Showing papers on "Liquid dielectric published in 1991"

Rotational dielectric friction on a generalized charge distribution

Abstract: The dielectric friction on a solute molecule reorienting in a liquid solution is computed by modeling the solute as a rigid collection of point charges rotating within a spherical cavity in a dielectric continuum. Such a calculation on an extended charge distribution is a logical progression from existing theories, which treat only single point charges or point dipoles. It is shown how a more realistic charge distribution can change the calculated friction coefficient by several orders of magnitude, and the generalized theory is applied to rotational diffusion data for three phenoxazine dyes in dimethylsulfoxide.

Dielectric charging processes and arcing rates of high voltage solararrays

Abstract: When high-voltage solar arrays are used in the low Earth orbit environment, serious interactions are known to occur between the solar cell material and the surrounding plasma. Arcing is known to be one of the most severe interactions. The charging processes of the dielectric coverglass by charged particles are studied numerically. If there is a field emission site with a high electric field enhancement factor /? on the interconnector, charging processes due to enhanced field electron emission (EFEE) can be initiated and lead to the collisional ionization in neutral gas desorbed from the coverglass. Based on this arcing onset model, an arcing rate is calculated for a high-voltage solar array and good agreement is found with experimental data.

Dielectric behavior of silicone and ester fluids for use in distribution transformers

Abstract: Investigations to determine the relevant electric and dielectric properties of certain insulating fluids which appeared most suitable from the viewpoint of environmental compatibility and inflammability are discussed. Two of these are silicone fluids based on linear polydimethyl siloxane (kinematic viscosity at 25 degrees C is 50 mm/sup 2//s) and an ester fluid based on penthaerythrithol tetraester. After a short description of the insulating fluids, the influence of aging on the breakdown and dissipation factor is determined. Furthermore, a comparison of the breakdown and aging behavior of fluid-paper composite dielectrics is made. The influence of partial discharge prestressing on the breakdown of the fluid-paper composite dielectric is shown. >

Technical aspects of interfacial phenomena in solid insulating systems

Abstract: HV insulation systems are often composed of different insulating materials. In the contact areas between these materials (interfaces) interfacing polarization may occur, resulting in an increase of both permittivity and loss tangent and, consequently, of dielectric losses. By the interaction of humidity such interfacial phenomena may be enhanced. Other important characteristics of insulating systems such as the treeing strength and the breakdown strength are also lowered by interfaces, especially when humidity has been adsorbed. Microscopic and macroscopic, internal and external interfaces are defined for composite insulation systems. Interfacial phenomena in such systems, for instance made out of fiber glass-reinforced polymeric materials, are described both under dry conditions and in the presence of water. It is demonstrated that the hydrophobic properties of materials improve the dielectric characteristics; this is true for bulk and surface properties. >

Flexible fuel sensor system

Abstract: A method and apparatus for determining the percentage of two different fluids having substantially different dielectric properties such as a gasoline/alcohol or a water/oil mixture. An inductive coil element immersed in the mixture exhibits a distributed capacitance level which is directly proportional to the dielectric constant of the fluid mixture surrounding the coil which, in turn, is directly proportional to the percentage of each fluid in the mixture. The loops of wire in the coil act as equivalent electrodes in creating a capacitance between each loop. The dielectric constant of a mixture will increase with the percentage of the higher dielectric fluid thus increasing the capacitance. An amplifier is constructed that oscillates at the resonant frequency of the LC circuit formed by the coil in the mixture. The resonant frequency decreases as capacitance increases. The subject invention includes a circuit which converts a frequency signal generated by energization of the coil to a voltage signal which, in turn, is sent to an engine controller. The output signal is used by the engine controller to selectively adjust the fuel ratio and the spark timing of the engine in accordance with the percentage of alcohol in the fuel mixture.

