Showing papers on "Liquid dielectric published in 1990"

Cooling of a multichip electronic module by means of confined two-dimensional jets of dielectric liquid

Abstract: Experiments were performed to investigate single-phase heat transfer from a smooth 12.7×12.7 mm 2 simulated chip to a two-dimensional jet of dielectric Fluorinert FC-72 liquid issuing from a thin rectangular slot into a channel confined between the chip surface and nozzle plate

Cooling of a Multichip Electronic Module by Means of Confined Two-Dimensional Jets of Dielectric Liquid

Abstract: Experiments were performed to investigate single-phase heat transfer froma smooth 12.7 {times} 12.7 mm{sup 2} simulated chip to a two-dimensional jet of dielectric Fluorinert FC-72 liquid issuing from a thin rectangular slot into a channel confined between the chip surface and nozzle plate. The effects of jet width, confined channel height, and impingement velocity have been examined. Channel height had a negligible effect ont eh theat transfer performance of the jet for the conditions of the present study. A correlation for the convective heat transfer coefficient is presented as a function of jet, width, heat length, flow velocity, and fluid properties. A self-contained multichip cooling module consisting of a 3 {times} 3 array of heat sources confirmed the uniformity and predictability of cooling for each of the nine chips, and proved the cooling module is well suited for packaging large arrays of high-power density chips.

Breakdown of transformer oil

Abstract: Some of the factors affecting the dielectric strength of transformer oil are investigated. These factors include the stabilization phenomenon, oil and electrode pretreatment, the effect of oil velocity, the effect of a capacitance parallel to the test cell, and the effects of electrode area and gap spacing. The experimental apparatus and procedure are described, and the results are presented for each of the above factors. Suggestions for future research are offered. >

Nonlinear interactions of particles in chains

Abstract: Measurements of the effective electric dipole moments of conducting particle chains suspended in insulating dielectric liquid reveal the influence of dielectric breakdown between particles. This breakdown can lead to reversal of the sign of the interparticle force from attractive to repulsive. Other measurements with a vibrating sample magnetometer of the effective magnetic dipole moments of ferromagnetic particle chains provide clear evidence that chaining enhances nonlinear magnetization at a field intensity about a factor of 10 below the value at which saturation is observed for single particles. Both of these physical situations are examples of how nonlinear effects can influence the electromechanical interactions of closely spaced particles. The nonlinearity is caused by the very strong field intensification that occurs in the gaps between particles for chains parallel to an applied electric or magnetic field. A correspondingly strong nonlinear effect is predicted for the forces between particles in chains.

Determination of electric field distribution in oil using the Kerr-effect technique after application of DC voltage

Abstract: A technique based on the Kerr electrooptic effect is used for the measurement of electric field strength in dielectric liquids such as transformer oil. An elliptically polarized laser beam is used as incident light and the applied DC voltage is modulated with an AC voltage. Using this technique, low-level electric fields are measured in liquids with small Kerr constants using a short electrode length. The change of electric field distribution with respect to time after application of a DC step voltage and the nonuniformity of the electric field in water-saturated transformer oil are also studied. The electric field in water-saturated transformer oil is shown to be distorted, and the charge density is shown to be about 1 nC/cm/sup 3/ when the applied step DC voltage is 2 kV. However, electric field distribution is found to be uniform in dry transformer oil, dry silicone oil, and water-saturated silicone oil. >

Progress in the field of electric properties of dielectric liquids

Abstract: It is noted that the past three decades have seen significant changes in the types of materials used for electrical insulation. These changes were brought about by the realization that some of the previously used materials were detrimental to the environment and to the people who came in contact with them. The use of polychlorinated biphenyls was prohibited, and replacement materials had to be developed. Paper was replaced to a large extent by polymer film, and paraffinic oils were finally used as replacement for oils derived from naphthene. At the same time progress was made in the understanding of the nature of electrical charges and how they move through dielectric fluids under the influence of externally applied electrical fields. The impact of these developments on the field of liquid insulating materials is discussed. Attention is also given to the information obtained with the latest ultra-high-speed electrooptical equipment. The generation and propagation of charge carriers are examined in detail, and their relation to electrical breakdown is analyzed. A brief survey of the special instruments used in these studies is presented, and the advantages and disadvantages of the various measuring techniques are discussed. >

The effect of pressure on streamer inception and propagation in liquid hydrocarbons

