1. ELECTRIC POWER GRID INTERDICTION
Javier Salmeron and Kevin Wood, Naval Postgraduate School
Ross Baldick, University of Texas at Austin
Sponsored in part by Department of Homeland Security, Office of Domestic Preparedness

2. What is VEGA?
VEGA is a tool for analyzing the vulnerability and defense of electric power systems under threats posed by terrorist attacks.
VEGA determines the worst possible disruption that could be caused by a terrorist attack,
Compares multiple attack plans terrorists might undertake under different resource-constrained assumptions,
Assesses security enhancement through preemptive measures, and
VEGA is based on powerful optimization techniques.

3. Vulnerability of Electric Power Grids: A Long-Recognized Issue
“One can hardly imagine a target more ideal than the U.S. domestic energy” (A.B. and L.H. Lovins, 1983)
“Any U.S. region could suffer lasting and widespread blackouts if three or more substations were targeted.” (OTA, 1990)
“The U.S. is at, or is fast approaching, a crisis stage with respect to reliability of transmission grids.” (NERC, 2001)
“The U.S. electric power systems must clearly be made more resilient to terrorist attack.” (Committee on Science and Technology for Countering Terrorism, NRC, 2002)

4. Terrorist Threat?
“And the threat isn't simply academic. U.S. occupation forces in Afghanistan discovered Al Qaeda documentation about the facility that controls power distribution for the eastern U.S., fueling fears that an attack on the power grid may one day become a reality.” (Energy Pulse, 2003)
(On Ahmed Ressam) “They were specifically trained to attack critical infrastructure, including electric power plants.” (CNN, 2002)
(On Colombian FARC) “They are leaving entire regions without service. We can’t post a soldier at every tower” (ISA spokesman, 2002)

5. Terrorist Threat? (cont.)
Potential targets:
Generating plants
Transmission and distribution lines
Substations
Easy disruption + Widespread damage + Difficult recovery

6. Modeling Assumptions
U.S. systems are operated so that a single failure does not disrupt the system (N–1 security)
We investigate vulnerability to multiple, coordinated failures (N–m).
Our approach uses optimization theory to:
Mathematically represent a power grid and power flows
Identify worst-case attacks to the grid (most “disruptive”)
Provide insight into physical vulnerabilities, and help guide protective plans that will mitigate disruptions should attacks occur
(We maintain the assumption of information transparency)

7. Key Questions What are the best
New investments (e.g., new facilities, lines, spare transformers)
Upgrades (e.g., replacing conductors)
Protective measures (e.g., hardening, surveillance...) in
Generating systems and/or
Transmission and distribution systems
that substantially reduce system vulnerabilities?
“Best”= Improve Security + Affordable (+ Market Benefits???)

8. Mathematical Analysis
To defend an electric grid, first learn how to attack it!
Optimal power flow model (minimize load shedding)
Interdiction model (maximize disruption, i.e., load shedding)
Additional features of the problem are:
Time scale: Very short-, short-, medium- and long-term
Customer types; ability to “share the pain”
Uncertainty about terrorist resources
(Protective measures???)

9. Integrating Three Levels of Optimization
Level 1: Optimal power flow model to minimize “disruption”:
(disruption = load shedding + increased costs)
Data: Power grid data
Level 2: Interdiction model to maximize “Level-1 disruption”
Data: Power grid data and terrorist resources
Level 3: Protective model to minimize “Level-2 interdiction”
Data: Power grid data, terrorist resource and counter-terrorist resources (budget for expansion, spares, upgrades, hardening)
(See mathematical details at the end of this presentation)

10. Other Factors: System Restoration, Demand Curves...
Grid Component
Interdictable
Resources (number of terrorists)
Outage Duration (h)
Lines (AC/DC) (overhead)
YES 1
72 (or 48)
Lines (underground) NO
N/A
Transformers 2
768 (or 168)
Buses
3 (or 2)
360 (or 168)
Generators
Substations 3
768 (or 360)
One to several days
No Repair t
(Attack)
MW shedding
Days to one week
Lines
Weeks
Trafos with Spares
(months)
Slow repair

11. IEEE Reliability Test System 96-99
BUS 24
BUS 15
BUS 14
230 kV
138 kV
BUS 22
BUS 23
BUS 18
BUS 21
BUS 16
BUS 19
BUS 20
BUS 13
BUS 12
BUS 3
BUS 11
BUS 4
BUS 5
BUS 9
BUS 1
BUS 2
BUS 7
BUS 8
BUS 6
BUS 10
Synch.
Cond.
cable
BUS 17 C G A E F D B
Total Load: 2,850 MW C
+360h A t MW
+72h
Attack B
+768h
Salmeron, Wood and Baldick (2004), IEEE Transactions on Power Systems

12. VEGA: Vulnerability of Electric
Power Grids Analyzer
Potential Users:
Utilities, ISOs...
Government analysts

13. VEGA: Main Menu • File mgmt. • Grid data • Optimization • Results
• One-Line GUI
• Help

14. Power Grid Data

15. One-Line GUI: Power Flow After Optimal Interdiction

16. Power Flow Model (DC Approx.)
DC-OPF:
s.t.
i: bus, l: line, g: generator, c: customer sector
PLine, PGen: power (MW) S: power shed  : bus phase

17. Interdiction max-min problem
Interdiction Model
I-DC-OPF:
s.t.
Can be converted into a standard mixed-integer model 
I-DC-OPF:
Interdiction max-min problem

18. Interdict the assets that maximize “Total Value”
Interdiction Model Heuristic
Solve the DC-OPF Power Flow Model given the current grid configuration ()
Based on present and previous flow patterns, assign a “Value” (V) to each interdictable asset
Interdict the assets that maximize “Total Value”

19. Exact (Mixed-Integer) Linearization of I-DC-OPF

20. Directly Interdicted Components
Results for the Linearized MIP
Case/Algorithm
Directly Interdicted Components
Time
Period
Power
Shed (MW)
Energy
Shed (MWh)
RTS-Two-Areas (M=12)
HEURISTIC
Substations: Sub-A1, Sub-A2, Sub-B1, Sub-B2
0-768
1,416
1,087,488
Total: 1,087,488
MIP
Lines: A23, B23
Transformers: A7, B7
Substations: Sub-A2, Sub-B2
0-72 h
1,804
129,888 h
985,536
Total: 1,115,424
Case/Algorithm
Directly Interdicted Components
Time
Period
Power
Shed (MW)
Energy
Shed (MWh)
RTS-Two-Areas (M=24)
HEURISTIC
Buses: 116, 118, 215, 218
Substations: Sub-A1, Sub-A2, Sub-B1, Sub-B2
0-360 h
2,693
969,480 h
1,416
577,728
Total: 1,547,208
MIP
Lines: A30, A33-2
Transformers: A7, B7
Buses: 115, 118, 215, 218
Substations: Sub-A2, Sub-B2
0-72 h
3,164
227,808 h
2,716
782,208 h
Total: 1,587,744

21. The VEGA Team Javier Salmeron, NPS jsalmero@nps.edu Kevin Wood, NPS
Ross Baldick, UT Austin