Showing papers by "Hydro-Québec published in 1984"

A New Technique for Rapid Tracking of Frequency Deviations Based on Level Crossings

Abstract: A novel frequency computation technique suitable for single or three phase voltage signals is proposed. The method is based on a generalization of the zero crossing detection to a level crossing detection. This yields several estimates of the frequency within one cycle. A composite "best estimatet" is obtained by an appropriate weighted average of these estimates. The method is insensitive to amplitude variations, unbalance and is capable of tracking small frequency deviations in as short a duration as a fraction of a cycle. The measurement scheme is particularily suitable for integration with the digital schemes for real-time monitoring control and protection of power systems.

A thermodynamic model for the compensation law and its physical significance for polymers

Abstract: This paper describes how the compensation law can be explained by a linear relation between the activation entropy and enthalpy of a given process in a polymer. These two variables are related by the thermal expansion coefficient and a constant approximately equal to the Rao acoustical parameter. A relation between the activation free energy and some thermodynamic parameters is presented. The activated volumes for the α and β relaxations of polyethylene are shown to vary with temperature and cry-stallinity. The activated volume has also been calculated for some other polymers and is of the order of 1 to 6 molar volumes at 295 K.

Dynamic current transducer

Abstract: The current transducer is of the type comprising a Rogowski coil extending around a first conducting element in which a current to be detected flows. The first conducting element is provided at one end with a first terminal connector. A second conducting element is mounted on the first one so as to cover and preferably embed the external periphery of the coil. The second conducting element is electrically connected to the first conducting element at the end thereof which is opposite to the one end provided with the first terminal connector. A second terminal connector is provided on the second conducting element on the same side of the plane of the coil as the first terminal connector. This arrangement forces the current flowing between the first and second terminal connectors via the first and second conducting elements to flow around the periphery of the coil and thus to shield the coil.

Substatiion Ground Impedance: Comparative Field Measurements with High and Low Current Injection Methods

Abstract: This paper describes ground electrode impedance field measurements and their analysis at Hydro- Quebec's Yamaska substation, using both high and low current injection methods. The results from both techniques are shown to compare satisfactorily. In the low current injection method, numerous measurements were performed in different directions, describing how the mutual coupling effects between the auxiliary current and potential probes can be removed with adequate analytical tools. A comparison is also made between ground impedance values at 60 and 70 Hz. Finally, an appendix includes characteristics of some of the equipment used during these measurements.

Simulator Study of Multiterminal HVDC System With Small Parallel Tap and Weak AC Systems

Abstract: The paper describes a simulator study of a four-terminal HVdc system with a small parallel tap and interconnected to an AC network with weak AC systems at the four dc terminals. The small tap is rated at 25% of the rating of the HVdc system and the effective short-circuit ratios at the dc terminals are in the range of 2.1 to 3.0. The study includes the transient performance of the dc system for various types of system disturbances, such as AC system faults, dc line faults, and commutation failure at the small inverter.

An Iterative Pole-Removal Method for Synthesis of Power System Equivalent Networks

Abstract: In power system simulation (by means of TNA or digital computer) equivalent networks can be used to reduce the simulation complexity. This paper presents an iterative pole-removal method based on the least-squares fitting techniq% to synthesize RLC equivalent networks according7 to their specified driving-point function in the frequency domain. The synthesized networks are composed of only passive components to represent the DC constant, complex poles as well as poles at zero and infinite. Poles are removed individually from the specified driving-point function applying the least-squares fitting with respect to the frequency domain around the relevant resonance. This algorithm converges quickly even for highly resistive systems.

Method and system for interconnecting two synchronous or asynchronous electrical alternating three-phase networks by means of variable reactive impedances

Abstract: A method and a system for interconnecting two electrical, alternating three phase networks operating asynchronously or synchronously at voltages of equal or adjacent frequencies, and in which, for corresponding phases, the voltages of the first and second networks are out of phase by a constant or varying angle. A plurality of three phase variable reactive impedances interconnect the two networks for carrying out a desired transfer of active power from one of the two networks to the other. The variable impedances are operated to establish between each phase of the first network and the three phases of the second network, three interconnections each having a different susceptance, which susceptances vary with the three phase variable reactive impedances. A regulator measures electrical parameters associated with at least one corresponding phase of the first and second networks, and operates the three phase variable reactive impedances to vary the susceptances of the interconnections in relation with the measured parameters so as to establish the desired transfer of active power from one of the first and second networks to the other network, while maintaining at a desired level a reactive power engaged in the transfer of active power.

