Showing papers on "Liquid dielectric published in 2001"

Aging of paper insulation in natural ester dielectric fluid

Abstract: Aging of transformer insulation paper in natural ester (vegetable oil) dielectric fluid is compared to that in conventional transformer oil. Sealed steel aging vessels containing copper, aluminum, thermally upgraded paper, and dielectric fluid (mineral oil and natural ester) were aged at 130, 150 and 170/spl deg/C for 500, 1000, 2000 and 4000 hours. Paper degradation after aging is determined using paper tensile strength and degree of polymerization measurements. The paper in natural ester aged at slower rates than did paper in conventional transformer oil, taking 5-8 times longer to reach end-of-life. Results obtained for mineral oil samples are similar to predictions based on IEEE transformer loading guide calculations. Mechanisms for the slower aging rate are proposed.

Relative properties of the new combustion-resist vegetable-oil-based dielectric coolants for distribution and power transformers

Abstract: Electrical distribution transformer insulation systems are being reevaluated based on their total life-cycle cost from economical, safety, and environmental perspectives. Due to the inherently higher efficiency design offered by liquid-cooled transformers, development has focused on fluids having improved environmental and health properties while maintaining the fire-resistant properties of "less-flammable" fluids. This paper reports our findings from several years of research and development on alternative dielectric systems using both natural and synthetic esters. Because esters have lower inherent resistance to oxidation than conventional mineral oil, a novel insulation system was developed to overcome this potential handicap. Single- and three-phase prototype field installations using these new dielectric coolants are discussed.

Cable with recyclable covering

Abstract: The invention describes a cable with recyclable covering, particularly for transporitng or distributing medium or high voltage energy, in which at least one covering layer is based on thermoplastic polymer material comprising a propylene homopolymer or a copolymer of propylene with ethylene or an .prop.-olefin other than propylene in mixture with a dielectric liquid. The cable of the invention possesses superior mechanical and electrical properties, including high dielectric strength, in particular enabling it to be used at high operating temperature.

Dielectric barrier discharge plasma reactor cell

Abstract: A dielectric barrier discharge plasma cell that generates a uniform, non-thermal plasma that is effective at neutralizing harmful agents. The cell is able to generate a uniform non-thermal plasma because it reduces arcing by controlling the distance between the conductor and dielectric, applying a low frequency alternating current voltage to the cell, and carefully applying the layers to the conductor and dielectric.

Bubble dynamics and transition into streamers in liquid dielectrics under a high divergent electric field

Abstract: The paper deals with the dynamics of a bubble initiated in the vicinity of a sharp electrode in a liquid dielectric gap submitted to an electric field, and to the conditions leading to the generation of a streamer at the bubble-liquid interface By taking into account the different stresses acting at any point of the surface of the bubble, we establish a mathematical expression describing the shape of the bubble and allowing us to analyse its deformation and instability The frequency of the disturbances at the interface is studied and the zone at which the local electric field is the highest is determined It is shown that depending on this frequency and therefore on the value of the local electric field, different streamer patterns can be generated Some examples of the topology of the disturbed interface are given and discussed

A dual fluid cooling system for high power x-ray tubes

Abstract: A cooling system (300) for use with high-power x-ray tubes (200). The cooling system (300) includes a dielectric coolant (304) disposed in the x-ray tube housing (202) so as to absorb heat dissipated by the stator (400) and other electrical components, as well as absorbing some heat from the x-ray tube itself. To improve heat absorption from the stator (400) and the x-ray tube (200), the dielectric coolant (304) is circulated throughout the housing by a circulating pump (306). The cooling system also includes a coolant circuit employing a pressurized water/glycol solution as a coolant (314). Pressurization of the water/glycol solution is achieved by way of an accumulator (500) which, by pressurizing the coolant (314) to a desired level, raises its boiling point and capacity to absorb heat. A coolant pump (308) circulates the pressurized coolant (314) through a fluid passageway (216) defined in an aperture (206) of the x-ray tube (200) and through a target cooling block (302) disposed proximate to the x-ray tube (200) in the y-ray tube housing (202), so as to position the coolant to absorb some of the heat generated at the aperture (206) by secondary electrons, and the heat generatd in the target cooling block (302) by the target anode (210) of the x-ray tube (200). The target cooling block (302) is in contact with the dielectric fluid (304) so that some of the heat absorbed by the dielectric coolant (304) is transferred to the coolant (314) flowing through the target cooling block (302). The heated coolant is then passed through an air/water radiator (310) where a flow of air serves to remove some heat from the coolant (314). Thus cooled, the coolant then exits the radiator (310) to repeat the cycle.

