Voltage Stability and Reactive Power Planning

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Voltage Stability and Reactive Power Planning
Entergy Transmission Planning Summit New
Orleans, LA July 8, 2004
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Presentation Outline

• Reactive Power/Voltage Issues from the Northeast
  Blackout
• NERC Recommendations
• Background on Voltage Stability
• Reactive Power Requirements for Generators
• Voltage Stability Concerns in Entergy
• Summary

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Voltage Profile During Aug 14th Blackout

• Voltages decay to almost 60 and initiates loss
  of load
• Slow recovery leads to generators tripping
• 60 voltage level also observed in 1995
  Phoenix-area blackout

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East Lake 5 Exciter Operation
Exciter trips to manual
Exciter trips completely
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Power System Outage Task Force

• Strengthen Reactive Power and Control Practices
  in all NERC Regions
• Reactive power problem was a significant factor
  in the August 14 outage, and they were also
  important elements in the several of the earlier
  outages
• -Quote from the outage report

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NERC Recommendations Pertinent to Reactive Power
Planning

• 7. Evaluate reactive power and voltage control
  practices.
• Evaluate the effectiveness of existing reactive
  power and voltage control standards and how they
  are being implemented in the NERC regions
• Recommend revisions to standards or process
  improvements to ensure voltage control and
  stability issues are adequately addressed
• 14. Improve system modeling data and data
  exchange practices.
• Establish and begin implementing criteria and
  procedures for validating data used in power
  flow/stability models by benchmarking model data
  with actual system performance
• Validated data shall be exchanged on an
  inter-regional basis

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What is Voltage Instability/Collapse?

• A power system undergoes voltage collapse if
  post-disturbance voltages are below acceptable
  limits
• Less than 0.8 PU
• voltage collapse may be due to voltage or angular
  instability
• Main factor causing voltage instability is the
  inability of the power systems to maintain a
  proper balance of reactive power and voltage
  control

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Voltage Instability/Collapse

• The driving force for voltage instability is
  usually the load.
• The possible outcome of voltage instability
• loss of loads
• loss of integrity of the power system
• Voltage stability timeframe
• Short term/transient voltage instability 0 - 30
  seconds
• Motor dynamics/stalling
• OELs
• long-term voltage stability 1 60 minutes
• Tap changers/Voltage regulators
• OELs

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Power-Voltage (P-V) Curve
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Power Voltage (P-V) Curve
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Possible Solutions forVoltage Issues

• Install/Operate Shunt Capacitor Banks
• Add dynamic Shunt Compensation in the form of
  SVC/STATCOM to mitigate transient voltage dips
• Add Series Compensation on transmission lines in
  the problem area
• Implement under-voltage load shed (UVLS) program
• Construct transmission/generation facilities

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Generator Capability Curve
Over-excitation Limit
Lagging (Over-excited)
0.8 pf line
Stator Winding Heating Limit
- Per unit MVAR (Q)
Normal Excitation (Q 0, pF 1)
MW
Leading (Under-excited)
Under-excitation Limit
Stability Limit
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Reactive Power Requirementsfor Generators

• The facility should generate reactive power in
  accordance with the voltage schedule prescribed
  by the system dispatcher.
• Above 230 kV 1.02 PU
• 230 kV 1.01 PU
• 69 kV 161 kV 1.00 PU
• The facility shall have a reactive power
  capability to maintain a power factor between
  0.95 lagging and 0.97 leading.
• Units must be operated with the voltage regulator
  in auto mode.
• Generator may be required to operate at its
  maximum reactive capability to meet required
  voltage schedules.
• Ensure that adequate reactive reserves are
  available so that the system can be restored
  satisfactorily.

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Areas of Voltage Stability Concern
North Arkansas
Mississippi
West of the Atchafalaya Basin (WOTAB)
Southeast Louisiana
Western Region
Amite South/DSG
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Reactive Power Projects Implemented in Entergy

• Down Stream of Gypsy (DSG) Area
• 300 MVAR Shunt Capacitor Banks - 2004
• Automatic Under Voltage Load Shedding Program -
  2004
• Static exciter at Ninemile 4 Unit - 2004
• 200 MVAR Shunt Capacitor Banks 2005
• 300 MVAR SVC at Ninemile 230 kV 2005
• Western Region
• Automatic Under Voltage Load Shedding Program
  1998/modified 2004
• Series Compensation on China-Jacinto 230 KV line
  2001
• 300 MVAR SVC at Porter 230 kV 2005
• Series Compensation on China Porter 230 kV line
  - 2005

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Summary

• The increasing need to operate the transmission
  system at its maximum safe transfer limit has
  become a primary concern at most utilities.
• Reactive power supply or VAR management is an
  important ingredient in maintaining healthy power
  system voltages and facilitating power transfers.
• Inadequate reactive power supply was a major
  factor in most of the recent blackouts.

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QUESTIONS ???