Showing papers by "Hydro-Québec published in 1991"

Fast adaptive schemes for tracking voltage phasor and local frequency in power transmission and distribution systems

Abstract: Devices specifically dedicated to highly accurate measurement of frequency have been described for specific applications like power system stabilizers. However, in most situations the digital estimate of the frequency deviation is needed concurrently with other decision quantities. Therefore, its value is usually obtained as a by-product of a more general-purpose algorithm, based, for instance, on the extended Kalman filtering or the recursive least error squares techniques. Unfortunately, a common problem with these Kalman filters is the high computational requirements, due to transcendental functions evaluation in real-time. Therefore, the need still exists for more clever implementations of the various real-time algorithms, which could alleviate the computational burden and enhance the adaptation speed during transients. To fulfil this need to some extent, two new methods suitable for fast adaptive estimation of voltage phasor and frequency deviation are outlined. >

Mercury evolution (1978–1988) in fishes of the La Grande hydroelectric complex, Quebec, Canada

Abstract: From 1978 to 1988, the evolution of the Hg content of fish has been monitored in the areas affected by the La Grande hydroelectric complex. Four fish species were considered: two non piscivorous, lake whitefish (Coregonus clupeaformis) and longnose sucker (Catostomus catostomus), and two piscivorous, northern pike (Esox lucius) and walleye (Stizostedion vitreum). The evolution of Hg concentrations in time depends upon fish species and type of reservoirs. Non piscivorous fish react more rapidly than piscivorous. Five years after filling, their Hg level had increased by a factor of four in reservoirs with rapid filling and short renewal rate; levels decreased thereafter. In the La Grande 2 reservoir, the Hg concentration of 400 mm lake whitefish went from 0.16 mg kg−1 before impoundment to 0.57 mg kg−1 5 yr after filling, and then started to decrease. For 700 mm northern pike, the Hg level went from 0.61 mg kg−1 to 2.99 mg kg−1 and was still increasing 9 yr after initial filling. In reservoirs where filling spans over a few years or with long renewal rate, their Hg content evolves more slowly. In river sections located downstream from reservoirs, the Hg content of non piscivorous species was significantly higher than in reservoirs. In 1988, whitefish exhibited values of 1.22 mg kg−1 in the tailwater of the La Grande 2 power station, compared to 0.48 mg kg−1 in the forebay. This phenomenon could be related to the drift of food organisms from the upstream reservoir. A study of several reservoirs of the Canadian Shield, which were created between 6 and 67 yr ago suggests that it could take between 20 and 30 yr before Hg concentration in fish return to preimpoundment levels.

Low Hydrogen Overpotential Nanocrystalline Ni‐Mo Cathodes for Alkaline Water Electrolysis

Abstract: Nanocrystalline fcc Ni x Mo 1−x (x=0.60, 0.85 atom percent) metallic powders prepared by high energy mechanical alloying were found to possess electrocatalytic activities for the hydrogen evolution reaction in 30 weight percent KOH at 70°C equivalent to that of the best electrocatalysts. The formation process and the structural properties of these nanocrystalline alloys were investigated. The active phase is a metastable solid solution of Mo in fcc Ni whose electrocatalytic activity is associated with the reduction in the size of the crystallites and correlates with the expansion of the Ni lattice

Digital measurement of voltage flicker

Abstract: The author deals with cyclic variations in the envelope of voltage waveforms. European power utilities have done substantial work already in their characterization, based on the effects on visual perception. They have also established a norm for the calculation of an instantaneous flicker level, a short-term severity coefficient, and a long-term severity coefficient. The measurement techniques that they propose are basically designed for analog instrumentation. Digital implementations of the analog design are neither cost effective nor optimal in performance. The author proposes a method for direct calculation of flicker level from digital measurements of voltage waveforms. The direct digital implementation uses a fast Fourier transform (FFT) as the first step in the computation. A pruned FFT, customized for the flicker level computation, is also proposed. >

Electromagnetic inductor with ferrite core for heating electric conducting material

Abstract: An induction heating device for heating electrically-conducting material to temperatures of up to at least 300° C. The device comprises an open core of ferrite material. A coil of Litz wire is wound around the core. A power source is connected across the coil to produce an excitation current in the coil, within a frequency range from 12 to 25 kHz, to generate a variable magnetic field when energized. Magnetic flux concentrator tubes of electrically-conductive material are disposed about the coil and close to the core embedded in a thermo-conductive electrically-insulating, material in the intend of maximizing the useful flux. A cooling fluid circulates through the concentrator tubes for cooling the tubes, the core and the coil. An induction zone is defined by said magnetic field generated between the opposed poles of the core and penetrating at the surface of the body to be heated. The body is heated by the eddy currents generated by the variable magnetic field on the surface.

