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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 - PowerPoint PPT Presentation
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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 EventsDate Area Impacts Duration
Nov 9, 1965 North America (NE) 20,000+MW, 30M people 13 hrs
Jul 13, 1977 North America (NY) 6,000MW, 9M people 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, 0.15MK people 19 hrs
Mar 11, 1999 Brazil 90M people hrs
Aug 14, 2003 North America (N-E) 61,800MW, 50M people 2+ days
Sep 13, 2003 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 Brazil 53M people, 8 statesSep 8, 2011 US & Mexico (S-W) 4,300MW, 5M people 12hrs
Sequence of Events in Blackouts
• Initial event• Vulnerable conditions• System islanding• Load/generation imbalance in islands• Blackout of islands
12
3
1
2
3
1GW generation tripped by SPS
4
4
Faulty zone 3 relay
5
5
6 8
67
7
8
Loss of key hydro units
Tripped by Zone 3 relay
9
9
10
Tree contact and relay mis-opt.
Example of Voltage Collapse -July 2nd, 1996 Western Cascading Event
11,600 MW loss
15,820MW loss
2,100 MW loss
970 MW loss
Blackout Event on August 10, 1996
1. Initial event (15:42:03):
Short circuit due to tree contact Outages of 6 transformers and lines
2. Vulnerable conditions (minutes)
Low-damped inter-area oscillations Outages of generators and tie-lines
3. Blackouts (seconds)
Unintentional separation Loss of 24% load
200 300 400 500 600 700 8001100
1200
1300
1400
1500
Malin-Round Mountain #1 MW
Time in Seconds
0.264 Hz oscillations3.46% Damping
0.252 Hz oscillations
Damping 1%
0.276 Hz oscillations
Damping>7%
15:42:0315:48:51
15:47:36
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 Inability of system operators or coordinators to visualize events on the entire system
o Failure to ensure that system operation was within safe limits
• Trainingo Inadequate training of operating personnelo Ineffective communication, failure to communicate status to
neighboring systems
• Treeso 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. Preparation (1-2 hours)
2. System restoration (1-3 hours)
3. Load restoration (4-6 hours)
9
Generating Units with Black-Start (BS) Capabilities [1]-[4]
• Hydroo may be started in 5-10 min.
• Dieselo small but has fast responseo may provide the start-up requirement of larger unitso cannot be used to pick up sizable loads or energize
transmission lines.
• Gas turbineo units with local battery power o 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
11
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
Sample Restoration Procedure
1. Initial assessmento Assessment of the extent of a blackouto 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 Determine generator status online/offline, location, type, damaged equipment, stability, reserve, connectivity to
the system, and blackstart capability.
o Call for extra manpower
12
Sample Restoration Procedure (cont’d)
2. Start generation unitso Restoration of offline units
Hydro: quickly started without an outside source Combustion turbine: quickly (10min) started, may be voltage-
dependent 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
NERC requirements Individual restoration plan Start-up time of a unit Availability of on-site auxiliary power Distance to blackout resources
o 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 systemo Multiple islands (bottom-up)
Stabilize remaining available generation Determine restoration transmission paths Expand islands by restoring transmission and load Synchronize islands when appropriate
o 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 loado Prioritize loads for restoration
Auxiliary power for generating plants Auxiliary power for substations Natural gas or oil supply facilities Customers:
- Critical (hospitals, airports, etc.)- Dispatchable (others)
o Frequency control 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]):
• Based on offline define electrical islands with blackstart capabilities
• Actions include o Start up BS unitso Crank non-BS unitso Restore multiple islands to
pick up loadso Synchronize islands
Build-Downward (Top-Down)
(e.g. Hydro Quebec [5]):
• Re-energizing the transmission network to pool blackstart power first
• Actions include:o Start up BS units, o Energize the transmission
networko Crank non-BS unitso Pick up loads
16
