METHODOLOGY FOR IDENTIFYING METHODOLOGY FOR IDENTIFYING NEAR-OPTIMAL INTERDICTION STRATEGIES NEAR-OPTIMAL INTERDICTION STRATEGIES

FOR A POWER TRANSMISSION SYSTEMFOR A POWER TRANSMISSION SYSTEM

Vicki M. Bier, Eli Robert Gratz, Naraphorn Vicki M. Bier, Eli Robert Gratz, Naraphorn J. Haphuriwat, and Wairimu MaguaJ. Haphuriwat, and Wairimu Magua

Department of Industrial and Systems EngineeringDepartment of Industrial and Systems Engineering

University of Wisconsin-MadisonUniversity of Wisconsin-Madison

Kevin R. WierzbickiKevin R. WierzbickiDepartment of Electrical and Computer EngineeringDepartment of Electrical and Computer Engineering

University of Wisconsin-MadisonUniversity of Wisconsin-Madison

ObjectivesObjectivesThe objectives of the project are to:The objectives of the project are to:

Develop a simple, inexpensive, and Develop a simple, inexpensive, and practical method for identifying practical method for identifying promising interdiction strategies promising interdiction strategies

Compare our method and results with Compare our method and results with those of other proposed approaches for those of other proposed approaches for vulnerability assessment vulnerability assessment

Study the effectiveness of protecting Study the effectiveness of protecting transmission lines transmission lines

System TopologySystem Topology

We use the IEEE Reliability TestWe use the IEEE Reliability Test

System – 1996 (RTS-96):System – 1996 (RTS-96):

Representative of typical systems Representative of typical systems

We base our analysis on decoupledWe base our analysis on decoupled

load (DC) flow with optimal dispatchload (DC) flow with optimal dispatch

System Topology System Topology (continued)(continued)

We model the RTS-96 systemsWe model the RTS-96 systems

as networks consisting of: as networks consisting of:

24 nodes and 38 arcs for the 24 nodes and 38 arcs for the One Area RTS-96One Area RTS-96

48 nodes and 79 arcs for the 48 nodes and 79 arcs for the Two Area RTS-96Two Area RTS-96

Schematic View of Process

Terminate(after a pre-determinednumber of iterations)

Load-Flow Algorithm(Determine optimal DC power dispatch)

Max Line Interdiction Algorithm(Interdict the line with maximum flow,

and any lines in close geographical proximity)

Hardening Algorithm(Make the first n sets of interdicted lines from the Max Line algorithm invulnerable)

Other ApproachesOther Approaches

The method of Apostolakis and The method of Apostolakis and Lemon (2005) applies only to Lemon (2005) applies only to distribution networks (with one-distribution networks (with one-directional flows)directional flows)

Salmeron et al. (2004) use a non-Salmeron et al. (2004) use a non-linear nested optimization method linear nested optimization method that is difficult to solve that is difficult to solve

Results (One Area RTS-96)Results (One Area RTS-96)

Attacked:33%

Load shed: 56%Attacked:11%

Load shed: 44%

Results (Two Area RTS-96)Results (Two Area RTS-96)

45%

44%

Results cont’d…Results cont’d…

The Max Line

interdiction strategy reasonably approximates the load shed by Salmeron et al.

The transmission lines interdicted by Salmeron et al. differ from those interdicted by our strategy

6430 19&21 78&78 23 41 52 11 74&73 34&35 21

MaxLine Salmeron

21&19 22 24 27&28 30 38&39 61&59 62 69 72&79 77&78

Results (Random Interdiction)Results (Random Interdiction)

Hardening Hardening

We apply the hardening algorithm to simulate an upgrade of the system

H0 represents the original interdictionstrategy

H1, H2, and H3 show the interdiction strategies obtained after three iterationsof hardening

Results (One Area RTS-96)Results (One Area RTS-96)

Strategy H0 results in a loss of 56%

Strategy H3, hardening 39% of all lines, results in a loss of 42%

Results (Two Area RTS-96)Results (Two Area RTS-96)

Strategy H0 results in a loss of 56%

Strategy H3, hardening 39% of all lines, results in a loss of 39%

ObservationsObservations

Our results cast doubt on the claim by Salmeron et al.:

“By considering the largest possible disruptions, our proposed plan will be appropriately conservative”

Hardening even a significant percentage of lines does not dramatically diminish the load shed by an attack

Hardening seems unlikely to be cost effective!

Conclusions Conclusions

We developed a simple, inexpensive, and We developed a simple, inexpensive, and viable method of identifying promising viable method of identifying promising attack strategiesattack strategies

Our results are comparable to those of Our results are comparable to those of Salmeron et al. Salmeron et al.

A single run of either method will not be A single run of either method will not be sufficient to identify critical vulnerabilitiessufficient to identify critical vulnerabilities

Hardening of transmission lines is unlikely Hardening of transmission lines is unlikely to be cost effectiveto be cost effective

Directions for Future Research Directions for Future Research

In future research, this method could In future research, this method could be extended to:be extended to:

Address other components of transmission Address other components of transmission

systems, such as transformerssystems, such as transformers Identify strategies that may trigger Identify strategies that may trigger

cascading power failurescascading power failures Take into account the importance of Take into account the importance of

different loadsdifferent loads Apply to other types of systems, such as Apply to other types of systems, such as

structures, water, and transportationstructures, water, and transportation

Acknowledgement Acknowledgement

This material is based upon work supported in part by: This material is based upon work supported in part by:

The U.S. Army Research Laboratory and the U.S. Army Research The U.S. Army Research Laboratory and the U.S. Army Research Office under grant number DAAD19-01-1-0502Office under grant number DAAD19-01-1-0502

The National Science Foundation under grant number ECS-0214369The National Science Foundation under grant number ECS-0214369

The Department of Homeland Security under grant number EMW-The Department of Homeland Security under grant number EMW-004-GR-0112004-GR-0112

Any opinions, findings, and conclusions or recommendations expressedAny opinions, findings, and conclusions or recommendations expressedin this material are those of the authors and do not necessarily reflect in this material are those of the authors and do not necessarily reflect the views of the sponsors. the views of the sponsors.

The authors would like to thank Prof. Ian Dobson of the University of The authors would like to thank Prof. Ian Dobson of the University of Wisconsin-Madison for his contributions to this study.Wisconsin-Madison for his contributions to this study.