Showing papers on "Liquid dielectric published in 1986"

Dielectric properties of water and water/ethylene glycol mixtures for use in pulsed power system design

Abstract: One class of modern pulse power generators use deionized water as an energy storage, switching and transmission dielectric. Water is chosen for its high dielectric constant and relatively high resistivity, which allows reasonably sized and efficient low-impedance high-voltage pulse lines where pulse durations are less than 100 µs. Water/ethylene glycol mixtures are being researched, so that rotating machinery, rather than the usual Marx generator, can be used as the primary energy store. The high resistivity and high dielectric constant of these mixtures at low temperature permit low-loss operation on millisecond time scales. Simple design criteria linking load parameters and charging circuit characteristics to the liquid dielectric are developed which show that the dielectric constant, breakdown strength, and relaxation time are the primary properties of interest to the pulse power engineer. On time scales greater than 100 µs, injection of space charge, with density q and mobility µ, affects the charging and discharging circuit characteristics, introduces the time constant of the time of flight for injected charge to migrate between electrodes, and increases the effective ohmic conductivity σ to σ + qµ. A drift-dominated conduction model is used to describe measured space-charge effects. Kerr electrooptic field mapping measurements show strong space-charge effects with significant distortions in the electric field distribution a few hundred microseconds after high voltage is applied. The injected charge magnitude and sign depends on the electrode material. Thus by appropriate choice of electrode material combinations and voltage polarity, it is possible to have uncharged liquid, unipolar-charged negative or positive, or bipolar-charged liquid. An important case is that of bipolar injection, which has allowed up to a 40 percent higher applied voltage without breakdown than with no charge injection, and thus a doubling of stored energy due to the space-charge shielding which lowers the electric field strengths at both electrodes. Although injected space charge increases the stored electric energy over the capacitive space-charge-free energy, (1/2)CV2, more energy is required from a source during charging and the energy delivered to a resistive load is reduced because of internal dissipation in the capacitor as the charge is conducted to the electrodes. However, it appears that this extra dissipation due to injected charge can be made negligibly small and well worth the price if the space charge allows higher voltage operation for long charging time or repetitively operated machines.

Dielectric liquid level sensor and method

Abstract: A sensor for sensing the level of oil or transmission fluid under both normal and extreme temperature conditions. The only active components of the sensor have input and leakage currents substantially lower than those of diodes and current sources under high temperature conditions. The sensor has a probe, including a pair of electrodes forming a level detecting capacitor, adapted to extend in the vessel to detect the level of the liquid. A reference capacitor is included which has a capacitance substantially the same as the capacitance of the level detecting capacitor when no dielectric liquid is present between the electrodes of the level detecting capacitor. Circuitry is provided for measuring the capacitance of each capacitor and for deriving from the capacitance measurements a signal proportional to the level of the dielectric liquid at the sensor. Circuitry is also provided for testing whether the reference capacitor is operating properly. One of the electrodes of the level detecting capacitor is insulated to render the output of the sensor independent of high temperature conductivity effects. Structure and a method are provided for compensating for varying dielectric constants of the oil or transmission fluid in which the sensor is immersed.

Electric Field Measurement in Liquid Dielectrics Using a Combination of AC Voltage Modulation and a Small Retardation Angle

Abstract: A modified Kerr electro-optic effect technique has been applied to the direct measurement of electric field intensity in dielectric liquids such as nitrobenzene, tricresylphosphate, benzene, transformer oil and silicone oil. In particular, by utilizing the incident elliptically polarized light with retardation angle ?=1 degree and modulating applied alternating voltage, it was possible to measure the electric field using short electrode lengths of 6 cm for low Kerr constant liquids such as transformer oil and silicone oil.

Static electrification properties of transformer oil

Abstract: In recent years much attention has been given to oil flow in power transformers with cellulosic insulation, due to the failure of some field units from discharges resulting from charge accumulation. Charge separation is a function of several factors: nature of oil, flow velocity, type of solid insulation, surface conditions, duct space, insulation geometry, temperature, and the presence of ionic impurities and charge producing species in the oil. This paper focuses on the role of transformer oil in the charge separation process.

