Showing papers by "Hydro-Québec published in 1989"

Dissolved gas analysis: It can save your transformer

Abstract: The use of dissolved gas analysis (DGA) to monitor the in-service behavior of transformers is discussed. Sampling techniques are briefly considered, and two commercial hydrogen-in-oil detectors are described. The first allows the hydrogen concentration to be measured at intervals of a few hours by a portable gas collector that can be connected to semipermeable tubes. Continuous remote monitoring from the substation is possible with the second model, which uses a fuel-cell-type detector. The use of DGA for fault diagnosis is examined, and acceptable gas levels are indicated. The use of expert systems to facilitate decision making on the basis of DGA results is discussed, as is international cooperation in sharing data and experience and reaching agreement on methods of analysis and interpretation. Further applications of DGA are indicated. >

A model for switching impulse leader inception and breakdown of long air-gaps

Abstract: A mathematical model is described for continuous leader inception and breakdown of long gaps under positive switching impulses with critical time-to-crest. The model deals with rod, sphere, and conductor-plane gaps. It provides novel analytical expressions for continuous leader inception voltage, height of the final jump, and breakdown voltage as well as analytical tools to determine the critical electrode radius for any gap spacing. The theory is extensively compared with previous experimental results and is tested against several formerly developed empirical formulas, relevant to several discharge parameters, for different electrode forms and over a wide range of gap spacings. >

A new fault location algorithm for radial transmission lines with loads

Abstract: Conventional fault location schemes do not take loads and their valuable impedance behavior into account. This leads to unacceptable errors in the case of radial transmission lines with loads, commonly found at the 120 Kv and lower levels. A new method for such lines is proposed in this paper. The fault distance is obtained by the solving an implicit equation. Single phase to ground, phase to phase and three phase to ground faults are treated. The effect of the new scheme is illustrated by simulated faults.

Switching impulse strength of air insulation: leader inception criterion

Abstract: The author introduces a general criterion for leader inception of phase-to-ground air insulation under positive critical switching impulses. This criterion established the correspondence between continuous leader initiation in the vicinity of the highly stressed electrode and conditions prevailing later at the instant of the final jump. The criterion is applied to several complex electrode configurations, including rod-rod, conductor-rod, and conductor-structure gaps, where both analytic and digital techniques are used to compute the leader inception voltage, 50% breakdown voltage, and gap factor. The theory has been systematically tested against available experimental results with quite satisfactory agreement. >

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

Interdiffusion during the formation of amorphous alloys by mechanical alloying

Abstract: By probing the Ni content of Zr crystallites as a function of milling time using Auger spectroscopy, we report the first direct measurements of the interdiffusion which takes place during the amorphization of Ni-Zr by the mechanical alloying of pure-metal powders. Based on the concentration variation of Ni in Zr as a function of the milling time and using a simple interdiffusion model, we can estimate an effective local temperature at the collision site.

A model of aging of dielectric extruded cables

Abstract: The authors present a model of electrical aging of extruded cables based on actual data and realistic experimental conditions. It is shown that a simple model partially based on the rate theory associated with the name of Eyring describes very well the aging of polyethylene (PE), crosslinked PE, and ethylene-propylene rubber cables under a wide variety of conditions. The significance of the physical and thermodynamic parameters used in the model is discussed in relation to the polymer morphology. It is speculated that severe and irreversible electric aging of dielectrics is preceded by the formation of microcavities in the 50-100-AA range. >

Insulator pollution performance at high altitude: major trends

Abstract: A survey of the data available from the literature was conducted in order to assess major trends in insulator performance with altitude. The literature comprised tests on individual insulator strings under natural and artificial conditions along with actual live-line performance. The data covered pollution performance as well as the air-gap breakdown performance of insulators under reduced pressure conditions for AC and DC applied voltages. The major trends reported here suggest a pressure dependence (p/p/sub 0/)/sup 0.35/ for DC and (p/p/sub 0/)/sup 0.5/ for AC, of V/sub 50/ for standard polluted insulators at altitudes lower than about 4 km (p approximately 0.6 atm). These pressure dependences impose a derating of the relative performance of leakage path length or flashover voltage with altitude, namely 6%/km for AC, 5%/km for positive DC, and 4%/km for negative DC applied voltages. Dielectric breakdown, in contrast, imposes a 10.5%/km degradation of insulating air gaps with altitude. >

