Showing papers by "Hydro-Québec published in 1978"

Optimal scheduling of thermal generating units

Abstract: Scheduling the operation of thermal generating units involves the selection of units to be placed in operation and the allocation of the load among them- These two decisions must be taken so as to minimize the sum of tile startup, banking, and expected riming costs subject to the demand, spinning-reserve, and minimum down-time and up-time constraints and, sometimes, to the following two additional limitations: a unit should not be started up more than once a day; and no more than two units of the same plant should be started up simultaneously. This optimization problem is formulated in this paper as a mixed-integer nonlinear programming problem. Then, by following the Bender's approach, the problem is partitioned into a nonlinear and a pure-integer nonlinear programming problem- The First problem, which represents the economic dispatch problem, is not solved here. The second problem, usually called the unit commitment problem, is solved by a variational method and a branch-and-bound algorithm. Numerical results obtained for a network of ten generating units are presented.

Estimation of Higher Frequency Network Equivalent Impedances by Harmonic Analysis Natural Waveforms

Abstract: A digital method of analysing harmonics in a power system has been developed which permits the equivalent network impedance to be estimated by means of the switching of capacitor banks. The method records voltage and current digitally and by data processing computes the amplitude and phase of the harmonics. By comparing results before and after the switching of a capacitor bank on one phase, the equivalent network impedance is estimated at the odd harmonics. Precision of results is acceptable in amplitude but less accurate in phase.

Apparatus for detecting and measuring the hydrogen content in a liquid substance

Abstract: The invention relates to an apparatus for measuring the concentration of gaseous hydrogen dissolved in a liquid substance. The apparatus comprises an electrochemical cell constituted of a polymeric membrane in contact with a sample of the liquid substance and which is permeable to hydrogen, of an electrolyte capable of causing an oxidation reaction of the hydrogen diffused through the polymeric membrane, at a first electrode, and a reduction reaction of an oxygenated gas at a second electrode, so as to deliver an electric current proportional to the hydrogen concentration to be measured. An electrovalve operates, when activated, to exhaust the liquid substance sample at a predetermined instant in the measuring process. Moreover, the circuit amplifies a voltage corresponding to the value of the current proportional to the concentration, which current flows through a load resistance mounted in parallel across the first and second electrodes and the input of the amplifying circuit. A display device is connected to the output of the amplifying circuit and supplies a digital measure of the hydrogen concentration in the liquid substance. A control unit determines the operation times of the electrochemical cell, of the electrovalve as well as of the digital display device pursuant to a predetermined sequence.

Stroboscopic beacons fed from a capacitive source

Abstract: The present invention relates to a system for energizing flash-tubes of beacons by means of the capacitive energy extracted from an insulated section of the overhead wire of power transmission lines. The supply system comprises a circuit for transforming the AC capacitive energy from the overhead wire into DC voltage, the latter feeding at least one flash-tube and a regulation circuit shunted across the transforming circuit for controlling a DC voltage threshold value supplying the tubes. Such regulation is achieved by detecting the predetermined DC voltage threshold value across the lamp terminals and by switching to the earth any capacitive energy extracted from the overhead wire exceeding that threshold value. Moreover, a circuit delivers a pulse at predetermined time intervals to control the firing of each flash-tube when the latter is subjected to a DC voltage corresponding to the predetermined threshold value and regulated by shunt switching.

A thermochemical approach to the gas-phase reduction of metal sulphates

Abstract: The reduction of different metal sulphates by hydrogen occurs at different temperatures and can lead to a variety of products. It has been shown that the starting temperatures for the reduction of several sulphates are directly related to the magnitude of their (exothermic) heats of formation per equivalent. The thermochemical data also provide a basis for the interpretation of the relative thermal stabilities (under nitrogen atmosphere) of several metal sulphates. A consideration of the appropriate heat of formation values can also be useful in understanding the different reduction products obtained for different metal sulphates. Finally, the reduction behaviour of some binary metal sulphates is also consistent with the thermochemical data.

