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Mitigating Cascading Failures in Interdependent Power Grids and Communication Networks 1 Eytan Modiano Joint work with Marzieh Parandehgheibi David Hay.

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Presentation on theme: "Mitigating Cascading Failures in Interdependent Power Grids and Communication Networks 1 Eytan Modiano Joint work with Marzieh Parandehgheibi David Hay."— Presentation transcript:

1 Mitigating Cascading Failures in Interdependent Power Grids and Communication Networks 1 Eytan Modiano Joint work with Marzieh Parandehgheibi David Hay IEEE SmartGridComm November 4, 2014

2 Motivation 2 Risk of Large blackouts such as 2003 blackout in North-East America Risk of blackout increases due to nature of Renewable Energies (fluctuations stress the grid more) Communication Network Power Grid What if we lose part of communication network in the presence of large disturbances in the power grid? Extra Failures in Power Grid Extra Failures in Communication Network ConcernsRequires Strong Interdependency Challenge

3 Abstract Interdependency Model 3  First Model on Interdependency: “Catastrophic cascade of failures in interdependent networks”, Buldyrev, et al, 2010  Many Follow-ups on this model Two Networks A and B Node i in network A operates if 1) it is connected to a node in network B 2) It is part of the largest component in network A One-to-one interdependency picture from “Catastrophic cascade of failures in interdependent networks” Interdependent Networks are more vulnerable than Single Networks Erdos-Renyi Graph with 500 nodes and expected degree of 4

4 Is this a good model for a power grid? 4 Power Flow Equations: When a Failure in power grid occurs 1)Power redistributes according to power flow equations 2)Some lines may be overloaded and fail 3)Steps 1 and 2 continue until no more lines fail

5 Very different behavior in Power Grid! 5 Random Power Grid - Erdos-Renyi with 500 Nodes and average degree of 4; 1/5 th of the nodes are generators and 1/5 th are loads with random value in range [1000,2000]; unit reactance Power Grids are More Vulnerable to Failures due to Cascading Failures Metric in Power Grid: Fraction of Served Load; i.e. Yield Metric: Ave size of largest component (fraction of remaining nodes)

6 Model: Dependence of Communication on Power 6 P c1 P1 P c2 P c3 P2 Transmission Power Grid Distribution Power Grid C1C1 C2C2 C3C3 Communication Network Network E CP C1C1 P1 C2C2 C3C3 P2 Transmission Power Grid Communication Network Dependency of communication on power grid Every communication node requires power P req for operation If Pc i > P i req for operation, then C i continues operating Simple model allows us to associate a load with every communication node

7 Dependence of Power on Communication 7 Each Power node depends on at least one communication node What happens if communication is lost? Loads may fail due to voltage drop If a power node loses its correspondent communication node, it cannot be controlled and fails (Deterministic Model) Extendable to a probabilistic model where the power node fails randomly with some probability Clearly, this is not what happens today, as the present grid does not depend on communications for its control in a critical way Generators may fail due to Frequency drop

8 Interdependent Power Grid 8 Metric in Power Grid: Fraction of Served Load; i.e. Yield The purpose of designing a communication network intertwined with the power grid is to provide real-time monitoring and control for the grid. a proper analysis of interdependent networks should account for the availability of control schemes that can mitigate cascading failures. Wrong Conclusion: power grid is vulnerable to communication failures, without taking advantage of communications for intelligent control and failure mitigation

9 Interdependent Power Grid Pessimistic Scenario: Vulnerable Communication Network, but communication nodes do not control the cascading failures inside power grid Optimistic Scenario: Robust Communication Network (e.g. all communication nodes are backed-up with batteries), and communication nodes control the cascading failures: i.e., using centralized load shedding and generator redispatch 9 Mitigation Policy inside Power Grid: Intelligent Load Shedding/redispatch

10 Accounting for Failures in the Communication Network 10 1)Mitigate Failures inside Power Grid using load shedding 2)Remove all the communication nodes that receive less than required power 3)Remove all power nodes that lose their correspondent communication node 4)go back to step 1 until no failure occurs Simple Mitigation Policy for Interdependent Networks: What if the communication nodes are vulnerable to power failures? Failures will cascade between the communication network and power grid

