Methodology for Risk Assessment of Part Load Resonance in Francis Turbine Power Plant

At low flow rate operation, Francis turbines feature a cavitating vortex rope in the draft tube resulting from the swirling flow of the runner outlet. The unsteady pressure field related to the precession of the vortex rope induces plane wave propagating in the entire hydraulic system. The frequency of the vortex rope precession being comprised between 0.2 and 0.4 times the turbine rotational speed, there is a risk of resonance between the hydraulic circuit, the synchronous machine and the turbine itself an acting as excitation source. This paper presents a systematic methodology for the assessment of the resonance risk for a given Francis turbine power plant. The test case investigated is a 1GW 4 Francis turbines power plant. The methodology is based on a transient simulation of the dynamic behavior of the whole power plant considering a 1D model of the hydraulic installation, comprising gallery, surge chamber, penstock, Francis turbine but also mechanical masses, synchronous machines, transformer, grid model, speed and voltage regulators. A stochastic excitation having energy uniformly distributed in the frequency range of interest is taken into account in the draft tube. As the vortex rope volume has a strong influence on the natural frequencies of the hydraulic system, the wave speed in the draft tube is considered as a parameter for the investigation. The transient simulation points out the key excitation frequencies and the draft tube wave speed producing resonance between the vortex rope excitation and the circuit and provide a good evaluation of the impact on power quality. The comparison with scale model tests results allows resonance risk assessment in the early stage of project pre-study

Turbine Speed Governor Parameters Validation in Islanded Production

The transient behavior of hydroelectric power plants is of high interest for ensuring stability of islanded electrical power networks. Therefore, it is suitable to determine and validate the set of parameters of a turbine speed governor using a realistic simulation model taking into account the hydraulic circuit, the rotating inertias, the electrical installations and the control systems. This paper presents the modeling of a 4x250 MW Francis turbine hydroelectric power plant taking into account the dynamics of all the aforementioned components. The transfer function of the turbine is determined through a time domain simulation using white noise excitation for the determination of an appropriate set of parameters. The performance of the regulator parameters are assessed using two different models: (i) a hydraulic model and (ii) a full hydroelectric model including the model of an islanded power network. The stabilization effect of Standard Power System Stabilizer (PSS) is evidenced

On the alleged simplicity of impure proof

Roughly, a proof of a theorem, is “pure” if it draws only on what is “close” or “intrinsic” to that theorem. Mathematicians employ a variety of terms to identify pure proofs, saying that a pure proof is one that avoids what is “extrinsic,” “extraneous,” “distant,” “remote,” “alien,” or “foreign” to the problem or theorem under investigation. In the background of these attributions is the view that there is a distance measure (or a variety of such measures) between mathematical statements and proofs. Mathematicians have paid little attention to specifying such distance measures precisely because in practice certain methods of proof have seemed self- evidently impure by design: think for instance of analytic geometry and analytic number theory. By contrast, mathematicians have paid considerable attention to whether such impurities are a good thing or to be avoided, and some have claimed that they are valuable because generally impure proofs are simpler than pure proofs. This article is an investigation of this claim, formulated more precisely by proof- theoretic means. After assembling evidence from proof theory that may be thought to support this claim, we will argue that on the contrary this evidence does not support the claim

FACTEURS DE RISQUES ASSOCIES A LA MORTALITE DES TUBERCULEUX FREQUENTANT LE CENTRE DE DEPISTAGE ET DE TRAITEMENT DE LA TUBERCULOSE MULTI RESTISTENTE DE LA ZONE DE SANTE LA POLICE DU CAMP LUFUNGULA EN REPUBLIQUE DEMOCRATIQUE DU CONGO

