Showing papers on "Liquid dielectric published in 1978"

Progress in the Field of Electric Breakdown in Dielectric Liquids

Abstract: For some fifty years the mechanism of electric breakdown in liquid insulation has been a subject of great interest for both theoretical as well as practical reasons. Over the years a number of promising hypotheses of breakdown have been advanced and it has been necessary to modify, and sometimes reject, interpretations of the breakdown data as additional experimental evidence has been accumulated.

Device for switching electrical circuits

Abstract: A device for switching a plurality of electrical circuits, each including a group of electrodes separated by insulators and a duct formed by coaxial holes made in the electrodes and insulators and filled partially with a conducting liquid wetting the surface of the electrodes within the duct. An element controls the flow of conducting liquid within the duct so as to close the electrodes. The element is linked mechanically with a duct sealing element in common with the ducts of all the groups. The sealing element has a cavity filled with a dielectric liquid communicating with the ducts of all the groups.

Capacitive liquid level sensor

Abstract: A capacitive liquid level sensor for sensing the height of liquid in a liquid storage tank at a plurality of locations. The liquid level sensor includes a cylindrical housing which extends along a line perpendicular to a predetermined reference level which is approximately parallel to the expected level of liquid in the storage tank. Several capacitors are included within the housing, each employing an air/liquid dielectric, whereby the capacitance values of the capacitors are individually variable due to any variations in the liquid height at each location. Several alternative cross-sectional structures are shown whereby the cylindrical housings are employed as a common plate to the several capacitors located within each housing.

Vaporization cooled and insulated electrical inductive apparatus

Abstract: Electrical inductive apparatus cooled and electrically insulated by a vaporizable liquid dielectric having a boiling point within the normal operating temperature range of the apparatus. When the electrical inductive apparatus is at ambient temperature, the liquid dielectric completely fills the enclosure providing electrical insulation for the electrical members. As the temperature of the apparatus increases towards its normal operating range, the liquid dielectric is gradually withdrawn into a reservoir until, at the normal operating temperature, only a quantity of liquid dielectric sufficient to completely cover the electrical inductive apparatus remains in the enclosure. In response to a temperature decrease, the liquid stored in the reservoir is gradually returned to the enclosure thereby maintaining a constant level of dielectric strength between the electrical members.

Ridged waveguide antenna submerged in dielectric liquid

Abstract: A system for remote microwave interrogation and imaging of biological tars comprises at least one microwave, double ridged waveguide antenna probe which operates at S-band frequencies, and a high dielectric liquid medium, preferably water, in which both the probe and the target are completely immersed. For imaging applications, the probe is positioned with respect to the target such that the target is in the near field of the antenna.

Corona charging element

Abstract: Corona discharge electrodes are coated with compressed dielectric materials. A corona discharge electrode is placed under tension and coated with a molten, viscous dielectric material, such as glass, while under tension. The dielectric material is allowed to cool so that the dielectric material becomes bonded securely to the corona discharge electrode. The tension upon the corona discharge electrode is released thereby causing a compression of the dielectric material adhered thereto. The resulting dielectric coated corona discharge electrode has a substantially improved life and delivers substantially uniform currents.

Breakdown in Ceramic Capacitors Under Pulsed High-Voltage Stress

Abstract: Failure in ceramic capacitors due to high-impulse voltages was investigated to determine the parameters which limit the breakdown voltage. It was found that the breakdown field strength is a function of the dielectric constant, the dielectric thickness, and the capacitor area. There was little correlation between the breakdown voltage and the rated voltage. Breakdown usually occurred at the edge of the electrodes, and only small changes in capacitance and dissipation factor resulted.

Vaporization cooled electrical apparatus

Abstract: Electrical apparatus cooled by dielectric fluid which vaporizes within the normal operating temperature range of the electrical apparatus. The electrical apparatus includes a plurality of fluid flow passages extending vertically therethrough which have widths within the range of approximately 0.010 inch to approximately 0.060 inch. The small width of the fluid flow passages causes the dielectric fluid to uniformly coat or wet both wall surfaces of the passages as it flows therethrough.

