Showing papers by "Hydro-Québec published in 1994"

Modeling of lightning incidence to tall structures. I. Theory

Abstract: The paper generalizes a physical approach to assess negative downward lightning incidence to apply to tall masts and hilly regions. Criteria for occurrence of an upward flash from a tall structure under negative cloud are formulated, both for flat and hilly terrain. Finally the effect of structure on statistical stroke current distribution is analytically investigated. >

New live line tester for porcelain suspension insulators on high-voltage power lines

Abstract: Until now at Hydro-Quebec, overhead power transmission line porcelain insulators had been tested by the buzz method which simply consists in applying a short-circuit to each insulator in a string and listening for a buzz-like sound indicating a good insulator. However, safety considerations that preclude short-circuiting insulators and other disadvantages of that method have led Hydro-Quebec to undertake and complete the development of a new insulator tester. The working principle of this new device is based on the automatic measurement and recording of the electric field along the insulator string which decreases considerably in front of an internally-shorted insulator. The tester is slid along the string while the insulators are counted automatically. The information from tests on up to 200 strings can be stored in the device to be later transferred in a host computer for interpretation and/or permanent storage. The new tester also gives information on voltage distribution along the insulator strings which can be useful for the design of future power transmission lines. >

Modeling of lightning incidence to tall structures. II. Application

Abstract: For pt.I see ibid., vol.9, no.1, p.162-71 (1994). The present paper comprises an extensive computer investigation of lightning incidence to tall masts, based on a theory presented in part I, for both flat and hilly regions. The investigation covers both downward negative lightning incidence and upward flash from tall masts under negative cloud. The factors investigated include: mast height, statistical distribution of the ground electric field, as well as mountain height and topology. Predicted lightning incidence and probability of upward flash are successfully verified against extensive field observations. >

Discrimination between PD pulse shapes using different neural network paradigms

Abstract: A comparison has been carried out on the partial discharge (PD) pulse shape recognition capabilities of neural networks, using the nearest neighbor classifier, learning vector quantization and multilayer perceptron paradigms. The PD pattern recognition capabilities were assessed on artificial cylindrical cavities of different sizes. The performance of the three neural network paradigms was found to be equivalent in all respects, with the exception of the case where a distinction was required between small cavity sizes; under those circumstances, the learning vector quantization paradigm was distinctly superior to the two other paradigms. The experimental results also demonstrated that, even with simple metallic electrode cavities, the discrimination capabilities of the three types of neural networks are not always perfect. >

Nanocrystalline Ni-Mo alloys and their application in electrocatalysis

Abstract: The structural and electrocatalytic properties of metastable Ni-Mo alloys have been investigated for the hydrogen evolution reaction in alkaline solutions. Amorphous and nanocrystalline phases have been prepared by mechanically alloying the elemental components under various milling conditions. Fcc nanocrystals are formed when the Mo concentration is smaller than 30 at. %. The nanocrystalline state becomes unstable with respect to the amorphous phase when the Mo content in the solid solution exceeds 30 at. %. The electroactive phase for the hydrogen evolution reaction in alkaline solutions is the nanocrystalline supersaturated solid solution. The presence of oxygen during the milling process improves the properties of the alloys.

Structural and magnetic characterization of granular Y1Ba2Cu3O7−δ nanocrystalline powders

Abstract: High energy ball milling has been used to produce nanocrystalline Y1Ba2Cu3O7-δ powders. These powders are being used as starting materials for manufacturing superconducting textured wires by a solid state recrystallization process. Magnetic and microstructural characterizations were performed as a function of milling time. The milling reduces the average crystal size and creates low and high-angle grain boundaries which increase the granularity of the superconductor. As a result, the long-range order on the oxygen sublattice and on the yttrium and barium sites is destroyed. A transition from orthorhombic to tetragonal and finally to a cubic metastable phase is observed. Total loss of superconductivity occurs after about 1 h of milling. Prior to this time, superconductivity can partially be restored by room-temperature aging. High-temperature heat treatment of the nanocrystalline phase produces a tetragonal structure with c = 3a.