Decision Support Tools
• Why important?o Supporting planning engineers in developing and evaluating
restoration strategieso Supporting system operators in developing, rehearsing,
coordinating and implementing restoration strategies
17
Offline, non-interactive Online, interactive
Today’s Restoration plan Restoration decision support
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)
18
Duke Energy Control Center (source: Patrick Schneider Photo.Com)
TVA Control Center (source: TVA.com
Milestones
Actions
Restoration Milestone-based Decision Support
Decision Support Tool
Simulation Tools(Security Constraints)
– Turn Left (Action 1)
– Turn Right (Action 2)
– Turn Right (Action 3)
– Turn Left (Action 4)
– Turn Right (Action 5)
– …
• Stop 1 (Milestone 1)
• Stop 2 (Milestone 2)Restoration Path
Optimization (Minimizing
Duration Time)
Path (Strategy)
A Restoration Milestones based Approach for Developing and Evaluating Restoration Strategies [6][7]
• 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
20
Generic Restoration Milestones (GRMs)
Generic Restoration Actions (GRAs)
• GRA1: start_black_start_unit• GRA2: find_path• GRA3: energize_line• GRA4: pick_up_load• GRA5: synchronize• GRA6: connect_tie_line• GRA7: crank_unit• GRA8: energize_busbar
• 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
Achieving GRMs by GRAs
21
GRM1: Form BS-NBS Building Block
• Objectiveso crank all generators (from a BS unit to NBS units)o 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)
• 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 solvedo No violation on generation limits, transmission limits
or voltage limits
GRM1: Form BS-NBS Building Block (cont’d)
23
Algorithms
• Split the complex multistage optimization problem into two sub-problems
24
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
Alg-4: Finding dispatchable loads by OPF
Primary problem:· Find sequence of generating unit;· Find transmission paths to
implement this sequence
Secondary problem:· Find outputs of generating units
at each state;· Find dispatchable load to balance
system
· Energized block of the system;· Outputs of generating units at the
last stage;· Loads level at the last stage
· Outputs of generating units at this stage;
· Loads level at this stage· Paths to pick up dispatchable
loads
Modeling of Generating Units
TypeCapacity
(MW)
Start-upPower (MW)
Ramping Rate
(MW/hour)
Min Output
(%)
Cranking to paralleling
time(hour)
Min.Interruption
Time(hour)
Max.Interruption
Time(hour)
BS/NBS
C R k α% T1 T2 T3
t0 t1
0
k
Time
MW
R
a%C
C
3 0 2T t T 1 0 1t t T
25
Demonstration Using a WECC Model
26
• 200-bus system• 31 generating units • 3 critical loads• 5 black start units• Time for energizing a line
is 5minutes
Generator and Load Characteristics
27
Critical Loads
Dispatchable Loads
Generators
Develop Restoration Strategies by GRMs
• The system is restored as 5 islands first and then synchronized
• GRMs:o GRM 1: Form BS_NBS_Building Blocks o GRM2: Establish Transmission Grido GRM3: Form Electrical Islando GRM4: Synchronize Electrical Islandso 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
37
GRM1 for Island 1 GRM3 for synchronizing Islands 1&2
Total Generation Output During Restoration
38
Comparison of Different Ramping Rates of the BS Unit (Island 5)
39
• If line 137-143 in Island 5 is unavailable
40
“Detour” Function
Original Detour
EPRI’s System Restoration Navigator [8]
41
• 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 on-line diagram or in text format
• Accept PSS/E raw data
Integration with OTS
• Operator Training Simulator (OTS)o Simulation engine:
power-flow based pseudo-dynamic
transient simulationo Products:
EPRI OTS PowerSimulator by
POWERDATA and IncSys
42(Source: powersimulator.net)
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 Hydro-Québec 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
Build-Upward (Bottom-Up)
(e.g. PJM):
• Based on offline define electrical islands with blackstart capabilities
• Actions include o Start up BS unitso Crank non-BS unitso Restore multiple islands to
pick up loadso Synchronize islands
Build-Downward (Top-Down)
(e.g. Hydro Quebec):
• Re-energizing the transmission network to pool blackstart power first
• Actions include:o Start up BS units, o Energize the transmission
networko Crank non-BS unitso Pick up loads
48
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