Hydro-Québec

About: Hydro-Québec is a government organization based out in Montreal, Quebec, Canada. It is known for research contribution in the topics: Electric power system & Dielectric. The organization has 2596 authors who have published 4433 publications receiving 100878 citations.

Fitting to magnetoresistance under weak localization in three dimensions

Abstract: We discuss a number of suggested explanations for observed discrepancies between theories of the quantum corrections to conduction, and recent magnetoresistance experiments on bulk metallic glasses. We emphasize the importance of competing effects, particularly the influence of magnetic impurities. Data showing these effects are presented and analysed using a theory of Beal-Monod and Weiner to account for the direct magnetoresistance from the spin scattering and magnetic field dependence of the spin-flip dephasing rate. Throughout, we provide useful numerical procedures for the efficient evaluation of the theoretical expressions used in analyzing such data, and point out that some theoretical expressions must be altered when considering strongly enhanced paramagnetic systems Ce travail etudie en detail les differentes explications presentement proposees qui tentent d'expliquer les ecarts observes entre les theories reliees aux corrections quantiques presentent dans les phenomenes de conduction des materiaux desordonnes et les recents resultats experimentaux touchant la magnetoresistance des verres metalliques amorphes. Nous soulignons l'importance de divers effets competitifs et en particulier de la forte influence des impuretes magnetiques. Pour demontrer celle-ci, nous presentons de nouveaux resultats relatifs a la presence de telles impuretes et les analysons en utilisant la theorie de Beal-Monod et Weiner qui permet de tenir compte de la magnetoresistance directement reliee a la diffusion des spins et a la dependance en champ du taux de dephasage du renversement de ceux-ci. Tout au long de l'article nous presentons certaines techniques numeriques qui permettent l'evaluation rapide et efficace des expressions theoriques necessaire a l'analyse de tels resultats. Finalement, nous montrons que certaines expressions theoriques doivent etre modifiees lorsque des systemes fortement paramagnetiques sont etudies

Electrical properties analysis of micro and nano composite epoxy resin materials

Abstract: This work deals with the study of micro and nanosilica filled epoxy resin samples carried out in the framework of CIGRE WG D1.24 cooperative test program. This program focused on chemical, electrical and electrostatic properties of epoxy based nanodielectrics for electrical engineering applications. Epoxy based samples filled with micro and/or nanoparticles of silica were characterized by transmission electron microscopy, dielectric spectroscopy, conduction current and space charge measurements. These mutually complementary techniques were used to examine the effect of the size and quantity of silica particles on the electrical properties of the analyzed materials. The analysis of charge injection, polarization, trapping and conduction phenomena has allowed the modeling of dielectric behavior of the studied materials under multiple stresses. The Schottky Injection and Space Charge Limited Current models were studied to explain conduction phenomena. A composition of micro and nano-sized silica particles accumulating the smallest amount of space charge is also proposed.

On the Accuracy Versus Transparency Trade-Off of Data-Mining Models for Fast-Response PMU-Based Catastrophe Predictors

Abstract: In all areas of engineering, modelers are constantly pushing for more accurate models and their goal is generally achieved with increasingly complex, data-mining-based black-box models. On the other hand, model users which include policy makers and systems operators tend to favor transparent, interpretable models not only for predictive decision-making but also for after-the-fact auditing and forensic purposes. In this paper, we investigate this trade-off between the accuracy and the transparency of data-mining-based models in the context of catastrophe predictors for power grid response-based remedial action schemes, at both the protective and operator levels. Wide area severity indices (WASI) are derived from PMU measurements and fed to the corresponding predictors based on data-mining models such as decision trees (DT), random forests (RF), neural networks (NNET), support vector machines (SVM), and fuzzy rule based models (Fuzzy_DT and Fuzzy_ID3). It is observed that while switching from black-box solutions such as NNET, SVM, and RF to transparent fuzzy rule-based predictors, the accuracy deteriorates sharply while transparency and interpretability are improved. Although transparent automation schemes are historically preferred in power system control and operations, we show that, with existing modeling tools, this philosophy fails to achieve the “3-nines” accuracy figures expected from a modern power grid. The transparency and accuracy trade-offs between the developed catastrophe predictors is demonstrated thoroughly on a data base with more than 60 000 instances from a test (10%) and an actual (90%) system combined.

Electrical aging of extruded dielectric cables. A physical model

Abstract: A model is proposed to describe all experimental results on electrical aging of cables reported in Part 1. It is based on simple thermodynamics concepts in the Eyring theory, includes the concept of submicrocavity formation proposed by Zhurkov, and supposes that the first step in electrical aging is essentially a molecular process, as in Crine and Vijh's model. Our model of electrical aging under ac fields supposes that molecular-chain deformation is essentially a fatigue process and, therefore, that high frequencies generate more defects and thus reduce cable life, as indeed demonstrated by others. An original feature of the model is the submicrocavity formation above a critical field F/sub c/, whose value can be approximately predicted knowing the energy of cohesion of the polymer. This leads to a simple lifetime equation depending on just two physical parameters /spl Delta/G/sub 0/ (energy of activation of the chain deformation process) and /spl lambda//sub max/ (the maximum size of submicrocavities) with no adjustable unknowns. Above F/sub c/, there is an exponential relation between time and field, whereas below F/sub c/, the breakdown strength of the insulation varies very little with time; in other words, there is very limited (if any) aging. The slope of the exponential regime gives the value of /spl lambda//sub max/ directly whereas the intercept gives the value of /spl Delta/G/sub 0/. The predictions made by the model are discussed in correlation with existing experimental data. In addition to these basic assumptions, the model confirms that there is a relation between cable endurance and insulation morphology. Actually, the size of submicrocavities is ultimately limited by the amorphous-phase thickness. The max values deduced from the slopes of the exponential regime between F and log t for polyethylene (PE) (Part 1), XLPE and EPR insulation are in excellent agreement with the size of the amorphous phase of these samples, as measured by X-ray spectroscopy. It is also shown that the presence of water results in a lower /spl Delta/G/sub 0/ value, i.e. a shorter life. The precise relation between /spl Delta/G/sub 0/ and the nature and concentration of the impurity (including water) needs more work. The impact of these conclusions on the experimental limits of a reliable accelerated aging test and on the final breakdown process are discussed in a subsequent paper.