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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
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Presentation Outline
• Background on Entergy
• Criteria
• Stability Problems
• Summary
• Issues/Concerns
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• 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
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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
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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
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Dynamic Voltage Stability Criteria
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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 %
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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
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Stability Problem in EntergyStability Problem in Entergy’’s s WOTAB area WOTAB area
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Problem Area
North Arkansas
Southeast Louisiana
West of the Atchafalaya Basin(WOTAB)
Mississippi
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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.
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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
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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.
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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
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WOTAB – Import Limits
North Arkansas
West of the Atchafalaya Basin(WOTAB)
MississippiMt. Olive – Hartburg 500kV line
Weber – Wells 500kV line
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Stability limits on Mt. Olive – Hartburg 500kV Line
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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
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McKnightMcKnight--Franklin Flow Limits Franklin Flow Limits
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• 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
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Loss of Webre-Wells-Richard & Grand Gulf
Franklin
McKnight
WebreToRichard
Bogalusa
Daniel-McKnight
Daniel
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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
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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
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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
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Voltage Stability Problem in Voltage Stability Problem in EntergyEntergy’’s Western Region s Western Region
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Areas of Stability Concern
West of the Atchafalaya Basin(WOTAB)
North Arkansas
Southeast LouisianaWestern Region
Mississippi
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Western Region – Overview
138 kV Tie Lines
≤ 230 kV Tie Lines
Generation
Load Center
Woodlands Network
New Caney Network
Conroe Network
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Criteria
Minimize motor tripping
Prevent UVLS activation
Voltage (pu)
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ResultsWithout motor tripping being simulated
Voltage = 0.7 pu
LegendGrimesRivtrinNavasotaConroeGoslinOakridge
Voltage (pu)
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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
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SVC Performance Dynamic Rating
VAR output of the SVC
Voltage (pu)
LegendGrimesRivtrinNavasotaConroe
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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
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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
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