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

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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

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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)

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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

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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

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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

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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

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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

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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

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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

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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

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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)

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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

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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

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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)

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Algorithms

• Split the complex multistage optimization problem into two sub-problems

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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

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Demonstration Using a WECC Model

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• 200-bus system• 31 generating units • 3 critical loads• 5 black start units• Time for energizing a line

is 5minutes

Generator and Load Characteristics

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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

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29

Restoration Strategy for GRM1 in Island 1

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Island 1

31

Island 2

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Island 3

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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

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Comparison of Different Ramping Rates of the BS Unit (Island 5)

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• If line 137-143 in Island 5 is unavailable

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“Detour” Function

Original Detour

EPRI’s System Restoration Navigator [8]

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• 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

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On-line Diagram

44

System Messages

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System Restoration Navigator

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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

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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

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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