Showing papers on "Liquid dielectric published in 2013"

50 years in the development of insulating liquids

Abstract: The role of electrical insulation is critical for the proper operation of electrical equipment. Power equipment cannot operate without energy losses, which lead to rises in temperature. It is therefore essential to dissipate the heat generated by the energy losses, especially under high load conditions. Failing to do so results in premature aging, and ultimately to failure of the equipment. Heat dissipation can be achieved by circulating certain liquids, which also ensure electrical insulation of energized conductors. The insulating-fluids market is therefore likely to be dominated by liquids, leaving to gases (such as compressed air and SF6) limited applications in power equipment such as circuit breakers and switchgear [1]-[3]. Several billion liters of insulating liquids are used worldwide in power equipment such as transformers (power, rectifier, distribution, traction, furnace, potential, current) [4], resistors [5], reactors [6], capacitors [7], cables [8], bushings [9], circuit breakers [10], tap changers [11], thyristor cooling in power electronics, etc. [12]. In addition to their main functions of protecting solid insulation, quenching arc discharges, and dissipating heat, insulating liquids can also act as acoustic dampening media in power equipment such as transformers. More importantly, they provide a convenient means of routine evaluation of the condition of electrical equipment over its service life. Indeed, liquids play a vital role in maintaining the equipment in good condition (like blood in the human body). In particular they are responsible for the functional serviceability of the dielectric (insulation) system, the condition of which can be a decisive factor in determining the life span of the equipment [13]. Testing the physicochemical and electrical properties of the liquids can provide information on incipient electrical and mechanical failures. In some equipment, liquid samples can be obtained without service interruption.

Streamer-Like Electrical Discharges in Water: Part I. Fundamental Mechanisms

Abstract: Electrical discharge plasma formed in liquid water is under intensive investigation for many possible applications in biomedical, environmental and chemical engineering as well as for general scientific issues in plasma chemistry and other engineering applications. The subject of pulsed breakdown of water has additionally begun to assume importance due to growing interest in decontamination, purification of water containing chemical impurities and industrial sludge, and also in the emerging area of bio-electrics. This review paper focuses on the plasma physics (Part I) and chemistry of electrical discharges in liquid water and the chemical effects of plasmas on the degradation of organic molecules (Part II). This part discusses dielectric liquid breakdown and its mechanisms, streamer propagation and the effect of electrode polarity on streamer dynamics.

Dielectric fluid in inhomogeneous pulsed electric field

Abstract: We consider the dynamics of a compressible fluid under the influence of electrostrictive ponderomotive forces in strong inhomogeneous nonstationary electric fields. It is shown that if the fronts of the voltage rise at a sharp, needlelike electrode are rather steep (less than or about nanoseconds), the region of negative pressure arises, which can reach values at which the fluid loses its continuity with the formation of cavitation ruptures. If the voltage on the electrode is not large enough or the front is flatter, the cavitation in the liquid does not occur. However, a sudden shutdown of the field results in a reverse flow of liquid from the electrode, which leads to appearance of negative pressure, and, possibly, cavitation.

Drop motion, deformation, and cyclic motion in a non-uniform electric field in the viscous limit

Abstract: Drop motion and deformation of a conducting drop in a perfect (or leaky) dielectric fluid and a leaky dielectric drop in a leaky dielectric fluid, in a non-uniform electric field is presented. The investigated non-uniform electrode configuration is of the pin-plate type. Systematic experiments and comparison with existing analytical models is carried out. The main results are summarized as follows: (i) The dielectrophoretic motion of a conducting drop in a non-uniform electric field is explained reasonably well assuming a spherical drop, although deviations are observed at large deformations. Thus dielectrophoretic motion shows a weak shape dependence. (ii) The deformation of a conducting drop in a non-uniform electric field has comparable contributions from the uniform and the non-uniform components of the applied field. (iii) The leaky dielectric nature of the medium results in three different states for a conducting drop (a) no movement, (b) near electrode cyclic motion, and (c) cyclic motion between the electrodes. The frequency of cyclic motion decreases with electric field for near electrode motion. On the contrary it increases with the applied field for electrode-electrode cyclic motion. The leaky dielectric system showing positive dielectrophoresis leads to the drop getting attached to the pin electrode causing emulsification at large field. A leaky dielectric drop suspended in a dielectric, system exhibiting negative dielectrophoresis shows oblate deformation which is augmented by the plate-drop hydrodynamic interaction.