Liquid dielectric tuning of an integrated circuit

Abstract: A desired performance characteristic of an electrical circuit employing a strip conductor is achieved by placing a fluid having a selected dielectric property in contact with at least a portion of the strip conductor, such that the dielectric property of the fluid effects one or more transmission characteristics of the conductor. In one embodiment, the circuit performance is measured and the dielectric property of the fluid adjusted, e.g., in an iterative process, until the desired performance characteristic of the circuit is achieved.

System and method for cooling transformers

Abstract: A system and method are provided for cooling transformers utilizing a fluid to air heat exchanger to cool dielectric fluid flowing through the transformer. The system includes multiple vertical cooling tubes in fluid communication with the transformer to cool the dielectric fluid. The tubes are configured to create vertical air passages such that the system utilizes natural convection air flow and thermal siphoning to cool the fluid.

Encased time domain reflectometry probe

Abstract: A probe adapted for use with a time domain reflectrometry device in primarily measuring the moisture content in soils and other mediums. This probe can however be used in may differing measurement applications involving materials of specific dielectric constants as well as apparent dielectric constants that are derived from a matrix of several differing dielectrics. In the probe according to the present invention, the inner core of the probe is composed of an inner conductive element, a conductor that is used to transmit a broadband pulse. A dielectric liquid, solid or gel surrounds this inner conductive core, and assists in retaining broadband signal strength. The dielectric material is then encased in a metallic outer shell that serves as a protective housing for the probe. This outer shell is electronically transparent to the electromagnetic pulse transmitted by the active inner conductive core and surrounding dielectric. The outer shell is preferably made of stainless steel, but can be made of other materials as they serve to protect the inner dielectric material and conductive core. This combination of features allows a broadband pulse transmitted through the probe to penetrate into the material being measured, returning a much larger reflection feature upon reaching probe end points, while protecting the dielectric-coated transmission elements inside.

DC-field in solid dielectric cables under transient thermal conditions

Abstract: The electric field in a dielectric changes from capacitive grading immediately after the voltage application to, resistive grading under steady state conditions. In the case of a polymeric dielectric, the conductivity is known to be strongly dependent on both the electric field and the temperature, characterized by an activation energy in the range of 0.5 to 1.2 eV. The dielectric constant /spl epsi//sub 0//spl middot//spl epsi//sub r/ for an olefinic polymer is almost independent of the applied field and temperature, in contrast to the electrical conductivity /spl sigma/, which has a strong dependence on both temperature and field, in the parameter range of engineering interest for a DC cable. During normal operating conditions, load current will heat the conductor and generate a temperature gradient across the dielectric. This temperature gradient will change the electric field distribution in a resistively graded dielectric, with a time constant determined by field- and temperature-dependent carrier mobility, which controls the evolution of space charge towards a steady state condition characterized locally by the dielectric time constant.

Electrohydrodynamic instability of two superposed Walters B viscoelastic fluids in relative motion through porous medium

Abstract: The electrohydrodynamic Kelvin–Helmholtz instability of the interface between two uniform superposed viscoelastic (B´ model) dielectric fluids streaming through a porous medium is investigated. The considered system is influenced by applied electric fields acting normally to the interface between the two media, at which there are no surface charges present. In the absence of surface tension, perturbations transverse to the direction of streaming are found to be unaffected by either streaming and applied electric fields for the potentially unstable configuration, or streaming only for the potentially stable configuration, as long as perturbations in the direction of streaming are ignored. For perturbations in all other directions, there exists instability for a certain wavenumber range. The instability of this system can be enhanced (increased) by normal electric fields. In the presence of surface tension, it is found also that the normal electric fields have destabilizing effects, and that the surface tension is able to suppress the Kelvin–Helmholtz instability for small wavelength perturbations, and the medium porosity reduces the stability range given in terms of the velocities difference and the electric fields effect. Finally, it is shown that the presence of surface tension enhances the stabilizing effect played by the fluid velocities, and that the kinematic viscoelasticity has a stabilizing as well as a destabilizing effect on the considered system under certain conditions. Graphics have been plotted by giving numerical values to the parameters, to depict the stability characteristics.

