Prevention and Mitigation of Cascading Outages
in Power Grids Using Synchrophasor-based
Wide-Area Measurements
Kai Sun
Project Manager
Grid Operations, Planning & Renewable Integration
Email: ksun@epri.com Tel: 650-8552087
May 8, 2012 @ Stanford University
Content
• Cascading outages (impacts, causes, new
challenges
h ll
and
d solutions)
l ti
)
• Intelligent system separation utilizing
synchrophasors
•S
Situational
tuat o a awareness
a a e ess ut
utilizing
g wide-area
de a ea
measurements (DOE demonstration project)
• Conclusions
© 2012 Electric Power Research Institute, Inc. All rights reserved.
2
Blackouts of Power Grids
Date
Area
Impacts
p
Nov 9, 1965
North America (NE)
20,000+MW, 30M people
13 hrs
Jul 13, 1977
North America (NY)
6,000MW,
26 hrs
Dec 22, 1982
North America (W)
12, 350 MW, 5M people
Jul 2-3, 1996
North America (W)
11,850 MW, 2M people
13 hrs
Aug 10,
10 1996
North America (W)
28 000+MW 7.5M
28,000+MW,
7 5M people
9 hrs
Jun 25, 1998
North America (N-C)
950 MW,
19 hrs
Mar 11, 1999
Brazil
Aug 14, 2003
North America (NE)
Sep 13, 2003
9M people
0.15MK people
Duration
90M people
hrs
50M people
2+ days
Italy
57M people
5-9 hrs
S 23,
Sep
23 2003
S d &D
Sweden
Denmark
k
5M people
l
5h
hrs
Nov 4, 2006
Europe
15M households
2 hrs
Nov 10, 2009
Brazil & Paraguay
Feb 4, 2011
Brazil
Sep 8, 2011
US & Mexico (S-W)
© 2012 Electric Power Research Institute, Inc. All rights reserved.
61,800MW,
17,000MW, 80M people, 18
states
53M people, 8
states
4,300MW, 5M people
3
7hrs
12hrs
Causes of a blackout
970 MW loss
Blackout event in Aug. 1996
1 Initial events (15:42:03):
1.
2 100 MW lloss
2,100
Short circuit due to tree contact ->
Outages of 6 transformers and lines
2 Vulnerable conditions (minutes)
2.
11 600 MW loss
11,600
Low-damped oscillations->
Outages of generators and tie-lines
15,820MW loss
3. Blackouts (seconds)
Grid separated into islands ->
Loss of 24% load
Malin-Round Mountain #1 MW
1500
Can we do anything
to stop cascade?
0 252 Hz
0.252
H oscillations
ill ti
15:42:03
1400
1300
0.276
0
276 Hz oscillations
Damping>7%
1200
1100
200
300
© 2012 Electric Power Research Institute, Inc. All rights reserved.
15:47:36
0.264 Hz oscillations
3.46% Damping
400
500
4
Time in Seconds
15:48:51
Damping 1%
600
700
800
New Challenges from Integration of Renewables
1. Reliability and congestion issues with long-distance
power transmission
Legend:
•
Wind
•
People
© 2012 Electric Power Research Institute, Inc. All rights reserved.
5
New Challenges from Integration of Renewables
(
(cont’)
)
2. More uncertainties in real-time operation
Mismatch in supply
and
d demand
d
d curves
Inaccuracy in short-term
forecasting
© 2012 Electric Power Research Institute, Inc. All rights reserved.
6
New Challenges from Integration of Renewables
(
(cont’)
)
3. Changing the grid’s dynamics
From OG&E synchrophasor presentation
Better monitoring applications are needed at the
control
t l room ffor real-time
l ti
situational
it ti
l awareness
© 2012 Electric Power Research Institute, Inc. All rights reserved.
7
Synchrophasor based Wide-Area
Measurement System (WAMS)
Oscillation Mode Analysis
© 2012 Electric Power Research Institute, Inc. All rights reserved.
8
Prevention of Cascading Outages
• Power System Stability Assessment:
• Limitations:
– Too manyy system
y
conditions
Offline probabilistic anal
analysis
sis on
system vulnerabilities and
potential cascading outages
– Combinatorial explosion of N-k
contingencies
– Inaccuracy in simulation models
Simulation-based contingency
analysis
4600
Observed COI Power (Dittmer Control Center)
Measured
4400
4200
Real-time stability analysis using
wide-area
id
measurements
t
4000
Simulated COI Power (initial WSCC base case)
4600
4400
Simulation-based approach
+
Measurement-based approach
© 2012 Electric Power Research Institute, Inc. All rights reserved.
9
Simulation
4200
4000
0
10
20
30
40
50
Time in Seconds
60
70
80
90
Intelligent System Separation
Blackstart
Restoration
I iti l events
Initial
t
Cascading blackouts
© 2012 Electric Power Research Institute, Inc. All rights reserved.
