Showing papers by "Hydro-Québec published in 1997"

Cathode materials for secondary (rechargeable) lithium batteries

Abstract: The invention relates to materials for use as electrodes in an alkali-ion secondary (rechargeable) battery, particularly a lithium-ion battery. The invention provides transition-metal compounds having the ordered-olivine, a modified olivine, or the rhombohedral NASICON structure and the polyanion (PO 4 ) 3− as at least one constituent for use as electrode material for alkali-ion rechargeable batteries.

Fish Diet and Mercury Exposure in a Riparian Amazonian Population

Abstract: The incorporation of mercury into the food chain and its assimilation by humans is a universally recognized potential health hazard. Studies carried out in the Amazon Basin have shown that mercury (Hg) is present in fish and in humans, however, the relation between fish diet and human exposure has received limited attention in this region. The present study focused on a small village, Brasilia Legal (3°59′00″S, 55°30′00″W), situated on the banks of the Rio Tapajos. A total of 181 fish (40 species) were captured in March, 1995 and analysed for Hg concentration. Of these, 132 fish were among species consumed by the population during the rainy season (mid-November to mid-May) and the dry season (mid-May to mid-November). Wide intra- and inter-species variations in Hg concentrations were observed. Thirty four fish (25.8% of the consumed species) had levels above 0.5 µg/g Hg fresh weight; all were among the piscivorous and omnivorous species. Hair Hg concentrations (HHg), showed that villagers with a high fish diet (n=31; median HHg=16.1 µg/g) and mixed fish diet (n=36; median HHg=14.8 µg/g) had significantly higher HHg concentrations compared to the low fish diet group (n=29; mean HHg=7.8 µg/g). Time series function of HHg measurements, made for 26 persons with over 24 cm of hair, revealed sinusoidal variations, with peaks during the rainy season and troughs during the low water period, paralleling the seasonal shift in dietary habits. Piscivorous and omnivorous fish species, with higher mercury levels, are the main component of the fish diet during the rainy season, while herbivorous fish species predominate during the dry season. Preventive actions should take into account the risk to human health, particularly for fetal and neonatal development, the importance of fish in the riparian diet, the wide intra- and inter -species variations in mercury content and seasonal fluctuations in diet.

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.

Study of the acceptable DC current limit in core-form power transformers

Abstract: The temperature rise in power transformers subjected to a DC source of excitation was measured on core-form single-phase 735 kV autotransformers rated 370 MVA and 550 MVA. The measurements were compared to the temperature rise values obtained on the same transformers operating in overexcitation at 1.95 T. The results show that the tie plates of this particular type of transformer are the components most susceptible to rapid temperature rise. Smaller-scale tests on 100 kVA transformers were performed to take a specific look at these tie plates under the effect of a temperature increase. Finite-element simulations combined with analytical studies of temperature rise were performed in an attempt to determine a tolerable DC current limit based on permissible temperature standards.

Creating an Electromagnetic Transients Program in MATLAB: MatEMTP

Abstract: The traditional method for developing electric network analysis computer programs is based on coding using a conventional computer language: FORTRAN, C or Pascal. The programming language of the EMTP (Electromagnetic Transients Program) is FORTRAN-77. Such a program has a closed architecture and uses a large number of code lines to satisfy requirements ranging from low level data manipulation to the actual solution mathematics which eventually become diluted and almost impossible to visualize. This paper proposes a new design idea suitable for EMTP re-development in a high level programming context. It presents the creation of the transient analysis numerical simulator MatEMTP in the computational engine frame of MATLAB. This new approach to software engineering can afford a dramatic coding simplification for sophisticated algorithmic structures.

A molecular model to evaluate the impact of aging on space charges in polymer dielectrics

Abstract: The understanding of space charge effects depends largely on how concurrent phenomena, such as thermal and electrical aging are understood. A model describing thermal and environmental aging of dielectric polymers is discussed. The model essentially is based on the rate theory associated with the name of Eyring. One basic feature of the model is that the proper energy term is a free energy of activation /spl Delta/G, which implies that the entropy change of the process cannot be neglected. Several examples are given to show that /spl Delta/G is related directly to some physical or chemical parameter involved in thermal or environmental aging. A model describing the mechanical aging of polymers is also discussed. It is shown that submicrocavities can be generated by mechanical stresses above a given critical level, the value of which depends on the energy of cohesion of the polymer. The size of these defects are in good agreement with the Griffith criterion. Finally, the same model adapted to electrical stresses is shown to describe the electrical aging of polyethylene. It predicts that the most deleterious influence of aging is above a given critical field (similar to the critical stress in mechanical aging), where submicrocavities are induced by the electromechanical forces associated with the ac field. Electrons can then move without scattering within the submicrocavities and this may lead to further degradation. The relations between thermal, mechanical and electrical aging and space charges in polymers are addressed briefly and domains requiring more work are mentioned.

Performance characteristics of dielectrics in the presence of space charge

Abstract: The short and long-term dielectric behavior of a number of representative electrical insulating systems is compared in the presence of space charge. Dielectric materials, used both in the communications and power application areas, are considered. In this overview, particular attention is given to thin inorganic films, organic solid-liquid and solid polymer systems as regards to the manner in which space charge affects their dielectric loss, voltage breakdown, treeing and electrical aging characteristics.

