Showing papers by "Hydro-Québec published in 1977"

Optical methods of electrical measurement at high voltage levels

Abstract: Optical methods to measure electric parameters and transmit the information from high voltage circuits to ground potential are described and evaluated in the light of the specific requirements of high-voltage measurement applications. The history and physics of a variety of optoelectrical methods found suitable for electrical measurement applications are introduced. Existing optical devices for measuring alternating, direct, and impulse currents and voltages in high-voltage circuits are reviewed with emphasis on the operation and features of several selected methods. The use of these techniques in industrial systems, in research laboratory apparatus, and in reference standards laboratories is discussed.

Corona characteristics of conductor bundles under impulse voltages

Abstract: This paper presents the results of an experimental study on the corona characteristics of single and bundle conductors under impulse voltage conditions in a large cage. Both lightning and switching impulses were used for the tests, most of which were performed with positive impulses. The influence of artificial rain on the corona characteristics was also studied. An analysis of the experimental results is presented with emphasis on the corona onset voltage gradient, the apparent change in the capacitance of the line conductor and the energy dissipated by corona. A simple analog circuit is suggested to simulate the influence of impulse corona on waves propagating along line conductors.

A method of predicting the corona performance of conductor bundles based on cage test results

Abstract: In the paper is presented a smmary of cage measurements of the radio interference, the audible noise, and the corona losses for a large number of conductors and conductor bundles. The analysis of the test results obtained also leads to the establisment of a theoretical method of predicting the corona performance of conductor bundles, based on experimental data obtained with single conductors and taking into account the actual distribution of the field strength at the surface of individual sub-conductors in the bundle. Some cases of practical interest are discussed with reference to the effect of conductor aging and the asymmetry of the bundle configuration. Application of the theoretical method to the prediction of the corona performance of long three-phase lines, taking the actual field distributions at the center and outer phase conductors into account, is also discussed.

Electric strenght and molecular properties of gaseous dielectrics

Abstract: A fundamental matter bearing on the use of dielectric gases is the delineation of the possible correlations between their molecular properties and dielectric strengths, under comparable conditions of electrode surface, electrode geometry, electrode separation, etc. Based on the criticism that a much larger number of dielectric gases be employed in the explorations of the foregoing type, it was decided to investigate whether some more general correlations could be established between the dielectric strength of gases and their molecular properties. The object of the present paper is to examine aspects of this matter with particular attention to the fact that a large number of gases will be considered in order to arrive at some general conclusions. It would be ideal to calculate the electron capture cross sections for the various gases (starting, e.g., from their molecular structure) and attempt to correlate them with the dielectric strength of gases, with an aim to formulate a quantitative measure of their "electronegativity" predictable from electron attachment cross sections, and, thence the molecular structure. It is believed, however, that a calculation of electron attachment cross-sections cannot be carried out, especially for multi-atomic gases possessing usefully high dielectric strengths. Here, we adopt an empirical, qualitative approach to the problem in which it is concluded that the electron attachment cross sections of gases would be proportional to their molecular volumes. However, for complex gases, molecular volumes are not easily calculated since one does not have data on the bonding arrangement, bond lengths, and the covalent radii of the constituent atoms of multiatomic dielectric gases of interest. As an approximation, however, one may take the molecular weight of a gas as an index of its molecular volume since a gas containing numerous and bulky atoms would tend to have both a large molecular weight and volume; the reverse would, of course, be true for a gas possessing fewer atoms, especially those of lower atomic weights.

Micro-ohm shunts for precise recording of short-circuit currents

Abstract: A new design of the tubular shunt is presented which offers a reduction of the response time up to 10 times without changing the volume of the resistive material and preserving a regularly shaped response. A new formula is derived which gives the necessary data for calculating the improved shunt. Another possible design option is also presented which gives a shunt with zero response time but then the response curve indicates a larger overshoot. A simple mechanical design is presented, particularly suitable for heavy current shunts in the microohm range. Two such shunts were built for precise recording of steep front, short-circuit currents with a large asymmetry. They were designed according to the new formula and experimentally examined with a step impulse current. The measured response time of these shunts are in agreement with the calculated data.

