Showing papers by "Hydro-Québec published in 1988"

Impulse testing of power transformers using the transfer function method

Abstract: The transfer function of a transformer winding is deconvoluted in the frequency domain from the digitally recorded neutral current and high voltage applied during impulse tests. The integrity of the winding insulation is determined by comparing the transfer function obtained at full and reduced test voltage. Differences between the transfer function plots reveal local breakdowns in the winding that can be dissociated from partial discharges. Thus the method permits unambiguous acceptance or rejection if the transformer and, since the transfer function is theoretically immune to changes in the applied impulse, also allows evaluation of the chopped-impulse test. Some 100 windings of large HV power transformers have been tested using the transfer function method, which on several occasions has revealed transformer faults as well a test setup problems that would have been missed or misinterpreted by conventional techniques. >

A comprehensive thermodynamic investigation of water-ethylene glycol mixtures at 5, 25 and 45°C

Abstract: A detailed thermodynamic study of water (W)-ethylene glycol (EG) mixtures has been carried out as function of temperature (5, 25 and 45°C) and over the entire composition range. The data comprise heats of mixing, densities, heat capacities and compression coefficients. Using excess free energy data from earlier work, molar excess functions were calculated for free energies GE, enthalpies HE and entropies TSE, volumes VE, isobaric and isochoric heat capacities C P E , C V E , adiabatic and isothermal compression KE, K T E and thermal expansion EE, as well as the temperature derivatives of K, C and E functions. The corresponding partial molar quantities were also calculated except for G, H and S and are reported for both EG and W. Also calculated were cohesive energy density, internal pressure and Kirkwood-Buff integrals. The data reported here for EG-W mixtures are compared with similar data for other mixtures as available in order to gain insight into: 1) the relative discriminating ability of various thermodynamic coefficients towards weak cooperative intermolecular interactions in liquids; 2) the quantitative similarities and differences between liquid water and ethylene glycol; 3) the intermolecular phenomena which dominate the properties of EG-W mixtures of varying composition; 4) the usefulness of a qualtitative description of liquid water proposed by Lumry et al. which involves hydrogen-bonding interactions, hydrogen-bonding connectivity and small cooperative fluctuation units.

Stability of Bernstein–Greene–Kruskal plasma equilibria. Numerical experiments over a long time

Abstract: Bernstein–Greene–Kruskal (BGK) equilibria for a Vlasov plasma consisting of a periodic structure exhibiting depressions or ‘‘holes’’ in phase space are under consideration. Marginal stability analysis indicates that such structures are unstable when the system contains at least two holes. An Eulerian numerical code is developed allowing noiseless information on the long time phase space behavior (about 103ω−1p) to be obtained. Starting with equilibria with up to six holes, it is shown that the final state is given by a structure with only one large hole, the initial instability inducing coalescences of the different holes. On the other hand, starting with a homogeneous two‐stream plasma it is shown that, in a first step, a BGK periodic structure appears with a number of holes proportional to the length of the system, followed, in a second step, by a coalescence of the holes to always end up with the above mentioned one large hole structure.

Occupational and residential 60-Hz electromagnetic fields and high-frequency electric transients: exposure assessment using a new dosimeter.

Abstract: One problem that has limited past epidemiologic studies of cancer and exposure to extremely low-frequency (0–100 Hz) electric and magnetic fields has been the lack of adequate methods for assessing personal exposure to these fields. A new 60-Hz electromagnetic field dosimeter was tested to assess occupational and residential exposures of a group of electrical utility workers and a comparison background group over a 7-day period. Comparing work periods only, utility workers' exposures were significantly higher than background levels by a factor of about 10 for electric (E) and magnetic (B) fields and by a factor of 171 for high-frequency transient electric (HFTE) fields. When overall weekly time-weighted averages combining work and nonwork exposures were compared, ratios of the exposed to background groups were lower. B and HFTE exposure ratios remained statistically significant, with values of 3.5 and 58, respectively, whereas the electric field exposure ratio was no longer significant, with a value of 1....