La tuberculose multi résistante demeure une crise de santé publique et une menace pour la sécurité sanitaire. L’objectif général de ce travail était  d’étudier  les facteurs de risque qui contribuent à la mortalité juvénile liée de la tuberculose multi résistante chez les malades  ayant  fréquenté le Centre de Santé de dépistage et traitement du camp Lufungula de la Zone de Santé de  Police Nationale Congolaise de 2010 à 2019  dans la Division Provinciale de la Santé de Kinshasa en République Démocratique du Congo. Nous pensions que Les facteurs sociodémographiques, culturels et environnementaux y seraient responsables. Nous avons opté pour  de faire l'analyse de survie à l'aide de Kaplan-Meier et la méthode de cox afin en identifier les facteurs de risque. Nous avons réalisé cette étude sur les données collectées de façon transversale en utilisant les données rétrospectives à travers la base des données du Centre bien identifié dont le nombre total de malades atteint de tuberculose multi résistante était de 404. Comme nous avons utilisé l’échantillonnage exhaustif, nous avons inclus tous les malades. Ces données ont été analysées et traitées à l’aide des logiciels SPSS Version 25, R et Stata12. Les résultats obtenus expliquent la tuberculose multi résistante  est plus observée chez les malades  ayant des antécédents de traitement  antituberculeux. Les autres facteurs d'occurrence y afférents étaient : l’âge, cas d’échec thérapeutique, cas de rechute, Il sied de noter que l’émergence de la tuberculose multi résistante peut être évitée par la mise en place des stratégies de diagnostic et de traitement appropriées.La tuberculose multi résistante demeure une crise de santé publique et une menace pour la sécurité sanitaire. L’objectif général de ce travail était  d’étudier  les facteurs de risque qui contribuent à la mortalité juvénile liée de la tuberculose multi résistante chez les malades  ayant  fréquenté le Centre de Santé de dépistage et traitement du camp Lufungula de la Zone de Santé de  Police Nationale Congolaise de 2010 à 2019  dans la Division Provinciale de la Santé de Kinshasa en République Démocratique du Congo. Nous pensions que Les facteurs sociodémographiques, culturels et environnementaux y seraient responsables. Nous avons opté pour  de faire l'analyse de survie à l'aide de Kaplan-Meier et la méthode de cox afin en identifier les facteurs de risque. Nous avons réalisé cette étude sur les données collectées de façon transversale en utilisant les données rétrospectives à travers la base des données du Centre bien identifié dont le nombre total de malades atteint de tuberculose multi résistante était de 404. Comme nous avons utilisé l’échantillonnage exhaustif, nous avons inclus tous les malades. Ces données ont été analysées et traitées à l’aide des logiciels SPSS Version 25, R et Stata12. Les résultats obtenus expliquent la tuberculose multi résistante  est plus observée chez les malades  ayant des antécédents de traitement  antituberculeux. Les autres facteurs d'occurrence y afférents étaient : l’âge, cas d’échec thérapeutique, cas de rechute, Il sied de noter que l’émergence de la tuberculose multi résistante peut être évitée par la mise en place des stratégies de diagnostic et de traitement appropriées

THE COOPERATIVE FIRM AS MONITORED CREDIT

Abstract. We develop a nancial-contracting theory of the cooperative rm where production requires three generic tasks: working, managing, and monitoring. Workers provide an intermediate input (or labor directly); managers convert the workers' input into a nal output; and directors monitor managers. We model the cooperative rm by letting the workers act also as directors. We show how bundling the labor and monitoring tasks can expand the scope for equilibrium market activity, even when doing so results in a strictly positive deadweight loss. Our theory provides new insight with respect to a substantial theoretical and empirical literature on the life cycle of worker-managed rms, and with respect to a complementary body of anecdotal evidence on the causes of worker buyouts and cooperative degeneration. Our theory is also consistent with dierences between the board compensation policies of cooperative rms, where members typically receive little more than travel and per-diem reimbursements, and of investor-owned rms, where members receive substantial pay often based in part on rm nancial performance

Le FORUM, Vol. 35 No. 3

https://digitalcommons.library.umaine.edu/francoamericain_forum/1031/thumbnail.jp

LSST: from Science Drivers to Reference Design and Anticipated Data Products

(Abridged) We describe here the most ambitious survey currently planned in the optical, the Large Synoptic Survey Telescope (LSST). A vast array of science will be enabled by a single wide-deep-fast sky survey, and LSST will have unique survey capability in the faint time domain. The LSST design is driven by four main science themes: probing dark energy and dark matter, taking an inventory of the Solar System, exploring the transient optical sky, and mapping the Milky Way. LSST will be a wide-field ground-based system sited at Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m effective) primary mirror, a 9.6 deg$^2$ field of view, and a 3.2 Gigapixel camera. The standard observing sequence will consist of pairs of 15-second exposures in a given field, with two such visits in each pointing in a given night. With these repeats, the LSST system is capable of imaging about 10,000 square degrees of sky in a single filter in three nights. The typical 5$\sigma$ point-source depth in a single visit in $r$ will be $\sim 24.5$ (AB). The project is in the construction phase and will begin regular survey operations by 2022. The survey area will be contained within 30,000 deg$^2$ with $\delta<+34.5^\circ$, and will be imaged multiple times in six bands, $ugrizy$, covering the wavelength range 320--1050 nm. About 90\% of the observing time will be devoted to a deep-wide-fast survey mode which will uniformly observe a 18,000 deg$^2$ region about 800 times (summed over all six bands) during the anticipated 10 years of operations, and yield a coadded map to $r\sim27.5$. The remaining 10\% of the observing time will be allocated to projects such as a Very Deep and Fast time domain survey. The goal is to make LSST data products, including a relational database of about 32 trillion observations of 40 billion objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures available from https://www.lsst.org/overvie