Monitor for Hydrogen Dissolved in Transformer Oil

Abstract: A new monitor of hydrogen gas dissolved in transformer oil is described and tested under different conditions. Hydrogen diffuses from the oil through a permeable membrane into the monitor and reacts electrochemically with oxygen from the ambiant air in a fuel cell type arrangement. The monitor can be installed on a transformer for in-service continuous analysis of evolved hydrogen. It can also be used as a portable analyzer for the rapid on-site estimation of hydrogen in oil samples. The monitor is not influenced by the presence of other commonly found gases in oil, and readings can easily be corrected for temperature. Preliminary results from a test on a 20 MVA transformer are presented.

The Characterization of Electrical Insulating Oils by High-Performance Liquid Chromatography

Abstract: A new method for the characterization of electrical insulating oils, which employs the recently-developed technique of high-performance liquid chromatography, is presented. The method is simple and rapid. It provides "fingerprints" of oils, with information about their molecular size distribution, aromatic types and their degree of alkylation. These fingerprints can be used to identify unmarked samples of oils and to differentiate, for the purposes of fault diagnosis, the typical degradations (e. g. polymerization or cracking) undergone by oils in service.

Corona performance of a conductor bundle for bipolar HDVC transmission at plusminus 750 kV

Abstract: As part of an overall study on the corona performance of bipolar HVDC transmission lines between ± 600 kV and ± 1200 kV, the corona performance of a 4 × 1.6 in. conductor bundle has been studied on an outdoor test line at a nominal voltage of ± 750 kV. The conductor bundle has been tested over a period of about six months covering summer, fall and winter conditions. The study included long-term measurements at ± 750 kV as well as periodic measurements at varying voltages between ± 600 kV and ± 900 kV and at monopolar voltages of + 750 kV and - 750 kV. The principal parameters measured are radio interference (RI), corona losses (CL) and audible noise (AN). Some measurements of ion current density at ground level have also been made. An analysis of the test results is presented in this paper showing the statistical corona performance of the conductor bundle on an annual basis, the generating quantities of RI, CL and AN as functions of the maximum bundle conductor gradient*, frequency spectra and lateral profiles of RI and AN.

Optimal unit commitment

Abstract: The paper describes a new and rigorous method for determining the mode of operation of an electrical power system that minimizes the operational cost. The power system consists of M thermal generating units and one constant-head hydroplant. The operational cost includes the fixed and variable start-up and running costs of the thermal units. The method uses the maximum principle of Pontryagin to determine the generation levels of the operating units, to devise additional criteria for fathoming a vertex in the branch and bound algorithm, and to reduce the number of units considered for shut down. The choice of which units to shut down from those suggested by the maximum principle is done by branch and bound.

Spectroscopic measurements in nitrogen arcs with respect to local thermodynamic equilibrium

Abstract: A wall-stabilized nitrogen arc at atmospheric pressure was studied spectroscopically in the current range from 20 to 70 A with the aim of detecting departures from LTE. Measurements of the relative intensity of several N(I) lines showed that the populations of the upper excited states are in equilibrium for currents greater than approx. 25 A. Comparisons of the excitation temperatures obtained from relative intensities with the electron temperature and with the temperature curves calculated for different departures from LTE show that deviations from equilibrium are small at the arc center for electron densities above approx. 4 × 1016 cm-3. Deviations between the radial profiles of the electron and excitation temperatures were observed for currents between 35 and 55 A.

Method for obtaining high activity electrocatalysts on pyrolytic graphite

Abstract: A process for obtaining electrocatalysts having a thin film of a noble metal such as palladium, platinum, gold or less noble such as silver or an alloy of noble metals or a noble metal together with a less noble one such as silver or nickel. These include metals from Group VIII of the periodic chart. The thin film is electrodeposited on nonporous pyrolytic graphite surface from an aqueous solution containing a salt of the noble metal or metals in the presence of a complexing agent. The solution is stirred mechanically or the pyrolytic graphite cathode is rotated to create conditions favorable for the electrochemical deposition to be carried out at the highest possible current densities. The electrochemical catalysts thereby obtained are useful in oxygen adsorption processes, oxygen and hydrogen evolution processes, oxide formation and oxygen reduction processes. The metal or alloy film is of a granular or nodular nature and of a depth not exceeding 7μ and has a grain size smaller than 2μ or of a filament nature with peaks each of a base size running from 0.1 to 0.2μ. The metal or the alloy is selected from the group comprising silver, palladium, gold, a gold-silver alloy and a silver-nickel alloy.

