190

240

290

340

390

440

490

540

590

640

L O A D - - - - - - ->

0 . 6 4 8

0 . 6 6 8

0 . 6 8 8

0 . 7 0 8

0 . 7 2 8

0 . 7 4 8

0 . 7 6 8

0 . 7 8 8

0 . 8 0 8

0 . 8 2 8

0 . 8 4 8 0 . 8 6 8

0 . 8 8 8

0 . 9 0 8

0 . 9 2 8

0 . 9 4 8

0 . 9 6 8

0 . 9 8 8

p.u.

Vol

tage

Limits Corresponding to Voltage Decline Criteria

Limits Corresponding to 5 % margin from Nose Point

Nose Point ( point before voltage collapse)

Voltage Stability Criteria

6

Dynamic Voltage Stability Criteria

7

Generator angle (degrees)

Time in seconds0.000 4.000 8.000 12.000 16.000 20.000

-120

-54

12

78

144

210

Damping Criteria: 3 %

8

Areas of Stability Concern

West of the Atchafalaya Basin(WOTAB)

North Arkansas

Southeast Louisiana

Stability problem in WOTAB AreaExport LimitsImport Limits

McKnight-Franklin Flow Limits

Western RegionVoltage Stability

9

Stability Problem in EntergyStability Problem in Entergy’’s s WOTAB area WOTAB area

10

Problem Area

North Arkansas

Southeast Louisiana

West of the Atchafalaya Basin(WOTAB)

Mississippi

11

WOTAB – Export Limits• WOTAB region is a high profile industrial area

accounting for ~25% of total Entergy load• Two major 500kV tie lines are primary sources for

WOTAB region– Weber – Wells 500kV line– Mt. Olive – Hartburg 500kV line (~180 mile long)

• Approximately 4,000 MW of additional generation in-service

• The limiting contingency is the Mt. Olive -Hartburg 500 kV line.

12

LOUISIANA

TEXAS

K

J

SABINE LASALLE

NATCHITOCHES

GRANT

AVOYELLES

RAPIDESVERNON

BEAUREGARD

EVANGELINE

ST. LANDRY

CALCASIEU

JEFFERSON DAVIS

LAFAYETTE

CAMERON

VERMILION

ALLEN

NEWTON

POLK

TRINITY

ANGELINA

LIBERTY

BRAZORIAGALVESTON

CHAMBERS

HARDIN

JASPER

TYLER

SABINE

NACOGDOCHES

HOUSTON

LIMESTONE

ROBERTSON

BRAZOS

BURLESON

WASHINGTON

GRIMES

WALLER

WALKER

MADISON

LEON

SAN JACINTO

MONTGOMERY

HARRIS

JEFFERSON

SAN AUGUSTINE

ACADIA

SAB

INE

RIVE

R

13

14

15

WOTAB – Export Limits

• Without PSS, the limit is 2,700 MW based on damping criteria ( < 3% damping).

• With PSS on new generating units, the export limit was found to be 3300 MW based on voltage collapse criteria.

• Major transmission improvements required to increase export limits.

16

WOTAB – Import LimitsBackground

• Under normal operating condition, high east-west MW flow on Weber-Wells 500kV line and low north-south MW flow on Mt. Olive –Hartburg 500kV line

• Upon loss of Weber-Wells 500kV line, most of the flow transfer onto the 180 mile long Mt. Olive – Hartburg line. This causes a severe voltage dip in WOTAB region

17

WOTAB – Import Limits

North Arkansas

West of the Atchafalaya Basin(WOTAB)

MississippiMt. Olive – Hartburg 500kV line

Weber – Wells 500kV line

18

Stability limits on Mt. Olive – Hartburg 500kV Line

19

WOTAB – Import LimitsConclusions

• WOTAB area is susceptible to transient voltage swings under certain extreme system conditions

• The low voltage dynamic swings are in violation of the Entergy criteria

• A flow based stability limit was established on the Mt. Olive – Hartburg 500kV line

20

McKnightMcKnight--Franklin Flow Limits Franklin Flow Limits

21

• Entergy performed a reliability upgrade on the McKnight – Franklin line to raise the thermal limit from a 2000 A (1732 MVA) rating to a 3000 A (2598 MVA) rating