Enhancement of Critical Characteristics of Transformer Oil Using Nanomaterials

Abstract: Maintaining continuous power supply is the major anxiety of power engineers throughout the world. Power transformer is one of the critical equipment which requires high level condition monitoring to sustain uninterrupted power supply. Insulation provided within the transformer is solid and liquid dielectrics, which plays a major role in determining the life time. Transformer oil (TOL) is a liquid dielectric which acts as an insulating medium as well as coolant. In this paper, an effort has been made to enhance the critical characteristics of transformer oil using nanoparticles. Nanofluids are prepared by mixing the nanoparticles (aluminium oxide, aluminium, copper oxide, and copper) for various volume concentrations with TOL as base fluid by sonication process. Various critical parameters like viscosity, breakdown voltage (BDV), Flash point, Fire point, pH value and Spectral response characteristics of nanofluids are analyzed.

Very high dielectric strength for dielectric elastomer actuators in liquid dielectric immersion

Abstract: This letter reported that a dielectric elastomer actuator (3M VHB), which is immersed in a liquid dielectric bath, is enhanced tremendously in dielectric strength up to 800 MV/m, as compared to 450 MV/m for the actuator operated in air. The bath consists of silicone oil (Dow Corning Fluid 200 50cSt), which is 6.5 times more thermally conductive than air, and it is found able to maintain the actuator at a stable temperature. As a result, the oil-immersed dielectric elastomer actuator is prevented from local thermal runaway, which causes loss of electrical insulation, and consequently avoids the damage by electromechanical instability.

Dielectrophoretic force-driven thermal convection in annular geometry

Abstract: The thermal convection driven by the dielectrophoretic force is investigated in annular geometry under microgravity conditions. A radial temperature gradient and a radial alternating electric field are imposed on a dielectric fluid that fills the gap of two concentric infinite-length cylinders. The resulting dielectric force is regarded as thermal buoyancy with a radial effective gravity. This electric gravity varies in space and may change its sign depending on the temperature gradient and the cylinder radius ratio. The linear stability problem is solved by a spectral-collocation method. The critical mode is stationary and non-axisymmetric. The critical Rayleigh number and wavenumbers depend sensitively on the electric gravity and the radius ratio. The mechanism behind the instability is examined from an energetic viewpoint. The instability in wide gap annuli is an exact analogue to the gravity-driven thermal instability.

Pump-enhanced, immersion-cooling of electronic component(s)

Abstract: Cooling apparatuses and methods of fabricating thereof are provided which facilitate pumped immersion-cooling of an electronic component(s). The cooling apparatus includes an enclosure having a compartment accommodating the electronic component(s), and dielectric fluid within the compartment at least partially immersing the electronic component(s). A liquid-cooled heat sink is associated with the enclosure to cool at least one cooling surface associated with the compartment, and facilitate heat transfer to the heat sink from the electronic component(s) via the dielectric fluid. A pump is disposed external to the compartment and in fluid communication therewith to facilitate pumped dielectric fluid flow through the compartment. The pumped dielectric fluid flow through the compartment enhances heat transfer from the electronic component(s) to the liquid-cooled heat sink via the cooling surface(s). In one implementation, the pumped dielectric fluid flow provides two-phase cooling to the electronic component(s) via flow boiling.

Influence of electrical discharge machining process parameters on surface micro-hardness of titanium alloy

Abstract: The resistance of a material to an indentation on microscopic scale is an indication of its micro-hardness. To a lubrication engineer, micro-hardness is synonymous with surface wear resistance of a material. In this study, an attempt was made to enhance the surface micro-hardness of titanium alloy (Ti-6Al-4V) through modification of electrical discharge machining process parameters. These parameters are the electrode, the dielectric fluid and the electrical variables of the machine. Cu–TaC composite electrode produced through powder metallurgy method was used during the electrical discharge machining with different urea concentrations in distilled water as dielectric fluid. The electrical variables used were the peak current, the pulse duration and the duty factor. Electrical discharge machining was also conducted with copper (Cu) powder metallurgy electrode with distilled water dielectric fluid for comparison. The results showed that the micro-hardness of the electrical discharge machined surfaces with C...

