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Voltage Stability and Reactive Power Planning


Evaluate the effectiveness of existing reactive power and voltage control standards and how they are ... in the form of SVC/STATCOM to mitigate transient ... – PowerPoint PPT presentation

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Title: Voltage Stability and Reactive Power Planning

Voltage Stability and Reactive Power Planning
Entergy Transmission Planning Summit New
Orleans, LA July 8, 2004
Presentation Outline
  • Reactive Power/Voltage Issues from the Northeast
  • NERC Recommendations
  • Background on Voltage Stability
  • Reactive Power Requirements for Generators
  • Voltage Stability Concerns in Entergy
  • Summary

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

East Lake 5 Exciter Operation
Exciter trips to manual
Exciter trips completely
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
  • -Quote from the outage report

NERC Recommendations Pertinent to Reactive Power
  • 7. Evaluate reactive power and voltage control
  • 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

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

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
  • Motor dynamics/stalling
  • OELs
  • long-term voltage stability 1 60 minutes
  • Tap changers/Voltage regulators
  • OELs

Power-Voltage (P-V) Curve
Power Voltage (P-V) Curve
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

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)
Leading (Under-excited)
Under-excitation Limit
Stability Limit
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

Areas of Voltage Stability Concern
North Arkansas
West of the Atchafalaya Basin (WOTAB)
Southeast Louisiana
Western Region
Amite South/DSG
Reactive Power Projects Implemented in Entergy
  • Down Stream of Gypsy (DSG) Area
  • 300 MVAR Shunt Capacitor Banks - 2004
  • Automatic Under Voltage Load Shedding Program -
  • 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
  • 300 MVAR SVC at Porter 230 kV 2005
  • Series Compensation on China Porter 230 kV line
    - 2005

  • 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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