Testing for low breakdown probability with special reference to liquid insulation

Abstract: Several techniques for the determination of withstand voltage of electrical insulation are investigated. As a basis for comparison, impulse tests are carried out on a uniform field gap in transformer oil. Measurements of breakdown time lags suggest that different breakdown initiating mechanisms may be simultaneously active, and contribute to the change found in the parameters of the breakdown probability curve between the low and high probability regions. Digital simulation of the dielectric test serves as a useful tool to rationalize the experimental procedure, as well as to identify the risk of breakdown corresponding to the measured withstand voltage.

Low-Frequency Shielding Effectiveness of a Double Cylinder Enclosure

Abstract: The low-frequency shielding effectiveness of a long double cylinder shield is determined through a solution of Maxwell's field equations. The shielding expression obtained is then compared with the results obtained by both the circuit approach and the transmission-line analogy. The findings of the present paper are also compared with the analysis by previous authors of the multishield problem. A digitalcomputer program for numerical evaluation of the effectiveness of adouble cylinder shield is developed and used to study the influence of the shield dimensions and material constants.

Series tapping of an HVDC transmission line

Abstract: A system for extracting and converting into complex power the electrical energy conveyed through a high voltage direct current (HVDC) transmission line, the system being serially mounted along that transmission line. The system comprises converter bridges to convert the transmission line high voltage into AC active power and a unit, connected to the line, for generating reactive power and feeding the latter through both the converter bridges and the load mounted across the system output. Moreover, there is provided a device for controlling the rate of extraction and conversion of the HVDC energy in function of the active power supplied by the generating unit. This control device ensures that the load requirements in active power are entirely supplied by the converter bridges alone. A voltage regulator is associated to the generating unit for the purpose of keeping constant the output voltages of that generating unit, thereby causing a nul output active power from the unit, in steady state. The tapping system is generally under a voltage proportional to the energy extracted on the transmission line whereas the metallic housing enclosing it is maintained at the transmission line voltage.

Cavity resonance effect in large HV laboratories equipped with electromagnetic shield

Abstract: The electromagnetic screening of High Voltage laboratories against external interference is required in order to facilitate measurements inside the laboratory of partial discharges and radio interference voltages during dielectric testing. Such laboratories have been found to behave as high quality cavity resonators when excited from inside by the rapid discharges of impulse generators. Due to the large physical dimensions of high voltage halls, some resonant frequencies may be as low as a few megahertz. The oscillatory electromagnetic fields produced by the currents which circulate in the cavity induce stray signals in the impulse voltage measuring circuits. Such circuits usually have pass-band widths sufficiently large to reproduce these oscillations. This interference is then superimposed on the impulse oscillograms and, in certain circumstances may hamper the interpretation of the test voltage oscillograms. The interference can be suppressed by coating the inner side of the shield with a special resistive paint, which reduces the Q factor of the resonant cavity. Although such paint is not yet commercially available the method has been experimentally verified on a reduced scale model.

The Effect of Surface Segregation of Mg on the Contact Resistance of Al-0.5-Percent Mg

Abstract: Silver and Ag-W (10 weight percent W) were operated in a 5.I-A (peak) 308-V (peak) full-wave rectified dc circuit. The experimental switching system was operated 1.5 times per minute; the opening and closing velocities were 4 x 10-2 and 3 x 10-4 cm/s, respectively; the fully open contact spacing was 200 µm; and the contacts were closed for 3 s. The opening and closing of the contacts were controlled by a heater-bimetal combination attached to the moving contact. The following contact pairs were used: Ag versus Ag, Ag-W versus Ag-W and Ag versus Ag-W. All combinations of contact material and contact polarity were used. The experimental results showed that there was always a net transfer of contact material from the cathode to the anode. The volume of material transferred was strongly dependent upon whether the anode was the moving (hotter) or the fixed (cooler) contact: the greater erosion occurring when the anode was the hotter contact. For Ag versus Ag contacts thc erosion pattern resulted inone pip on the anode and one crater on the cathode. For Ag-W versus AgW contacts the presence of the small percentage of W resulted in multiple pip and crater formations. The experiments with the Ag versus Ag-W showed that the cathode electrode material determined the erosion pattern observed, i.e., when the Ag-W was the cathode, multiple pip and crater'formations occurred, but when Ag was the cathode, only a single pip and crater structure was observed. The presence of the W either in the cathode or in the anode decreased the observed erosion. These experimental results are discussed in terms of how the presence of W affects the emission characteristics of the cathode region and also affects the movement of the arc roots.