11 Intelligent Mitigation Policy The previous mitigation strategy did simple load shedding, and as a result cause communication nodes to fail A more intelligent policy will shed load “intelligently” to avoid the failure of critical communication nodes Load Control Policy Phase 1) Find the Set of all unavoidable failures (i.e., disconnected nodes) Phase 2) Re-dispatch the generators and loads so that – All remaining communication nodes can operate (receive enough power) – Minimum amount of load is shed; i.e. Maximize Yield 11

12 Unavoidable Failures Due to Loss of Connectivity Phase 1) Find the Set of all unavoidable failures 12 Power node Generator Control node Control center Power line Communication line Communication NetworkPower Grid C C G G Unavoidable Failures – Without Considering the Power Flows A Power node fails if it loses its connection to 1) Communication Network OR 2) Generator A Communication node fails if it loses its connection to 1) Power Grid OR 2) Control Center

13 Unavoidable Failures Due to Loss of Connectivity Phase 1) Find the Set of all unavoidable failures 13 Power node Generator Control node Control center Power line Communication line Communication NetworkPower Grid C C G G Unavoidable Failures – Without Considering the Power Flows A Power node fails if it loses its connection to 1) Communication Network OR 2) Generator A Communication node fails if it loses its connection to 1) Power Grid OR 2) Control Center

14 Unavoidable Failures Due to Loss of Connectivity Phase 1) Find the Set of all unavoidable failures 14 Power node Generator Control node Control center Power line Communication line Communication NetworkPower Grid C C G G Unavoidable Failures – Without Considering the Power Flows A Power node fails if it loses its connection to 1) Communication Network OR 2) Generator A Communication node fails if it loses its connection to 1) Power Grid OR 2) Control Center

15 Unavoidable Failures Due to Loss of Connectivity Phase 1) Find the Set of all unavoidable failures 15 Power node Generator Control node Control center Power line Communication line Communication NetworkPower Grid C C G G Unavoidable Failures – Without Considering the Power Flows A Power node fails if it loses its connection to 1) Communication Network OR 2) Generator A Communication node fails if it loses its connection to 1) Power Grid OR 2) Control Center

16 Unavoidable Failures Due to Loss of Connectivity Phase 1) Find the Set of all unavoidable failures 16 Power node Generator Control node Control center Power line Communication line Communication NetworkPower Grid C C G G Unavoidable Failures – Without Considering the Power Flows A Power node fails if it loses its connection to 1) Communication Network OR 2) Generator A Communication node fails if it loses its connection to 1) Power Grid OR 2) Control Center

17 Load Control Mitigation Policy Phase 1) Find the Set of all unavoidable failures Phase 2) Re-dispatch the generators and loads 17 Minimum Load Shedding Communication Nodes receive enough Power Connecting communication and power grid

18 Load Control Mitigation Policy 18

19 Improvement due to Interdependency 19 Even with the strong assumption that failure in one network can lead to the immediate failure in the other network, interdependency can improve the power grid

20 Sensitivity Analysis: Load Factor Load Factor: the ratio of power required by the communication network to the total load in the power grid 20 Note that IT infrastructure uses an increasing fraction of total power in grid.

21 Sensitivity Analysis: Interdependent Degree 21 Power Interdependent Degree: average number of communication nodes that support every power node Communication Interdependent Degree: average number of power nodes that support every communication node

22 Summary Highlight importance of power flow in the analysis – Results from abstract connectivity model don’t hold Proposed a new model for interdependent power grid and communication network – Power nodes depend on communication – Communication nodes depend on power Interdependency could benefit the power grid instead of making it more vulnerable Intelligent load shedding scheme attempts to keep critical communication nodes operating – Most residual failures are due to loss of connectivity – If communication node is connected to the grid, it receives sufficient power – Good justification for using the abstract connectivity model Model can be generalized to “partial dependence” – I.e., account for available back-up power – Allow for probabilistic failure in the event of loss of connectivity 22


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