Stationary instabilities in a dielectric liquid layer subjected to an arbitrary unipolar injection and an adverse thermal gradient

Abstract: The effect of temperature variations of both ionic mobility and dielectric constant on the stability of a horizontal layer of dielectric liquid subjected to a DC electric field with heating and an arbitrary injection of unipolar charge from below is analysed. The marginal stability boundaries for steady convection are determined by numerical solution of the linearised thermo-electrohydrodynamic perturbation equations.

Distribution of atoms at the surface of liquid mercury

Abstract: Theoretical studies of the anisotropic distribution of atoms in the liquid/vapour interface have led to two conclusions. First, the density along the normal to the interface (the longitudinal one particle distribution function) has different forms in a liquid dielectric and a liquid metal. In a dielectric1, the density decreases monotonically as one passes from the liquid to the vapour, while in a metal2 the liquid/vapour interface is stratified for about three atomic diameters into the bulk liquid, Fig. 1 shows examples. Second, the transverse structure factor at the surface of a liquid (the Fourier transform of the in-plane distribution of pairs of atoms) is very similar to the bulk liquid structure factor except near the origin, the difference arising from long-range correlations in the surface1. The very few experiments3,4 that can be interpreted in terms of the properties of the density along the normal to the liquid surface are in agreement with the first set of predictions. There have been no published reports on the transverse structure factor in the liquid/vapour interface. Here we describe the transverse structure factor of the room temperature liquid/vapour interface of mercury, determined using the method of grazing incidence X-ray diffraction5. Our experimental results are consistent with the above predictions.

High-power pulse transformer for short high-voltage and/or high-current pulses

Abstract: A high-power pulse transformer for short, high-voltage and/or high-current pulses includes: a base plate in a container, an insulating, cooling dielectric liquid with a given heat transfer coefficient in the container; at least one magnet core on the base plate with self-enclosed magnet legs around a central window and wide sides with axes normal to the axis of the window; at least an undervoltage and an overvoltage winding in the liquid wrapped in each other around parts of the magnet core immersed in the liquid and linked to the magnet core and to each other, the windings including turns of substantially mutually doubly-wound electrically insulated metallic conductors having winding ends disposed in leadthroughs in the container walls, the conductors having surfaces with a heat transfer coefficient higher than that of the dielectric liquid; the turns of each winding being self-supported and spaced apart from the turns of the other winding by a first minimum spacing and spaced from the magnet core by a second minimum spacing; support insulators partly disposed in the liquid and adjacent and spaced from at least one side of the magnet core by a third minimum spacing being greater than the sum of the second minimum spacing and the thickness of the turns, at least the ends of the windings being secured in recesses formed in the support insulators; and a device for retaining the magnet core and the support insulators on the base plate.

A New Impregnant for HV Power Capacitors

Abstract: The main properties of a newly developed impregnant ant for high voltage power capacitors are given. This new liquid, a mono dibenzyltoluene blend (M/DBT), has a very high degree of aromaticity. The results of many tests carried out both on model and large capacitors are reported. A screening test using a transparent micro-model of an all-film capacitor has been used to study the properties of the fluid when submitted to very high electrical stresses resulting from transient overvoltages at low temperature. re. The correlation between the results obtained with micro-models and with real capacitors are reported. Partial discharge extinction ability of M/DBT is compared to that of liquids being used at present for this application. The authors describe the laboratory test that they have developed to evaluate the performances of the polypropylene filmliquid iquid insulation at high temperature. Using this test, the influence of many parameters is studied. They cast new light on all-film capacitor technology.

Physical Aspects of Vapor-Mist Dielectrics

Abstract: In earlier work it was shown that by acoustically cavitating a liquid dielectric, a dense mist (~2 x 105 droplet/cm3) of micron-size droplets could be formed which considerably increased the electrical strength of an insulating gas. The high electrical strength of these vapor-mist dielectrics results from a combination of the vapor from the droplets enhancing the gas strength and the droplets collecting electrons and ions. This latter effect helps prevent the formation of electron avalanches which precede breakdown. Within the vapor-mist dielectrics, complex mechanisms are involved, ranging from the enhanced vapor pressure at the droplet surface to surface tension effects and droplet charge which help prevent droplets from both freezing and evaporating. These aspects of vapor-mist dielectrics are examined and discussed in relation to the acoustic cavitation method used for generating the mist.