Thin electrode supported on electronically conductive sheet and process of manufacture

Abstract: Process of manufacturing thin electrodes, supported on an electronically conductive sheet, the electrodes being made from an element selected from lithium, lithium alloy, or doped lithium, whose melting point does not differ from the melting point of lithium by ±50° C. and whose thickness is constant, from a roller of the sheet and a source of the element. According to the invention, there is provided a bath of the element in molten state, the sheet is continuously unrolled, a constant quantity of the molten element is continuously applied on one of the two faces of the sheet, so as to produce a film on the sheet, whose thickness is constant and between about 0.1 and about 40μ and whose surface is homogeneous and uniform. The process is carried out in such a manner that the molten element is prevented from solidifying while in contact with the sheet, and the solidification of the element on the sheet takes place after formation of the film on the sheet. Electrode made of a sheet coated with a layer of lithium whose thickness is 0.1 to 40μ.

Electrical conduction of polyethylene below and above its melting point

Abstract: The electrical conduction of low-density polyethylene (LDPE) has been investigated between 20 degrees C and 150 degrees C and up to 1 MV/cm. Special molded specimens and a self-compensating test cell were used; particular care has been taken in the control of experimental conditions. Absorption currents show broad maxima, while resorption currents display polarity reversal. Steady-state currents increase with a power law of the electrical field, and they tend to saturate at high fields and temperatures. Results are discussed in the framework of space-charge-limited conduction and dispersive hopping transport models. >

Measurement of switching transients in 735 kV substations and assessment of their severity for transformer insulation

Abstract: An automatic measuring system that digitally records transients generated by EHV-transmission-system switching operations and lightning strokes has been developed. The severity of these transients was assessed by comparing them with test voltages applied to the transformers during acceptance tests. In order to quantify in-service transients with respect to the impulse-test voltages, the frequency spectra of the time-domain records were calculated and expressed as a percentage of the test level. The presence of high-frequency winding oscillations was revealed by simultaneous measurements of the bushing voltage and neutral current. The results of these measurements are presented in the form of a transfer function, which can also be used to detect winding displacements in service. >

Self-powered electrical measuring system isolated from electrical perturbances

Abstract: A self-powered electrical measuring system for measuring current in a high voltage circuit. The system comprises a Rogowski coreless coil disposed about a conductor for sensing current flowing in the conductor and producing a voltage signal proportional to the magnitude of the current. An electronic conditioning circuit is provided for conditioning the voltage signal for transmission by optical link means to a remote receiver operating which is at ground potential and totally isolated from the measuring system in the high voltage circuit. A floating supply circuit comprising a tapping coil having a magnetic core disposed about the conductor is provided whereby to produce a supply voltage for the electronic conditioning circuit means.

Variable-voltage application for insulator pollution tests

Abstract: The speed and precision of salt fog contamination testing of insulators is improved using stepwise voltage application to give numerous flashovers in a single test. A similar technique for the clean fog method, which gives comparable results to conventional tests at constant voltage, is proposed. Valuable information on the performance of naturally contaminated ceramic insulators, directly comparable to that for artificial contamination, can also be obtained. With the same technique, the performance of naturally or artificially aged and contaminated nonceramic insulators can be studied and the aging process monitored as it proceeds. >

Slip power recovery induction generators for large vertical axis wind turbines

Abstract: Simulation results are presented for the performance of a slip power recovery induction generator coupled to a vertical-axis wind turbine. The suitability of this type of generator for wind-driven applications is discussed. A qualitative comparison with two other alternatives is made, highlighting the basic features of the generator configuration studied. Quantitative simulation analysis showed that it is possible to reduce the ripple in the electrical power substantially with stable operation through various changes in wind speed. Regenerative braking is possible, especially in the upper range of speed, which reduces the wear on the mechanical brakes. The design described ensures smooth motor start-up for the induction machine in the motor-mode. >

Effect of the Nickel Content in the Pitting of Stainless Steels in Low Chloride and Thiosulfate Solutions

Abstract: The effect of the nickel content on the pitting resistance of AISI 304 stainless steel (SS) and Alloys 800 and 600 in chloride-thiosulfate solutions was investigated using two techniques, ...

