Showing papers by "Hydro-Québec published in 1996"

On separating customer and supply side harmonic contributions

Abstract: In this paper, we propose an approach to quantifying the distortion caused by a single customer, when there are many customers in the network. We have described a method for isolating the contributions to waveform distortion from a customer side and the supply side. The voltage and current measurements at a single point are sufficient. This approach will be useful in arriving at equitable ways of settling customer complaints, sharing the cost of waveform distortion through rate structures, penalties, etc. The principle is illustrated using six example loads. The method proposed can be implemented in any power quality measurement device, which monitors the voltage as well as the current harmonics simultaneously.

A closed-form approximation for ground return impedance of underground cables

Abstract: Calculation of the ground return impedance generally requires the evaluation of a complex infinite integral. Converging infinite series that usually converge to the exact value have been known for many years, and most handbook formulas were derived from these series, with only the first one or two terms retained. Several approximations with closed-form solutions have been proposed for overhead lines, but nothing seems to have been done in the case of underground cables. This paper describes a complete, simplified closed-form approximation for the self and mutual impedances of underground cables. The simplified equations are first presented and then related to Pollaczek's and Wedephol's equations. Finally, the errors, which in most cases are very satisfactory, are numerically evaluated.

Methylmercury in a benthic food web of two hydroelectric reservoirs and a natural lake of Northern Québec (Canada)

Abstract: Total mercury (Hg) concentrations in benthic insects from a 14 years old hydroelectric reservoir (La Grande 2) were 2 to 3 times higher than those from a reference lake and, in some groups, up to 7 times. The difference was even more pronounced for methylmercury (MeHg) concentrations, with a mean of 4 fold and a maximum of 12 fold between systems. The enrichment factors (dw) of insects, relative to the substrate in which they reside was around 3 for total Hg and 6 to 22 for MeHg. On the basis of their diet, we have classified the insects into four different trophic levels: detritivores, grazers, grazers-predators and predators. In insects collected in the reservoirs, the McHg:Hg ratio was 20–25% in dipterans-ephemeropterans (detritivores) and 30–40% in trichopterans (grazers), but 60–85% in heteropterans-coleopterans (grazers-predators) and 95% in odonates (predators). The pattern was similar in the lake with slightly lower values. In both systems, the proportion of MeHg increases in direct relation to our defined trophic levels. Given that insects are an important food source for many fish, our results suggest that they are a strong vector of McHg to these fish in hydroelectric reservoirs. The bioavailability of MeHg to insect larvae appears to depend on the nature and composition of the substrate in which they reside.

Plasma atomization: A new process for the production of fine, spherical powders

Abstract: A new atomization process, plasma atomization (P.A.), has been developed to produce fine, spherical powders. Unlike conventional high-pressure atomizers, PA utilizes multiple nontransferred direct-current arc plasmas to accelerate the atomization gas. In the P.A. process, metal wires are fed into the apex of the multiple plasmas, where they melt and are atomized in a single step. This process offers the unique ability to produce spherical powders of reactive metals with a typical average particle size of 40 μm.

Influence of internal mechanical stress and strain on electrical performance of polyethylene electrical treeing resistance

Abstract: Crosslinked polyethylene (XLPE) and low-density polyethylene (LDPE) insulations used in HV cables are not only subjected to electrical and thermal stresses, but also exposed to mechanical stresses, whether residual internal stresses created during the cooling process of the fabrication, external forces when cables are bent during installation or thermomechanical stresses caused by differential thermal expansion between the conductor and the polymeric material. In order to investigate the possible influence of mechanical stresses on dielectric properties of polyethylene, measurements were conducted on pin-plane XLPE and LDPE samples with various magnitudes of residual mechanical stresses around the embedded electrode. The time to inception, the growing rate and the shape of the electrical trees under different voltages are reported in this paper. Specimens with the highest values of residual stresses were found to have the shortest inception times and the longest trees after one hour of aging under different voltages. When the mechanical stress was allowed to relax, the treeing resistance was measured to be significantly improved.

