7,629 research outputs found
Changes in Cascading Failure Risk with Generator Dispatch Method and System Load Level
Industry reliability rules increasingly require utilities 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 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.Comment: Submitted to Transmission and Distribution Conference and Exposition
(T&D), 2014 IEEE PE
A Large Mass of H_2 in the Brightest Cluster Galaxy in Zwicky 3146
We present the Spitzer/IRS mid-infrared spectrum of the infrared-luminous (L_(IR) = 4 × 10^(11) L_☉) brightest cluster galaxy (BCG) in the X-ray-luminous cluster Zwicky 3146 (Z3146; z = 0.29). The spectrum shows strong aromatic emission features, indicating that the dominant source of the infrared luminosity is star formation. The most striking feature of the spectrum, however, is the exceptionally strong molecular hydrogen (H_2) emission lines, which seem to be shock-excited. The line luminosities and inferred warm H_2 gas mass (~10^(10) M_☉) are 6 times larger than those of NGC 6240, the most H_2-luminous galaxy at z ≲ 0.05. Together with the large amount of cold H_2 detected previously (~10^(11) M_☉), this indicates that the Z3146 BCG contains disproportionately large amounts of both warm and cold H_2 gas for its infrared luminosity, which may be related to the intracluster gas cooling process in the cluster core
Development of vibration design procedures for representative structural types Final technical report, Sep. 1965 - Jul. 1966
Effects of multimode and damping on random fatigue of cantilever beams and bracket
Cascading Power Outages Propagate Locally in an Influence Graph that is not the Actual Grid Topology
In a cascading power transmission outage, component outages propagate
non-locally, after one component outages, the next failure may be very distant,
both topologically and geographically. As a result, simple models of
topological contagion do not accurately represent the propagation of cascades
in power systems. However, cascading power outages do follow patterns, some of
which are useful in understanding and reducing blackout risk. This paper
describes a method by which the data from many cascading failure simulations
can be transformed into a graph-based model of influences that provides
actionable information about the many ways that cascades propagate in a
particular system. The resulting "influence graph" model is Markovian, in that
component outage probabilities depend only on the outages that occurred in the
prior generation. To validate the model we compare the distribution of cascade
sizes resulting from contingencies in a branch test case to
cascade sizes in the influence graph. The two distributions are remarkably
similar. In addition, we derive an equation with which one can quickly identify
modifications to the proposed system that will substantially reduce cascade
propagation. With this equation one can quickly identify critical components
that can be improved to substantially reduce the risk of large cascading
blackouts.Comment: Accepted for publication at the IEEE Transactions on Power System
- …