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**1 - 3**of**3**### 1Changes in Cascading Failure Risk with Generator Dispatch Method and System Load Level

"... Abstract—Industry reliability rules increasingly require utili-ties to study and mitigate cascading failure risk in their system. Motivated by this, this paper describes how cascading failure risk, in terms of expected blackout size, varies with power system load level and pre-contingency dispatch. ..."

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Abstract—Industry reliability rules increasingly require utili-ties to study and mitigate cascading failure risk in their system. Motivated by this, this paper describes how cascading failure risk, in terms of expected blackout size, varies with power system load level and pre-contingency dispatch. We used Monte Carlo sampling of random branch outages to generate contingencies, and a model of cascading failure to estimate blackout sizes. The risk associated with different blackout sizes was separately estimated in order to separate small, medium, and large blackout risk. Results from N − 1 secure models of the IEEE RTS case and a 2383 bus case indicate that blackout risk does not always increase with load level monotonically, particularly for large blackout risk. The results also show that risk is highly dependent on the method used for generator dispatch. Minimum cost methods of dispatch can result in larger long distance power transfers, which can increase cascading failure risk. Index Terms—Cascading failure risk, Monte Carlo simulation, security-constrained optimal power flow I.

### SENSITIVITY ANALYSIS OF RARE-EVENT SPLITTING APPLIED TO CASCADING BLACKOUT MODELS

"... Splitting is a technique that can be used to improve the efficiency in simulating rare events. The basic idea is to create separate copies (splits) of the simulation whenever it gets close to the rare event. To implement splitting, several decisions must be made – for example, choosing a level funct ..."

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Splitting is a technique that can be used to improve the efficiency in simulating rare events. The basic idea is to create separate copies (splits) of the simulation whenever it gets close to the rare event. To implement splitting, several decisions must be made – for example, choosing a level function, choosing the number of simulation runs for each level, etc. This paper analyzes the sensitivity of the variance of the rare-event estimator to several parameters used within the splitting framework. We specifically consider a two-level fixed-effort variation of splitting for which analytic results can be derived. Results are applied to a simple model of cascading blackouts. The results illustrate that a good choice for the locations of levels may be more important than a good choice for the importance function for these types of problems. 1