On the Nature of Dielectric Loss in High-Voltage Insulation

Abstract: Experimental observations have been made on resin samples containing one single cavity and on micaceous high voltage insulation. The results conflict with the generally accepted mechanism of voltage variation of the electrical characteristics of such samples, which mechanism is based on the influence of internal partial discharges. One different dissipative mechanism, namely the interfacial polarization or Maxwell-Wagner effect, is considered to fit these observations on a semi-quantitative basis. It takes into account the increase of the electrical conductivity of the surfaces struck by partial discharges, and the increase of the resistivity of the solid part of the insulation during its ageing under voltage. The relative contribution of these two mechanisms to the variation of the loss with applied voltage is influenced by voltage, temperature, frequency and of course, by the nature of the materials. According to the proposed model, the significance of some test specifications which consider the variation with applied voltage, of electrical properties of HV insulations, should be reconsidered.

Capacitor with ester dielectric fluid

Abstract: A capacitor is disclosed of alternating layers of plastic film and metal foil impregnated with a dielectric fluid which is an ester of a benzene tri- or tetracarboxylic acid. The esters are preferably trimellitic acid esters, especially tri-isodecyl-trimellitate. The dielectric fluid is sufficiently non-flammable to meet safety requirements and has a relatively high dielectric constant and low power factor.

Dielectric Behavior of the Coolant for a Gas Insulated HVDC Thyristor Valve

Abstract: The objective of this paper is to report on studies made on a fullscale model of the coolant system for a gas insulated, fluorocarbon liquid cooled HVDC thyristor valve. Confidence in the selection of the coolant system and its associated dielectric containment structure stemmed from the parametric study of the coolant, and the more than adequate dielectric strength of the coolant even when it was in the cavitated state. An explanation is proposed on the apparent anomoly of the exceptional dielectric strength of the system, even when bubble nucleation is induced by the injection of a dielectrically weak (nitrogen) gas into the flowing coolant.

Development of ±400 KV/±High and Medium-Pressure Oil-Filled Paper Insulated DC Power Cable System

Abstract: This paper describes the steps to be taken to optimize the design of oil-paper insulated power cable for high voltage dc operation. Experimental data is presented on models to establish the steady-state dc dielectric strength and the switching surge polarity reversal dielectric strength of oil-paper insulations. Laboratory data is presented on factory made prototype cables tested under voltage stress conditions applicable to a ±600 kV dc system. Optimized designs of high-pressure oil-filled pipe-type and medium-pressure oil-filled self-contained cables are presented.

High voltage dual dielectric capacitor roll

Abstract: A medium high voltage capacitor roll section comprises a sheet of double metallized plastic film and a sheet of paper adjacent thereto, with the paper and film forming parallel dielectrics. A dielectric liquid impregnant is used and the roll is wound sufficiently tightly so that after impregnation with a dielectric liquid impregnant and consequent swelling there is an essentially zero negative space factor within the roll.

Electrostatic charge generator

Abstract: An electrostatic charge generator for continually providing charge carriersf a given polarity in a flow of dielectric fluid. The charge generator comprises a coaxial tube with an inner conductor wire coaxial with a hollow, cylindrical outer conductor. A D.C. potential is applied between the inner and outer conductors of the coaxial tube and a dielectric liquid, such as oil, is caused to flow therethrough. Since the intensity of the non-uniform electric field in the conductor tube is highest near the inner conductor, the electrostatic charges of the opposite polarity as the inner conductor are removed from the dielectric fluid faster than charges of the same polarity are removed at the outer conductor. This results in the dielectric fluid exiting the conductor tube carrying a charge of the remaining polarity.

Kinetics of flowing dispersions. Part 11.—Dielectric constants of streaming suspensions of spheroids

Abstract: The variations in dielectric constant of a dilute suspension of rigid spheroids in a dielectric fluid in a combined uniform shear and electric field have been examined. Electrical polarization of the particles perturbs the local electric field thus causing additional electrical displacements which, when compared with the electrical displacement of the pure medium, makes it possible to calculate the dielectric constant of the suspension as a function of particle orientation.By combining the dielectric theory with that for the distribution of particle orientations, dielectric constants in both the transient and steady states are evaluated. Since the particle rotations, and hence the orientation distributions, depend on the relative magnitudes of electrical to hydrodynamic torques acting on the particles, the dielectric constant depends on the intensity of electric field, i.e., the suspensions show non-linear dielectric and anisotropic behaviour. It is shown that the dielectric constant oscillates when shear is applied, but that for various reasons which are considered the oscillations are damped in practical suspensions and eventually a steady state value is attained.Preliminary measurements with metal coated fibres confirm this general pattern of behaviour.

