6,978 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
High performance N2O4/amine elements: Data dump covering. Task 1: Literature review
The phenomenon of reactive stream separation (RSS) in the N2O4/amine earth-storable propellant combinations is reviewed. Early theoretical models of RSS are presented, as are experimental combustion data under simulated rocket conditions. N2O4/amine combustion chemistry data is also provided. More recent work in the development of a comprehensive model is described
Experimental investigation of combustor effects on rocket thrust chamber performance
The results are reported of a program to develop special instrumentation systems and engine hardware, conduct tests using LOX/GH2 propellants wherein radial mixtures ratio stratification was controlled, and subsequently compare the results of four selected tests with the predictions of the JANNAF performance-prediction computer programs. During the experiments, the overall propellant mixture ratio was varied from 4.4 to 6.6, while the mixture ratios in the core and outer zone were varied from 5.7 to 8.8 and from 3.7 to 7.2, respectively. A nominal 10 percent of the total fuel flow was used as boundary layer collant in a majority of the firings. Nominal chamber pressure was either 225 or 250 psia, with nozzle expansion ratios of either 25:1 or 4:1. Measurements of the axial chamber pressure and wall heat flux profiles, together with samples of the exhaust gas, were obtained. The corrected experimental specific impulse and characteristic exhaust velocity efficiencies were approximately 97.5 and 98.5 percent, respectively
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
Faculty and Librarian Collaboration on Problem-Based Learning
This report describes a case study using a collaborative model of problem-based learning in library instruction as an innovative alternative to traditional methods. The authors examine the use of problem-based library instruction in three courses, including an examination of the results of the assignment students were given as part of the exercise. The authors found that the problem-based learning model increased student engagement with library resources and provided a mechanism for identifying and correcting deficiencies in students’ information literacy knowledge and skills. If a specific session of library instruction is intended to provide guidance on the use of the library for a particular assignment or project, then using a problem-based learning approach in collaboration with teaching faculty is a simple way to improve library instruction
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