A 735 kV shunt reactors automatic switching system for Hydro-Quebec network

Abstract: Hydro-Quebec has undertaken a major program to upgrade the reliability of its transmission system. Much effort has been directed toward increasing the system's capacity to withstand extreme contingencies, usually caused by multiple incidents or the successive tripping of transmission lines. In order to counter such events, Hydro-Quebec has adopted a defensive scheme. Based entirely on automatic action, this scheme will mainly rely on: a 735 kV shunt reactor switching system (called MAIS); a generation rejection and/or remote load-shedding system (called RPTC); and an underfrequency load-shedding system. The MAIS system, which is the subject of this paper, will be implemented in 22 substations and is required to control voltage on the system after a severe event. Each MAIS system, acting locally, is entirely independent and will close or trip shunt reactors in response to local conditions.

Stainless steel pitting in thiosulfate solutions with electrochemical noise

Abstract: Resistance of stainless steels (SS) to generalized corrosion is provided by growth of a protective thin film of mixed oxides. In aqueous solutions, impurities can destroy this passive laye...

Hydrogen absorption by nanocrystalline and amorphous Fe-Ti with palladium catalyst, produced by ball milling

Abstract: The effects of microstructure on hydrogen absorption in FeTi are reported. Powders of FeTi with different microstructures (nanocrystalline and amorphous) were prepared by high-energy ball-milling. FeTi powders were also modified with small amounts (less than 1 wt%) of palladium catalyst to eliminate activation. Enhancements in hydrogen absorption for both nanocrystalline and amorphous FeTi powders were observed.

Apparatus and method for charging a DC battery

Abstract: The battery charger comprises a power factor correcting and voltage regulating apparatus having an inductor through which current is modulated by a modulator to obtain an efficient regulation and an efficient power factor correction. According to a first embodiment, the modulator comprises two rectifying elements connected to two controllable high frequency bidirectional switch elements. According to a second embodiment, the modulator comprises a rectifying element connected to a controllable high frequency switch. According to a third embodiment, an efficient battery charger is provided. It comprises an inverter including four controllable high frequency bidirectional switch elements connected in a bridge configuration. According to a fourth embodiment, a two-part battery charger is provided. It has an indicator for indicating quality of the coupling between the two parts thereof. According to a fifth embodiment, a two-part battery charger is provided. It has the necessary means for detecting the voltage delivered at the terminals of the battery and using it for controlling its operation.

Interpretation of resistivity sounding measurements in N-layer soil using electrostatic images

Abstract: Geophysical inversion involves the estimation of soil parameters from a set of observations. Multilayer soils are modeled by N horizontal layers with distinct resistivities and depths. For known soil parameters, the apparent resistivity distribution can be computed efficiently from electrostatic images. Since the model responses are generally nonlinear functions of the model parameters, least-squared minimization techniques prove to be useful for evaluating layer resistivities and depths to agree with measurements. This paper demonstrates how electrostatic images can be combined for increasing efficiency in the computation of apparent resistivities and sensitivity factors such as the first and second gradient of the distance with respect to the model parameters. The factors are then used to solve the more demanding task of resistivity interpretation of measurements from Wenner, Schlumberger, Dipole or alternate electrode configurations. Results are presented for two-layer soil and for actual cases with three layer soil.

A New Fuel Cell Electrocatalyst Based on Highly Porous Carbonized Polyacrylonitrile Foam with Very Low Platinum Loading

Abstract: In recent years, interest in the development of a polymer electrolyte fuel cell (PEFC) has considerably increased due to its advantages (e.g., high power density) compared with other fuel cell systems, and its potentials to become the power plant for the next generation, nonpolluting automobile engine. For large scale application of fuel cells, low platinum loading electrode structures are necessary. An electrode based on a highly porous carbonized polyacrylonitrile foam material with very low platinum loading ({approximately} 13 {micro}g/cm{sup 2}) was prepared. The performance of this electrode for oxygen reduction was evaluated and compared with bulk platinum and glassy carbon electrodes.