Erodibility Tests on a Sensitive, Cemented Marine Clay (Champlain Clay)

Abstract: Laboratory tests conducted on the erodibility of a sensitive, cemented clay (Champlain clay) have indicated highly dispersive characteristics (sodium cations content of the pore water, 85 to 90 percent; Soil Conservation Service Laboratory Dispersion Tests, 60 to 100 percent). Pinhole tests performed on undisturbed and remolded specimens have also confirmed the high erodibility of the clay. However, field observations and investigations could not substantiate this behavior; on a practical basis, the clay formation cannot be considered as a dispersive, erodible material. The particular nature and mineralogy of the clay can probably explain the discrepancy. The mineralogical analysis of the clay shows that is composed mainly (90 percent plus) of inert, nonclay minerals; consenquently, the deflocculation mechanism of erosion cannot be considered. It seems that the chemical composition of the pore water is not related to the mineralogy of the clay, but rather to the environmental conditions prevailing during its formation. The high sensitivity of the clay, which liquefies around the hole when the specimen is punched with a pin, probably explains the positive pinhole test results recorded.

Measurements of Spontaneous Currents and Magnetic Fields in Laser-Produced Plasmas

Abstract: An extensive experimental study of the associated electrical currents and magnetic fields generated in plasmas produced by nanosecond CO2 and Nd-glass laser irradiation of a copper target in a background of air, N2, Ar and He at pressure ranging from 10-5 to atmospheric was conducted. Space and time resolved measurements of current, magnetic field, UV radiation and laser pulse structure were performed. The results show correlations between a) the distribution of laser target irradiation and the distribution of emitted current, and b) the dependences, on the background pressure, of both the UV radiation and the magnetic field, and reveal a two-phase expansion — diffusion and convection — of the magnetic field.

Surface Flashover Voltage of Spacers in Vacuum at Cryogenic Temperatures

Abstract: An electrical insulator in low-temperature equipment is stressed not only by the electrical field but also by mechanical forces, partly due to thermal gradients. At cryogenic temperatures some electrical properties, such as the dielectric losses, may be expected to improve. However, some mechanical properties of the dielectrics may deteriorate and in turn affect their electrical performance.

Numerical study of a CO(2) laser beam focused on a theta-pinch plasma in the axial direction.

Abstract: Using two different empirical density profiles for the end region of a theta-pinch plasma, one with a maximum density on the axis (radiation-dispersing profile) the other with a pronounced axial minimum (radiation-trapping profile), the trajectory of the CO2 laser beam (10.6 μm) focused axially on such a plasma was studied numerically. This calculation is used to evaluate the optical influence of the plasma, since the maximum power density in the focal plane can be reduced by several orders of magnitude owing to the presence of the plasma. This influence can be substantial even for very subcritical electron densities (ne ≪ 1019 cm−3). In cases of large dispersion, the characteristics of a multifocal lens capable of producing perfect focusing are found, and it is shown that the solution is not unique. The radial distribution of the laser beam power density is also calculated and shows numerous irregularities and discontinuities due to the nonuniform beam dispersion.

A Surface Chemistry Approach to the Study of Soild Electrodes in Insulating Liquids

Abstract: The liquid meniscus height at copper and aluminum cylinders partially immersed in mineral oil was measured as a function of the applied voltage. The results are interpreted on the basis of assumed variatins tions in the metal/liquid and liquid/vapor interfacial tensions.

Chemical Treatment of a Sensitive, Cemented Clay (Champlain Clay)

Abstract: Significant changes in the geotechnical characteristics of a highly sensitive, cemented, marine clay (Champlain clay) were recorded following its treatment with hydrated lime (by mechanical mixing). Increase of the liquidand plastic limit, decrease of the sensitivity, and also increase of the unconfined compression strength were observed. Following the lime treatment, the clay also became non-erodible. The improvement of the geotechnical characteristics are dependent of the lime concentration; however, it seems that a peak is reached for about 3 to 4 percent lime concentration, above which no significant increase can be detected. These improvements are also curing time dependent.