A computer simulation of transient electrohydrodynamic motion in stressed dielectric liquids

Abstract: Using a finite difference formulation of the Navier-Stokes equation coupled with a mathematical description of electrical charge migration. The authors examined transient electrohydrodynamic (EHD) phenomena in an electrically stressed liquid duct. Perturbations resulting from electrode injection are studied as a function of time by examining the liquid vorticity vector and stream function. The response of local pressure to advancing charge fronts is evaluated. The theoretical simulation is supported by previous laboratory studies of EHD motion. Experimentally recorded flow patterns are compared with the predicted results.

Electrical Conduction and Dielectric Breakdown in Liquid Dielectrics

Abstract: Carrier injection and transport in various liquid dielectrics are influenced strongly by space charge effects. Intensive studies have been performed in time-resolved observations of the pre-breakdown and the breakdown phenomena, using ultra-short pulse techniques and high-speed optical measurement techniques utilizing a high-speed camera and lasers in combination with schlieren, Mach-Zehnder and shadowgraphic methods. Both electronic processes and bubble processes play roles depending on conditions: time range, pressure, electrode distance, etc. The influence of the molecular structure on the breakdown characteristics and the laser-induced breakdown are discussed.

Partial discharges and the electrical aging of XLPE cable insulation

Abstract: This report describes a search for a possible relationship between partial discharges and electrical aging of XLPE cable insulation. It is well known that partial discharges can deteriorate polymeric insulating materials. Recently several theories on the relationship between partial discharges and aging have been published. In order to explore this relationship by experiments a method for the detection and localization of small partial discharges (less than 1 pC) in high voltage cables has been developed. A number of test cables has been aged during six months at a stress of 15 kV/mm rms at the conductor; three cables were held at room temperature and three cables were heated to 9ifc conductor temperature. The following measurements were carried out: partial discharge measurements, tan 0 measurements, breakdown voltage measurements and measurements on physical and chemical properties. The results show no significant aging and therefore no correlation between aging and partial discharge activity could be established. Wolzak, G.G., A.M.F.J. van de Laar and E.F. Steennis PARTIAL DISCHARGES AND THE ELECTRICAL AGING OF XLPE CABLE INSULATION. Department of Electrical Engineering, Eindhoven University of Technology, 1986. EUT Report 86-E-160 Addresses of the authors Dr.ir. G.G. Wolzak High-Voltage Laboratory Department of Electrical Engineering Eindhoven University of Technology P.O. Box 513 5600 MB Eindhoven The Netherlands Ir. A.M.F.J. van de Laar Research and Development Department NKF Kabel B.V. P.O. Box 26 2600 MC Delft The Netherlands Ir. E.F. Steennis Electrical Research Department N.V. KEMA P.O. Box 9035 6800 ET Arnhem The Netherlands

Capacitance and Dissipation Factor Measurements

Abstract: The history and applications of capacitance and dissipation factor measurements are thoroughly explained in this tutorial article.

Statistics of prebreakdown current pulses in n-Hexane

Abstract: In a stressed liquid dielectric there are electrical, optical, acoustical, mechanical, and chemical processes. As conditions approach those which favor complete electrical breakdown, instabilities are assumed to develop and grow to some ‘point of no return’, which may be the key to understanding breakdown for the purpose of inhibiting it. The events occurring before breakdown have often been considered as “noise”, but almost certainly contain useful information. In these studies, prebreakdown events are observed with state-of-the-art, low-noise electronics and high-speed digital equipment, and are analyzed with mathematical techniques for random processes to reveal the conditions for and mechanisms of the instability inception.

Electrification by liquid dielectric flow

Abstract: For lack of basic information and engineering guidelines, common practice in the design and operation of liquid-cooled power distribution equipment allows for applied electrical potentials, but not for those generated inadvertently by the flow of the semi-insulating coolant. The electric field generation initiated by the turbulent flow of semi-insulating liquids through insulating tubes is the subject of a recent study [1] because of its practical importance where the coolant must be conveyed between metallic elements constrained to different potentials. A limiting case from that study is summarized here to illustrate how to integrate into a self-consistent model the four basic processes of electrification: charge generation, transport, accumulation and leakage.