Influence of anions on the passivity behavior of copper in alkaline solutions

Abstract: The competitive effect of the inorganic anions OH-, Cl-, Br-, I-, ClO-4, NO-3, SO2-4, CO2-3 and phosphates on the behavior of copper in alkaline aqueous solutions at pH 12 was investigated. The nature of changes occurring on the copper surface was analyzed by potentiodynamic and potentiostatic methods in conjunction with different instrumental surface analysis techniques. The influence of these anions on the anodic dissolution of copper was classified into three distinct categories. In the first group, comprising NaCl, NaBr and NaI solutions, copper(I) salts form insoluble, nonprotective films on the metal surface and the copper is expected to dissolve via the formation of CuA( n - 1 )- n complexes. In the second group, comprising NaClO4, Na2SO4 and NaNO3 solutions, substantial dissolution of copper is caused by the formation of easily soluble Cu2+ salts, and copper (II) ions precipitate as hydroxides and oxides. In the third group, the hydroxide, phosphate and carbonate passivate the copper surface. In some solutions the phosphate and carbonate inhibit the anodic dissolution of copper. The aggressive nature of the anions investigated against the passivity of copper increases in the order SO2-4

Density profiles, electric field and energy dissipation in a short gap breakdown: a two-dimensional model

Abstract: A two-dimensional model of the short gap breakdown in He has been developed consisting of conservation equations for electrons, ions and metastable atoms and the Poisson equation. Direct stepwise and Penning ionisation are considered and cathode emission takes into account the ion and metastable impact as well as photo-emission. Time development is followed up to 1.11 mu s, when the electron, ion and metastable densities reach maximum values of 1.6, 25 and 180 (*1010 cm-3) respectively.

Fretting damage in tin-plated aluminum and copper connectors

Abstract: A number of bolted-type tin-plated aluminum and copper connectors commonly used for distribution transformers were examined using scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), Auger electron spectroscopy (AES), X-ray analysis, and optical microscopy. In addition, the contact resistance of the connector contact zones was measured using a point probe. The connectors studied had been removed from service because of unsatisfactory performance under normal operating conditions as manifested either by overheating or instability. The results of the detailed examination show the presence of extensive fretting damage in the contacting surfaces. The fretting debris was composed mainly of tin oxide and oxidized base metal particles. Localized melting and wear of the tin plating down to the underlying substrate were also observed in some of the connectors examined. >

High voltage measuring circuit coupled to the capacitive grounding tap bushing of an HV device

Abstract: A high voltage measuring circuit for broadband measurement of transient signals occurring in high voltage apparatus The measuring circuit is housed in a shielded housing having an input sensing circuit for connection to a capacitive grounded tap of the high voltage apparatus The sensing circuit is connected to an output circuit through an electrical shielded connection The measuring circuit generates output signals which are replicas of the transient signals appearing on the bushing of the high voltage apparatus The broadband of the measuring circuit extends over a frequency range of from about 1 Hz to 1 MHz and has a signal level higher than background noise

Fluid heating device incorporating transformer secondary winding having a single electrical turn and cooling means optimized for heat transfer

Abstract: A fluid heating device which comprises a non-conductive magnetic core having a primary winding of an electrically conductive wire. A secondary electrically conductive jacket surrounds or is concentric with the primary winding in close contact therewith through a thermally conductive and electrically non-conductive medium. The primary winding has an input connection connectible to a voltage supply source. A power control device is connected to the input connection. The secondary electrically conductive jacket has passages therein for the flow of a fluid, at predetermined flow rate, from an input to an output of the passages. The fluid extracts heat from the secondary conductive jacket, generated by joule effect, whereby to heat the fluid and simultaneously cool the jacket to maintain the secondary electrically conductive jacket at a substantially constant temperature.