Abstract: High-speed electrooptical techniques are used to study prebreakdown behavior in n-hexane and toluene at pressures between 0.1 and 5 MPa. The results show that pressure inhibits the formation of low-density regions and increases prebreakdown inception voltage. The observed pressure effects suggest that the low-density region is the result of liquid vaporization near the electrode. Results obtained with a chopped voltage pulse indicate that the shape of the applied voltage is not critical to streamer growth. Streamers were observed growing after the voltage pulse had been removed, which suggests that the streamer growth process is: (1) to some extent locally controlled by the presence of injected charge, or (2) controlled by thermal expansion of the low-density region. It was also observed that the streamer would initiate, grow, and then disappear under impulse voltage conditions. >

Enhanced partial discharges due to temperature increase in the combined system of a solid-liquid dielectric

Abstract: Partial discharges which emanate from solid dielectrics immersed in insulating oil when high impulse voltages are applied under different environmental temperatures (20, 40 and 80 degrees C) are discussed. The solid dielectrics used for the measurements are phenol-impregnated pressboard and industrial bakelite. The samples are cut in wafers of 150 mm diameter and are 1 or 2 mm thick. The insulating oil is a typical transformer oil. The switching type of the impulse voltage used, 250/2500 mu s, corresponds to functional situations and is long enough to produce the effects that can be detected without the consideration of charge transfer phenomena due to fast rates of field changes. Experimental results show that the total charge transfer due to partial discharge is increased by temperature. A possible explanation of the undergoing physical process may be that in the low-field regime, temperature perturbation effects on the injected current are characterized by the conductivity changes in the volume of the dielectric, while as partial discharges start occurring, avalanche multiplication of conduction electrons appears to be the dominant phenomenon, characterizing the behavior of a metal/thick insulator/metal structure in the high-field regime. The circuits, measurement, and measuring procedures are discussed. >

The influence of morphology on the electrical breakdown strength of polypropylene film

Abstract: The relationship between the microscopic structure morphology and the electrical strength of polypropylene (PP) film used in PP-laminated paper (PPLP) in very high voltage oil-filled cable is studied by several methods including infrared spectrum, X-ray diffraction and dynamic mechanical spectra. It is found that the key to improve the breakdown strength, the tensile strength and the stability in oil for PP film is to increase its structure parameters, namely, its crystallinity, orientation and molecular weight. The interaction between PPLP and liquid dielectric is also studied. It is found that when it is immersed in dodecyl benzene at 100 degrees C, the strength of PP film decreases because the amorphous part dissolves and disorientation occurs. >

Streamer propagation over a liquid-solid interface

Abstract: A needle immersed in transformer oil is located just above a sheet of glass of which the opposite surface is conducting. By applying high-voltage (HV) steps, streamers which propagate radially with numerous branches are generated. The characteristics of these discharges (mean propagation velocity, final extension, and electric current and charge) are determined, and the measured charge is compared with the predictions of two simple models. A technique for guiding the discharges gives single quasi-rectilinear streamers, which allows a more accurate investigation. The mean electric current and the final charge indicate that the streamer channels are, to a first approximation, at the potential of the needle. The simple picture of a finite potential gradient along the channels is discussed with reference to the intermittent character of the discharge phenomena. >

The high voltage design of superconducting power transmission systems

Abstract: The special problems that arise when designing a superconducting system are examined. These are: (1) that the voltage and current levels chosen must permit economic integration into existing transmission and generation facilities; (2) the mechanical design of components that get cold must permit relatively large absolute contraction and possibly differential contraction without damage that may affect successful operation, and cool-down and warm-up cycles throughout the life of the system should not cause deterioration of the dielectric insulation; and (3) the dielectric losses of the insulation must be carefully controlled in AC systems. Basic research on cryogenic dielectrics is briefly reviewed, and 11 projects around the world that have engaged or are engaging in electrical insulation testing of prototype cables are described. The development of accessories is discussed. >

Bouncing motions of liquid drops between tilted parallel‐plate electrodes

Abstract: The paper reports on experimental and analytic studies on translational motions of liquid drops in an immiscible, dielectric liquid confined by a pair of tilted parallel-plate electrodes, across which a steady electric field is being applied. With an increase of the strength of the field, drops begin to bounce back and forth between the electrodes while falling down along the axis of tilt of the electrodes. The bouncing motions are found to be predictable with a reasonable accuracy by using a simple model constructed within the framework of conventional fluid mechanics and electrostatics.