Graphitization and particle size analysis of pyrolyzed cobalt phthalocyanine/carbon catalysts for oxygen reduction in fuel cells

Abstract: Cobalt phthalocyanine (CoPc) adsorbed on a carbon black support (Vulcan XC-72) and pyrolyzed at various temperatures is a potential catalyst for the reduction of oxygen in solid polymer electrolyte fuel cells. This paper reports the results of the microstructural characterization of β-Co particles that are formed after pyrolysis at temperatures of 700, 900, and 1050 °C. Transmission electron microscopy (TEM) indicated that (i) for a pyrolysis temperature of 700 °C, the size distribution of the Co particles is bell-shaped with an average value of 4 nm and mean deviation of 1 nm; (ii) for a pyrolysis temperature of 900 °C, the Co particle size distribution skews toward larger particle sizes. The most probable particle size is about 6 nm, and the average particle size is 13 nm. By comparison with the TEM results, the particle size estimated from a spectroscopic method like x-ray absorption is underestimated, while from x-ray diffraction is overestimated. The TEM images show that Co particles act as heterogeneous nucleation sites for the graphitization of amorphous carbon. It is shown that (i), at least for pyrolysis temperature of 900 °C and above, most of the β-Co particles are surrounded by a shell of graphitic carbon layers that appears to protect the particles from corrosion in acidic media; (ii) for pyrolysis temperature of 1050 °C, graphite strings also appear throughout the amorphous carbon support in areas where Co particles are not detected. This behavior was not observed after pyrolysis of as-received carbon support at 1050 °C. These results allow for a better understanding of the behavior of the pyrolyzed catalysts immersed in an acidic solution or in a solid polymer fuel cell.

Three-transfer-function approach for building phenomenological models of synchronous machines

Abstract: The established practice of using only two transfer functions when modelling the d-axis of a synchronous machine at rest is physically questionable since it leads, from the network theory point of view, to ambiguous equivalent circuit realisations. The paper provides analytical and experimental evidence for the claim that a triple transfer function (3TF) parameterisation is the only one general enough to cope with both stator and rotor voltage perturbations, thus broadening the range of physical phenomena the model can account for. It is proposed that the third transfer function can be conveniently chosen from three closely related impedance operators, only two of which are classical. Using standstill frequency response test data from the Ontario Hydro's Lambton generator, it is shown that, for a given number of damper windings (3, 5, or 6), at least one equivalent circuit exists capable of accurately modelling the stator input inductance Ld(s) and the short-circuit stator to rotor transfer function sG(s), but failing dramatically to fit the third transfer function, i.e. the stator to field transfer inductance with field open Lafo(s). Only the 3TF approach consistently leads to equivalent circuits with definite phenomenological significance, thus enhancing the understanding of machine behaviour as affected by damper-cage design and excitation system.

AC/DC harmonic interactions in the presence of GIC for the Quebec-New England Phase II HVDC transmission

Abstract: During the spring of 1991, several severe geomagnetic disturbances were recorded in North America, and particularly in Northern Quebec, where Hydro-Quebec's La Grande generation complex and transmission system are located. As a result of these disturbances, the Quebec-New England Phase II HVDC system was affected by transformer saturation and harmonic voltage distortion due to geomagnetic induced current (GIC). This paper presents an analysis of the phenomenon observed at Radisson, the northernmost terminal in the system. A central issue which is discussed in the paper is the reflection of the DC side impedance to the AC side for operating converters, and the effect of this reflection on the harmonic impedance as viewed from the AC side. >

Monitoring living tissues by electrical impedance spectroscopy

Abstract: Solving the experimental difficulties associated with measurement of the electrical impedance of living tissues gives access to valuable tissue compartment parameters which are sensed within seconds using minimally invasive, simple metallic electrodes. Extracellular conductivity and cell membrane capacitance can be followed over time under conditions of metabolic toxicity, perfusion loss and thermal stress in liver, brain cortex, and muscle, respectively. Application of this technique in burns therapy allows an accurate estimation of the severity of thermal injury to skeletal muscle, supporting predictions on tissue survival.