Device for packaging a lithium battery

Abstract: Two metallic foils each have a continuous band of polyethylene film adhesively bonded thereto. The lithium battery is sandwiched between these two metallic foils and a thermo-seal is provided to join the two polyethylene films. This construction prevents any outside substance from contacting the lithium battery.

Identification of generalised models of synchronous machines from time-domain tests

Abstract: Recent developments have shown that numerical models of synchronous machines are, in many cases, improved by introducing an increased number of dampers or dynamic constants. The major issues affecting the model identification by such an extension, which in fact becomes necessary when the machine possesses a solid rotor are discussed from a time-domain point of view. The first result is that all methods which determine the equivalent circuit from test data in an indirect manner, by using the time constants or operational impedances as intermediate tools, give rise, along the d-axis, to systematic errors in the sub-transient and sub-subtransient time constants of the estimated circuits. Unfortunately, when the identification experiment is the standard short circuit, even the direct method suffers from the drawback of weak identifiability of the model, with the result that the uniqueness of the equivalent circuit, directly estimated from test data, is not at all guaranteed. In fact, from an information content point of view, the richer tests are those made at standstill, with a perfect decoupling between the two axes. It is demonstrated by simulation that if the direct approach is applied to such a test, with pulse wave modulated (PWM) voltages as the excitation signals, a numerically cheap and accurate one-step procedure for time-domain identification of circuit models is obtained.

High-resolution electron microscopy study of NiMo nanocrystals prepared by high-energy mechanical alloying

Abstract: A growing interest has emerged in the past few years over a new class of materials called “nanocrystalline solids” (NS). These materials are made of extremely small crystals with dimensions ranging from 1 nm to 10 nm. Up to now, most of these solids were fabricated from the gas phase by an evaporation/ condensation process. Recently, however, high energy mechanical alloying (MA) has been shown to be an excellent tool to produce various types of metastable structures, including NS. Through high energy MA we have fabricated nanocrystalline nickel oversaturated with molybdenum which shows an extremely high electrocatalytic activity for the hydrogen evolution reaction in alkaline solutions. In order to fully understand the chemical properties of these new alloys, we have investigated, through high resolution electron microscopy, the microstructure and the size distribution of the crystalline throughout the milling process. A detailed study of the crystalline interfaces and grain boundaries is also presented.

Dynamic interactions between HVDC systems connected to AC buses in close proximity

Abstract: As AC/DC systems become further integrated, multiple-infeed converter (MIC) systems can be expected to become more common. Different categories of MIC systems are defined, and: (1) the impact of the AC system strength; and (2) the coordination of the reactive power demand of the converters on the dynamic performance of such systems are discussed. Analog or physical simulator study results are presented which provide some insight into the dynamic behavior of one category of such systems. In relation to MIC systems which have a common AC bus or are connected to AC buses which are electrically close to each other, the following conclusions can be drawn: (1) careful evaluation of interactions between converters is necessary since even a remote fault affecting one DC system may affect other DC systems within the MIC system; (2) coordination of reactive powers at the common AC bus is necessary to avoid unnecessary mode shifts; and (3) coordination of the operating and control characteristics (i.e. VDCL characteristics) of converters within a MIC system is essential for satisfactory dynamic behavior of the total system. >

Theoretical and experimental investigations on the process of high-pressure discharge development

Abstract: The voltage breakdown behavior of a plane-parallel gap of 0.48-mm length filled with helium was examined at atmospheric pressure with admixtures of dry air at relative pressures of 0, 10/sup -4/, 3*10/sup -4/, and 10/sup -3/. The initial stages of the breakdown were investigated by means of a quantitative model consisting of the electron, ion, and excited-particle conservation equations and the Poisson equation. The system of equations was solved for an applied voltage of 180 V, at one single partial pressure of the impurities. Two numerical routines were used for the solution: a commercial IMSL subroutine TWODEPEP, and a newly developed method of solution in several fractional steps. The results were compared and found to be in reasonable agreement although the new method indicated a somewhat slower rate of rise, particularly concerning electron density. The new method permits extension of the calculation up to electron densities equal to almost two orders of magnitude above the earlier limit. >