Large Electrocaloric Effect in a Dielectric Liquid Possessing a Large Dielectric Anisotropy Near the Isotropic–Nematic Transition

Abstract: The recent findings of large electrocaloric effects (ECEs) in ferroelectric polymers and in ferroelectric ceramic thin films have attracted great interest for developing new cooling cycles that are environmental friendly and have the potential to reach better efficiency than the existing vapor-compression approach. Compared with these solid state ECE materials, a dielectric fluid with a large ECE can be more interesting because it may lead to new cooling cycles with simpler structures than these based on solid state ECE materials. Here it is shown that a large ECE can be realized in the liquid crystal (LC) 5CB near its nematic–isotropic (N-I) phase transition. 5CB has a large dielectric anisotropy, which facilitates the electric-field-induced large polarization change. As a result, a large ECE, i.e., an isothermal entropy change of more than 23.6 J kg−1 K−1 is observed just above the N-I transition.

Assessment of non-uniform aging of solid dielectric using system poles of a modified debye model for oil-paper insulation of transformers

Abstract: Dielectric parameters of insulation used in High voltage equipments like power transformers are dependent on insulation size and geometry. As a result parameters evaluated from the model of one insulation system finds limited use in predicting the condition of other. Poles calculated from branch parameters of insulation model, on the other hand are independent of insulation geometry. However such technique requires accurate modeling of dielectric response function. Conventional Debye model does not consider the effect of temperature gradient that exists across the length of the insulation during its operation. In the present paper it is shown that for more accurate modeling and better understanding of dielectric response of oil-paper insulation, a new model which considers the effect of temperature gradient on insulation properties, is necessary. The present paper reports a methodology that is capable of identifying such a model using PDC measurement data. It is also shown that use of conventional Debye model overestimates the pole values and the error increases with usage of the insulation.

Stand Alone Immersion Tank Data Center with Contained Cooling

Abstract: A stand-alone immersion tank datacenter (SITDC) includes: a multi-phase heat transfer immersion cooling tank having external walls surrounding a tank volume within which a dielectric liquid is maintained and heated to a boiling point temperature; a plurality of servers having one or more processing and memory components submerged within the dielectric liquid for cooling of the one or more components via heat dissipation from the one or more components into the dielectric liquid when the one or more components are connected to an electric power supply; and a condenser located vertically above the plurality of servers and in a direct path of rising dielectric vapor created when the dielectric liquid absorbs sufficient heat from the one or more components to reach a boiling point temperature of the liquid. The condenser can be a passive heat exchanger, created by providing a heat conductive material as a top lid of the tank.

New operating limits for applications with electroactive elastomer: effect of the drift of the dielectric permittivity and the electrical breakdown

Abstract: Dielectric elastomer generators are a promising solution to scavenge energy from human motion, due to their lightweight, high efficiency low cost and high energy density. Performances of a dielectric elastomer used in a generator application are generally evaluated by the maximum energy which can be converted. This energy is defined by an area of allowable states and delimited by different failure modes such as: electrical breakdown, loss of tension, mechanical rupture and electromechanical instability, which depend deeply on dielectric behaviors of the material. However, there is controversy on the dielectric constant (permittivity) of usual elastomers used for these applications. This paper aims to investigate the dielectric behaviors of two popular dielectric elastomers: VHB 4910 (3M) and Polypower (Danfoss). This study is undertaken on a broad range of temperature. We focus on the influence of pre-stretch in the change of the dielectric constant. An originality of this study is related to the significant influence of the nature of compliant electrodes deposited on these elastomers. Additionally, the electrical breakdown field of these two elastomers has been studied as a function of pre-stretch and temperature. Lastly, thanks to these experiments, analytic equations have been proposed to take into account the influence of the temperature, the pre-stretch and the nature of the compliant electrodes on the permittivity. These analytic equations and the electrical breakdown field were embedded in a thermodynamic model making it possible to define new limits of operation closer to the real use of these elastomers for energy harvesting applications.

Cavitation in dielectric fluid in inhomogeneous pulsed electric field

Abstract: This paper proposes a method for studying the early stages of the cavitation development in arbitrary, non-stationary conditions. This method is based on the comparison of the results of calculations in the framework of a theoretical model of the liquid dielectrics motion in a strong non-uniform electric field and experiments with controlled parameters. This approach allows us to find the critical negative pressure, at which cavitation begins to develop, and to determine the values of the constants in the classical models of cavitation.

Dielectric frequency response of oil-paper composite insulation with transient moisture distribution

Abstract: Because the temperature and load of transformer are variable, the moisture is usually inhomogeneous in oil-paper, especially for the traction transformer. In order to research the dielectric relaxation behavior of the oil-paper composite insulation with an inhomogeneous moisture distribution, it was proposed that a theoretical model for dielectric medium with an arbitrary distribution of conductivity and dielectric constant. The dielectric frequency response of oil-paper with transient moisture distribution was simulated by using the proposed model. The results show that transient moisture distribution caused the concentration polarization(CP), which enhanced the low-frequency relaxation. The model is validated against experimental data.

