ECE620 – CURENT Course:
Decision Support for Power System
Restoration
Kai Sun
October 15, 2014
Content
•
•
•
•
Historical power system blackouts
Industry practices in system restoration
Why do we need decision support tools?
Introduction of a Generic Restoration Milestone
based approach
• Case studies
• System Restoration Navigator by EPRI
2
Historical Blackout Events
Date
Area
Impacts
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, 1996
North America (W)
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 (N-E)
Sep 13, 2003
9M people
0.15MK people
90M people
Duration
hrs
61,800MW, 50M people
2+ days
Italy
57M people
5-9 hrs
Sep 23, 2003
Sweden & Denmark
5M people
5 hrs
Nov 4, 2006
Europe
15M households
2 hrs
Nov 10, 2009
Brazil & Paraguay
17,000MW, 80M people, 18 states
7hrs
Feb 4, 2011
Sep 8, 2011
Brazil
US & Mexico (S-W)
53M people, 8 states
4,300MW, 5M people
12hrs
Sequence of Events in Blackouts
•
•
•
•
•
Initial event
Vulnerable conditions
System islanding
Load/generation imbalance in islands
Blackout of islands
7
4
Tripped by
Zone 3 relay
Faulty zone 3
relay
9
2
5
6 8
3
1GW generation
tripped by SPS
1
Tree
contact
and
relay
mis-opt.
Loss of key
hydro units
10
1
2
3
Example of Voltage Collapse July 2nd, 1996 Western
Cascading Event
4
5
6
7
8
9
Blackout Event on
August 10, 1996
970 MW loss
1. Initial event (15:42:03):
Short circuit due to tree contact 
Outages of 6 transformers and lines
2,100 MW loss
2. Vulnerable conditions (minutes)
Low-damped inter-area oscillations 
Outages of generators and tie-lines
11,600 MW loss
15,820MW loss
3. Blackouts (seconds)
Unintentional separation 
Loss of 24% load
Malin-Round Mountain #1 MW
1500
15:42:03
15:48:51
15:47:36
1400
1300
1200
1100 200
0.276 Hz oscillations
0.252 Hz oscillations
Damping>7%
300
0.264 Hz oscillations
3.46% Damping
400
500
Damping 1%
600
Time in Seconds
700
800
System
islanding and
blackouts
Losses Due to Blackouts [1][2]
The faster we bring the system back,
the less we would lose
7
Common Factors: The
3 “T”s
• Tools
o
o
Inability of system operators or coordinators to visualize events
on the entire system
Failure to ensure that system operation was within safe limits
• Training
o
o
Inadequate training of operating personnel
Ineffective communication, failure to communicate status to
neighboring systems
• Trees
o
Conductor contact with trees, inadequate vegetation
management
8
Status of Power System Restoration
• Restoration is basically manual work performed by operators in
control rooms
• Restoration plans or guidelines are offline designed by planning
engineer and evaluated once/twice a year
• Regional system restoration trainings/drills based on OTS
(Operator Training Simulators) are conducted every year
• Typical Restoration stages (assume 6-10 hours) [1]-[3]:
1.
2.
3.
Preparation (1-2 hours)
System restoration (1-3 hours)
Load restoration (4-6 hours)
9
Generating Units with Black-Start (BS)
Capabilities [1]-[4]
• Hydro
o
may be started in 5-10 min.
• Diesel
o
o
o
small but has fast response
may provide the start-up requirement of larger units
cannot be used to pick up sizable loads or energize
transmission lines.
• Gas turbine
o
o
units with local battery power
larger units with an on-site diesel unit
10
North American Electric Reliability Corporation
(NERC) Standards for System Restoration
EOP-005-1 System Restoration Plans
To ensure plans, procedures, and resources are available to restore the
electric system to a normal condition in the event of a partial or total
shut down of the system
EOP-005-2 System Restoration from Blackstart Resources
Ensure plans, Facilities, and personnel are prepared to enable System restoration
from Blackstart Resources to assure reliability is maintained during restoration and
priority is placed on restoring the Interconnection
EOP-006-1 Reliability Coordination - System Restoration
The Reliability Coordinator must have a coordinating role in system restoration to
ensure reliability is maintained during restoration and priority is placed on restoring
the Interconnection
EOP-006-2 System Restoration Coordination
Ensure plans are established and personnel are prepared to enable effective
coordination of the System restoration process to ensure reliability is maintained
during restoration and priority is placed on restoring the Interconnection
EOP-009-0 Documentation of Blackstart Generating Unit Test Results
A system Blackstart Capability Plan (BCP) is necessary to ensure that the quantity
and location of system blackstart generators are sufficient and that they can
perform their expected functions as specified in overall coordinated Regional
System Restoration Plans
11
Sample Restoration Procedure
1. Initial assessment
o
o
Assessment of the extent of a blackout
Communications (essential)
 Verify communication with ISO/RTO, control centers, energy
providers, hydro, and other affected systems
 Verify backup communications
 Effective communication with all stakeholders
o
o
Determine generator status
 online/offline, location, type,
 damaged equipment, stability, reserve, connectivity to
the system, and
 blackstart capability.