Transient deformation of freely-suspended liquid droplets in electrostatic fields

Abstract: The problem of freely-suspended liquid droplets deforming due to an applied electrostatic field is examined. Developed is a numerical model capable of predicting the complete transient histories of droplets in systems with a wide range of dispersedand continuous-phase densities, viscosities, relative permittivities, and electric field strengths. For liquid/gas systems, the predictions of the numerical model demonstrated that the critical field strength and critical permittivity ratio during actual transient breakup are not necessarily the same as those predicted by steady-state theories. An approximate analytical model of transient droplet deformation is also developed, which is able to predict the deformation time histories for large Ohnesorge number, small-deformation liquid/liquid systems. The approximate analytical model agreed well with the results of the complete numerical model.

Electric field in transformer oil measured with the Kerr-effect technique

Abstract: The electric field distribution in transformer insulating oil was measured as a function of time, both after application of a DC step voltage and after polarity change of the DC voltage, using a highly sensitive advanced Kerr electro-optic technique. The lower limit of the applied electric field intensity was 100 V/cm in insulating oil with an electrode length of 8 cm. Charge distribution as a function of time was calculated from the measured electric field distribution. The mobility of ionic carriers, 2.1*10/sup -5/ cm/sup 2//Vs, in paraffinic transformer oil was obtained from the relationship between the saturation time of charge density and the applied DC voltage. The relaxation time of accumulated charge near the electrodes after short-circuiting the electrodes was independent of the pre-applied DC voltage. >

A singular flashover path observed on the surface of synthetic-resin-bonded paper cylinders immersed in transformer oil under switching impulse voltage conditions

Abstract: In order to clarify basic surface flashover phenomena in transformer oil under switching impulse voltage, the flashover characteristics on four kinds of large insulating cylinders are studied for positive lightning impulse of 1.2/50 mu s, positive switching impulse of 500/3600 mu s, and 50 Hz alternating voltage. The insulating cylinders are made from material containing about 40 wt.% phenol resin and 60 wt.% kraft paper. A singular surface flashover path is observed under switching impulse voltage which includes a partial jump of the discharge channel around the HV electrode. The peak value of the flashover voltage for the switching impulse is nearly equal to that of a 50 Hz voltage; this was not expected before the experiment, because breakdown voltage of switching impulse for oil-immersed insulation is generally intermediate between the lightning implulse and AC voltage. The singular flashover path of the switching impulse is explained by an electric field analysis taking account of the remaining charge of 100 pC/mm/sup 3/ which has the same polarity as the applied voltage and is spread out along about 10 to 40% of the distance between the HV electrode to the grounded electrode. >

Interface influence on the high‐field conduction phenomena of a thin dielectric liquid layer

Abstract: We report experimental work on the ac conduction phenomena of a thin dielectric liquid (capacitor impregnant) layer at high‐electric field for several interfacial situations. The features revealed by these experiments show a strong dependence of the liquid electric losses (at frequency 50 Hz) and according to that, the liquid is in contact with a metallic or a polymer interface. An attempt is made to comment these measurements in terms of the existing theories of ionic conduction in nonpolar liquids: it turns out that charge‐carrier injection in the neighborhood of the interface is the dominant contribution of the high‐field liquid conductivity. A theoretical evaluation based on a unipolar injection model is given in agreement with the experimental results obtained in the different configurations.

Development of a perfluorocarbon liquid immersed prototype large power transformer with compressed SF/sub 6/ gas insulation

Abstract: A prototype of a three-phase nonflammable high-power transformer has been developed. It uses nonflammable perfluorocarbon liquid as both a coolant and an insulating material for windings, and compressed SF/sub 6/ gas as the insulation from the outer windings to the tank. Using cooling and insulation models, the cooling and insulation characteristics of the disk windings were clarified. Stress analyses and pressure tests on the transformer tank were carried out to evaluate its mechanical characteristics. A prototype of a 275 kV 100 MVA three-phase transformer was developed, and its excellent performance was confirmed. >

Influence of ageing on depolarization currents in polymer-insulated medium-voltage cables

Abstract: Depolarization currents in a larger number of virgin and aged polymer-insulated medium-voltage cables have been measured as a function of the magnitude of the applied electric field. In comparison with new cables some service-aged cables revealed unusual dielectric properties. As expected, unaged cables show a lineal relation between the depolarization current and the polarizing field at moderate electric field strengths. In contrast, for many service-aged cables a more than proportional increase of the depolarization current with the applied electric field was observed (indicating some nonlinearity). Visual inspection of the cables showed a very high density of bow-tie trees in the 'non-linear' cables. Furthermore, it was observed that the nonlinearity vanished when the cable was dried and reappeared again after wetting the cable. As a conclusion from these observations, it is believed that the non-linear dielectric behaviour is a consequence of the presence of bow-tie trees in the cables. In our opinion it may be worthwhile considering the measurement of depolarization currents as a diagnostic measurement technique to detect water trees in buried cables.