Electrochemical behaviour of tin in bicarbonate solution at pH 8

Abstract: The anodic oxidation of tin in 0.1 to 1M bicarbonate solutions at pH 8 has been studied. The process may be divided into three potential regions: (1) a short active dissolution (Tafel) region; (ii) a dissolution-precipitation region; and (iii) a large region of electrode passivity. The rate-determining step of the reaction in the active-dissolution region is attributed to the diffusion of an ionic species into the solution, the diffusing species being generated at the metal surface. In the region of the first oxidation peak, the reaction rate is controlled by diffusion of CO 3 2− species in solution. When the potential becomes more positive than −0,1 Vsce, a highly passivating (most likely SnO2) film is formed on the electrode surface.

Method and electrical measuring apparatus for analyzing the impedance of the source of an actual alternating voltage

Abstract: Procede et appareil de mesure electrique (10) servant a analyser une tension alternative reelle presente sur un fil electrique (11) ou dans un materiel electrique afin de determiner si la tension provient d'une source a impedance faible ou elevee et d'assurer ainsi la securite de l'operateur. Method and electrical measuring device (10) for analyzing an actual alternating voltage present on a wire (11) or in an electrical equipment to determine if the voltage from a source to low or high impedance, thus ensuring operator safety. On raccorde une sonde a bi-impedance (12) a la tension a analyser et l'on traite les signaux de tension. Is connected to a bi-impedance probe (12) to the voltage to be analyzed and treating the voltage signals. La sonde proprement dite est constituee d'une premiere serie d'elements unidirectionnels (13) et d'une deuxieme serie parallele d'elements a resistance elevee (14). The actual sensor consists of a first series of unidirectional elements (13) and a second series of parallel high-resistance elements (14). Les sorties de la serie d'elements raccordes en parallele sont raccordees a une troisieme serie d'elements a faible resistance (15, 16, 18). The outputs of the series of elements connected in parallel are connected to a third series of low resistance elements (15, 16, 18). Un circuit de mesure (17) est raccorde a ladite troisieme serie d'elements a faible resistance peut discriminer entre les signaux de tension issus des deux series d'elements a resistance, et est pourvu d'un circuit de calcul (28) destine a determiner si les signaux de tension proviennent d'une source a impedance faible ou elevee. A measuring circuit (17) is connected to said third series of low resistance elements can discriminate between the voltage signals from the two sets of resistance elements, and is provided with a calculation circuit (28) for whether the voltage signals come from a high or low impedance source. Les sorties de la sonde sont mises a la terre (19). The probe outputs are grounded (19). Un indicateur (32) indique l'etat de la source a impedance. An indicator (32) indicates the status of the source impedance. Un avertisseur (32) peut signaler un quelconque depassement d'une valeur de seuil predeterminee representative d'une source a faible impedance. An alarm (32) may report any exceeding a predetermined threshold value representative of a low impedance source.

Similarity laws of the internal damping of stranded cables in transverse vibrations

Abstract: Similarity laws governing the internal damping of stranded cables in transverse vibrations are based on the assumption of hysteretic loss factor associated with the flexural rigidity of the cable and the assumption that this loss factor is the same for all cables of the same construction. These laws are derived from the basic cable differential equation. The proportionality factors, the exponents of the various parameters in the laws, are obtained from the experimental results of a typical member of a family of similar cables. The same set of laws has been found to apply very well to ACSR (aluminum conductor steel reinforced) conductors having the same number of strands and fairly well to all ACSR conductors. Other families of cables, such as ACAR (aluminum conductors aluminum reinforced), steel cables, etc., could each have their own set of similarity laws, which would all look alike. >

The compensation law revisited-Application to dielectric aging

Abstract: The fundamental origin of the compensation law observed by P. K. David (1987, 1988) and G. C. Montanari (1988) in several aging mechanisms of dielectrics is discussed. It is shown that this is due to a linear relation between activation entropy and enthalpy of a given process. An aging model, partially based on the rate theory, is presented. One of its advantages is that it characterizes dielectric aging by a free energy change, rather than by an apparent activation energy. Some aging data are analyzed with the proposed model, and it is shown that under high stresses the failure time varies exponentially with stress. Some critical comments are made regarding the use of arbitrary end points as a method of selection for a failure criterion. >