•Detailed study to assess voltage and angle stability problems was conducted to establish power flow limits under base and critical contingency conditions

Background

22

Loss of Webre-Wells-Richard & Grand Gulf

Franklin

McKnight

WebreToRichard

Bogalusa

Daniel-McKnight

Daniel

23

TSATTransient Security Assessment Tool

Powertech Labs Inc.Nanjing Automation Research InstituteCopyright © 2002 All rights reserved

Thursday, March 14, 2002, 13:41:14

Buf. Binary Result File Scenario Contingency

Bus # Bus Name ID Buf.Generator angle (degrees)

Time in seconds0.000 4.904 9.808 14.712 19.616 24.520

-200

120

440

760

1080

1400

6 mktfrankrating.bin Fault and Trip Mcknight-Franklin with Daniel-Mcknight O/S - Stability Index Unstable 1 -- MKT-FRK OUT

97915 G6NELSON 1 698231 G1RVRBN 1 698245 G5WGLEN 1 698538 WAT U3 25.0 1 698605 NMIL U5 20.0 1 698954 GGULF 1 699489 ANO U2 22.0 1 699820 ISES U2 22.0 1 696876 DANIST4 13.8 4 696475 BARRY 526.0 5 6

Mcknight-Franklin PreContingency Flow

1619 MW, 35 MVAR

24

Mcknight-Franklin PreContingency Flow

1522 MW, 56 MVAR

TSATTransient Security Assessment Tool

Powertech Labs Inc.Nanjing Automation Research InstituteCopyright © 2002 All rights reserved

Wednesday, April 24, 2002, 09:38:34

Buf. Binary Result File Scenario Contingency

Bus # Bus Name ID Buf.Generator angle (degrees)

Time in seconds0.000 5.000 10.000 15.000 20.000 25.000

-120

-56

8

72

136

200

2 mktfrankrating.bin Fault and Trip Mcknight-Franklin with Daniel-Mcknight O/S - Damping Ratio Stable 1 -- MKT-FRK OUT

97915 G6NELSON 1 298231 G1RVRBN 1 298245 G5WGLEN 1 298538 WAT U3 25.0 1 298605 NMIL U5 20.0 1 298954 GGULF 1 299489 ANO U2 22.0 1 299820 ISES U2 22.0 1 296876 DANIST4 13.8 4 296475 BARRY 526.0 5 2

25

Results

• Angle Stability limits found to be lower than voltage stability limits

• Rating of the McKnight-Franklin 500kV line limited to 2,070 MVA due to unacceptable damping– With Webre-Richard out of service, the flow limit is 1,958

MVA– With Daniel-McKnight out of service, the flow limit is 1,522

MVA

26

Voltage Stability Problem in Voltage Stability Problem in EntergyEntergy’’s Western Region s Western Region

27

Areas of Stability Concern

West of the Atchafalaya Basin(WOTAB)

North Arkansas

Southeast LouisianaWestern Region

Mississippi

28

Western Region – Overview

138 kV Tie Lines

≤ 230 kV Tie Lines

Generation

Load Center

Woodlands Network

New Caney Network

Conroe Network

29

Criteria

Minimize motor tripping

Prevent UVLS activation

Voltage (pu)

30

ResultsWithout motor tripping being simulated

Voltage = 0.7 pu

LegendGrimesRivtrinNavasotaConroeGoslinOakridge

Voltage (pu)

31

System recovers to healthy voltages

• Criterion for motor trip : Voltage < 0.7 pu for > 20 cycles

ResultsWith motor tripping being simulated

Motors Trip

Voltage (pu)

LegendGrimesRivtrinNavasotaConroeGoslinOakridge

32

SVC Performance Dynamic Rating

VAR output of the SVC

Voltage (pu)

LegendGrimesRivtrinNavasotaConroe

33

Overall Summary

• PSS installation mandatory for all new generation locating on the Entergy system

• Flow limits imposed to address stability issues• SVCs installed to solve voltage stability

problems

34

Stability Issues/Concerns• Load Modeling

– static load– motor load

• Generation Modeling and Testing– Generators– Exciters– Governors– PSS

• Reactive Power Margin• Stability Criteria – Voltage dip, Damping Ratio• Tools for Real Time Stability Analysis