Download Voltage Stability and Reactive Power Planning

Voltage Stability and Reactive
Power Planning
Entergy Transmission Planning Summit
New Orleans, LA
July 8, 2004
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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.
#14.
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
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 postdisturbance 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
• OEL’s
– long-term voltage stability: 1 – 60 minutes
• Tap changers/Voltage regulators
• OEL’s
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Power-Voltage (P-V) Curve
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Power – Voltage (P-V) Curve
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Possible Solutions for
Voltage 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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Over-excitation Limit
- Per unit MVAR
(Q) +
Leading
(Under-excited)
Lagging
(Over-excited)
Generator Capability Curve
0.8 pf
line
Stator Winding Heating Limit
Normal Excitation
(Q = 0, pF = 1)
MW
Under-excitation Limit
Stability Limit
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Reactive Power Requirements
for 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 ???
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