Simultaneous measurements of thickness and temperature profile in a wavy liquid film falling freely on a heating wall

Abstract: A technique far measuring the thickness of liquid films was developed and successfully tested. The feasibility of this technique was demonstrated in stagnant liquid films as well as in liquid jets. A procedure for in-situ calibration of the thickness probe was developed, allowing the adaptation of the probe to measurements of wavy liquid films. The thickness probe was constructed from a platinum-rhodium wire that was stretched across the film. A constant DC current was supplied through the probe wire, and film thickness was determined from variations in the probe voltage drop resulting from the large differences in the electrical resistances of the wetted and unwetted segments of the wire. Unlike electrical admittance thickness probes, the new probe did not require dissolving an electrolyte in the liquid, making the new probe well suited to studies involving sensible heating of a film of pure dielectric liquid that is in duvet contact with a current-carrying wall. Also presented is a composite probe that ...

Light control device

Abstract: PURPOSE: To improve the response speed of a transmission rate of light when the impression of an electric field is released by forming films which control the surface free energy consisting of org. matter or inorg. matter on dielectric side surfaces. CONSTITUTION: The control films 4 which consist of the org. matter or inorg. matter and control the surface free energy are formed on the dielectric side surfaces of a pair of electrodes by which the electric field is impressed to a suspension. The control films 4 are not limited in material quality and film thickness, insofar as the films are not changed by contact with a liquid dielectric 5 and fine particles 6 and have excellent durability and weatherability. The preferable inorg. matter includes graphite fluoride, graphite, etc., and the preferable org. matter includes polyimide, silicone, fluororesin, etc. The films 4 which control the surface free energy are formed on the surfaces of the electrodes 7 in contact with the suspension in such a manner and, therefore, the polarity component forces in particular are greatly decreased and the interaction between the fine particles and the electrodes 7 is decreased and the since the vigorous Brown motion of the fine particles 6 is obtd., the relaxation performance is improved. COPYRIGHT: (C)1992,JPO&Japio

Liquid Breakdown and Its Relation to Gas Breakdown

Abstract: Breakdown of dielectric media occurs via a fast succession of irreversible processes which produce a high conductivity between electrically stressed conductors when the voltage exceeds a certain value. Breakdown can also be achieved in gases, liquids and solids through the action of an intense beam of light produced by a laser (laser-induced breakdown). Depending on the particular situation, breakdown takes place in times ranging from ps to ms. The breakdown voltage depends not only on the dielectric itself, its purity and the way it is handled, but also on the geometry of the gap, the nature and finish of the electrodes, pressure, temperature and on the shape and duration of the applied voltage (DC, AC, impulse). Another point of importance is that the vast majority of high voltage equipment is insulated with a combination of at least two of the generic media, breakdown of the whole insulation issuing from complex interactions between each other.

The interpretation of electrohydrodynamic mobility under unipolar injection in dielectric liquids

Abstract: The EHD (Electrohydrodynamic) mobility with unipolar injection in the transient regime has been investigated theoretically in terms of the EHD interfacial instability. A new expression of the transient EHD mobility is given by considering the dynamics of the interface between the space charge layer in front of the injecting electrode and the bulk of the dielectric liquid. It is shown that the EHD mobility depends on not only the ( in / rho )/sup 1/2/, but also on the characteristics of the interface and electrode separation. The dynamics of the space charge/liquid interface plays a very important role in the conduction process, especially in the dielectric liquids in which the ion 'injection' is the predominant mechanism of providing charge carriers. The type of instability proposed leads directly to the observed EHD delay time, mobility, and fine filamentary structure of the transient electroconvection which has been observed experimentally. >