Computational methods for the analysis of explosions in oil-insulated electrical equipment

Abstract: Two methods are presented for analyzing the dynamic response of electrical equipment tanks completely filled with oil under fault conditions liable to cause explosions. Both methods simulate the same infinite cylindrical model subjected to an eccentric arc, but differ in their approach. The first is based on an analytical formulation of a thin-walled shell containing an incompressible liquid; the solution is obtained by superimposing orthogonal components and numerically integrating the equations of motion. The other approach is more general and involves the use of the highly specialized software PISCES adapted for arc-induced excitation. The method can be applied, after modifications, to the analysis of partially filled equipment such as distribution transformers. Comparison of the computer results provides a means of mutually validating the two methods and thus indicates that the use of PISCES may be extended to complex models with a more representative tank configuration. >

Digital simulation of source-insulator interaction in HVDC pollution tests

Abstract: A technique is presented for digital computer simulation of the interaction between a polluted insulator and a high-voltage, direct-current test source. Both uncontrolled and feedback-controlled voltage-double sources are considered. The polluted insulator is represented by one or more arcs in series with the wet conducting layer. The arc is represented by a simple dynamic equation, and an attempt is made in the model to account for thermal phenomena in the unbridged wet layer. The simulation technique is then used to investigate the effect of the DC source parameters on the error obtained in the insulator flashover voltage. Both the effects of maximum and mean dynamic voltage drops are studied. It is shown that the approach applies well for both controlled and uncontrolled sources, while the effect of an external damping resistor is treated separately. Wherever possible the simulation results are compared to experiments, and in view of the complexity of the problem, the agreement is satisfactory. >

Microwave drying of the paper insulation of high voltage electrotechnical equipments

Abstract: The water and microwave permeable dielectric insulation in an electrotechnical high voltage equipment is dried by means of microwaves. The electrotechnical equipment has a central conductor on which the insulation is wrapped, and it is disposed within an electrically conducting hollow cylinder with its central conductor coaxial with the latter cylinder to form a coaxial, microwave transmission line. Microwaves are propagated through the coaxial transmission line to heat the water in the dielectric insulation, to transform it into water vapor, and to thereby dry the insulation. The microwave transmission line is air-tight and the water vapor is evacuated through a vacuum pump or cold trap.

In situ activation of cobalt cathodes in alkaline water electrolysis

Abstract: The hydrogen evolution reaction (HER) on polished pure cobalt cathodes in 30 w/o KOH at 70°C in the presence of dissolved metallic impurities has been investigated in constant current and potential modes combined with the potential-sweep method. Potentiostatic tests show that the cell current decreases with time during the first 1000 s, which is tentatively attributed to the penetration of atomic hydrogen into the metal lattice. The deposition of copper, iron and zinc, observed after several hours' incubation significantly influences the Tafel parameters for HER.

Activation in situ de la cathode de nickel par le molybdate de sodium

Abstract: In situ activation of a solid nickel cathode was achieved by adding sodium molybdate during the electrolysis of an aqueous solution of 30 wt.% KOH at 70 °C. The resulting improvement in the electrocatalytic activity with regard to the hydrogen evolution reaction reaches a maximum when 4 × 10-3 M of molybdenum is added. This is attributed to the formation of a spongy deposit on the electrode surface resulting from the deposition of molybdenum and iron. A continuous growth of nodules on the surface is observed while the current, for a constant applied potential of -1.5 VHg/HgO increases linearly with the logarithm of time, the slope being 230 mA cm-2 (decade time)-1 for t < 50 000 s.