Thermal aging study of insulating papers used in power transformers

Abstract: Paper is a low-cost base material with outstanding mechanical and electrical properties, which is why it is still a key element in the insulation of electrical apparatus. Under the effect of a variety of factors including temperature, paper can substantially lose its properties, thus jeopardizing the service life of costly equipment. To remedy this situation, new so-called thermally upgraded papers are being made by certain manufacturers. A study carried out jointly by Hydro-Quebec, Electricite de France and the Ecole Nationale Superieure de Chimie de Toulouse has allowed researchers to qualify the thermal resistance of three different types of thermostable paper. These papers have been selected as being representative of what is available on the market today. The paper samples were subjected to two types of thermal aging tests in the presence of mineral oil in order to represent normal condition of operation (150/spl deg/C) as well as thermal failure (hot spot, 200/spl deg/C and 250/spl deg/C). The thermal degradation of the paper insulation is characterized by various physicochemical methods including measurement of the degree of polymerization, determination of 2-furfural in mineral oil by HPLC as well as determination of various sugars (monosaccharides, polysaccharides and anhydrosugars) in the paper using ion chromatography. This last method allows us to verify the formation of cellobiose, which is the real repeat unit of cellulose, as well as that of levoglucosan, which is an anhydrosugar and a precursor of 2-furfural. The evolution of all of these parameters, measured as a function of time, has allowed us to compare the thermal resistance of various insulating papers. The results of this study seem to show that, compared to traditional kraft paper, certain paper types are more susceptible to being thermally upgraded than others. This study also allowed us to demonstrate that the use of an inhibitor in mineral oil (DBPC) does not seem to influence the thermal degradation of these papers.

Critical evaluation and optimization of the thermodynamic properties of liquid tin solutions

Abstract: Thermodynamic and phase equilibrium data for the following 18 elements in molten Sn were collected and critically evaluated: Al, Ca, Ce, Co, Cr, Cu, Fe, H, Mg, Mo, Na, Ni, O, P, S, Se, Si, and Ti. Binary and ternary data were optimized to give polynomial expressions for the excess Gibbs energies as functions of temperature and composition. For some solutes, the optimized expressions are valid over the entire composition range 0 ≤ XSn ≤ 1. In other cases, the expressions apply to Snrich solutions. Solute-solute interaction terms were estimated where data were not available. The optimized Gibbs energy expressions are also presented in the form of interaction parameters, and the equivalence between the polynomial and interaction parameter formalisms is discussed. Through the Kohler equation, or the modified interaction parameter formalism, the thermodynamic properties of the multicomponent solution of 18 elements in Sn can be calculated. The database is suitable for computer storage and manipulation.

On-line tracking of changing harmonics in stressed power systems: application to Hydro-Quebec network

Abstract: This paper applies, to a practical test case, two schemes for determining harmonics in power systems that are not limited to stationary waveforms, but can equally estimate harmonic phasors in waveforms with time-varying amplitudes and changing fundamental frequency. The first scheme relies on the short-time Fourier analysis performed using the fast Fourier transform (FFT) with time-domain windowing and frequency-domain interpolation. Another scheme combines fundamental-frequency tracking with a Kalman filter-based harmonic analyzer, yielding a uniformly sampled, self-synchronizing harmonics tracker. The performance of these advanced measurement schemes for changing harmonics is illustrated convincingly on nonstationary waveforms generated in the EMTP using a realistic series-compensated transmission network.

