Stability Issues in Entergy System Entergy Transmission Planning Summit New Orleans, LA July 10, 2003

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Stability Issues in Entergy System Entergy
Transmission Planning Summit New Orleans, LA
July 10, 2003
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Classification of Power System Stability

• Transient/Angle Stability
• Voltage Stability
• Small Signal/Oscillatory Stability

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Static Voltage Stability Criteria
Limits Corresponding to Voltage Decline Criteria
Limits Corresponding to 5 margin from Nose Point
Nose Point ( point before voltage collapse)
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Dynamic Voltage Stability Criteria
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Damping Criteria 3
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Areas of Stability Concern in 2002
I. Joint Stability Study between Entergy,
Southern, and TVA
North Arkansas
Northwest Quadrant
West of the Atchafalaya Basin (WOTAB)
Southeast Louisiana
II. McKnight-Franklin Flow Limits
III. Stability problem in WOTAB Area
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I. Joint Stability Study between Entergy,
Southern, and TVA
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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 doesnt exist any more
  due to cancellation of some IPP generation.

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II. McKnight-Franklin Flow Limits
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Problem Area
North Arkansas
Mississippi
West of the Atchafalaya Basin (WOTAB)
Southeast Louisiana
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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

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III. Stability Problem in Entergys WOTAB
area
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Problem Area
North Arkansas
Mississippi
West of the Atchafalaya Basin (WOTAB)
Southeast Louisiana
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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 ( lt 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.

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New Areas of Stability Concern
North Arkansas
Mississippi
West of the Atchafalaya Basin (WOTAB)
Southeast Louisiana
V. Western Region Voltage Stability
IV. Amite South Stability
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IV. Stability Problem in Entergys Amite
South Area
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Problem Area
North Arkansas
Mississippi
West of the Atchafalaya Basin (WOTAB)
Southeast Louisiana
Amite South Region
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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

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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

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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

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System Separation
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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

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V. Voltage Stability Problem in Entergys Western
Region
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Areas of Stability Concern
North Arkansas
Mississippi
West of the Atchafalaya Basin (WOTAB)
Southeast Louisiana
Western Region
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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.

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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

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Power Voltage (P-V) CurveLoss of one Lewis
Creek unit and Grimes Crockett 345 kV line
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Voltage Profile at Critical Buses
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Results for 2005 Summer Peak

• Voltage Instability
• Slow voltage recovery
• Several motor loads at risk
• Depressed voltages can lead to UVLS operation

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Possible Solutions

• Static Devices MS Shunt Cap Banks
• Series Compensation
• New transmission facilities (for details, see
  EGSI-TXs area planning presentation)
• Dynamic VAR support device (e.g., SVC, STATCOM,
  D-SMES)

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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.