Device for heating the bacterial proliferation zone of a water heater to prevent legionellosis

Abstract: A domestic electric water heater comprises a cylindrical tank having a vertical wall and an inwardly curved bottom, the latter defining with the vertical wall an annular stagnant water zone susceptible of bacterial contamination by, for example, legionella bacteria. The tank is provided with an upper immersion heating element and a lower immersion heating element, the latter being located above to the annular zone of contamination. The tank further comprises an outer electric heating element mounted on the outer surface of the vertical wall at the level of the contamination zone and below the lower immersion element. This outer heating element is capable of bringing water in the contamination zone to a temperature sufficient to eliminate the danger of such bacterial contamination, the temperature being in the order of 46° C.

Modelling of HVDC wall bushing flashover in nonuniform rain

Abstract: The authors present the first mathematical model to provide necessary and sufficient conditions for flashover of a high voltage direct current (HVDC) wall bushing under nonuniform rain. The suggested mechanism is initiated by streamer bridging of the dry zone. The findings of the model have been satisfactorily compared with previous experiments and field observations and can account for the following aspects of the flashover mechanism: critical dry zone length, polarity effect, specific leakage path, wet layer conductance per unit leakage length, and the DC system voltage. >

Analysis of degradation products on epoxy surfaces subjected to pulse and glow type discharges

Abstract: The degradation of epoxy specimens, exposed to pulse type and pulseless glow discharges, was investigated. Epoxy coverered, plane- parallel electrodes were employed; the mean discharge magnitude of the pulse type discharges was measured as a function of exposure time. The glow discharge light intensity was monitored as a function of time using a photomultiplier tube (PMT). Preliminary results indicate erratically changing magnitude of both the pulse type discharge and the photoemission prior to the disappearance of the pulses, at which point the PMT output is observed to assume a relatively constant value. The latter result infers a quasi constant glow discharge intensity for long exposure times. The change in the discharge behavior is ascribed to the chemical reactions occurring in the vapor phase and on the epoxy specimen surface. The surface deposition products are analyzed using ESCA, Debye-Scherrer X-ray diffraction and Ion Chromatography measurement techniques.

Calculation of magnetic flux profiles and deduction of critical current densities for type II superconductors

Abstract: The critical state concept for the calculation of internal flux profiles in type II superconductors is used to model the magnetization behavior of high-T/sub c/ materials. In this application of the model, the field-dependent reversible magnetization and critical current density are incorporated flexibly into numerical solutions of the basic equations. The solutions are compared to results obtained by using the Bean (constant J/sub c/) and Kim (field dependent J/sub c/) approximations. The authors use theoretically calculated magnetization curves to analyze experimental magnetization data for bulk, textured Y/ErBaCuO samples obtained from their own work and from recently published work. Pitfalls and guidelines when using such measurements to obtain intrinsic material critical current densities are discussed.

Critical switching impulse strength of long air gaps: modelling of air density effects

Abstract: A physical modeling approach to investigate the effect of reduced air density on leader inception and sparkover of long air gaps under positive switching impulses with critical front time is presented. The model accounts for the effect of air density on continuous leader inception voltage, leader length, and sparkover voltage. The results of the model provides critical positive switching impulse air density correction factors for rod-plane, rod-rod, conductor-plane, conductor-rod, and conductor-tower window gaps over a wide range of gap distances and relative air densities. The model findings were extensively checked against previous experimental results with quite satisfactory agreement. >

Evaluation of different platings for aluminum-to-copper connections

Abstract: A number of coating materials commonly used for aluminum-to-copper connections were evaluated on the basis of their effect on the contact resistance-force/torque relationships, the performance of coated joints under current-cycling and fretting conditions, and ability to protect the contact against galvanic corrosion in saline and industrially polluted environments. The results showed that the use of nickel-plating of both aluminum and copper and copper-plating of aluminum ensures the greatest stability while bare aluminum in contact with tin- and silver-plated copper shows the poorest performance under different operating conditions. >