I t lli t separation
Intelligent
ti
10
Key Questions on System Separation
Q
Question
i
N
Nature
WHERE
Network optimization
(locations)
WHEN
(ti i )
(timing)
HOW
(
(control)
t l)
Nonlinear system
stability
Implementation of
control
t l strategies
t t i
© 2012 Electric Power Research Institute, Inc. All rights reserved.
11
Three-Step Approach
• Offline Studies (daily ~ yearly)
Offline
procedure
– Synchrophasors
S
h h
siting
iti (near
(
generators)
t )
– Separation point optimization
– Validation of a control-strategy table
Where
How
• Online Monitoring (every second)
Online
software
– Identify most vulnerable grid interface based on the shape
of the dominant oscillation mode
Where
– Predict the timing of instability on the interface
When
• Real-Time Control (milliseconds)
– Perform a control strategy
gy matching
g the current condition
© 2012 Electric Power Research Institute, Inc. All rights reserved.
12
How
WHERE to Separate
Generation
Coherency
y
1. Cluster generators into coherent
groups (by EPRI DYNRED software)
2 Reduce
2.
R d
th
the network
t
kb
by graph
h th
theory
© 2012 Electric Power Research Institute, Inc. All rights reserved.
Slow mode
(weak connection)
13
Fast mode
(strong connection)
WHEN to Separate
• Modal analysis
– Identify the dominant oscillation mode by synchrophasors
– Predict a vulnerable grid interface from the mode’s shape (phasing)
k

M
  ki
 k (t )   k 0   Aki e
1 ki2

t
 ki t
i 1
Monitored
variable
Oscillation
O
ill ti
frequency
© 2012 Electric Power Research Institute, Inc. All rights reserved.
cos( ki t  ki )
Phasing
(mode shape)
14
“Phase Clock” on mode i
WHEN to Separate (cont’)
PMU1
Area 1 
• Stability analysis
PMU2
Area 2
– Estimate the state of a simplified
model about the interface
– Predict instability using the
energy function of the model
Boundary of Stability
State estimation on a simplified model
Equilibrium point
© 2012 Electric Power Research Institute, Inc. All rights reserved.
v
15
Example: 179-bus System
System loses stability
after 6 line outages
1
6 5
2
3
California-Oregon
Intertie
4
© 2012 Electric Power Research Institute, Inc. All rights reserved.
16
Example: 179-bus System (cont’)
1
5
FFT
T
1-2
1-3
1-4
1-2
1-3
1-4
Dominant mode
4
3
“Phase
Phase Clock
Clock” about
0.2Hz mode
(120-160s)
(120-160s)
(120-160s)
(160-200s)
(160-200s)
(160-200s)
Strategy 1-234
2
1
0
0
0.1
0.2
0.3
0.4 0.5 0.6 0.7 0.8
Frequency (Hz)
0.9
1
1.1
0.2Hz
1.2
4
Frequency of the mode
1-2
1-3
1-4
Frequency(Hz)
0.28
0.26
0.24
2
0.22
0.2
0.18
0.16
40
60
80
100
120
Time (
Ti
(s)
)
140
160
180
200
Phasing (shape) on the mode
PhaseDifference(deg.)
180
120
60
0
-60
-180
40
3
1-2
1-3
1-4
-120
60
80
100
120
Time (s)
140
© 2012 Electric Power Research Institute, Inc. All rights reserved.
160
180
200
17
Strategy 14-23
Example: 179-bus System (cont’)
• Perform strategy 1-234 once the
angle distance exceeds a threshold
P h a s e D iffe re n c e (d e g .)
180
90
• Shed 4.9% system load
1-234
14-23
0
40
80
120
Time (s)
160
200 210
80
120
Time (s)
160
200 210
180
A n g e D iffe re n c e (d e g .)
160
1-234
14-23
140
120
100
80
60
40
40
© 2012 Electric Power Research Institute, Inc. All rights reserved.
18
Synchrophasor-based Situational Awareness
and Decision Support
pp
Online Monitoring
Real-time Stability Assessment
Risk
Key
Interface
Dominant oscillation mode
Phase Clock on
the mode
Simplified model on the interface
Phasor data
Scenario N
Scenario 2
Scenario 1
Time
Risk &
Control
Timing
Look-Up Table
Control Action
Visualization at Control Room
Interconnected Power System
© 2012 Electric Power Research Institute, Inc. All rights reserved.
19
DOE Synchrophasor Demonstration Project
((DOE Grant #DE-OE0000128;; 2009-2012))
Real-time PMU Data (IEEE C37.118)
Online Event
Detection
• Phase 1
(research)
Location of
Disturbance
Near Real-Time
Event Replay
p y
• Phase 2 (software
development)
Power System
y
Wide-Area
Visualization
• Phase
Ph
3
(demonstration at
TVA in 2012))
© 2012 Electric Power Research Institute, Inc. All rights reserved.