A new approach to the electric aging of dielectrics

Abstract: A simple model partially based on the rate theory is proposed to describe the electric aging of polyethylene (PE) and cross-linked PE (XLPE) cable insulation. It is assumed that the stress (electric or mechanical) reduces the height of the energy barrier controlling the process under study. The model describes very different effects of high electric fields on the properties of polymers. It relies on two parameters whose physical significance is discussed in the light of electric aging of PE and polarization reversal of PVDF. A preliminary study indicates that very long lifetimes of polymers can be achieved provided the applied field is lower than the critical field controlled by the chemical and morphological structure of the material. >

Studies on modeling corona attenuation of dynamic overvoltages

Abstract: An experimental and theoretical study is presented on the corona characteristics of conductor bundles under dynamic overvoltages. Measurements have been made in the outdoor test cages of Institut de Recherche d'Hydro-Quebec on two bundles, under conditions of fair weather and heavy rain, for steady 60 Hz voltages as well as dynamic overvoltages. Based on the data on corona currents and losses obtained, a nonlinear resistance model of corona is proposed for attenuation studies. The Suliciu model for corona, originally developed for unipolar impulses, has been adapted for dynamic overvoltages. Both these corona models are used to study the influence of corona on the dynamic overvoltages developed during line energization and load shedding of a single-phase line. Among other findings, it is shown that the corona phenomenon stabilizes after the first half-cycle of the dynamic overvoltage. The corona losses of conductor bundles under fair weather conditions increase rapidly with the conductor surface voltage gradient; they approach losses under heavy rain at higher gradients. >

Process for making nanocrystalline metallic alloy powders by high energy mechanical alloying

Abstract: There are described metallic powders comprising agglomerated nanocrystals of an electroactive alloy. The main component of the alloy can be of nickel, cobalt, iron or mixtures thereof while the alloying element is one or more transition metals such as Mo, W, V. Preferably the nanocrystals will be made of an alloy of nickel and molybdenum. An electrode which is used by compacting the powders is also disclosed. Also disclosed, is a process for producing the metallic powders by providing particles of nickel, cobalt and iron with particles of at least one transition metal, (Mo, W, V) and subjecting the particles to high energy mechanical alloying such as ball milling under conditions and for a sufficient period of time to produce a nanocrystalline alloy. Electrodes produced from these powders have an electrocatalytic activity for the hydrogen evolution which is comparable or higher than the electrodes which are presently used in the electrochemical industry. Moreover, these materials present an excellent chemical, electrochemical and mechanical stability.

Plasma reactor used to treat powder material at very high temperatures

Abstract: Disclosed is a plasma reactor for use to treat ores or other material at a very high temperature in order to physically or chemically transform the same. The reactor comprises a vertical, electrically insulated sleeve disposed at the upper end with a hollow torch of a conventional structure, for use to generate a plasma column. A gas is tangentially injected into the torch to create a vortex inside the same. The material to be treated is dropped, in powder form, vertically downward inside the sleeve from the upper end thereof, beside the hollow torch, so as to form a substantially uniform cylindrical curtain of particles falling down into the sleeve. The particles that are centrifugally projected against the internal wall of the sleeve by the vortex escaping from the hollow torch, entirely cover the internal wall of the sleeve and shield, while simultaneously being treated by heat generated by the plasma arc column. The reactor further comprises a crucible positioned under the sleeve to collect the treated particles in molten form, which drip down from the sleeve at the lower end thereof. The plasma column may be generated by the hollow torch exclusively, when the reactor is intended to be used in a non-transferred arc mode. The reactor may also be used in a transferred arc mode. In such a case, the arc is transferred to a melt contained in the crucible. Another electrode is provided for this purpose at the bottom of this crucible, and is electrically connected to the power supply.