Study of the time to breakdown in transformer oil under impulse conditions

Abstract: The time to breakdown in dielectric fluids has been studied extensively, and it has been shown that the time elapsed between the start of the pulse and breakdown decreases with increasing voltage. Basically, two regimes can be distinguished, depending on whether breakdown occurs on the rise of the pulse or on its tail. The first regime occurs at much higher voltages than the latter one and it usually occurs at small electrode separations. In the first regime the time to breakdown decreases more or less regularly with increasing crest voltages while in the second one the time to breakdown shows interesting statistical fluctuations. The significance of these fluctuations is discussed. An attempt is made to show that these temporal fluctuations at more or less constant crest voltage are a reflection of the electron emission characteristics of the cathode. >

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

Abstract: This paper reports on a technique for measuring the thickness of liquid films that was developed and 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 direct contact with a current- carrying wall. Also presented is a composite probe that facilitated simultaneous measurements of temperature profile across a wavy liquid film and film thickness. Experimental results demonstrate a strong influence of waviness on liquid temperature in a film of deionized water falling freely on themore » outside wall of a vertical, electrically heated tube for film Reynolds numbers smaller than 10,000.« less

Dielectric relaxation in polar and viscoelastic fluids

Abstract: The generalized evolution equations for the polarization vector and the total stress tensor (viscous plus Maxwell’s electric stress tensors) are obtained in the framework of extended irreversible thermodynamics. The coupling of these equations represents the mutual influence between mechanical and dielectric properties of a viscoelastic and dielectric fluid. The dipolar memory and the associated correlation functions are discussed in order to give an understanding in the current way of thinking based on linear response theory. A comparison with studies of polarization charge diffusion is included as a particular result obtained from the generalized constitutive equations. Calculations of the complex electric susceptibility and the complex viscosity for the linear and incompressible case are presented.

The inception and structure of prebreakdown streamers in perfluorinated polyethers

Abstract: Electrical measurements of perfluorinated polyethers were performed to determine the suitability of this class of material as a liquid dielectric. Measures of the breakdown strength and streamer inception voltage are obtained under electrical impulse stress. The breakdown strength is nearly independent of polarity. Under high magnification photography the cathode-originated streamers are seen to have a subsonic mode of growth. The transition to fast growth occurs on time and spatial scales shorter than those found in liquid hydrocarbons. The gas-phase electrical properties and the high heat of vaporization of this material are considered as mechanisms for this behavior. >

The effect of an axial electric field on the stability of a rotating dielectric cylindrical liquid bridge

Abstract: The branching points of the shape families bifurcating from a cylindrical liquid bridge anchored on two plane‐parallel electrodes, when subjected to rotation and an electric potential difference, are determined. It is shown that the cylindrical shape may be destabilized through either an axisymmetric mode or a C mode. The stable region in the parameter space is always enlarged as the electric field is increased.

Beam collector with low electrical leakage

Abstract: The collector in a linear-beam electron tube is insulated from its heat sink so that it can be operated at a depressed potential. The insulation comprises two bands of dielectric sequentially in contact between the collector and heat sink. The intervening space is sealed off and preferably filled with a dielectric fluid to improve heat transfer and inhibit voltage breakdown. Gaps in one band are preferably aligned with solid parts of the other to reduce electric leakage.

Transition from Trichel-pulse corona to dielectric barrier discharge

Abstract: An investigation was undertaken to examine the influence that thin circular solid dielectric barriers placed on the planar anode surface have on the stochastic behavior of Trichel pulses. It is shown that charging of the dielectric surface by the corona discharge introduces another memory effect that becomes increasingly significant as the point-to-plane gap spacing is reduced. At a sufficiently short gap distance, the charge on the dielectric causes the field at the point electrode to drop below the level required to sustain a corona discharge and at that point Trichel pulses cease. >

Relaxation currents in dielectric liquids

Abstract: Measurements of charging, discharging and voltage-reversal currents were carried out in dielectric liquids of simple molecular structure (benzene and carbon tetrachloride) and complex molecular structure (two kinds of fluorocarbon liquids). The experiments were carried out under dynamic and steady-state conditions. The slope of the voltage-current characteristics was n>1 for results obtained under dynamic conditions and n >

Nonlinear Marangoni instability in dielectric superposed fluids

Abstract: The nonlinear Marangoni instability of two dielectric superposed fluids is investigated. The system is stressed by a normal electric field such that it allows for the presence of surface charges at the interface. The method of multiple scale perturbations is used in order to obtain uniformly valid expansions. Two nonlinear Schrodinger equations describing the perturbed system are obtained. One of these equations is used to describe analytically and numerically the necessary conditions for stability and instability near the marginal state, while the other equation is used to obtain the nonlinear electrohydrodynamic cutoff wavenumber separating stable and unstable disturbances for the system.