Thermoelastic ratcheting effect in bolted aluminum-to-aluminum connections

Abstract: The effect of thermoelastic ratcheting on the mechanical integrity of bolted aluminum-to-aluminum connections using different mechanical contact devices was studied. Thermoelastic ratcheting was studied under current cycling conditions using currents 800 to 2000 A. The results show that the mechanical integrity of the connections is strongly affected by the joint configuration, which differs according to the mechanical devices used. To explain this finding, a rather simplified model of the processes occurring in the connections is derived and shows very good agreement with the experimental results. >

The microbeam facility at the University of Montreal

Abstract: The 4.5 MV Dynamitron injector for our 6 MV Tandem is now used to provide a proton beam for a dedicated FIXE, RBS, PIGE microbeam facility. An electrostatic quadrupole triplet lens produces a beam spot of 20 μm diameter. The target chamber, which is a modified 4 in. Dependex cross, houses an electron flood gun, and SB detectors. The targets are mounted on a stepper motor controlled HPT 040 micromanipulator. A 30 mm2 Si(Li) detector (FWHM = 154 eV at 5.9 keV) is used for PIXE measurements. Data on the impurities found in “water trees”, which are associated with breakdown in electrical cables, will be presented.

Rule-based relay modelling for transient-stability studies

Abstract: A novel approach to relay modeling for transient-stability studies is presented. It is based on a simulation language which offers many characteristics of AI (artificial intelligence) technology, it is close to natural, declarative, rule-based, and inclusive of concepts used in protective relaying. The proposed option gives users great autonomy, which would lead to better productivity since relay models and/or protection schemes can be developed within a few hours of the many weeks required under normal circumstances. Moreover, systems involving many coordinated relays can be easily described. >

AC breakdown characteristics of in-service aged XLPE distribution cables

Abstract: AC breakdown tests were performed on field-aged XLPE distribution cables. For these measurements, a special test assembly consisting of air/distilled water terminations was developed. The tested cable specimens were examined for the occurrence of halos and water trees. The results suggest a correlation between the AC breakdown strength and operating stress. The incidence of halos is also found to be related to the AC breakdown strength, but no such relation appears to exist for the water tree length or density. >

Déshydrogénation du méthylcyclohexane sur le catalyseur industriel Pt-Sn/Al2O3

Abstract: Une solution au probleme de l'utilisation de l'hydrogene comme carburant dans les moyens de transport consiste a le produire in situ par deshydrogenation de naphtene cyclohexanique, le methylcyclohexane par exemple. Les resultats obtenus anterieurement avec un catalyseur industriel Pt-Sn/Al2O3, bien qu'encourageants, montrent qu'il n'est pas possible d'effectuer la deshydrogenation sans respecter certaines contraintes. En effet, pour conserver l'activite du catalyseur, il faut maintenir, lors de la reaction, une certaine pression partielle d'hydrogene. Dans le but de s'affranchir autant que possible de cette contrainte, le catalyseur a ete modifie. Cette modification, visant a attenuer l'activite craquante et isomerisante du catalyseur industriel, confere au catalyseur une resistance accrue vis-a-vis de la desactivation. Dans les conditions operatoires utilisees, cette resistance se manifeste par un facteur de cinq. Le modele cinetique etabli pour le catalyseur initial a ete ajuste pour le catalyseur modifie. Ce modele est base sur le meme mecanisme reactionnel que celui qui represente la reaction sur le catalyseur non modifie.

Oxidation and thermal resistance of HMW-PE and XLPE HV

Abstract: The thermal oxidation of the insulation of several unaged and aged transmission and distribution cables has been measured by Fourier transform infrared (FTIR) spectroscopy. It is shown that all cables, even unaged ones, contain traces of oxidation which increases with aging, especially near the conductor shield. The antioxidant content has been investigated by FTIR and ultraviolet spectroscopy and sulfur content measurements. It is shown that the amount of residual antioxidant can be related to the oxidation induction time as measured by differential scanning calorimetry at 200 degrees C in oxygen. The influence of various parameters on cable thermal resistance is discussed. >