1.
Predicting Risk of Cascading Outages Stephen Lee Senior Technical Executive October 2008

2.
Cascading Outages Rip Across an Interface – Triggered by Next Random Outage Higher Power Transfer Stretches the Fabric and Makes Cascades More Likely

3.
Testing the Strength of a Holely Fabric Pulling at a location of the fabric tests vulnerability to Higher net export or import in a local area

4.
Acceptable Consequences of Contingency Categories A, B, C and D Planning Criteria Likelihood Consequences Credible and Acceptable Unlikely and Acceptable Unlikely and Extreme consequences Credible and Unacceptable 0 Generator Outage N-1 Line Outage N-2 Line Outage Extreme Events Deterministic Criteria D A B C Category of Contingencies, A, B, C and D

5.
Online Reliability Monitor of Standard Contingencies & Potential Cascading Modes Likelihood Consequences Credible and Acceptable Unlikely and Acceptable Unlikely and Extreme consequences Credible and Unacceptable 0 Generator Outage N-1 Line Outage N-2 Line Outage Extreme Events Deterministic Criteria Potential Cascading Modes A B C D Category of Contingencies

6.
Normal Weather Risk Exposure to One Cascading Mode With 1 Line on Maintenance Outage & System (6750 MW Load) Not Compliant with N-1 PRI = 150 MW PRI = 90 MW PRI = 50 MW PRI = 25 MW Initiating Event Tier 1 Cascade Tier 3 Cascade PRI = 200 MW Tier 2 Cascade

7.
Storm Increases Risk Exposure to One Cascading Mode With 1 Line on Maintenance Outage & System (6750 MW Load) Not Compliant with N-1 PRI = 150 MW PRI = 90 MW PRI = 50 MW PRI = 25 MW Initiating Event Tier 1 Cascade Tier 3 Cascade PRI = 200 MW Tier 2 Cascade

8.
Identification of Other (Non-Cut-Set) Potential Cascading Modes by Simulation Initiating Event (Tier 0) Tier 1 Lines with overload > threshold P(Tier 1 lines opening)=? <ul><li>Assess Consequences </li></ul><ul><li>Line overloads </li></ul><ul><li>Load and generation dropped </li></ul><ul><li>Load shed to prevent voltage collapse </li></ul>Tier 1 Cascade P(Tier 0) No overload Voltage collapse Island(s) formed Tier 2 Lines with overload > threshold No overload Voltage collapse Island(s) formed Line overloads Line overloads

9.
Conclusions <ul><li>Structural degradation and increasing system stress may lead to cascading transmission outages </li></ul><ul><li>Simulation-based method to identify Potential Cascading Modes </li></ul><ul><li>Online risk monitoring of both traditional contingencies and potential cascading modes </li></ul><ul><li>Hold promise for practical applications </li></ul>