Power generator making use of electrostatic force

Abstract: PURPOSE:To generate powerful torque by filling a space between each of stators and a movable element with a liquid dielectric constituted of tricresolphosphate. CONSTITUTION:An electrostatic linear motor is such that a large number of electrodes 2 are projected at specific intervals to the opposite surface of each of stators 1 opposed to each other at an interval. Rectilinear motion elements 3 forming movable elements by opposing to the stators 1 respectively are so arranged between the stators 1 that they can make a rectilinear motion, and the rectilinear motion elements 3 are such that two kinds of dielectrics 4 and 5 having different dielectric constants are alternately arranged at different intervals from intervals between adjacent electrodes in each of the stators 1. A liquid dielectric 6 constituted of tricresolphosphate having specific inductive capacities 6.5 and dielectric strength 14kV/mm is filled between each of the stators 1 and the rectilinear motion elements 3. As the result, the rectilinear motion elements 3 can be moved in the right and left directions of a drawing by impressing voltage successively to the electrodes 2 of each of the stators 1 in the specific order.

Effect of dissolved water in several kinds of liquid dielectrics on conduction

Abstract: 1 .Introduction Generally it is known that water in liquid dielectrics influence to electrical conduction and breakdown phenomena. Such water in dielectrics has been understood that they behaved as the carrier with electrical charge sometimes or the conduction bridge sometimes. In the past studies on conduction of liquid insulators, it is doubtful whether dissolved water can be measured completely or not. Still more the state of water in liquid dielectrics can not be measured by Karl Fisher’s method also. Because Karl Fisher’s Method which use chemical reaction can not measure whole water in liquid and their state always. Therefore the relation between the amount of the water and the electrical phenomena had not been clearly. On the other hand the observing method of state and agglomeration of water has been published by chemical researchers as the result measured by Near Infra Red Ray(N1R) or Infra Red Ray(1R) Method. At the region IR, it has been published that the agglomeration of the water classified into Monomer, Dimmer, Trimmer((H20)1,(H20)2,(H20)3 or n). In this paper, using FT-IR Method and Karl Fisher’s Method the state and agglomeration of water and the amount of water in several kinds of liquid materials are measured. And using amount of the Monomer, Dimmer and Trimmer measured by FT-IR Method under electrical stress, the relation between the water in these liquids and conduction are discussed. At the result, it is seen that the conduction in the liquids depend on amount of Dimmer except Silicon Oils which consist of polymeric structure. And, at the case of Silicon Oils the increasing Dimmer which is little part of whole Dimmer influence to conduction phenomena.

Linear oscillations of a drop in uniform alternating electric fields

Abstract: Oscillations of a conducting drop immersed in a dielectric fluid in an alternating electric field has been modelled in order to understand the enhancement of the transport processes by the electric field. Numerical solutions for oscillation amplitude, velocity distribution, resonant frequency and streamlines were obtained. The effects of viscosity and density on the resonant frequency and the velocity distribution were investigated. It was found that the resonant frequency of viscous fluids was always smaller than the free oscillation frequency of the same droplet. The predicted scanning frequency response curve and the streamlines agree well with the experimental observations.

Fluctuations of potential induced by turbulent flows of dielectric liquids through metallic pipes

Abstract: An analysis is presented of the fluctuations of the potential difference between two parts of metallic tube insulated to each other and through which a dielectric liquid is flowing with a turbulent flow. First, the phenomenon of the convection of the double layer appearing at the contact solid/liquid and in the case of a turbulent flow is described. Then, the expected reasons of the potential fluctuations existing are proposed. Equipment is developed to measure the potential difference, and the experiments are presented and discussed. >

Dielectric performance of gas-insulated switchgear and possible methods of on-line monitoring

Abstract: The dielectric performance of gas-insulated switchgear (GIS) is critical to its long term service integrity. Many parameters that are of little significance to open type air insulated switchgear are of vital importance to GIS. Detailed on-site examination is necessary to ensure chamber cleanliness during site erection as a foreign object left inside can in itself induce dielectric breakdown. In addition loose, or ineffectively bonded, line or earth side components can vibrate under the effects of both magnetic and electrostatic forces to induce partial discharge activity.