The Effect of Polarity Reversals on the Dielectric Strength of Oil-Impregnated Paper Insulation for H.V.d.c. Cables

Abstract: A laboratory investigation involving tests on models and on full-sized cables has been carried out into the behaviour of oil-impregnated paper insulation under the simultaneous action of a pre-stressing direct voltage and a voltage surge of either the same or opposite polarity. It has been found that the dielectric strength does not depend on the level or polarity of the pre-stressing direct voltage or on the duration of the surge, except when a series of reversed polarity surges is applied at intervals of a few seconds, progressively increasing the level until breakdown occurs. In this typical case reductions from 130 MV/m at zero d.c. to 45 MV/m at 100 MV/m d.c. have been observed and explained in terms of bubble formation and growth in the paper tape "butt-spaces" adjacent to the metallic conductors. This effect is entirely eliminated by increasing the oil pressure to suppress bubble formation.

Producing sulphuric acid

Abstract: This invention is based on the factors that both oxygen gas and oxides of sulphur as well as hydrogen sulphide are highly soluble in saturated, halogenated hydrocarbon liquids which are also dielectric liquids. The absorber liquid, saturated with dissolved oxygen and sulphur dioxide and/or hydrogen sulphide is then ozonated using the solvent or absorber liquid dielectric as the dielectric in an ozone generator. The sulphur trioxide produced by the ozone reacting with the sulphur dioxide and hydrogen sulphide in the presence of a catalyst (accelerates reactions) also carried in the liquid dielectric or, in the liquid stream at the ozonator, is then mixed with sufficient water to absorb the sulphur trioxide and produce the strength of sulphuric acid desired from the system. The sulphuric acid having a different specific gravity than the inert absorber liquid is gravity separated from the absorber liquid. The absorber liquid is returned to the scrubber or dissolver of the gaseous sulphur compounds for recycle use.

Thermal Brealdown and Thermal Runaway Phenomena in EHV Cables

Abstract: The paper describes a new method of estimating thermal breakdown in EHV oil-impregnated paper-insulated cables with some experimental data. In the analysis it is shown with the computed results that the heat generation in the insulation can be exactly approximated by the average temperature of the insulation. In addition this method can calculate the critical voltage at which EHV cables go into thermal breakdown. The values here calculated compare agreeably with the breakdown voltages of 500 kV OF cables.

Method and apparatus for propagating electrical signals through a conducting dielectric fluid

Abstract: Apparatus for propagating electrical signals through a conducting dielectric fluid such as salt water includes a pair of electrodes, one of which is a point electrode composed of a nipple or finger-like member, and the other of which is a plane electrode composed of an annular plate. The two electrodes are immersed in the conducting dielectric fluid and spaced apart along an axis and then electrical energy is applied to the two electrodes to produce a varying voltage therebetween. The voltage difference is modulated in accordance with information to be transmitted and, as a result, a time-varying polarization field is produced in the conducting medium and this field propagates through the medium.

Method of producing a perforated metal foil

Abstract: To produce a perforated metal foil, especially for use in a screen printer, a decomposable, dissoluble or vaporizable dielectric substance is deposited on a cylindrical conductive substrate in a dot pattern under the control of a photoelectrically scanned master. The spaces between the dots are then filled with an electrolytically deposited metal forming a coherent layer which is subsequently stripped off the substrate. The deposition of the dot pattern is carried out through a spray nozzle, sweeping the rotating substrate, which has an outlet in a bottom wall of a narrow space filled with the liquid dielectric to be dispensed, that space being separated by an apertured partition from an overlying plenum chamber in which the air is intermittently pressurized by an electromagnetic armature to expel a limited quantity of dielectric through the outlet; the membrane may be vibrated at supersonic frequencies to generate the necessary discharge pressure.