Electrical aging of extruded dielectric cables: a physical model

Abstract: A model is proposed to describe the electrical aging of polymeric cable insulation. It is based on simple thermodynamic concepts in the Eyring theory and supposes that the first step in electrical aging is essentially a molecular process. The authors' model of electrical aging under AC fields supposes that the molecular-chain deformation which will generate submicrocavities in the amorphous region of the insulation, is essentially a fatigue process. Above a critical field 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 aging. The model confirms that there is a relation between cable endurance and the insulation morphology, and that the size or submicrocavities is ultimately limited by the amorphous-phase thickness.

EMTP modelling of CIGRE benchmark based HVDC transmission system operating with weak AC systems

Abstract: An EMTP based study of a CIGRE benchmark based HVDC system operating with weak AC systems is carried out. The modelled system provides a starting point for (a) educators teaching HVDC transmission courses, and (b) for utility planners to develop their own low-cost dedicated digital simulators for training purposes. In this paper, modelling details of the AC-DC system, DC converters and controls are presented. To validate the control schemes presented, the HVDC system is tested under AC-DC fault conditions. Results obtained from an EMTP-based study under these fault conditions are also presented in this paper.

Human perception of electric fields and ion currents associated with high-voltage DC transmission lines.

Abstract: The objective of this study was to assess the ability of humans to detect the presence of DC electric fields and ion currents. An exposure chamber simulating conditions present in the vicinity of high-voltage DC (HVDC) lines was designed and built for this purpose. In these experiments, the facility was used to expose observers to DC electric fields up to 50 kV/m and ion current densities up to 120 nA/m{sup 2}. Forty-eight volunteers (25 women and 23 men) between the ages of 18 and 57 years served as observers. Perception of DC fields was examined by using two psychophysical methods: an adaptive staircase procedure and a rating method derived from signal-detection theory. Subjects completed three different series of observations by using each of these methods; one was conducted without ion currents, and the other two involved various combinations of electric fields and ion currents. Overall, subjects were significantly more likely to detect DC fields as the intensity increased. Observers were able to detect the presence of DC fields alone, but only at high intensities; the average threshold was 45 kV/m. Except in the most sensitive individuals, ion current densities up to 60 nA/m{sup 2} did not significantly facilitate the detectionmore » of DC fields. However, higher ion current densities were associated with a substantial lowering of sensory thresholds in a large majority of observers. Data analysis also revealed large variations in perceptual thresholds among observers. Normative data indicating DC field and ion current intensities that can be detected by 50% of all observers are provided. In addition, for the most sensitive observers, several other detection proportions were derived from the distribution of individual detection capabilities. These data can form the basis for environmental guidelines relating to the design of HVDC lines.« less

Electrooxidation of stainless steel AISI 304 in carbonate aqueous solution at pH 8

Abstract: The electrochemical behaviour of stainless steel AISI 304 (SS304) has been investigated in deaerated 0.1–1 m NaHCO3 solutions at pH 8 using a rotating disc electrode. The polarization curves are characterized by a broad range of passivity at low potentials (−0.8 to 0.3 V), a depassivation region at 0.4 V vs SCE and, at high potentials (0.5 to 0.85 V), a passive region before oxygen evolution. In the low potential range, the SS304 electrode behaves like a Cr-rich metallic phase, and the dissolution of Fe2+ ions into the solution is hindered by the formation of a Cr2O3 layer. As the potential reaches 0.4V, the oxidation-dissolution of Cr(iii) oxide/hydroxide to CrO4 2 ions occurs, with the participation of bicarbonate/carbonate as a catalyst in the dissolution reaction. Since the chromium oxide/hydroxide dissolution and subsequent surface enrichment of iron oxides occur, the applied potential, exposure time and oxidation charge have a considerable effect on the passive film properties. At high potentials, the presence of a passive film of iron oxides/hydroxides or oxyhydroxides plays a key role in the SS304 passivity with the presence of Fe(vi) species incorporated or adsorbed into the passive films. Colouration of the SS304 surface is observed in the second passive region. A film of a uniform gold colour formed on SS304, mild steel 1024 and iron in carbonate and borate solutions at pH 8. The colour of the electrode surfaces remain unchanged in air and in solutions at positive potential but it disappears at open-circuit potential or is easily reduced in the first negative-going potential scan.

