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1
Stability Issues in Entergy Stability Issues in Entergy
System System
Entergy Transmission Planning Summit Entergy Transmission Planning Summit
New Orleans, LA New Orleans, LA
July 10, 2003July 10, 2003
2
Classification of Power System Stability
• Transient/Angle Stability
• Voltage Stability
• Small Signal/Oscillatory Stability
3
190
240
290
340
390
440
490
540
590
640
LOAD ------->
0.648
0.668
0.688
0.708
0.728
0.748
0.768
0.788
0.808
0.828
0.848
0.868
0.888
0.908
0.928
0.948
0.968
0.988
p.u
. V
oltage
Limits Corresponding to Voltage Decline Criteria
Limits Corresponding to 5 % margin from Nose Point
Nose Point ( point before voltage collapse)
Static Voltage Stability Criteria
4
Dynamic Voltage Stability Criteria
5TSATPowertech Labs Inc.
Nanjing Automation Research Institute
Copyright © 2002 All rights reserved
Thursday, March 14, 2002, 13:39:57
Generator angle (degrees)
Time in seconds
0.000 4.000 8.000 12.000 16.000 20.000-120
-54
12
78
144
210
Damping Criteria – 3 %
6
Areas of Stability Concern in 2002
West of the Atchafalaya Basin(WOTAB)
North Arkansas
Southeast Louisiana
Northwest Quadrant
III. Stability problem in WOTAB AreaII. McKnight-Franklin Flow Limits
I. Joint Stability Study between
Entergy, Southern, and TVA
7
I. Joint Stability Study I. Joint Stability Study
between Entergy, Southern, between Entergy, Southern,
and TVA and TVA
8
Results/Northwest Quadrant
• New generation added without PSS severely deteriorated system damping.
• The most limiting contingency from a damping standpoint was the Miller - Bellefonte 500 kV line.
• The most limiting contingency from a voltage standpoint was the Farley - Mitchell 500 kV line.
• With PSS on new generating units, the export limits were found to be 3,850 MW.
• Current Status: Problem doesn’t exist any more due to cancellation of some IPP generation.
9
II. McKnight-Franklin Flow II. McKnight-Franklin Flow
Limits Limits
10
Problem Area
North Arkansas
Southeast Louisiana
West of the Atchafalaya Basin(WOTAB)
Mississippi
11
Results/Southeast Louisiana
• Angle Stability limits found to be slightly 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
• No transient voltage security violations observed
12
III. Stability Problem in III. Stability Problem in
Entergy’s WOTAB area Entergy’s WOTAB area
13
Problem Area
North Arkansas
Southeast Louisiana
West of the Atchafalaya Basin(WOTAB)
Mississippi
14
Results/WOTAB
• The limiting contingency is the Mt. Olive - Hartburg 500 kV line.
• 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.
• Limit based on voltage decline criteria (0.92 pu) is 2,100 MW.
• Major transmission improvements may be required to increase export limits.
15
New Areas of Stability Concern
West of the Atchafalaya Basin(WOTAB)
North Arkansas
Southeast LouisianaV. Western Region Voltage Stability
IV. Amite South Stability
Mississippi
16
IV. Stability Problem in IV. Stability Problem in
Entergy’s Amite South Area Entergy’s Amite South Area
17
Problem Area
North Arkansas
Southeast Louisiana
West of the Atchafalaya Basin(WOTAB)
Mississippi
Amite South Region
18
Background
• Major Load Center
• Large Concentration of Generation
• Expected 2003 conditions:– 6,280 MW of load (including CLECO & LaGEN
loads)– 8,400 MW of native and new generation
19
Background
• 230 kV loop out of Waterford is critical– Approximately 3,100 MW generation in the loop– System stable for primary clearing faults– Additional generation can lead to instability for
stuck breaker faults
20
Results
• Under stuck breaker faults– Fault clearing time very important for the stability
of the region– Units in Amite south region and close vicinity can
separate from the rest of the system– Can lead to lines tripping
21
System Separation
22
Solutions Proposed
• Faster fault clearing devices (relays, breakers)
• Remedial action scheme to trip certain units to protect against stuck breaker fault conditions
• Power system stabilizers on the new units
• IPO breakers
23
V. Voltage Stability Problem V. Voltage Stability Problem
in Entergy’s Western Region in Entergy’s Western Region
24
Areas of Stability Concern
West of the Atchafalaya Basin(WOTAB)
North Arkansas
Southeast LouisianaWestern Region
Mississippi
25
Background
• Western Region load growth: ~ 5.1 %
• Generation sources: Two Lewis Creek units (226MW & 230MW, 150 MVAR each)
• With one Lewis Creek unit out of service, certain line outages can cause low voltages leading to potential voltage collapse.
• Critical tie lines are Grimes – Crockett 345 kV and China – Jacinto 230 kV.
26
Background
• Currently, Under Voltage Load Shedding (UVLS) scheme is in place.– Voltage at critical buses below 0.92 pu
– Loss of both Lewis Creek generators
– Lewis Creek units go into over excitation mode
• Series Compensation on China – Jacinto 230 kV line• Static capacitors installed – 770 MVAR• Two D-SMES units (8 MVA each) installed at New
Caney and Metro in 2001
27
0.92
0.94
0.96
0.98
1
1.02
1.04
1300.00 1350.00 1400.00 1450.00 1500.00 1550.00 1600.00
Western Region Load Level (MW)
Vo
ltag
e (P
.U.)
Metro138
Conroe138
Lewis138
Tamina138
Goslin138
Jacinto138
Jacinto230
NAVSOTA138
Grimes138
CALVERT69
NewCaney138
Rivtrin138
Dayton138
Cypress138
Power – Voltage (P-V) CurveLoss of one Lewis Creek unit and Grimes – Crockett 345 kV
line
28
Voltage Profile at Critical Buses
29
Results for 2005 Summer Peak
• Voltage Instability– Slow voltage recovery – Several motor loads at risk – Depressed voltages can lead to UVLS operation
30
Possible Solutions
• Static Devices – MS Shunt Cap Banks
• Series Compensation
• New transmission facilities (for details, see EGSI-TX’s area planning presentation)
• Dynamic VAR support device (e.g., SVC, STATCOM, D-SMES)
31
System Stability Summary
• PSS installation mandatory for all new generation locating on the Entergy system
• PSS tuning mandatory in WOTAB and Southeast Louisiana
• Traditional methods are needed to fix stability problems (alleviate thermal constraints, additional static reactive power support devices, series compensation)
• New technologies (FACTS devices, e.g., SVC, STATCOM, D-SMES, UPFC, etc.) may be required.