A drift/diffusion conduction model for flow electrification of turbulent liquid dielectrics

Abstract: A drift/diffusion flow electrification model is developed for bipolar conduction in a turbulent liquid dielectric between rotating concentric cylindrical electrodes with open-circuited, short-circuited, or DC voltage energized electrodes. Experimental data are used to estimate model parameters such as the density of each charge carrier at the electrode walls and the mobility ratio of the charge carriers. Typical experimental measurements indicate wall charge densities much larger than the equilibrium charge densities of each carrier, invalidating a quasiequilibrium ohmic conductivity model as the local conductivity near the wall is enhanced over the equilibrium conductivity. Specific electrode wall charge densities are found which yield near self-consistent solutions with measurements of open-circuit voltage, short-circuit current, and turbulent core charge densities. Experimental DC voltage excitation across the cylinders is treated in anticipation of future measurements. >

Natural convection immersion cooling of an array of heated protrusions in an enclosure filled with dielectric liquid: effects of enclosure width and fluid Prandtl number

Abstract: : An experimental investigation of natural convection immersion cooling of an array (3 by 3 horizontally-placed heated discrete protrusions) in an enclosure filled with dielectric fluids has been conducted. Each rectangular protrusion simulates a 20 pin dual-inline-package. Effects of enclosure width and fluid Prandtl number were examined. Five different spacings from 42 mm to 7 mm and two dielectric fluids, FC-75 (Pr=25 at 27 C) and FC-43 (Pr=82 at 27 C) were used. The top boundary of the enclosure was kept constant at 10 C and the bottom boundary was insulated during the experiments. Power dissipation levels per component ranged from 0.115 W to 2.9 W. Component surface temperature measurements were used to obtain the nondimensional heat transfer parameters. In the case of FC-75 and 30 and 7 mm spacings, and in the case of FC-43 and 7 mm spacing, timewise fluctuations of temperature at steady state in several locations were recorded with increasing power level.

Liquid dielectric resistivity/resistance tester

Abstract: The utility model is composed of a liquid dielectric storing device, a temperature control circuit, a temperature display circuit, a direct current high-voltage circuit, an impedance converter circuit, a resistivity resistance converting circuit, an A/D conversion circuit, a data processing circuit, a drive circuit, a display circuit and a sequence circuit. The utility model with compact structure, stable operation, convenient use and high precision is in particular suitable for measuring the resistivity and the resistance of transformer oils.

Natural convection immersion cooling of an array of vertically oriented heated protrusions in an enclosure filled with a dielectric liquid: Effects of enclosure width, Prandtl number and component orientation

Abstract: : The natural convection heat transfer characteristics of a 3x3 array of vertically oriented heated protrusions, immersed in a dielectric liquid, were investigated. Aluminum blocks, 24mm x 8mm x 6mm, were used to simulate 20 pin dual in-line packages. Surface temperature measurements of the components were made by imbedding copper-constantan thermocouples below the surface of each component face. A constant heat flux was provided to each component using an Inconel foil heating element. Power supplied to each component varied from 0. 115W to 2.90W. The aluminum blocks were mounted on a plexiglass substrate to form a 3x3 array of simulated electronic components. The circuit board containing the components was placed in a rectangular, plexiglass enclosure with inner dimensions: L = 203.2mm H = 152.0mm W = 82.6mm, and a wall thickness of 25.4mm. The upper boundary was maintained at 10 C, while all other exterior surfaces were insulated. The chamber width, measured from the surface of the circuit board to the opposite, inner wall of the enclosure, was varied from 42mm to 7mm by inserting plexiglass spacers into the enclosure. Two dielectric liquids, FC-75 and FC-43, were used as working fluids. Non dimensional data from this study was combined with the data obtained for a horizontal component orientation, to develop an empirical correlation which predicts the Nusselt number as a function of Rayleigh number, Prandtl number, component orientation and chamber width. This correlation was found to be accurate to within 11% of the original curve fit data.