Electrochemical and Electrocatalytic Behavior of an Iron‐Base Amorphous Alloy in Alkaline Solutions at 70°C

Abstract: An alloy exhibiting high electrocatalytic activity for the hydrogen evolution reaction (HER) has been prepared by anodic oxidation of amorphous in 30 weight percent (w/o) at 70°C. Electrochemical studies show that the anodic process involves a dissolution‐precipitation mechanism for the Fe(II) species. Surface studies by SEM, EDX, AES, and x‐ray diffraction reveal that the electrode produced is covered by a thick and porous film of . At the beginning of the HER, the oxidized electrode is reduced and fine Fe particles are formed on the amorphous matrix. It is suggested that the reduction mechanism involves also a dissolution‐precipitation process. The iron particles grow and coalesce during the first thousand seconds, producing a highly porous material. After anodic oxidation at 1 mA cm−2 and hydrogen evolution of 104s at −1.3V, the Tafel slope is 77 mV and the exchange current density is 2.3 mA cm−2 in 30 w/o, 70°C.

Empirical model of a current-limiting fuse using EMTP

Abstract: An empirical model is discussed for research on current-limiting (CL) fuses used in distribution system applications. The main characteristic of a CL fuse is that it develops a voltage at its terminals which reduces the amount of energy generated in the protected equipment during a fault. The various stages of fuse operation are modeled using electric components. The model is of limited use, but its simplicity enables a nonexpert to use it without spending months to learn and program a sophisticated model. The model makes it possible to establish which closing angle of source voltage will produce the greatest of I/sup 2/t, assuming a melting time shorter than a quarter of a cycle. The model can also show how the let-through value of I/sup 2/t will be influenced by the voltage versus time profile of the fuse voltage. The electromagnetic transient program, EMTP, proved a useful tool for this development. >

Thermal stability of morpholine additive in the steam-water cycle of CANDU-PHW nuclear power plants

Abstract: La decomposition thermique de la morpholine, un additif ajoute dans les cycles eau-vapeur des centrales nucleaires, a ete etudiee en laboratoire dans un reacteur haute-pression. Les constantes de vitesse de la reaction sont respectivement 2.67, 8.73 et 21.25x10 -7 s -1 aux temperatures de 260, 280 et 300˚C. La cinetique est du premier ordre et l'energie d'activation de 131.9 kJ/mol. L'ammoniac, l'ethanolamine, l'amino-2 ethoxy ethanol, la methylamine, l'ethylamine, l'ethylene glycol et les acides acetique et glycolique ont ete identifies comme principaux produits de decomposition. Un schema reactionnel est propose et il a ete valide en retracant ces composes dans les echantillons d'eau preleves a la centrale nucleaire Gentilly 2

Evaluation of the effectiveness of shielding and filtering of HVDC converter stations

Abstract: The application of the Numerical Electromagnetic Code (NEC) to the problem of EMI (electromagnetic interference) from HVDC (high-voltage direct current) converter stations is investigated, with particular emphasis on evaluating the effectiveness of valve hall shielding and filtering. It is shown that valve hall shielding alone is not effective in reducing the EMI of converter stations. Appropriate combinations of shielding and filtering produce EMI attenuation of the order of 20 to 30 dB. In order to reduce the EMI, the length of busbars and other connecting elements should be reduced to a minimum, both inside and outside valve halls. The location of filters should be chosen to minimize the length of high-frequency return-current paths. >