Effect of liquid impregnation on electrical tree initiation in XLPE

Abstract: The tree initiation voltage of impregnated crosslinked polyethylene (XLPE) with a dielectric liquid is drastically improved compared to normal XLPE for both ac and impulse voltage application. It is considered that liquid fills the polymer free volume, and removes space for electrons to be accelerated to high energy. The experimental results support that collision impact of electrons accelerated in polymer free volume is the dominant cause of electrical tree initiation, and also show that liquid impregnation is a promising way to improve performance and prolong the life of polymeric insulating materials.

Large signal dielectric characterization measurement for integrated passive devices

Abstract: Many of the existing methods of dielectric characterization measurement are based on small signal measurement. Through those methods, some important information, such as dielectric constant at different voltages, a critical concern for integrating passive modules, cannot be obtained. This paper presents a new method to measure dielectric characterization under resonant and constant current conditions for ranges up to 850 V and 10 A. With this circuit, the characteristics of dielectric materials under representative large signal renditions and time down to 1 /spl mu/s can be found.

A bulk acoustic wave resonator for sensing liquid electrical property changes

Abstract: A thickness shear mode (TSM) bulk acoustic wave (BAW) sensor for liquid electrical property (conductivity and dielectric constant) measurements is presented. This sensor, which is configured as a resonator structure, employs a sensing electrode geometry, which allows the accurate measurement of the liquid electrical properties. The frequency response of the sensor has been measured in both conductive (NaCl) and non-conductive (2-proponal) solutions. A theoretical model has been developed to describe the sensor operating in liquids and the calculated impedance is shown to agree well with the measured impedance. The sensitivity of this sensor to the change in liquid dielectric constant has been determined. Compared with other sensing technologies, the present sensor may provide a more reliable, portable and low cost solution for on-line monitoring of the liquid electrical property changes.

Apparatus for dampening standing wave pattern generation in microwave oven

Abstract: An apparatus (10) for dampening standing wave pattern generation in a closed cavity of a microwave oven, includes a fluid table (12) having an enclosure (14) made of a microwave energy transparent material, such as plastic, and a structure, such as top flat platform (16) held in place by the enclosure (14), for defining a processing surface (18) for placement thereupon of samples to be processed, and a quantity of dielectric fluid (20) contained by the enclosure (14) so as to provide a large flat surface (22) of the dielectric fluid (20) beneath the flat platform (16) and thus below the processing surface (18). The apparatus (10) also includes mechanisms (24) for recirculating the dielectric fluid to and from the enclosure (14) and for cooling the dielectric fluid (20) to maintain the dielectric fluid within a given narrow range of temperatures.

Chaotic oscillation of a bubble in a weakly viscous dielectric fluid under electric fields

Abstract: The dynamics of a bubble in a weakly viscous dielectric fluid under electric fields is studied. The dynamical equations for the volume and shape mode oscillations are derived using the domain perturbation method with first-order accuracy in deformation. For the volume mode oscillation, we obtain the modified Rayleigh–Plesset equation which includes a forcing term due to the effect of electric field. For the shape mode oscillations, the Prosperetti–Seminara equation [Phys. Fluids 21, 1465 (1978)] is also extended. The dynamical equations are analyzed with two types of electric fields: the uniform field and the axisymmetric straining field. Equilibrium analysis is performed to find the equilibrium points in the phase planes and their stabilities in static electric fields. Then, the effects of time-periodic electric fields on the bubble dynamics are considered at two levels of viscosity effect [the inviscid limit and the case of Re=O(10)]. The nonlinear dynamics theory is used for analysis of the complicated...

Behavior of inhomogeneous high-temperature SF/sub 6/ gas in a gas circuit breaker

Abstract: The purpose of the present paper is to show the dielectric characteristics of inhomogeneous hot SF/sub 6/ gas in a gas circuit breaker (GCB) experimentally. High-temperature and low-density SF/sub 6/ gas generated by a heavy current interruption is distributed inhomogeneously in the grounded tank, and can strongly threaten the dielectric capability of the GCB. Few studies, however, have been carried out on the dielectric characteristics of the inhomogeneous hot gas. Using small gap discharges, the hot gas behavior of a GCB model, having breakdown or no breakdown, was investigated. The temperature of the hot gas flowing through the exhaust tube was estimated from the sparking voltage of the small gap installed in the exhaust tube. It was also found that there was very little or no effect on breakdown voltages of the cool gas in the breakdown paths. This suggests that the breakdown voltage of inhomogeneous hot gas could be obtained as the applied voltage at which the electrical field strength equals E/sub crit/ of local hot gas at the location concerned.