Capacitive Power Tap-Off from Transmission Lines Using Ground Wires: Calculation of the Equivalent Circuit Parameters

Abstract: The capacitive coupling between the ground wire and the phase conductors of a transmission line can be used to supply small loads in remote regions along the line. A theoretical analysis is presented in this paper to determine the parameters defining an equivalent circuit for the case of single as well as two insulated ground wires. Results are presented to show variations of the equivalent circuit parameters as functions of geometrical parameters of lines in the range of 300- 750 kV. Finally, some results of measurements on Hydro-Quebec's lines are presented and compared with theoretical calculations.

Effect of Large Electrodes on Sparkover Characteristics of Air Gaps and Station Insulators

Abstract: The paper constitutes a laboratory investigation into the influence of large electrodes on the dry and wet sparkover characteristics of air gaps and high voltage insulator supports. Tests were carried out with power frequency and switching impulse voltages.

Computer simulation of the sideband instability

Abstract: The physical origins of the growth of sidebands of a large amplitude plasma wave are studied numerically. It is shown that in the first phase of the nonlinear evolution of a large amplitude plasma wave the spatially averaged distribution function shows the formation of a stable bump and, for the case presented, the phase velocity of the lower sideband falls on the side of the bump having a positive slope. In the second phase of the evolution of the system, the sidebands saturate and the bumpy region of the spatially averaged distribution function takes a shape close to a flat plateau.

Switching-Impulse Corona Inception and Breakdown of Large High-Voltage Electordes in Air

Abstract: It has been shown in the past that irregularities on the surface of an electrode reduce the corona-inception voltage and, under certain conditions, the breakdown voltage of the corresponding gaps. Recent work indicates that rain may reduce the breakdown voltage of large sphere-plane gaps to that of rod-plane gaps of the same clearance. In the present study, laws are established according to which surface irregularities of various shapes and sizes reduce the corona-inception surface gradient of large electrodes stressed by positive switching impulses. The conditions are-also determined under which acceleration of corona inception may reduce the breakdown voltage of a gap formed by a large electrode and a plane, to the level of the breakdown voltage of a rod-plane gap of the same clearance.

Transient Measurement Techniques in EHV Systems

Abstract: Two different measuring techniques have been developed in order to reduce the measurement errors observed during recording of transients in EHV systems, caused by interference due to ground potential differences. The first one is based on the application of an opto-electronic link between the HV measuring apparatus and the remotely located multi- channel recorder. The second, more conventional technique utilizes a large copper band llaced in parallel with the measuring cable shield. An optimum geometry for the band and the cable was determined from a model study. Results of application of these two measuring techniques in EHV system tests are presented.

Bundled-Conduuctors for EHV Transmission Systems with Compressed -- SF 6 Insulation

Abstract: This report presents the results of a theoretical study to evaluate the practicability of bundled conductors in SF6-insulated transmission systems operating at EHV levels. The bundled conductors are evaluated according to their ability to maintain the electric-field intensity at the conductor surface below the corona-on-(or breakdown) level of the conductor, and are compared with practical coaxial-conductor systems. The results obtained show that the concept of bundled conductors can be adapted for use in SF6-insulated systems. The proposed bundle configuration consists of a central conductor surrounded by n small subconductors forming an electrostatically protective screen, the conductor bundle itself enclosed within an outer envelope. Compared with conventional coaxial configurations, it presents several advantages, namely, flexibility of design to meet the system's high-current, mechanical and insulation requirements separately, smaller electrode area exposed to high field intensities, and less stringent specifications for the supporting epoxy spacers.

Sensibility of parameters of the ssarr model

Abstract: The most powerful use of the SSARR model is in its flexibility which permits the user to model hydrologically any watershed. However, hydrologie experience and familiarity with the program are needed for the successful use of this model. The great flexibility of the model comes from the watershed parameters (sixteen) introduced in the model. The present studies give a basis understanding of these parameters and their effects on the streamflow computation. An attempt has been made to quantify these effects in giving in per cent the variations of discharge, runoff volume, etc. in relation with the variations of each parameter. Results of this studies could be used by anyone who applies the SSARR program to the model any particular watershed.