Effect of fretting in aluminium-to-tin connections

Abstract: The degradation of aluminium-to-tin plated electrical connections under fretting conditions is studied. In addition to contact resistance measurements, scanning electron microscopy (SEM) and X-ray fluorescence (EDX) analyses were used to study the processes involved. The results showed that fretting adversely affects the contact resistance of aluminum-to-tin plated connections, which show a rapid increase and substantial fluctuations after prolonged exposure to fretting. Two sustained plateaus in the contact resistance characteristics were observed: one coinciding with the melting voltage of tin and aluminum, and the other in the range corresponding to the voltage range of the melting, sublimation, and decomposition of the oxides, and vaporization of contact materials. The effects of fretting were reduced significantly by applying higher contact loads. SEM and EDX analysis revealed that considerable damage of the contact zones resulted from the fretting action and substantial exchange of material occurred. >

Dissolution of tin in the presence of Cl − ions at pH 4

Abstract: The anodic dissolution of tin, investigated in an acidic solution at pH 4 containing 0.1–1 M NaCl at 25°C, displays Tafel behavior as long as the electrode surface is bare (E≤−0.5 V vs SCE). The main characteristics can be derived from the proposed dissolution mechanism, i.e $$(\partial E/\partial \log i)_{a_{Cl} } = 40 mV/d.c., (\partial log i/\partial a_{Cl^ - } )_E \approx 1$$ and $$(\partial i/\partial \omega )_{E, a_{Cl^ - } } \approx 0$$ . The mechanism involves two consecutive steps, each corresponding to the transfer of one electron, the second step being rate determining. ForE values anodic to ∼−0.5V vs SCE partial coverage of the surface by a corrosion product is observed and the behavior is no longer Tafelian. From 0.4 to 1V vs SCE, a plateau current is observed on logi vsE curves and the anode is completely covdered by a corrosion product. Results obtained with a rotating disc electrode suggest that the rate-determining step of the dissolution process in this region of potential is the diffusion of an ionic species into the solution.

Measurement of the electromagnetic environment of HVDC converter stations

Abstract: The results of an experimental study on the electromagnetic environment of HVDC (high-voltage direct-current) converter stations are presented. Transient EMI (electromagnetic interference) as well as steady-state RI (radio interference) and TVI (television interference) measurements were made at the Arnott station of BC Hydro and the Chateaguay station of Hydro-Quebec. The maximum values of the electric and magnetic fields measured inside the valve halls of Arnott station are 1.8 kV/m and 3.2 A/m; outside, they are 0.28 kV/m and 0.4 A/m respectively. These values cover the range of normal operation, including start-up and stopping of the converter station. During normal operation of the Chateauguay station, maximum electric and magnetic fields of 0.7 kV/m and 1.1 A/m are measured inside the valve hall; outside, they are below the sensitivity of the measuring system. It is recommended that immunity testing be carried out on electronic equipment to be used either inside or outside the valve halls of converter stations at transient electric and magnetic field levels of 5 kV/m and 10 A/m, respectively, with approximately 1 mu s risetime and 10 mu s duration. >

Digital acquisition and processing of partial discharges during acceptance test of HV transformers

Abstract: A six-channel digital recording system has been developed for monitoring partial discharges (PDs) in the HV insulation of power transformers during acceptance tests. The analog PD signals are converted to digital words describing their apparent charge, polarity and the point on the wave (phase) of the test voltage at which the PD pulse appears. The data are recorded during a 1 s acquisition period, processed, displayed and stored during the time (up to 7 s) the system is preparing for the next acquisition. The complete record of PDs acquired during the test is stored on a hard disk, and specialized programs have been developed for post test evaluation of the transformer performance. Different presentation formats allow easy identification of interference signals induced in the test circuit by external sources, correlation of PD patterns recorded on different transformer windings, and evaluation of changes in PD activity during the test. >

The compensation law and polymer aging and relaxations

Abstract: It has been shown previously by the author (1957, 1984) that the relaxation of polyethylene (PE) can be well described by the rate theory. It is shown here that the rate theory applies to aging at temperatures below the melting temperature. It is also shown that the aging process has different energy parameters on the two sides of a thermodynamic transition. The importance of performing accelerated aging tests within the appropriate temperature range is stressed. >