Apparatus for the dynamic and non-contact measurement of small distances

Abstract: A method and an apparatus for the dynamic and non-contact measurement of the distance separating the surface of a first part that may be conductive or not, from the surface of at least one second conductive part closely spaced from the first conductive part. The method resides in positioning, on the surface of the first part, at least one sensor including two conductive plates that are parallel, superimposed and electrically insulated from one another. The two plates of this at least one sensor are then fed with a same high frequency signal under the same voltage and the current generated by this high frequency signal, between the plate of the sensor which is closest to the surface of the second conductive part and this second conductive part, is measured. This measured current varying as an inverse function of the distance separating the surface of the second conductive part from the surface of the sensor which is closest to this second conductive part, it is then easy to determine the value of the distance separating the first and second conductive parts as a function of the value of the measured current. This method as well as the apparatus for carrying it out are particularly well adapted for measuring the air gap in any type of rotating machine such as an electric generator.

Influence of Some Chemical and Mechanicaleffects on XLPE Degradation

Abstract: It is shown that the relatively large concentration of impurities in cables is even higher in water trees. Gas bubbles observed in cavities filled with different salt solutions generate very high pressures able to fracture XLPE samples. It was also observed that fracture in XLPE under a cyclic mechanical load is frequency-dependent. The influence of oxidation on dielectric properties is also discussed.

An apparatus for sensing and measuring a current on a power transmission line

Abstract: An apparatus for sensing and measuring a DC or AC current on an LV or HV power circuit. The apparatus comprises a shunt element having an input connected to the transmission line. The current flowing through the shunt is measured by an electronic circuit which is located in a conductive housing connected in series with the shunt element. The housing conducts the current from the shunt back to the power circuit. The housing is dimensioned to contain therein the electronic circuit whereby to shield the circuit from thermal effects of the shunt element, the magnetic field effect of the measured current, and environmental electrostatic interference.

Protection circuit against electric shocks during welding

Abstract: A circuit for controlling the power supply to an electrode of the shielded type, such as that used in a shielded metal arc welding process (SMAW) whereby to protect a user from electric shocks. The control circuit is a protection circuit which serves to protect welders against electric shocks by decreasing the circuit voltage between the electrode tip and the workpiece to be welded. An AC or DC power supply may be used to feed the electrode. The control circuit is comprised of a high impedance voltage source applied to the electrode, a detection circuit for determining the level value of the impedance appearing between the electrode and the workpiece. The detection circuit compares the impedance thus detected with a threshold impedance and generates a control signal when the detected impedance is lower than the threshold impedance. The control signal operates a driver circuit which energizes a power feed device serially connected between the electrode power supply and the electrode itself. The predetermined threshold impedance value is set at about 500 ohms whereby a wet human body will not be subjected to an electric shock by contacting the electrode and the workpiece simultaneously.

Purification of effluent gases

Abstract: The disclosure describes a method and a system for treating gaseous effluents to remove impurities therefrom, these gaseous effluents flowing out from a high temperature reactor, into which a particulate material is being fed. The method comprises directing the flow of gaseous effluents counter-currently through the particulate material which is fed into the reactor, and independently controlling the particulate material feed rate and the velocity of the gaseous effluents so that particles in the gas feed are substantially all trapped by the particulate feed material and are returned to the high temperature reactor. Volatile materials may also be condensed on the particulate feed material. The purified gaseous effluents are then allowed to exit. A system for carrying out this method is also disclosed.

Dielectric Breakdown in Polyethylene at Elevated Temperatures

Abstract: A two-terminal dielectric test cell for the study of the dielectric properties of viscous polymers above their softening temperature was used to perform 60 Hz breakdown measurements in polyethylene between 23 and 150°C. Molded specimens of polyethylene with embedded electrodes of parallel-plane configurations were employed. The interelectrode spacing was kept constant over the entire temperature range by suitable compensation of differential thermal expansion effects in the test cell. Low density (0.919 g/cm3) polyethylene was used for this study. The results show a marked decrease of the breakdown strength as a function of temperature between room temperature and the crystalline melting temperature, Tm. Above Tm the breakdown strength appears to be only weakly dependent on temperature. The results are analyzed with the help of Weibull statistics. The temperature dependence of the breakdown strength is discussed in the light of Artbauer's theory of free volume breakdown.

Co containing austenitic stainless steel with high cavitation erosion resistance

Abstract: A soft, austenitic stainless steel alloy showing a high cavitation erosion resistance making it particularly useful for the manufacture and/or repair of hydraulic machine components. The alloy comprises from 8 to 30% by weight of Co; from 13 to 30% by weight of Cr; from 0.03 to 0.3% by weight of C; up to 0.3% by weight of N; up to 3% by weight of Si; up to 1% by weight of Ni; up to 2% by weight of Mo; and up to 9% by weight of Mn; the balance being substantially Fe. The amount of the above mentioned elements that are respectively known as ferrite formers (Cr, Mo, Si) and as austenite formers (C, N, Co, Ni, Mn) and, among said austenite and ferrite formers, the amount of each of the elements that are respectively known to increase and lower the stack fault energy, are respectively selected and balanced so that at least 60% by weight of the alloy is, at ambient temperature, in a metastable, face centered cubic phase having a stack fault energy low enough to make it capable of being transformed under cavitation exposure to a fine deformation twinning, hexagonal close pack e-phase and/or α-martensitic phase.