Call for extra manpower
12
Sample Restoration Procedure (cont’d)
2.
Start generation units
o
Restoration of offline units
 Hydro: quickly started without an outside source
 Combustion turbine: quickly (10min) started, may be voltagedependent to allow starting
 Thermal steam: 1-20 hours (24-48 hours for nuclear); hot units
may be returned quicker
o
Prioritization of units to start





o
NERC requirements
Individual restoration plan
Start-up time of a unit
Availability of on-site auxiliary power
Distance to blackout resources
Generating plant operators
 Safe plant shutdown (prepared for restoration)
 Governors and AVR should be on
 Plant operators control frequency around 60Hz
13
Sample Restoration Procedure (cont’d)
3. Restore the system
o
Multiple islands (bottom-up)




o
Stabilize remaining available generation
Determine restoration transmission paths
Expand islands by restoring transmission and load
Synchronize islands when appropriate
Large islands (Top-down)
 Restore the EHV transmission (maybe from outside
sources if available)
 Restore critical generating plants and substations
along the restored transmission
 Bring on more generation
 Restore underlying transmission
14
Sample Restoration Procedure (cont’d)
4. Restore load
Prioritize loads for restoration
o




Auxiliary power for generating plants
Auxiliary power for substations
Natural gas or oil supply facilities
Customers:
Critical (hospitals, airports, etc.)
Dispatchable (others)
Frequency control
o


Maintain frequency around 60Hz (e.g. 59.75-60.05Hz)
Increase frequency to >60Hz (e.g. 60-60.05Hz) prior to
restoring a block of load
15
Restoration Strategies
Build-Upward (Bottom-Up)
(e.g. PJM [4]):
Build-Downward (Top-Down)
(e.g. Hydro Quebec [5]):
• Based on offline define
electrical islands with
blackstart capabilities
• Actions include
o Start up BS units
o Crank non-BS units
o Restore multiple islands to
pick up loads
o Synchronize islands
• Re-energizing the transmission
network to pool blackstart
power first
• Actions include:
o Start up BS units,
o Energize the transmission
network
o Crank non-BS units
o Pick up loads
16
Decision Support Tools
• Why important?
o
o
Supporting planning engineers in developing and evaluating
restoration strategies
Supporting system operators in developing, rehearsing,
coordinating and implementing restoration strategies
Today’s Restoration plan
Offline, non-interactive
Restoration decision support
Online, interactive
17
Online Interactive Decision Support Tool
•
Optimize the path (minimizing the
restoration time)
•
Able to re-calculate when necessary
(operators make mistakes or meet
unexpected events)
TVA Control Center (source: TVA.com
Duke Energy Control Center (source: Patrick Schneider Photo.Com)
18
Restoration Milestone-based Decision Support
Path (Strategy)
Milestones
• Stop 1 (Milestone 1)
– Turn Left (Action 1)
– Turn Right (Action 2)
• Stop 2 (Milestone 2)
– Turn Right (Action 3)
Decision
Support Tool
Restoration Path
Optimization
(Minimizing
Duration Time)
– Turn Left (Action 4)
– Turn Right (Action 5)
– …
Simulation Tools
(Security Constraints)
Actions
A Restoration Milestones based Approach for
Developing and Evaluating Restoration Strategies [6][7]
• A specific restoration strategy is a combination of specific milestones
• Under each milestone, an optimization problem can be formulated to solve
restoration actions achieving that milestone with the shortest time
• Constraints about, e.g., voltages, overloading and stability, can be checked
for each restoration action by a power system simulation tool
Generic Restoration Milestones
(GRMs)
•
•
•
•
•
•
GRM1: Form BS_NBS_Building Blocks
GRM2: Establish Transmission Grid
GRM3: Form Electrical Island
GRM4: Synchronize Electrical Islands
GRM5: Serve Load in Area
GRM6: Connect with Neighboring
System
Generic Restoration Actions
(GRAs)
•
•
•
•
•
•
•
•
GRA1:
GRA2:
GRA3:
GRA4:
GRA5:
GRA6:
GRA7:
GRA8:
start_black_start_unit
find_path
energize_line
pick_up_load
synchronize
connect_tie_line
crank_unit
energize_busbar
20
Achieving GRMs by GRAs
21
GRM1: Form BS-NBS Building Block
• Objectives
o
o
crank all generators (from a BS unit to NBS units)
pick up all critical loads as quickly as possible.
• Dispatchable loads are picked up when necessary to balance
restored generation and maintain voltage.