Arc degradation of SF 6 in the presence of polymeric insulating materials

Abstract: An investigation has been made of the degradation reactions due to the application of an electric are at the polymeric insulating material/SF 6 interface. Polyethylene, Teflon, epoxy and phenolic resins were used as the solid insulating materials in the study. The degradation process was observed to occur in two separate steps. In the first step, the polymeric materials are pyrolyzed by the are (are degradation). The second step involves a gas-phase reaction between the SF 6 and the volatile products generated by the are degradation. Analysis of the arc-degradation products by gas chromatography, mass spectrometry and infrared spectrophotometry indicates a significant difference between the composition of the various reaction products and the corresponding products of a degradation reaction carried out thermally. The principal reaction products of the gas-phase reactions between SF 6 and the volatile degradation products were identified as CF 4 , SOF 2 , SF 4 , SiF 4 , HF and also CO in the cases of epoxy and phenolic resins. General reaction mechanisms for the formation of these products are proposed. The implications of these results regarding the use of such insulating systems in electrical apparatus are discussed.

Instantaneous three-phase reactive power for digital implementation: Definition and determination

Abstract: Two methods of computing the instantaneous reactive power from concurrent samples of voltages and currents are suggested. The advantages are not having to wait for a quarter of a cycle, consistency with the active power computation, and a simple measurement of the deformation factor. Such a fast computation finds applications in protection, load behavior modelling, state estimation, reactive power compensation, etc.

Behavior of Air Insulating GAPS Stressed by Switching Overvoltages with a Double Peak

Abstract: For calculating the risk of failure of an electric system due to switching overvoltage stresses, rules are needed for simulating field-generated overvoltages with laboratory-produced impulses The present study deals with switching overvoltages that present two successive peaks and provides guidelines for estimating the response of air insulating gaps to such overvoltages

Energy extraction system from a capacitive source with shunt switching regulation

Abstract: A system for and a method of extracting energy from a capacitive source, for example the energy induced in an insulated section of the overhead wire of an AC transmission line. The energy is extracted from the overhead wire by tapping the primary winding of a voltage step-down transformer which develops at its secondary an AC voltage the value of which is regulated through shunt switching. The shunt switching regulation as such is achieved by power thyristors the firing of which is selectively controlled in accordance with the phase and the amplitude of the output voltage. A comparator is used to compare the output voltage value with that of a signal delivered by an internal ramp generator. Moreover, the firing instant of the thyristors is governed by the output signal of the comparator and also in function of the information on the polarity of the output voltage cycles. Such shunt switching regulation allows the extraction from the overhead wire a maximum of power per kilometer of insulated wire and ensures a high stability of the output voltage despite substantial variations in the load connected to the secondary of the step-down transformer. The instant extracting system allows inter alia an economic and steady supply of power to microwave repeater stations which usually run along energy transmission lines and remote from central supply sources.

Evaluation of epoxy resin formulations for SF 6 cable spacer materials

Abstract: Research is underway at IREQ on the insulation performance of compressed SF 6 insulated cables for power transmission at system voltages up to 800 kV. The work reported here is concerned with the choice of materials for the design and testing of model size and full size spacers for 138 kV and 800 kV system voltage respectively. Five epoxy resin formulations were considered together with the effect of the filler. The electrical evaluation of the materials included the study of surface properties such as dry are resistance and tracking and erosion resistance and volume properties such as dielectric losses, permittivity and dielectric strength with point to plane geometry. The mechanical impact resistance was measured. Thermal measurements consisted in the evaluation of the heat distorsion temperature and the coefficient of thermal expansion. The test results and the usefulness of the tests with respect to the judicious choice of spacer dielectric materials are discussed.

Circuit for controlling induction in current transformers

Abstract: The present invention is directed to a circuit for controlling induction in current transformers so as to maintain such induction at a level below its saturation level in presence of a primary current having an asymetric component. The control circuit comprises a detection part connected to the secondary of the current transformer for detecting an increase in the transformer induction; an auxiliary load of high resistive value at the secondary of the transformer; and a switching part governed by the detection part operative to insert the auxiliary load in series with the secondary of the transformer when the polarity of the secondary wave reaches a polarity inverse with respect to the asymetrical component of the primary current.