Multiphase brushless AC electric machine

Abstract: The multiphase brushless AC electric machine comprises a stator frame having a surface provided with parallel slots and projections disposed alternately, each of the openings being substantially as wide as the widest width of the corresponding slot; and a rotor frame having a surface provided with permanent magnet means having respective surface sections facing the slots and projections. All of the surface sections of the magnet means produce a magnetic flux density having a component average amplitude B r (θ) perpendicular to the corresponding surface of the stator, which is substantially defined by the following equation: B.sub.r (θ)=M.sub.r (θ)·L.sub.a (θ)/L.sub.v (θ) where L a (θ) is defined by the following equation: ##EQU1## where θ is a position angle in radians with respect to a reference position on the rotor frame; B r (θ) is the component average amplitude at the position angle θ; L v (θ) is a gap distance between the projections and the surface of the rotor frame at the position angle θ; M r (θ) is a component of residual induction of the magnet means at the position angle θ, M r (θ) being perpendicular to the corresponding surface of the stator, M r (θ) being alternative with a period corresponding to 4π/K; K is an even number representative of all of the surface sections; and C is an arbitrary constant. The present invention is also concerned with a method of operating the multiphase brushless AC electric machine.

Accurate voltage phasor measurement in a series-compensated network

Abstract: This paper describes the feasibility studies concerning an accurate voltage phasor measurement in a series-compensated network undergoing large disturbances. The principal modes of distortions in such a network are described. Some of these modes are changing with the fundamental frequency. The phasor evaluation is based on a new digital filter approach in which the fundamental frequency is estimated using a least-square algorithm. The need to have special potential (voltage) transformers is also discussed. This approach would be used in a shunt reactor switching scheme for an overall voltage control of a transmission network. >

Conductor section for a stator frame of a polyphase dynamoelectric machine

Abstract: The conductor section is for a stator frame of a polyphase dynamoelectric machine. The stator frame is provided with a series of elongated parallel slots for receiving respectively conductor sections. The conductor section comprises two parallel conductor sides of substantially rectangular cross section adapted to fit respectively into two corresponding parallel slots of the stator frame, the two sides defining a plane; and at least one conductor head of substantially rectangular cross section, connecting two adjacent ends of the parallel sides. The head shows a substantially U-shaped body when seen from a top view perpendicular to the plane, and a waved-shape body when seen from a front view contained in the plane. The head having top and bottom surfaces facing only one side of the plane from one end of the head to the other end thereof. Methods for mounting conductor sections of stator winding onto a circular shaped stator frame are also described.

Stability transfer limit calculation in a power transmission network

Abstract: A transient or voltage stability transfer limit is calculated for a power network having at least two independent AC generators supplying a common load via separate AC transmission lines having at least one bus. Steady state values for variable characteristic electrical parameters of variable elements of the network are determined based on particular values for power transferred by the transmission lines. Static values for passive characteristic electrical parameters of passive conductive elements of the network are determined. A contingency resulting in a sudden change of at least one of the variable electrical parameters and the passive electrical parameters is selected. A post contingency steady state value for a voltage at one of the buses is calculated. A voltage over time during a transition period at the bus is calculated, the transition period extending in time from a start of the contingency through a discontinuity during which the voltage is abnormally altered, and recovery during which the voltage will tend toward a steady state terminal value. An integral sum of squares of a difference between the post contingency steady state voltage and the transition period voltage over the transition period is calculated to obtain an energy value. Using two such energy values from two power values, a transfer limit estimate for the transmission line is obtained as being an asymptote of the energy values, the energy values being an inverse function of the stability limit less the power value.

On equivalent circuit structures for empirical modeling of turbine-generators

Abstract: This work is aimed at extending a discussion offered concerning a paper presented at the 1993 IEEE/PES Winter Meeting (Boldea and Nasar, 1987) which attempted to show that the "differential leakage" was not required and, in general, seriously questioned the need for a third-order model. Unfortunately, the simplifications were possible only using a per-unit system not compatible with industry standards and current engineering practices for saturation analysis. In this paper, mathematical reasoning is combined with maximum-likelihood estimation from actual SSFR data to show that, for network structures preserving the main-field magnetizing impedance, the differential leakage contributes significantly to the dynamic response and proves mandatory for adequately modeling rotor impedance. Besides, the claim made that a third-order model may not be sufficiently parsimonious is not home out by further verification of the author's own data end extensive experience with real SSFR data from a 1100 MVA turbine-generator. >

Power steering system

Abstract: A power steering system for use in a land vehicle with separately driven steerable wheels (30). Servo-control is produced by creating a differential torque by means of motors (40). The servo-control is provided when a torque is applied to the steering wheel (10), by generating a differential torque through the motors (40) to create servo-control forces due to virtual lever arms (39) defined between the centre of traction (34) of each wheel (30) and the imaginary intersection between the ground and a virtual extension of the steering axis (32) of the wheel (30).