Electric conduction phenomena and carrier mobility behavior in dielectric fluid with dissolved impurities

Abstract: Electric conduction phenomena and carrier mobility behavior in mineral base electrical insulating oil and various synthetic base dielectric fluids have been investigated in the low voltage region and compared with the data for these fluids containing such impurities as antioxidant, W/0 type surface active agent, etc. It was shown that the carrier mobility of fluids with industrial purity seems to obey Walden's rule while the fluids with artificial impurities show some ionic conduction behavior and their carrier mobilities seem not necessarily governed by Walden's rule, depending on the type of the fluids and the impurities. Thus, it would appear advisable that the electrical behavior of the artificial impurities in the dielectric fluids should be dealt with apart from that of the natural impuritiy.

Breakdown Mechanism Studies in XLPE Cable -- Part II

Abstract: This research explores the basic hypothesis that microporosity plays a significant role in the mechanism of breakdown at high stress(15 to 30 times operating stress). The relative performance of gas-impregnated cable models on volt-time studies at several pressures and with several gases is analyzed using established gas breakdown techniques.

Electrolytic working method

Abstract: PURPOSE:To prevent an unnecessary working by mingling a dielectric liquid to an electrolyte passing through the side of an electrode. CONSTITUTION:An electrode 1 is moved to a position above a working part of a work 6 to be worked and the land 3 of the electrode 1 is faced to the work 6. And the electrode 1 is connected to a negative terminal and the work 6 is connected to a positive terminal and then, the electrolyte and a dielectric liquid are separately made to flow from an electrolyte supplying port 2 and a dielectric liquid supplying port 8 of the electrode 1, respectively. While keeping this state, when the electrode 1 and the work 6 are approached mutually, a working is performed between the work 6 and the land 3 and the work 6 is eluted. At this time, a mixture of an electrolyte and a dielectric liquid flows in a working hole side surface adjacent to the land 3 and an electric insulating layer is formed, as a result, working to the part is not performed.

New Materials for Superconductive Communication Cables

Abstract: The feasibility of superconductive coaxial cables as a communication medium with an enormous capacity may be increased by applying superconductive materials with low surface resistances and high critical temperatures as well as dielectrics with low loss. This paper discusses the mechanisms affecting metallic conduction and dielectric properties of materials in relation to their application in a low temperature transmission line. It starts with a brief report on the present state of rf-superconductivity, but it particularly deals with the measurements of low temperature dielectric microwave losses of polymeric materials, because the dielectric loss mainly determines the overall-attenuation of the cable. Our investigations resulted in the smallest loss tangent of any solid material measured so far: \tan \delta (4.2 K, 6.5 GHz) = 6.6 \dot 10^{-7}\pm 5% for polyethylene. This corresponds to a cable attenuation of roughly 0.5 dB/km at 10 GHz and extends the bandwidth of superconductive communication lines appreciably.

Vaporization cooled electrical inductive apparatus

Abstract: Electrical inductive apparatus cooled by a two-phase dielectric fluid which vaporizes within the normal operating temperature range of the apparatus. The electrical inductive apparatus consists of a sealed enclosure surrounding a magnetic core and electrical winding assembly. A non-condensable gas fills a major portion of the enclosure at no-load conditions to provide adequate dielectric strength around the apparatus and is substantially removed to a storage tank when the apparatus reaches normal operating conditions. The required volume of the storage reservoir is proportional to the free volume of the enclosure and the volume of liquid dielectric disposed therein. The bottom surface of the enclosure includes a recessed channel portion configured to closely surround the lower yoke of the magnetic core and which serves to reduce the amount of liquid dielectric utilized and the free volume of the enclosure thereby minimizing the required volume of the storage reservoir for the non-condensable gas.

Dielectric aspects of prebreakdown phenomena in insulators

Abstract: By means of some experiments and considerations it is shown, that frequency dependent dielectric losses contribute to critical power densities independently of and equally to resistive losses in materials being characterized by a spacely inhomogenous charge carrier transport and especially in insulators.