System Considerations in Converting One Circuit of a Double Circuit AC Line to DC

Abstract: The paper presents the results of a study of the possible interaction between the AC and DC lines placed on the same tower. The study was carried out on a simulator using physical models. Modelling procedures for representing the mutual coupling between the lines are presented. Results of tests of contact faults, electromagnetic coupling, dynamic response, loadrejection and ground faults are discussed.

Wirewound Shunts For Measurement Of Fast Current Impulses

Abstract: The paper describes the operating principle, design features and measuring characteristics of wirewound shunts. Fast response and reduced thermal-resistance drift are the main goals to be achieved, although a sturdy structure is also required to meet the demands of an industrial laboratory environment. A low cost, making the shunt competitive to impulse current transformers, is another design objective. Useful in many applications, these shunts are primarily employed for recording neutral current during impulse tests of power transformers.

System and method for detecting proximity to electrical power lines

Abstract: @ A system and method for detecting the proximity of an object to an electrical power line. The system comprises an antenna (3) for receiving, by capacitive effect, a current of which the intensity if a function of the distance separating the antenna from the electrical power line. The other factors that influence the current are fixed, constant or are considered negligible. A measuring and conditioning circuit converts the current at the output of the antenna into a coded signal and transmits this coded signal to a control unit (6). The control unit (6) compares the coded signal to predetermined values stored therein. Alarms are generated by the control unit when the current from the antenna exceeds the predetermined values.

Angular distribution of hot electrons incident on a laser-irradiated target

Abstract: Angular distributions of bremsstrahlung emission are calculated for various energy and angular distributions of hot electrons incident on a laser-irradiated plastic target. These theoretical results are used to interpret experimental data of x-ray continuum emission from a C${\mathrm{O}}_{2}$-laser-produced plasma. It is shown that at low irradiance (${I}_{L}\ensuremath{\le}5\ifmmode\times\else\texttimes\fi{}{10}^{12}$ W/${\mathrm{cm}}^{2}$) the incident electrons are normal to the target surface but that at higher irradiance, the incident electrons' angular distribution (spatially integrated over the target surface) is semi-isotropic. The influence of the directional distribution of hot electrons on axial energy transport is also studied by comparing calculated continum x-ray spectra as well as energy-deposition profiles with experimental results.

Potentiodynamic Investigation of Copper in LiCl Solutions

Abstract: The dissolution of copper has been investigated in an aqueous solution of pH 4 having up to 6M LiCl at temperatures ranging from 22 to 64 C. The anodic dissolution of copper is characteriz...

Improving Transmission Line Design by Using Reliability Techniques

Abstract: This paper discusses present design methods of transmission lines and shows how they can be improved by using reliability and statistical techniques. Methods of calculating line reliability are discussed with special emphasis on the most important parameters. This paper also deals with possible formats for a new design standard based on reliability techniques with a comparison of IEC/TC11 proposed format and the load and resistance factor (LRFD) proposed in EPRI research project 1352.

Substation Electromagnetic Interference, Part II: Susceptibility Testing and EMI Simulation in High Voltage Laboratories

Abstract: Susceptibility testing techniques for conducted and radiated interference are presented in detail. Withstand levels and test procedures are described. The relationship between substation transients and those generated in high voltage laboratories is discussed with data presented. The problem of instrumentation in these laboratories is presented with quantitative comparisons to substation EilI levels. A qualitative evaluation of those transients which Cdn be generated in thie typical laboratory is included. The use of interference sinmulators is also discussed.

Transient currents in silicone oils subjected to voltage steps with polarity reversal

Abstract: We have studied the transient currents flowing in silicone oils subjected to voltage steps with polarity reversal The experiments have been carried out, at room temperature, on two 50 cSt viscosity polydimethylsiloxane silicone oils (Rhone-Poulenc 604 V 50 and Dow Corning 561) in a parallel plate conductivity cell as a function of the applied electric field strength (04 ≦ E(kVcm−1) ≦ 10), of the cell gap (005 ≦ d(cm) ≦ 055), of the oil viscosity (50 cSt to 300 cSt) and of the oil purity From our measurements we can assert that: 1) the peaks appearing on the wave forms corresponding to the commercial oils are due to some impurities present in these oils; 2) these peaks cannot reflect the migration of a charged layer between the electrodes; 3) they are more certainly correlated to some dipole reorganization near the electrodes after each voltage polarity reversal