A New Fuel Cell Electrocatalyst Based on Carbonized Polyacrylonitrile Foam The Nature of Platinum‐Support Interactions

Abstract: X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) have been conducted on a new fuel cell electrocatalytic material based on a highly porous carbonized polyacrylonitrile (PAN) microcellular foam with very low platinum loading ({approximately}13 to 23 {micro}g/cm{sup 2}) TEM images of this material clearly show the existence of nanometer size platinum particles which are homogeneously distributed in the highly porous carbonized PAN matrix An XPS study of Pt-loaded PAN indicates that C 1s, O 1s, and N 1s peaks shift to lower binding energies, compared to virgin PAN It was concluded that special metal-support interaction exists, through the formation of a charge-transfer complex between platinum and pyridine-type nitrogen atoms of PAN support This interaction leads to the enhancement of the catalytic activity, and the improvement of the long-time stability of this electrocatalyst

CYRANO: a computational model for the detailed design of plate-fin-and-tube heat exchangers using pure and mixed refrigerants

Abstract: A computational model for the detailed design of finned coils has been developed. This programme discretises heat exchangers into tube elements for which the governing equations are solved using local values of temperature, pressure, physical properties and heat transfer coefficients. Single-phase, condenser and evaporator cases can be automatically treated using water, R22, R134a, and refrigerant mixtures based on R32, R125, and R134a. The software can handle non-conventional coil circuits with different numbers of inlets and outlets, non-uniform air distribution at the coil inlet face, using smooth, wavy and louvered fins, and smooth and internally finned tubes. The programme has been validated on seven finned coils using pure fluids, with and without moisture condensation on the fins. Comparisons with tests show errors of less than 5% on the coil duty and of the order of 30% on the refrigerant pressure drop. A performance simulation of a coil using R22 and a ternary mixture is presented to validate the programme algorithms developed for mixtures.

Testing and modelling of inductive superconducting fault current limiters

Abstract: Fault current limiters are expected to be amongst the first applications of high-temperature superconductors in power engineering. The use of the intrinsic property of a superconductor to transit from a zero (or near zero in the case of AC currents) resistance state to a highly resistive state when the critical current is exceeded is the basis for a fast acting fault current limiter. In this article, the authors report test results (43 kVA nominal power: 450 V RMS and 95 A RMS) and comparisons to theoretical simulations. Circuit analysis is used to study design issues and to extract the superconducting material's (BSCCO 2212) properties during the application of the short-circuit. EMTP simulation is employed to predict fault current limiter behaviour in the utility network in order to coordinate with other equipment.

Leached nanocrystalline materials process for manufacture of the same, and use thereof in the energetic field

Abstract: Leached nanocrystalline materials having a high specific surface are particularly useful for storing hydrogen or as catalysts or electrocatalysts in the manufacture electrodes, especially for fuel cells. Such materials can be manufactured by preparing a nanocrystalline material consisting of a metastable composite or alloy of at least two different chemical elements. To be nanocrystalline, this material must have a crystalline structure with the grain size lower than 100 nm. Then, the so prepared nanocrystalline material can be subjected to a leaching treatment in order to eliminate partially or totally one of the elements of the composite or alloy. This leaching results in nanocrystalline materials having a porous structure and, thereby, the requested high specific surface.

Dielectric Performance of Interfaces in Premolded Cable Joints

Abstract: Great progress has been made in developing high-quality insulating materials, in maintaining consistent manufacturing processes, and in designing cable joints for easy installation. However, little attention has been given to the interfaces in cable joints. Greases are generally used as a lubricant for installation of premolded cable joints (excluding heat-shrink and cold-shrink splices), and are therefore always found at these interfaces. Analysis of field-aged cable joints has revealed two common problems related to greases: dry and sticky interfaces causing great difficulties in power disconnection, and interfacial discharges (or surface tracking) leading to dielectric breakdown. The focus of this study is on the dielectric performance of interfaces in cable joints. Measurements of breakdown voltage and pressure were carried out at interfaces of both new and field-aged cable joints. The effect of surface conditions was also investigated. Results show that the dielectric performance at interfaces is intimately related to the surface conditions, and a distinct long-term behavior is found for each type of interface in cable joints. The significance of the results and their implications are discussed.

Capacitive divider substation

Abstract: The development of a passive damper-filter has made it possible to achieve a stable capacitive-coupling substation (SCC). This paper presents the underlying theory and analyzes the impact of the SCC on a power network system. The related nuisance phenomena (overvoltage, ferroresonance) are described together with the solutions applied. Test results are presented as proof that the nuisance phenomena have been satisfactorily eliminated: overvoltage is adequately limited at the worst node by protecting the equipment and ferroresonance never lasts more than two cycles. Lastly, the paper describes Hydro-Quebec's first such capacitive-coupling substation installed at Riviere Ste-Anne (Quebec).