Extensive evaluation of high performance protection relays for the Hydro-Quebec series compensated network

Abstract: This paper reports on an extensive study to compare the performance of 8 preselected high performance power line protection systems on the Hydro-Quebec series compensated network. The paper first presents an evaluation of the commissioning aspects and manufacturing quality of the tested relays. It then describes the simulated network, the relay testing procedure, and the laboratory test results obtained on a modern real time power system simulator. Published results of relay performance on series compensated lines are scarce and this paper provides valuable information for utility protection engineers. A total of 115,000 network disturbances were simulated and recorded on 20 different 735 kV lines; fractional test results for 84,030 cases are presented in the paper. The approach using real time power system simulation proved to be an efficient technique for evaluating protection relay performance. The laboratory test results demonstrated that the two best protection principles to be applied on the Hydro-Quebec series compensated network are those based on current differential and segregated phase comparison. The analysis does not take into account telecommunication requirements or other external constraints. >

Comparative study of copper behaviour in bicarbonate and phosphate aqueous solutions and effect of chloride ions

Abstract: Copper oxidation in aqueous solutions of pH 8 showed some differences in the presence of bicarbonate and phosphate ions. The bicarbonate ions did not interfere with Cu2O film formation but the Cu2+ ions were stabilized by the complexing action of CO2−3anions. In phosphate solutions, copper dissolved in the range of potentials associated with the Cu(I) oxidation state and the Cu(II) compound on the surface resulted in an extensive passivation region. In both solutions, a higher ion concentration caused an increase in the anodic current, suggesting that the copper ions were stabilized by the complexing action of the electrolyte. The copper oxidation current in a bicarbonate solution was higher than that observed in a phosphate solution of the same concentration. The thickness of the Cu(II) film rather than the Cu(I) layer appears to be the important factor related to the stability of the passive layer on the copper surface. The shift in the breakdown potential toward more positive values indicates that both bicarbonate and phosphate ions inhibit localized corrosion due to the presence of chloride ions. Their protective effect depends on the concentration of each anion, although the concentration of chloride ions necessary for pitting is larger in phosphate solutions than in bicarbonate solutions. In both solutions, long-term immersion of copper under anodic polarization results in the precipitation of a protective coating.

Proliferation‐differentiation pathways of murine haemopoiesis: correlation of lineage fluxes

Abstract: . A quantitative analysis of literature data on muiine bone marrow haemopoiesis was performed in order to determine how the haemolpoietic system fulfils requirements of cell turnover in the normal steady state. In particular, the production rates (fluxes) of erythrocytes, megakaryocytes, monocytes, neutrophils, eosinophils, basophils and mast cells have been calculated and normalized. Subsequently, based on available data on relationships of various lineages, a working model of the developmental schema of haemopoiesis was derived. Since, according to the principle of conservation, the effluxes of all lineages from bone marrow in the steady state must be equal to effluxes from the compartments of respective precursors divided by the coefficient of multiplication, the correlation of lineage fluxes was used to determine the position of branching points. It was concluded that all the quantita.tive data on lineage proliferation in the normal steady state in vivo, available for analysis, are fully consistent with a simple binary model of the sequential type, similar to that suggested by Brown and coworkers (Brown G., Jones NA, Bunce CM, Owen PJ, IPatton WN. (1988) Haemopoiesis: a lottery or determinism?Differentiation, 39, 83).

Interfacial breakdown in cable joints

Abstract: Electrical breakdown at the interface of two dielectric surfaces is a complex phenomenon and is one of the major causes of failure for cable accessories. The dielectric strength of an interface increases with interfacial pressure and is substantially improved by the presence of electrical insulating greases. In order to better understand this phenomenon, interfacial breakdown experiments were carried out on interfaces found in cable joints. Measurements of breakdown voltage, interfacial pressure and grease conductivity were made to provide a comprehensive set of data for the investigation. This paper describes the experimental approach and discusses the preliminary results of the investigation on breakdown voltages found in new and field-aged cable splices. >

Phenomenological models of large synchronous machines from short-circuit tests during commissioning-a classical/modern approach