Influence of paper insulation on acceptable gas-in-oil levels in transformers

Abstract: The influence of cellulose on acceptable gas-in-oil levels in high-voltage transformers as indicated by the value of the CO/sub 2//CO ratio is assessed by means of dissolved-gas analysis. The results presented here are based on 6932 gas-in-oil analyses on 1320 Hydro-Quebec transformers over a period of 20 years. Preliminary results indicate that C/sub 2/H/sub 4/ levels are affected by cellulose participation for both arcing and hot spots. The effect can be felt starting from CO/sub 2//CO ratios >

Influence of iron impurities on the time dependence of the hydrogen evolution reaction on platinum cathodes during electrolysis of 30 w/o KOH

Abstract: The hydrogen evolution reaction (HER) on polished pure platinum cathodes in 30 w/o KOH at 70°C in the absence or presence of dissolved metallic impurities has been investigated at 100 mA cm-2. During the first thousand seconds, the loss of efficiency for the HER, taking the form of an increase in the cathodic overpotential with time, is tentatively attributed to the penetration of atomic hydrogen into the platinum lattice. The deposition of copper and iron, observed after several hours of polarization in the presence of a non-purified electrolyte, is found to be detrimental to the hydrogen discharge. Marked improvement in the electrocatalytic activity of the cathode after 103s in the presence of 14 ppm dissolved iron is ascribed to the formation of small crystallites of pure iron on the cathode surface.

Quantitative model of mononuclear phagocyte lineage proliferation in murine bone marrow.

Abstract: mathematical model are proposed. The first consists of two dividing generations of granulocyte-macrophage colony-forming cells (GM-CFC) and two dividing generations of macrophage colony-forming cells (M-CFC), differentiating into promonocytes (PM) and then Into monocytes (MC). The second version consists of two generatIons of GM-CFC and three generations of M-CFC, followed by PM and MC. Both are compatible with experimental data, and further evidence Is needed to elaborate a unique representatIon. The kinetic constants have been taken from published material whenever possible and estimated from available data and model kinetics In the case of unknown quantities. The models are applIed to a pulse labeling assay, and calculated labeled subpopulatlons are compared with experimental values. Agreement is satIsfactory for both versions in the case of MC, while a calculated PM labeling index falls more rapidly than the experimental values. However, Inconsistency also exists between PM and MC experimental data.

Optimization of transmission towers and foundations based on their minimum cost

Abstract: In order to model the cost of a tower in terms of steel, fabrication, assembly and erection costs, all important parameters have been itemized and their cost models (or variation) have been developed either through direct monitoring of the applicable process (time and motion studies) or through a detailed evaluation undertaken with various steel mills, tower fabricators and transmission line contractors The cost models have been used for tower-foundation optimization of the 1100 km DC line from James Bay to the Des Cantons substation at the southern border of Quebec, Canada An example given shows how a tower weighing significantly more than another can nevertheless be more economical to fabricate and erect Two computer programs, COUPYL for tower costs and COUFON for foundation costs, were written >

A laser-triggered spark gap for 750 kV, 20 ns risetime impulse generator

Abstract: A description is given of a nanosecond-risetime, 750-kV spark gap impulse generator that is triggered by an ultraviolet laser pulse (KrF, lambda =249 nm). The SLITS (SF/sub 6/ laser-induced triggering system) is an add-on fast switching capability that makes use of the existing equipment (Marx, AC or DC) and can be triggered at voltages as low as 10% of the spontaneous breakdown voltage of the gap. The output voltage can be varied simply by adjusting the internal delay of the laser or the source voltage, eliminating the awkward adjustment of the sphere gaps required in a conventional pulse generator. Jitter is reduced too less than 10 ns at 80% of the spontaneous breakdown voltage, making the output waveform highly reproducible. >