Modeling a mixed residential-commercial load for simulations involving large disturbances

Abstract: A detailed EMTP model of a mixed residential-commercial load valid for large voltage variations has been developed. Once validated against field recordings, the model has been used to study the static, dynamic and post-fault recovery characteristics of the real load. From the simulation results, guidelines for modeling this type of load in dynamic studies such as first swing, transient and voltage stability were established. It is expected that the same methodology applied to other loads of reasonably known composition would guarantee more realistic results than those obtained with current practices.

Low stray interconnection inductance power converting molecule for converting a DC voltage into an AC voltage, and a method therefor

Abstract: The low stray interconnecton power converting module is for converting a DC voltage into an AC voltage. It comprises two DC voltage terminals for receiving the DC voltage, an AC voltage terminal for delivering the AC voltage, and a half-bridge including a pair of power switching elements connected as a series totem pole between the DC voltage terminals via the AC voltage terminal. It also comprises a decoupling device for decoupling the half-bridge. The decoupling device comprises a series of at least two adjacent superimposed electrode plates separated by a dielectric material and extending proximately in overlapping relation with the half-bridge. Each of the adjacent electrode plates is connected to a different one of the DC terminals. The electrode plates form with the two power switching elements, the DC terminals and the AC terminal, a reduced cross section belt-like current closed loop by which a low stray interconnection inductance power converting module is obtained.

High energy ball-milled Ti2RuFe electrocatalyst for hydrogen evolution in the chlorate industry

Abstract: The high energy mechanical alloying of a Ti{endash}Ru{endash}Fe powder mixture (atomic ratio 2:1:1) has been performed by extensive ball-milling in a steel crucible. The structural evolution of the resulting materials has been studied by x-ray powder diffraction analysis. The identification of the various phases present in the materials, as well as the crystallite size and strain, has been performed by Rietveld refinement analysis. In the first stage of the material transformation, Ru or Fe atoms dissolved into Ti to yield to the formation of {beta}{minus}Ti. Upon further ball-milling, almost all the original constituents of the powder mixture have disappeared and a new simple cubic Ti{sub 2}RuFe phase is formed, with a crystallite size as small as 8 nm. The electrochemical properties of these materials have been tested in a typical chlorate electrolyte by cold-pressing the powders into disk electrodes. At 20 h of ball-milling, where the phase concentration of Ti{sub 2}RuFe reaches 96{percent}, a reduction of the activation overpotential at 250 mA cm{sup {minus}2} of nearly 250 mV is observed when compared to that of a pure iron electrode. {copyright} {ital 1997 Materials Research Society.}

Characterization of phase and amplitude comparators in UHS directional relays

Abstract: In this paper, conventional techniques to compute the phase angle between a voltage and a current waveform are applied to assess the directionality as it is necessary in ultra high speed (UHS) directional relays. It is shown that with this type of relay the main difficulty stems from the fact that in order to compute the angle, a prior knowledge of the amplitudes of the superimposed voltage and current magnitudes is necessary. Therefore very fast algorithms have to be devised that would take into account anticipated values of these magnitudes in order to assure secure trips in the shortest possible time.

Electronic panoramic camera

Abstract: The panoramic camera according to the invention has a housing having first and second sections, coaxial with a rotation axis. The second section can be driven in rotation about the axis with respect to the first section by a motor connected to a gear. A lens is mounted on the second section of the housing and is both perpendicular and radial to the axis. A linear CCD array is placed at the focal point of the lens in order to capture the images transmitted by the lens. An analog-to-digital converter is connected to the CCD array to convert the analog signal generated by the CCD array into digital information. The digital information is stored on a hard disk drive, and includes data corresponding to the azimuth of the camera. Finally, a micro-computer controls the rotation of the housing, sends a control signal to the analog-to-digital converter to digitize the image and sends a control signal to the hard disk drive to save the digital information generated by the converter.

Turn insulation aging of motors exposed to fast pulses of inverter drives

Abstract: The effects of fast pulses from PWM inverter AC drives on motor insulation are not well understood and their impact on long term reliability is not known. Turn insulation stresses have been simulated on small "layer-to-layer" specimens subjected to typical pulses of 120 ns rise-time at a repetition rate of 10 kHz. Voltage pulse overshoots reached 920 V. Under these conditions no partial discharge was detected. Measurements of capacitance, dielectric losses, relaxation currents, return voltage and thermally stimulated current (TSC) have been used to characterise insulation modifications resulting in the cumulative effects of multiple pulses. Preliminary results indicated that changes in the dielectric properties after a short exposure (1310 hours) to voltage alone were negligible. When specimens were exposed to both temperature and voltage, TSC results showed that some modifications of the dielectric properties could be initiated after short exposure time, even below the partial discharge inception voltage.

Wave climate of large reservoirs and a revised wave hindcast formula

Abstract: Since impounding of the various reservoirs of the La Grande Complex in northern Quebec, the riprap of several dams and dykes has suffered some damage during the fifteen-year period that followed. A mandate was given to the Societe d'energie de la Baie James (SEBJ) in January 1992 to review the riprap design and evaluate the necessary repairs. This paper focuses on the revaluation of the design wave with revised wave hindcast formulas based on the large amount of wind and wave data collected.