Electrode for electrical cell fusion

Abstract: PURPOSE:To prevent the adhesion of cell to an electrode in cell fusion, by applying a dielectric layer having small pores on the surface of an electrically conductive member. CONSTITUTION:A dielectric layer 11a having small pores 14a, 14b is applied to the surface of an electrically conductive member 12a. The dielectric material is preferably silicone, Teflon, etc. The formation of the dielectric material to a dielectric layer can be carried out e.g. by spray-coating powder of dielectric material or coating the surface of an electrically conductive material with a liquid dielectric material, etc. The thickness of the dielectric layer is preferably several tens nm - several tens mum. The diameter of the small pores 14a, 14b is smaller then the diameter of the cell. The fusion operation or induction operation can be easily and surely carried out by the use of the electrode while preventing the adhesion of the cell to the electrode.

Interpretation of Megohmmeter Tests on Electrical Apparatus and Circuits

Abstract: This article shows the interpretation of megohmmeter tests in electrical apparatus and circuits to ensure that insulation used in cables, motors, and switchgear is sound.

An experimental study of electrohydrodynamic dispersion from a liquid film flowing down an inclined plate into a continuous liquid phase.

Abstract: A water film flowing down an inclined copper plate with flash-boards was dispersed as charged drops into a stagnant dielectric liquid phase under a direct electric field applied vertical to the film surface. The dispersion characteristics were examined experimentally for three kinds of dielectric liquids under various operating conditions. The holdup fraction of the drops formed depends significantly on applied voltage, inclination angle of the plates and flow rate of the film phase. The electrical dispersion from the film phase and the electrical coalescence between drop and film phases contribute to effective agitation between the liquids adjacent to the interface, and rising and falling motion of the drops provides satisfactory mixing in the bulk of the continuous phase.

Machining apparatus working with electric discharge

Abstract: Machining apparatus working with electric discharge, in which inaccuracies in the machining as a consequence of temperature changes between the dielectric fluid and the machining device of the machining apparatus after the start of the machining operations are removed. An ambient-temperature sensor (21) records the temperature of the ambient air and a fluid-temperature sensor (22) records the temperature of the dielectric fluid. As a function of the initial values from these sensors and in accordance with the expected operating temperature of the machining device during the machining operations, the dielectric fluid is preheated in such a way that T1 + DELTA T, where T is the ambient temperature, T1 is the initial temperature of the dielectric fluid and DELTA T is the temperature rise of the dielectric fluid.

Current transformer cooled by a circulating dielectric fluid

Abstract: A current transformer has a hollow tube made from an electrical conductor which is bent at its center so as to form a loop which functions as a primary winding and two parallel straight portions at the ends of the tube which function as leads for the primary winding. The tube has a longitudinally-extending fluid-carrying passageway for a dielectric fluid formed at its center. Both ends of the tube are open and communicate with the inside of a reservoir for a dielectric fluid. A longitudinally-extending electrically-insulating member is inserted into the fluid-carrying passageway of one of the straight portions of the tube so as to decrease the cross-sectional area of the passageway in that portion and increase its resistance to flow. The increase in flow resistance produces a temperature difference within the tube, promoting circulation of the dielectric fluid by convection.

Optical Electric Field Assessment in a Dielectric Liquid

Abstract: A new experimental method is described in which the electrostrictive effect in a liquid is made visible. A real-time interferometer employing a Q-switched ruby laser was used to record transient optical disturbances. When a pulse voltage, synchronized with the laser pulse, was applied to the test object, interference fringes were produced in the viewing plane that could be recorded on photographic film. Experimental results are presented, together with a model for interpretation.

New Liquid Insulating Materials

Abstract: The transition in liquid insulating materials is not so remarkable as in gaseous materials and solid materials. But important changes have occurred concerning the toxicity problem of PCB. This non-flammable liquid is being replaced by low-flammable liquids in transformers and capacitors.