Stability of Plane Flow of a Liquid Dielectric in a Transverse Alternating Electric Field

Abstract: The effect of an alternating arbitrary-frequency electric field on the stability of convective flow of a dielectric liquid occupying a vertical layer is investigated within the framework of the electrohydrodynamic approximation when charge formation is associated only with the nonuniform liquid polarization. The stability thresholds are determined in the linear approximation using Floquet theory. The competition between the dielectrophoretic and thermogravitational instability mechanisms is explored. It is shown that in the case of a harmonically modulated field either quasiperiodic perturbations or perturbations synchronous with the external action may be the most dangerous. One further critical perturbation mode corresponding to the subharmonic response to variation of the external field develops for triangular modulation. In the limiting case of low-frequency modulation the asymptotic behavior of the critical parameters is investigated using the Wentzel-Kramers-Brillouin method.

Correlation between space charge distribution under DC voltage and dielectric breakdown properties in XLPE under impulse voltage superposed onto DC voltage

Abstract: Describes breakdown tests under DC long term application measuring space charge in XLPE. The time transition of space charge showed that dielectric breakdown cannot be explained by only the local maximum electric field in the bulk, but should be considered as the deterioration of insulating material caused by the increase of carrier density. In order to make a rational insulating design method for DC XLPE cables, space charge distribution immediately before dielectric breakdown under impulse voltage superposed DC voltage is studied. Correlation between the space charge distribution immediately before dielectric breakdown by DC impulse superposed voltage and the dielectric breakdown strength are discussed in this report.

Renewable liquid reflection grating

Abstract: A renewable liquid reflection grating. Electrodes are operatively connected to a conducting liquid in an arrangement that produces a reflection grating and driven by a current with a resonance frequency. In another embodiment, the electrodes create the grating by a resonant electrostatic force acting on a dielectric liquid.

Fundamental Study on Dry-WEDM.

Abstract: This paper describes the development of a new dry wire electrical discharge machining (dry-WEDM) method which is conducted in a gas atmosphere without using dielectric liquid in order to improve the accuracy of finish cutting. In dry-WEDM, since the process reaction force is negligibly small, the vibration of the wire electrode is minute. The gap distance in dry-WEDM is narrower than that in conventional WEDM using dielectric liquid, enabling dry-WEDM to realize high accuracy in finish cutting. Moreover, since there is no need to use water as dielectric liquid, there is no corrosion of the workpiece, making dry-WEDM advantageous for the manufacturing of high-precision dies and molds.

a Conduction Model Describing Particle-Particle Interaction in the Case of Surface Conducting Particles

Abstract: We propose an analytical conduction model describing particle-particle interactions for the case of electrorheological fluids based on surface conducting particles. The system consisting of two contacting spheres immersed in a dielectric liquid is modeled by a distributed impedances network, from which we derive analytical expressions for the potential at the spheres surface, for the electric field in the liquid phase, and finally for the interaction force. The theoretical interaction force is compared with experimental results obtained on insulating spheres coated with a thin conducting polyaniline film. A good agreement is found between the theory and experiment.

Method of fabricating integrated circuit devices having dielectric regions protected with multi-layer insulation structures

Abstract: A dielectric region, such as a ferroelectric dielectric region of an integrated circuit capacitor, is protected by a multi-layer insulation structure including a first relatively thin insulation layer, e.g., an aluminum oxide or other metal oxide layer, and a second, thicker insulating layer, e.g., a second aluminum oxide or other metal oxide layer. Before formation of the second insulation layer, the first insulation layer and the dielectric preferably annealed, which can increase a remnant polarization of the dielectric region. The first insulation layer can serve as a hydrogen diffusion barrier during formation of the second insulation layer and other overlying structures. In this manner, degradation of the dielectric can be reduced. Devices and fabrication methods are discussed.

The Effect of an Alternating Electric Field on the Liquid Dielectric Convection in a Horizontal Capacitor

Abstract: The electroconvective instability in a low conducting nonuniformly heated liquid occurring in an alternating electric field between plates of a horizontal plane capacitor was studied in terms of the equations of electrohydrodynamics for arbitrary field modulation frequencies and various shapes (harmonic and triangular). In the gravitational field, the instability is determined by the interplay of dielectrophoretic and thermogravitational mechanisms. The layer heated from above can feature the parametric instability. In the low-frequency range, a numerical solution to the problem obtained by the Floquet method well agrees with the asymptotic results.

Renewable liquid reflecting zone plate

Abstract: A renewable liquid reflecting zone plate. Electrodes are operatively connected to a dielectric liquid in a circular or other arrangement to produce a reflecting zone plate. A system for renewing the liquid uses a penetrable substrate.