Influence of dielectric fluids on surface properties of electrical discharge machined titanium alloy

Abstract: Dielectric fluid is one of the major components of electrical discharge machining. In this article, the influence of two dielectric fluids on the surface properties of workpiece was investigated. Machining was conducted on the titanium alloy (Ti-6Al-4V) with the new Cu-TaC composite electrodes under the two dielectric fluids, which are the urea solution and distilled water. Cu-TaC electrodes were produced from copper and tantalum carbide powders by powder metallurgy method with 50/50% composition at compacting pressure of 24.115 MPa. The main objective is to compare the effect of these dielectric fluids on the electrical discharge machined surface properties—microhardness (Mh) and surface roughness (Ra). The machining variables used to investigate the Ra and Mh were peak current and pulse duration. The surface roughness was found to be generally higher in the specimens machined with urea solution dielectric fluid, the highest being 19.05 µm. For the specimens machined with distilled water dielectric fluid...

Fluorinated nitriles as dielectric gases

Abstract: An electrical device containing a dielectric fluid, the dielectric fluid comprising heptafluoroisobutyronitrile or 2,3,3,3-tetrafluoro-2-(trifluoromethoxy) propanenitrile.

Cavitation in dielectric fluid in inhomogeneous pulsed electric field

Abstract: This paper proposes a method for studying the early stages of the cavitation development in arbitrary, non-stationary conditions. This method is based on the comparison of the results of calculations in the framework of a theoretical model of the liquid dielectrics motion in a strong non-uniform electric field and experiments with controlled parameters. This approach allows us to find the critical negative pressure, at which cavitation begins to develop, and to determine the values of the constants in the classical models of cavitation.

System and Method for Powering Multiple Electronic Devices Operating Within an Immersion Cooling Vessel

Abstract: An immersion cooling tank comprises: a dielectric liquid disposed within a lower volume of the tank; at least one electronic equipment immersed within the dielectric liquid and which requires electrical power to operate; and at least one power distribution unit and/or a bus bar distribution system submerged beneath a surface of the dielectric liquid and providing electrical power to the at least one electronic equipment. The immersion cooling tank further includes a condenser located vertically above the dielectric fluid and the at least one electronic equipment, and through which is flowing a condensation fluid that has a lower density than the dielectric liquid. A leak of the condensation fluid into the tank volume results in the condensation fluid floating atop the dielectric liquid and prevents the condensation liquid from coming into contact with the power distribution unit. The bus bar distribution system enables blind mating of inserted electronic components.

Alteration of gas phase ion polarizabilities upon hydration in high dielectric liquids.

Abstract: We investigate the modification of gas phase ion polarizabilities upon solvation in polar solvents and ionic liquids. To this aim, we develop a classical electrostatic theory of charged liquids composed of solvent molecules modeled as finite size dipoles, and embedding polarizable ions that consist of Drude oscillators. In qualitative agreement with ab initio calculations of polar solvents and ionic liquids, the hydration energy of a polarizable ion in both types of dielectric liquid is shown to favor the expansion of its electronic cloud. Namely, the ion carrying no dipole moment in the gas phase acquires a dipole moment in the liquid environment, but its electron cloud also reaches an enhanced rigidity. We find that the overall effect is an increase of the gas phase polarizability upon hydration. In the specific case of ionic liquids, it is shown that this hydration process is driven by a collective solvation mechanism where the dipole moment of a polarizable ion induced by its interaction with surrounding ions self-consistently adds to the polarization of the liquid, thereby amplifying the dielectric permittivity of the medium in a substantial way. We propose this self-consistent hydration as the underlying mechanism behind the high dielectric permittivities of ionic liquids composed of small charges with negligible gas phase dipole moment. Hydration being a correlation effect, the emerging picture indicates that electrostatic correlations cannot be neglected in polarizable liquids.

Measurement of the Interfacial Tension in an Ionic Liquid–Dielectric Liquid System Using an Electrically Deformed Droplet

Abstract: The unique chemical and physical properties of ionic liquids (ILs) are attracting an increasing amount of interest in energy and biological fields. However, some physicochemical properties of ILs are not well-known. Here, we present an alternative method for the measurement of the interfacial tension in an IL–dielectric liquid system by means of the small deformation of a charged IL droplet in a dielectric medium. Using the pendant drop method, the validity of the proposed measurement method is confirmed. The interfacial tension between ILs and silicone oil has been found to be lower than that between water and silicone oil, and the tension is negatively correlated to the size of the IL ion. Further analyses of Girifalco-Good’s interaction parameters of the two liquid–liquid systems demonstrate that the lower interfacial tension of IL can be attributed to the stronger intermolecular interaction between IL and silicone oil molecules. Due to a universal feature of the interaction parameter for a given class...