Numerical experiments of axisymmetric flow in a nonuniform gravitational field

Abstract: A numerical study of the steady, axisymmetric flow in a heated, rotating spherical shell is conducted to model the Atmospheric General Circulation Experiment (AGCE) proposed to run aboard a later Shuttle mission. The AGCE will consist of concentric rotating spheres confining a dielectric fluid. By imposing a dielectric field across the fluid, a radial body force will be created. The numerical solution technique is based on the incompressible Navier-Stokes equations. In the method, a pseudospectral technique is used in the latitudinal direction; a secondorder-accurate finite-difference scheme discretizes time and radial derivatives. The performance of this numerical scheme is discussed for the AGCE, which has been modeled in the past only by pure finite-difference formulations. In addition, previous models have not investigated the effect of using a dielectric force to simulate terrestrial gravity. The effect of this dielectric force on the flowfield is investigated, as well as the effects of varying rotation rates and boundary temperatures. Among the characteristics noted are the production of larger velocities and enhanced reversals of radial temperature gradients for a body force generated by the electric field. Correlation among flowfields with uniform, inverse-square and inverse-quintic force fields is obtained using a modified Grashof number.

Optical shutter device

Abstract: PURPOSE:To control the position of dielectric liquid in a container, to control the transmission state of light and to improve reliability and speed up operation by providing the dielectric liquid in the container movably and controlling an electric field established in the container. CONSTITUTION:When switch contacts 7a and 7c are connected to each other, an electric field is established between a common electrode 3 and an on electrode 5 and the liquid 2 is therefore attracted to an area where the electric field is intense and positioned between the electrodes 3 and 5. In this state, incident light 8 passes through a shutter device and guided out as projection light 9. When switch contacts 7b and 7b are connected to each other, on the other hand, an electric field is produced between an off electrode 4 and the common electrode 3 and the liquid 3 moves to an area where the electric field is intense with its electric strain force and is positioned in the opposite area of the electrodes 3 and 4. At this time, the incident light 8 is cut off by the liquid 2, so the projection light 9 is not guided out. The time required for the movement of the liquid is short, so the light is brought under on/off control at a high speed.

Some Effects of Quench Rate on The Properties and Microstructures of Amorpous and Crystalline Materials Produced by Spark Erosion

Abstract: Spark erosion provides a means for producing fine particles (5 nm to 75 um) of metals, alloys, and semiconductors. Since the powders are formed from liquid droplets solidified in a liquid dielectric, the rate of solidification of the particles can be very high, varying according to particle size and the dielectric used. This paper examines some effects of different dielectrics on the microstructures, magnetic properties,and crystallization characteristics of amorphous and crystalline metals. It is seen that these properties depend upon the quench rate provided by the dielectric. In the case of the organic dielectrics, the quench rate appears to be associated with specific properties of the dielectric.

High-voltage capacitor of high energy density

Abstract: Elementary high-voltage capacitor of high energy density for applications in energy storage, discharge, switching or filtering, consisting of two conductive armatures separated by at least one sheet of dielectric, characterised in that at least one sheet of a first dielectric is associated with each armature, that each armature consists of a metallisation which has a resistance of 2 to 30 ohms per unit area, deposited on a second dielectric consisting of a support which has a fibrous structure promoting regeneration, so that the capacitor is regenerating (self-healing), that the capacitor is impregnated with a liquid dielectric and that the nature and the thickness of each of the dielectrics as well as the liquid dielectric are chosen so that at the time when the capacitor is subjected to its nominal voltage the ratio of the electrical field to the dielectric strength is substantially equal for each of the dielectrics When this capacitor is charged at its nominal voltage, the average electrical field prevailing in the dielectric is approximately 200 V/ mu m to more than 400 V/ mu m, and its energy density per unit volume is from approximately 05 J/cm to more than 2 J/cm

Heat transfer element and its use in a circuit package

Abstract: A heat transfer element has through holes (17,19) formed as a narrow entrance opening (19) to one surface and a wider diameter cavity opening (17) to the other surface. Two foils (12a,12b) are laminated with the narrow entrances opening to the outside and with the wider cavities closed by the inside surface (22b) of the other foil. In the completed structure the cavities and their entrances form nucleate boiling sites. In a manufacturing step of forming the through holes, the junction (21) between the narrow entrance and the wider diameter cavity is shaped to prevent a heat transfer liquid from flooding the cavities. The structure is particularly useful for fins for cooling circuit devices that are immersed in a dielectric liquid. In one heat transfer structure, the fins are formed by laminating two metal foils that have differing co­efficients of thermal expansion. The fins spread apart as their temperature increases, and components are cooled in proportion to the heat they produce.