20
Early Warning of
Grid Instabilityy
Performance Testing Using Simulated or Real
Synchrophasor Data
Separation
strategies
PMU_Config.XML
Contingencies
g
DSA Tool
SQL
database
Models
PMU_Data.CSV
Historical
Data
Software
A li ti
Application
PMU data stream in
IEEEC37.118
IEEEC37 118
© 2012 Electric Power Research Institute, Inc. All rights reserved.
Energy
E
Management
System data
21
Tests on Simulated WECC PMUs
© 2012 Electric Power Research Institute, Inc. All rights reserved.
22
Separating the grid when risk=100%
Island 1
Island 2
Frequencies after Separation
Frequencies before Control
© 2012 Electric Power Research Institute, Inc. All rights reserved.
23
Tests on Simulated TVA PMU Data
© 2012 Electric Power Research Institute, Inc. All rights reserved.
24
Conclusions
• Online situational awareness and decision support
applications are important for grid operators to
prevent or mitigate cascading outages
• Wide-area
Wide area synchrophasor measurements would
enable next-generation grid monitoring applications
• Technologies to help prevent cascading outages are
such as
– System
y
reduction (topological
( p g
and dynamical)
y
)
– Signal processing
– Data mining
© 2012 Electric Power Research Institute, Inc. All rights reserved.
25
References
[1] K. Sun, D. Zheng, Q. Lu. Splitting Strategies for Islanding Operation of Large-scale Power Systems
Using OBDD-based Methods, IEEE Trans. Power Systems, vol.18, May 2003
[2] Q. Zhao, K. Sun, et al, A Study of System Splitting Strategies for Island Operation of Power System: A
Two-phase Method Based on OBDDs, IEEE Trans. Power Systems, vol.18, Nov 2003
[3] K. Sun, D. Zheng, et al, Searching for Feasible Splitting Strategies of Controlled System Islanding,
IEE Proceedings Generation, Transmission & Distribution, vol.153, Jan 2006
[4] K. Sun, D. Zheng, Q. Lu, A Simulation Study of OBDD-based Proper Splitting Strategies for Power
Systems under Consideration of Transient Stability, IEEE Trans. Power Systems, vo.l.20, Feb 2005
[5] M. Jin, T. S. Sidhu, K. Sun, A New System Splitting Scheme Based on the Unified Stability Control
y
vol. 22, Feb 2007
Framework, IEEE Trans. Power Systems,
[6] K. Sun, S. Likhate, V. Vittal, et al, An Online Dynamic Security Assessment Scheme using Phasor
Measurements and Decision Trees, IEEE Trans. Power Systems, vol. 22, Nov 2007.
[7] R. Diao, V. Vittal, K. Sun, et al, Decision Tree Assisted Controlled Islanding for Preventing Cascading
Events,, IEEE PES PSCE,, Seattle,, 2009
[8] K. Sun, S. Lee, P. Zhang, An Adaptive Power System Equivalent for Real-time Estimation of Stability
Margin using Phase-Plane Trajectories, IEEE Trans. Power Systems, vol. 26, May 2011.
[9] K. Sun, K. Hur, P. Zhang, A New Unified Scheme for Controlled Power System Separation Using
Synchronized Phasor Measurements, IEEE Trans. Power Systems, vol. 26, No. 3, Aug. 2011
© 2012 Electric Power Research Institute, Inc. All rights reserved.
26
Q&A
Kai Sun
Ph
Phone:
650
650-855-2087
855 2087
E-Mail: ksun@epri.com
© 2012 Electric Power Research Institute, Inc. All rights reserved.
27
NERC Categories of Contingencies
Co
onsequencce Index
• Most utilities manually
select Category D
contingencies to simulate:
Unlikely
and
Extreme consequences
– Loss of a key
substation
Credible
and
Unacceptable
– Outages of tie lines
– Outages close to a
generation/load pocket
D
0
Unlikely
and
Acceptable
C
Credible
and
Acceptable
B
Category of Contingencies
When System is Stressed (e.g. Storm
Approaching), the likelihood may increase
© 2012 Electric Power Research Institute, Inc. All rights reserved.
Deterministic
A
Criteria
Likelihood Index
28
Generator Outage
N-1 Line Outage
N-2 Line Outage
Extreme Events
Northeast Coherent Generation Groups
From NPCC (Northeast Power Coordinating Council) Study Results
© 2012 Electric Power Research Institute, Inc. All rights reserved.
29
Building a strategy table
PG=28.3GW
PL=26.4GW
1
Total load: 60.8GW
• 7 potential separation points
• 6 strategies
g
((2 islands):
)
PG=12.5GW
=12 5GW
PL=10.6GW
1-234, 2-134, 3-124, 4-123
12-34, 14-23
4
• 12 potential islands
• Validate control actions by
simulations
Island
Shed
Load
Island
Shed
Load
1
0
23
7.3%
2
3 6%
3.6%
34
1 5%
1.5%
3
3.8%
124
0
4
0
123
4.1%
12
0
234
4.9%
14
0
134
0
© 2012 Electric Power Research Institute, Inc. All rights reserved.
2
PG=5.1GW
PL=6.4GW
3
30
PG=15.5GW
PL=17.4GW