• GRAs:
o
Start the BS unit (GRA1)
o
Find transmission path from the BS unit to a NBS unit (GRA2)
o
Build a transmission path (GRA3)
o
Pick up load (GRA4)
o
Crank a NBS unit (GRA7)
GRM1: Form BS-NBS Building Block (cont’d)
• At stage S, solve the shortest time fS to restore all
generators and critical loads by Dynamic Programing:
S: the set of restored generators
xi: the state (restored generators and loads) at stage S
• Constraints:
o Power flow equations are solved
o No violation on generation limits, transmission limits
or voltage limits
23
Algorithms
• Split the complex multistage optimization problem
into two sub-problems
Primary problem:
· Find sequence of generating unit;
· Find transmission paths to
implement this sequence
· Outputs of generating units at
this stage;
· Loads level at this stage
· Paths to pick up dispatchable
loads
· Energized block of the system;
· Outputs of generating units at the
last stage;
· Loads level at the last stage
Alg-1: Finding a neighboring
region (within a given depth)
around an energized block
Alg-2: Finding a transmission
path to crank a generator
Alg-3: Solve OPF to find an
operating point without
violation to minimize the
duration time
Secondary problem:
· Find outputs of generating units
at each state;
· Find dispatchable load to balance
system
Alg-4: Finding dispatchable
loads by OPF
24
Modeling of Generating Units
Type
Capacity
(MW)
Start-up
Power
(MW)
BS/
NBS
C
R
Ramping
Rate
(MW/hour)
Min
Output
(%)
Cranking to
paralleling
time
(hour)
Min.
Interruption
Time
(hour)
Max.
Interruption
Time
(hour)
k
α%
T1
T2
T3
MW
C
a%C
t0
t1
k
R
T3  t0  T2
0
t1  t0  T1
Time
25
Demonstration Using a WECC Model
•
200-bus system
•
31 generating units
•
3 critical loads
•
5 black start units
•
Time for energizing a line
is 5minutes
26
Generator and Load Characteristics
Generators
Critical Loads
Dispatchable Loads
27
Develop Restoration Strategies by GRMs
• The system is restored as 5
islands first and then synchronized
• GRMs:
o
o
o
o
o
GRM 1: Form BS_NBS_Building Blocks
GRM2: Establish Transmission Grid
GRM3: Form Electrical Island
GRM4: Synchronize Electrical Islands
GRM5: Serve Load in Area
28
29
Restoration Strategy for GRM1 in Island 1
30
Island 1
31
Island 2
32
Island 3
33
Island 4
34
Island 5
35
36
Voltage Profiles
GRM1 for Island 1
GRM3 for synchronizing Islands 1&2
37
Total Generation Output During Restoration
38
Comparison of Different Ramping Rates
of the BS Unit (Island 5)
39
“Detour” Function
• If line 137-143 in Island 5 is unavailable
Original
Detour
40
EPRI’s System Restoration Navigator [8]
•
•
•
•
•
Establish GRM-based
algorithms to develop or
evaluate a restoration
strategy
Interactive GUI to provide
automatic or interactive
strategy development
Milestones and priorities
assigned by users
Restoration report on online diagram or in text
format
Accept PSS/E raw data
41
Integration with OTS
• Operator Training Simulator
(OTS)
o
o
Simulation engine:
 power-flow based pseudodynamic
 transient simulation
Products:
 EPRI OTS
 PowerSimulator by
POWERDATA and IncSys
(Source: powersimulator.net)
42
GIS Visualization
43
On-line Diagram
44
System Messages
45
System Restoration Navigator
46
References
1. M. M. Adibi and L. H. Fink, "Overcoming restoration challenges associated with major
power system disturbances - Restoration from cascading failures," Power and Energy
Magazine, IEEE, vol. 4, pp. 68-77, 2006.
2. M. M. Adibi and N. Martins, "Power system restoration dynamics issues," IEEE Power
and Energy Society General Meeting 2008.
3. L. H. Fink, K.-L. Liou, and C.-C. Liu, "From generic restoration actions to specific
restoration strategies," IEEE Trans. Power Syst., vol. 10, pp. 745-752, 1995
4. J. W. Feltes and C. Grande-Moran, "Black start studies for system restoration,"
presented at Power and Energy Society General Meeting 2008
5. F. Levesque, S. T. Phan, A. Dumas, and M. Boisvert, "Restoration plan — The HydroQuébec experience," presented at Power and Energy Society General Meeting Conversion and Delivery of Electrical Energy in the 21st Century, 2008 IEEE, 2008.
6. Y. Hou, C. C. Liu, K. Sun, et al, “Computation of Milestones for Decision Support
during System Restoration”, IEEE Trans. Power Systems, vol. 26 , No. 3, pp. 1399
1409, Aug. 2011
7. Y. Hou; C.-C. Liu; P. Zhang; K. Sun, “Constructing power system restoration
strategies”, IEEE International Conference ELECO 2009. Page(s): I-8 - I-13, 2009
8. System Restoration Navigator (SRN) Version 2.0, EPRI Product ID: 1021715, 2011
47
Homework – Power System Restoration
Find a real-world example for each of the Bottom-Up and Top-Down
restoration strategies other than PJM and Hydro Quebec, and describe
the restoration milestones
Build-Upward (Bottom-Up)
(e.g. PJM):
Build-Downward (Top-Down)
(e.g. Hydro Quebec):
• Based on offline define
electrical islands with
blackstart capabilities
• Actions include
o Start up BS units
o Crank non-BS units
o Restore multiple islands to
pick up loads
o Synchronize islands
• Re-energizing the transmission
network to pool blackstart
power first
• Actions include:
o Start up BS units,
o Energize the transmission
network
o Crank non-BS units
o Pick up loads
48