Efficient computation of electric field in high voltage equipment

Abstract: The efficient indirect boundary-element method is applied to the calculation of 3-D electric fields in high-voltage devices. For solving this problem with sophisticated boundary conditions and with dielectric media, the authors adopt real surface elements, a fast and accurate computation approach, and thin-layer medium treatment. Numerical results are given to verify the efficiency of the program and the accuracy of the calculation. It is noted that the computer program based on the efficient boundary-element method is an important tool for transformer insulation design. It has been used to identify regions of high field strength where electrical breakdown might occur. >

Stator and rotor device for producing high voltage impulses - in which electric field does not exceed breakthrough electric field strength

Abstract: Appts. for producing periodic electric high voltage impulses or the same or opposite polarity comprises a rotor housing (21) with attached electrodes (22) having concave shaped internal surfaces and a fixed stator with electrodes (12) connected together by solid dielectric material (14). The space between (30) is filled with dielectric fluid. Specifically, either the inner or outer electrode body may move with the other being fixed. The curved radius of the outer electrode from the point of minimal gap between the electrodes increases as we move outwards and that of the inner electrode decreases. The end of the outer electrodes is actually convex. USE/ADVANTAGE - In material working or producing electron or laser beams where high impulse power is required. At no time during charging or discharging of the voltage is an electric field strength produced which exceeds the break-through field strength.

Dielectric-liquid pulsed power switch

Abstract: This disclosure identifies dielectric liquids for use as opening and closing switching media in pulsed power technology, and describes a dielectric-liquid-pulsed-power switch empolying flashlamps.

The effect of residual conduction on weak unipolar injection and buoyancy driven instabilities

Abstract: The effect of residual conductivity on the stability of a horizontal dielectric liquid layer subjected to a weak unipolar injection and buoyancy is analyzed. Cases of heating from below and from above have been considered. Regions of steady and oscillatory instability are delineated by direct integration of the electrothermohydrodynamic equations for the case of constant mobility and permittivity. >

Method for reclassifying PCB transformers

Abstract: The present invention is directed to a method for reducing PCB concentration in an electrical induction apparatus containing a dielectric fluid with greater than 500 ppm PCB to a level of less than about 50 ppm PCB. Dielectric fluid containing greater than 500 ppm PCB is drained from an electrical induction apparatus, and the drained apparatus then is filled with tetrachloroethylene as a first interim dielectric fluid. The apparatus is then electrically operated with the first interim dielectric fluid so as to attain about an equilibrium PCB concentration in the first fluid. The first interim dielectric fluid then is drained from the apparatus and replaced with fresh tetrachloroethylene as a second interim dielectric fluid. The apparatus then is electrically operated with the second interim dielectric fluid so as to attain about an equilibrium PCB concentration in the second fluid. The second interim dielectric fluid then is drained from the apparatus and replaced with a silicone fluid as a permanent dielectric fluid. The apparatus filled with permanent dielectric fluid is electrically operated and the permanent dielectric fluid is filtered through a carbon filter, so as to attain a PCB concentration in the permanent fluid of less than about 50 ppm.

Formation of single charged drops from a dielectric liquid jet in a nonuniform electric field.

Abstract: 帯電液柱と同軸接地円筒電極により形成された不平等電場中において誘電液柱からの帯電液滴生成について実験を行い, 前報で提出した理論解析の妥当性を検討した.実験には, 気液系として, 分散相に水, キシレン, 連続相に空気を, 液液系として, 分散相に水, 連続相にシクロヘキサン, ヘキサン, シリコンオイルを用いた.印加電圧の増加とともに液柱長さ, 液柱半径および生成液滴径は減少した.前報で提出した電場を考慮した液柱の線形安定性理論より求まる液柱界面波の最大成長速度と最大波数を用いて, 生成液滴径の推算を行った.各実験系ともに, 滴径の実測値と計算値は誤差±10%程度で一致した.高電圧印加時の液柱の鞭打ち現象についても, 実験的検討を行い, 液柱界面に作用する静電圧力が界面圧力を上回ると鞭打ち現象が生じることを明らかにした.

Nonlinear electrohydrodynamic Kelvin–Helmholtz instability conditions of an interface between two fluids under the effect of a normal periodic electric field

Abstract: The electrohydrodynamic Kelvin–Helmholtz instability conditions of an interface separating two dielectric streaming fluids, stressed by a normal electric field in absence of surface charges on the ...