Calorimetric ac loss measurements of silver sheathed Bi-2223 superconducting tapes

Abstract: A new calorimetric method has been developed to measure ac losses in superconductors. Calibration of the losses requires a reference heater of the same size and shape as the superconductor mounted in a symmetric environment. Its main advantage is the direct determination of the total losses. Variations of the method include a null technique and averaging of the main Fourier component to reduce noise effects. The method has been tested on Bi-2223 tapes and gives the expected hysteresis losses as well as a frequency independent loss which can be attributed to flux creep. The measured losses are similar to those obtained by other groups with other methods.

Experimental investigation on the dynamic behavior of flexible conductors between substation equipment during an earthquake

Abstract: The effects of connections made of flexible conductors must be included in the seismic design of substation equipment. A common practice is to take account of their effects as static loading only, providing sufficient slack to permit the expected relative displacement between interconnected equipment during an earthquake. This paper presents the approach and the results of an experimental study performed to investigate the significance of the dynamic behavior of connections made of flexible conductors under earthquake excitation. It is found that they can be excited in resonance and generate significant forces on the equipment to which they are interconnected, even when sufficient slack is provided. The study shows that the dynamic reactions of connections must be considered for the proper design of substation equipment. A method of establishing the natural frequencies of connections likely to be excited during an earthquake is proposed.

Mitigation of circuit breaker transient recovery voltages associated with current limiting reactors

Abstract: BC Hydro and Hydro-Quebec utilize current limiting reactors on medium voltage distribution feeders to limit the magnitude of fault current. The reactors make a significant contribution to the severity of the transient recovery voltage experienced by feeder and bus circuit breakers on clearing feeder faults. Based on the conclusions of an investigation of actual circuit breaker failures while performing this duty, the mitigation of the transient recovery voltage associated with the reactors is described.

Experience with optimization software for distribution system planning

Abstract: This paper presents a computerized optimization tool used to improve the planning of major investments in the distribution system over the coming years. The system allows the planner to identify, from load forecasts, data on the existing distribution system and all future projects, the projects to be carried out, together with the commissioning year, in such a way that the investment and maintenance costs, as well as the cost of losses are minimized over the planning horizon. The system is based on a dynamic model of network planning solved by a heuristic method comprising five phases. At the present time, the two first phases are implemented and the software is used by Hydro-Quebec planners. Substantial savings on investment, maintenance and loss costs have already been realized.

Impedance study of the passive film on stainless steel 304 in pH 8 carbonate solution

Abstract: The effects of applied d.c. potential and polarization time on the passivation of stainless steel 304 (SS304) were investigated in deaerated 1 M NaHCo3 aqueous solutions at pH 8. Electrochemical impedance spectroscopy was used in conjunction with a rotating disc electrode. The data were analysed by considering an equivalent circuit. The changes in impedance parameters at applied d.c. potential signal changes in the properties of passive films on SS304 and allow to distinguish the parameters at low potential (−0.6 to 0.3 V vs SCE) from a different one at high potential (0.5 to 0.8 V vs SCE). The oxidation reactions were controlled by both charge transfer and mass transfer processes. Diffusional resistance was high for both passive films and was considered to represent the resistance to movement of ions or vacancies through the surface layer of oxide films. It is deduced that the passive film present in the low potential region is partially dissolved at 0.4 V vs SCE and that a new passive film is formed in the higher potential region. The equivalent circuit used to obtain the best fit and the fitting parameters was dependent on the electrode potential and the polarization time. The reproducibility of the impedance spectra at constant potentials demonstrate that the passive film formation is highly irreversible process. No traces of localized corrosion were detected but, for a high potential and long polarization time, the electrode surface coloration to a uniform gold colour confirms the film thickening.