Power loss due to Corona on High Voltage Transmission Lines

Abstract: The effect of corona on high-voltage transmission lines is one of the causes power loss and this is uneconomical and undesirable. The study of corona and factors responsible for the loss is investigated through sample calculation based on Peek's formula and the results are then simulated through matlab program. This paper presents the relations between power loss due to corona to corona parameters through matlab programs When in an insulation system, the voltage gradient (voltage stress) exceeds a critical voltage, the air molecules surrounding the high voltage transmission line conductors become ionized (transient gaseous ionization) resulting in partial discharges. Corona loss occurs if the line to line voltage exceeds the corona threshold. The conductive region is not high enough to cause electrical breakdown or arcing to any nearby objects (1). Corona can occur within voids of an insulator, at the conductor or at the insulator interface. Rough surfaces are more liable to corona because the unevenness of the surface decreases the value of the breakdown voltage. It can be detected due to its visible light in form of purple glow consisting of micro arcs and its sound can be heard through its hissing and cracking sound (2). The smelling of the presence of ozone production is noticed during corona activity (3). The effects of corona are cumulative and permanent and the failure can occur without warning. In insulation system, corona discharges result in voltage transients. The effects of corona associated with the operation of high voltage transmission lines include radio interference, audible noise, gaseous effluents (Ozone and Nitrogen oxide) and shock potential. Conductor voltage, diameter and shape, dusts, water drops, and surface irregularities such as scratches are factors that affect the performance and conductor's electrical surface gradients. The energy loss due to corona is transformed into sound, radio noise, chemical reactions of the air components and heat (4). Corona reduces the reliability of insulation system thereby degrading insulation and causes system failure due to dielectric breakdown. The study becomes necessary because of the prevailing negative effect of corona parameters on the power loss of high voltage transmission lines. The power loss under fair weather conditions and under stormy weather conditions when investigated, analyzed and simulated using matlab programs gives the results which help us to take necessary measures to minimize the power loss under fair and stormy weather conditions. High quality insulated and good service design underground high transmission cables can help to eliminate the loss due corona effect The advantage of corona is that the sound generated during corona activity can be used to build high accuracy audio speakers and also it has no mass to be moved to create the sound so that transient response is improved. The controlled corona discharge can be used for filtrations and printing.

Electric double layer at the interface of ionic liquid-dielectric liquid under electric field.

Abstract: The structure of the electric double layer (EDL) is analyzed in order to understand the electromechanical behavior of the interface of ionic liquid-dielectric liquid. The modified Poisson–Boltzmann equation proposed by Bazant et al. is solved to see the crowding and the overscreening effects that are the characteristics of an ionic liquid (Bazant, M. Z.; Storey, B. D.; Kornyshev, A. A. Double layer in ionic liquids: Overscreening versus crowding. Phys. Rev. Lett.2011, 106, 046102.). From the simple one-dimensional (1-D) analysis, it is found that the changes of the composition and the material properties in the EDL are negligible except under some extreme conditions such as strong electric field overO(108) V/m. From the electromechanical view points, an ionic liquid behaves like a pure conductor at the interface with a dielectric liquid. Based on these findings, three specific application problems are considered. In the first, a new method is suggested for measuring the interfacial tension of an ionic liq...

Performance analysis of natural esters as transformer liquid insulation — Coconut, castor and sesame oils

Abstract: Due to the poor biodegradability, transformer mineral oil insulation is now slowly being replaced by natural esters and synthetic oil However, prefect replacement to mineral oil has not been introduced yet because of the poor properties of such alternative oils, ie high conductivity, high pour point etc This paper presents a comparison of chemical and electrical properties of three such alternative oils namely coconut, castor and sesame oil Performance comparison with mineral oil has also been presented to check their suitability of using as transformer liquid insulation In chemical properties acidity, viscosity and pour point were considered whereas complex capacitance, loss tangent, breakdown voltage and corona effects were compared in the electrical properties For complex capacitance and loss tangent measurements Frequency Domain Dielectric Spectroscopy test was conducted It was found that castor oil and sesame oil had the potential to use as an alternative liquid insulation for transformers Further studies are recommended to improve some of the physical properties such as viscosity