Abstract: To date, synchronous-machine short-circuit oscillograms have been analyzed, either numerically or graphically by applying the basic simplified concepts set forth in ANSI Standard 115. This paper attempts to evaluate the pitfalls of this approach by comparing its results with those obtained using modern multiresponse estimation techniques. Within the two-axis theory framework, the phenomenological models considered are the ANSI dynamic constants, operational impedances and equivalent circuits. Each model containing a damper winding in each axis is identified independently from the three phase currents using a constrained nonlinear estimation scheme; the cost function is chosen as a suitable norm of the weighted-covariance matrix of residual errors. Short-circuit data obtained during the commissioning of 360 MVA synchronous condensers at Manitoba Hydro's Dorsey substation are extensively analyzed for retrieving the pertinent stability constants. It is found that the graphically-oriented approach, even carefully executed on a microcomputer in accordance with Std-115 recommendations, still proves somewhat unsatisfactory, whereas modern estimation techniques applied to the same data provide consistent parameters for all models, even for the weakly excited q-axis. >

Method and apparatus for starting up a synchronous machine

Abstract: The method and the apparatus are for starting up a synchronous machine having a rotor and a stator provided with a winding. The rotor has an initial position with respect to the stator. The method comprises the steps of (a) initializing a starting phase of a first vectorial sum of successive vectorial sums of currents to be applied to the winding; (b) applying successive vectorial sums of currents to the winding; (c) detecting, for each of the vectorial sums of currents applied in step (b), a movement of the rotor and a direction thereof; (d) compensating, for each of the movement and direction detected in step (c), the phase of a subsequent vectorial sum of currents applied to the winding to bring back the rotor towards its initial position; (e) detecting whether the rotor has moved with respect to the stator after applying of the successive vectorial sums of currents and either increasing the starting phase by a value different from a multiple of 180 electrical degrees if the rotor has not moved and returning to step (b), or going to a step (f); and (f) after step (e), storing the phase value of the last of the successive vectorial sums applied to the winding, whereby said machine is now ready to operate from the phase value stored in step (f).

Improved control systems simulation in the EMTP through compensation

Abstract: The control systems, devices and phenomena modelled in TACS, and the electric network modeled in EMTP are solved separately with one-time-step error at the interface. This provides an efficient time-step solution, but there can be numerical stability and accuracy problems associated with the one-time-step error. This paper shows a technique which can eliminate the time delay, without having to use a simultaneous EMTP and TACS solution. >

Dross treatment in a rotary arc furnace with graphite electrodes

Abstract: Aluminum baths are always covered with a layer of dross resulting from the aluminum surface oxidation. This dross represents 1–10% of the melt and may contain up to 75wt.% aluminum. Since aluminum production is highly energy intensive, dross recycling is very attractive from both energy and economic standpoints. The conventional recycling process using salt rotary furnaces is thermally inefficient and environmentally unacceptable because of the production of salt slags. Hydro-Quebec has developed a new technology using a rotary arc furnace with graphite electrodes. This process provides aluminum recovery rates of 80–90%, using a highly energy efficient, environmentally sound production method.

Process for assembling LPB batteries

Abstract: Before laminating the electrolyte with the positive electrode, the electrolyte is heated at a temperature higher than its softening temperature or the melting temperature of its crystallites, and the heated electrolyte is allowed to return to room temperature before laminating the positive electrode to the electrolyte at room temperature. This enables to prevent the formation of wrinkles on the collector of the positive electrode.

Influence of mechanical strain and stress on the electrical performance of XLPE cable insulation

Abstract: XLPE insulation used in high-voltage cables is not only subjected to electrical stress but also to mechanical strains, either from internal residual strains created during manufacturing or externally applied when the cable is bent sharply. Due to thermally activated viscoelastic motion in the polymeric material, the original mechanical stress responsible for the strain may be completely or partly relaxed, with the permanent strain remaining unchanged. It is generally accepted that mechanical strain has a strong influence on the structural integrity and electrical performance of polymeric insulating materials. However, the influence of mechanical strain on the life and performance of insulating materials has still to be fully ascertained, since it depends on the nature (compression or tensile) and the direction of the strain and the magnitude of the remaining (unrelaxed) mechanical stress. In this paper, long-term and short-term breakdown tests were conducted on XLPE ribbon samples. To isolate the effect of the strain, a series of samples was drawn at different drawing ratios; the drawing rate and temperature allowed a situation of near-total stress relaxation. Results are presented for samples subjected to simultaneous tensile mechanical and electrical stress. >