Power converter simulation module connected to the EMTP

Abstract: A novel approach for power converter simulation in the electromagnetic transients program (EMTP) is presented. It is based on simultaneous interfacing of a converter simulation module with the EMTP network equations. Hybrid analysis, demonstrated to be more general than the compensation method, is used to model the nonlinear converter module network. The procedure used to formulate hybrid port equations is general and can be used for any converter module network with nonlinear branch functions. The valve model selection has no theoretical restrictions, and the particular case of valve modeling by ideal switches is simple to accommodate. The new approach is more general and efficient than the standard EMTP method for power converter simulation. Modularity permits incorporation of dedicated initialization procedures and programming of digital control schemes. >

Influence of insulation morphology, impurities and oxidation on some electric properties of cables

Abstract: It is shown that the AC breakdown strength and dielectric loss of unaged and field-aged transmission and distribution cables vary with insulation crystallinity, contamination, and oxidation. It is also shown that the influence of these parameters is particularly important near the conductor shield and varies with aging. The influence of curing on cable properties is briefly discussed. The sample preparation, crystallinity, impurity, oxidation, AC breakdown, and dielectric loss measurements are described. >

Accelerated aging tests for polymer insulated cables under wet conditions

Abstract: The effectiveness of various aging test procedures utilized in the past to evaluate aging in polymeric cables under wet conditions is examined. It is pointed out that the prime parameters affecting the aging rate and its mechanisms are those of electrical stress, frequency, water solution, temperature, mechanical strain, and testing time duration. Any valid fixed-time or time-to-breakdown test procedure that is based on the stress/frequency acceleration concept must, therefore, be carefully specified and defined in terms of these parameters. >

An experimental method to determine the electro-thermal model parameters of metal oxide surge arresters

Abstract: The energy absorption capability of a metal oxide surge arrester is limited by the temperature of its elements. To predict this temperature, a computer model can be a valuable tool, but it needs to have exact parameters. An experimental method using only a single test to determine such parameters is proposed. An electrothermal model couples the electrical heat production from metal oxide varistor elements with the thermal characteristics of the housing. The watt losses are computed from the voltage-current-temperature characteristic of the arrester when the applied voltage and temperature are known. With the proposed experimental method for the determination of the thermal parameters, a single high-energy discharge is sufficient to find the four values of the thermal model. The method is based on linear system analysis and makes use of least-square minimization curve fitting. The method is validated with real data on a full section of a 735 kV system station class arrester. The influence of error in the parameter values is evaluated by a sensitivity analysis. >

The contribution of strain and plastic deformations to the amorphization reaction of NiZr alloys by mechanical alloying

Abstract: The elastic strain in the nickel and zirconium crystallites has been measured by X-ray diffraction during the amorphization reaction (AR) which takes place when a mixture of pure nickel and zirconium powders is subjected to intense mechanical deformations. The strain in the zirconium increases up to a maximum value at the onset of the amorphization then decreases while the reaction proceeds. Calorimetric measurements (DSC) taken after various milling times reveal three regions of interet. The first exothermic peak around 315°C corresponds to the thermally induced solid state amorphization reaction (SSAR). The second peak at about 410°C is mainly associated with structural recovery and recrystallization, and the third peak corresponds to the crystallization of the amorphous phase. The structural defects are thermally stable at the temperatures where the SSAR takes place and therefore they can play an important role in the mechanism of amorphization. The elastic strain energy as well as the total energy released from the annihilation of defects have been evaluated and compared with the heat of mixing and the heat crystallization of the alloy. Conclusions are drawn on the relative importance of each component.

Oxygen evolution in 30% KOH at 70°C on nickel anodically coated with CoOOH/Co3O4

Abstract: The oxygen evolution reaction (OER) was investigated on polished pure nickel electrodes preanodized for 30 min in nonpurified 30 wt% KOH at 70°C prior to determinating the kinetic parameters of the OER. The electrolyte contained up to 0.8mm dissolved cobalt and the preanodization current,ia, ranged from 0.05 to 5 A cm−2. In the presence of dissolved cobalt, an anodic coating of CoOOH/Co3O4 is formed on the nickel substrate. The electrocatalytic activity increases asia or the concentration in dissolved cobalt is increased. With 0.4mm dissolved cobalt, the improved electrocatalytic activity is due to a linear increase in exchange current density through the charge associated with the reduction of the loading. The Tafel slope remains unaffected.