June 23 – June 27, 2019
Overview and details of the sessions of this conference. Please select a date or location to show only sessions at that day or location. Please select a single session for detailed view (with abstracts and downloads if available).
|Date: Monday, 24/Jun/2019|
|8:00am - 5:30pm||Registration|
|8:30am - 9:30am||Opening Ceremony|
Session Chair: Massimo Pompili, University of Roma "La Sapienza", Italy
|9:30am - 10:15am||S0: Tropper Lecture|
Session Chair: Maks Babuder, Elektroinštitut Milan Vidmar, Slovenia
ID: 1368 / S0: 1
Transport of Heat and Mass with Electrical Field – from Earth to Space
WPI, United States of America
Pumping of single-phase liquid or two-phase liquid/vapor is encountered in a wide range of technological applications. Utilization of electro-hydrodynamics (EHD) to induce fluid motion is known as an effective approach for situations where special requirements and restrictions are imposed, while enhanced heat and mass transfer are required. The implementation of the EHD phenomena to heat and mass transport introduces complex interactions among inter-dependent variables. The EHD pumping phenomena involve interaction of electric fields and flow fields in a dielectric fluid medium. This interaction induces the fluid motion through the presence of electric body force. In this paper, the fundamentals of EHD driven fluid flow are described. The evolution of EHD driven heat and mass transport technologies for space applications are presented. Specifically, the results of single-phase liquid and two-phase heat transport experiments that were conducted on board variable-gravity parabolic flights are provided. The EHD conduction pumping technology is expected to provide technological advances that will support various space missions.
|10:15am - 10:45am||Coffee Break|
|10:45am - 1:00pm||S1: Basic Properties and Fundamental Studies|
Session Chair: Armando Francesco Borghesani, University of Padua, Italy
Session Chair: Lars Lundgaard, SINTEF Energy Research, Norway
ID: 1271 / S1: 1
Investigation of the factors affecting the dielectric dissipation factor of synthetic and natural esters
M&I Materials, United Kingdom
Traditionally, mineral oil has been used as the insulating liquid in transformers due to its high electrical breakdown strength and cooling ability. More recently, natural and synthetic ester based dielectric liquids are increasingly adopted as alternatives, offering much improved fire safety and environmental protection. The dielectric dissipation factor (DDF), via tan delta measurement, has traditionally been used as one of the key metrics for quality evaluation of unused transformer mineral oils. Understanding the chemical differences between esters and mineral oil and which factors affect material properties such as ester DDF is rapidly becoming of greater importance. By monitoring the individual effects of increased ambient temperature and UV exposure on the DDF of synthetic and natural esters, this investigation aims to provide data which can be used to refine interpretation of dielectric dissipation factor for esters. The overall condition of high DDF esters, and the implications this could have for a transformer, are also evaluated to allow conclusions to be drawn on the relevance of a DDF limit in ester standards.
ID: 1116 / S1: 2
Thermodynamic Model for the Mobility of Oxygen Anions in Dense Neon Gas
1University of Padua,Italy; 2University Grenoble Alpes, C.N.R.S., G2Elab
Recently a thermodynamic model has been developed to describe and predict the ion mobility in He. It aims at computing the free volume available for the ionic drift motion through the medium. The radius of the free volume per particle is the hydrodynamic effective radius in the Stokes formula whose validity is extended to the region of large Knudsen number by using the Millikan-Cunningham slip factor correction. We used this model to describe new data of O− 2 ion mobility in supercritical Ne on several isotherms in a broad density range. The model parameters are adjusted once and for all by fitting the data on the isotherm closest to the critical one and allows the description of the density dependence of the mobility up to temperatures well above room temperature.
ID: 1278 / S1: 3
The Relationship Between the Physical, Chemical, and Functional Properties of Insulating Liquids
Ergon, United States of America
The chemical composition of insulating liquids determines the physical properties and the functionality of the liquids in electrical equipment. The chemical composition is determined by the feedstocks and the processing technology. The chemical structures found in both mineral and ester-based insulating liquids (isoparaffinic, cycloparaffinic, aromatic, olefinic, carbonyls, and heteroatoms) will be discussed. Structure-property relationships provide insight on the functional properties, e.g., dielectric insulation, heat transfer, oxidation stability, hydrolytic stability, component compatibility, and physical properties.
ID: 1134 / S1: 4
Numerical Study of the Thermal Excitation Applied to a Dielectric Liquid Film
1Institut Ppirme (CNRS - Université de Poitiers - ISAE-ENSMA), France; 2IES, Université de Montpellier, CNRS, MONTPELLIER, FRANCE
The study of the electrical double layer in transitory regime seems to be a good way to reach a better understanding of its origin. Recent numerical studies have shown the importance of taking into account the thermal dependence of the liquid intrinsic properties, such as the electrical permittivity or ionic mobility. In this paper, a film of dielectric liquid trapped between two metallic plane electrodes is studies via its electrical current response to the thermal step.
ID: 1121 / S1: 5
Electron Self-Trapping in Vortex Rings in Superfluid Helium
Joint Institute for High Temperatures RAS, Russian Federation
The mobility of electrons injected in the majority of nonpolar dielectric liquids is a few orders of magnitude higher than the mobility of positive ions. However, the behavior of electrons in liquid helium is anomalous. The electron mobility is a few orders of magnitude lower than the value expected according to the classical Langevin theory and even a few times lower than the mobility of positive ions. The reason is that it is energetically favorable for an electron to be localized in nanobubble owing to a strong exchange repulsion from helium atoms. In addition to ordinary electron bubbles, two more types of negative charge carriers were discovered many years ago in superfluid helium: “fast” and “exotic” ions. The mobility of fast ions is approximately seven times higher than the mobility of electron bubbles, whereas the mobility of a family of exotic ions (more than ten members) lies between these two values. In the present work a model according to which fast and exotic negative ions in superfluid helium represent the localized states of electrons in vortex rings is presented. The quantization of radial and longitudinal motions of electrons inside the vortex core and the quantization of the vortex motion of liquid helium around the charged complex lead to the existence of a whole family of excited states of electron vortices with different radii and quanta of vorticity. The proposed simple model of autolocalization of injected electrons in vortex rings allows to understand the nature of fast and exotic ions in superfluid helium.
ID: 1293 / S1: 6
Pressure Dependent Propagation of Positive Streamers in a long Point-Plane Gap in Transformer Oil
1SINTEF Energy Research, Norway; 2ABB Corporate Research, Västerås, Sweden
The propagation of positive streamers in a naphtenic transformer oil in an 80 mm point-plane gap has been investigated under an impulse voltage being close to a step voltage and under pressures ranging from 0.1 to 1.7 MPa. As has previously been found in short gap experiments of 1 – 7 mm in various liquids, increasing voltage leads to shorter stopping length of non-breakdown streamers and higher breakdown voltages while the velocity is close to independent of pressure. The "acceleration" voltage from which streamer velocity rapidly increase with increasing voltage is also close to pressure independent. It is argued that this indicates that the processes determining velocity must take place in the liquid phase at the streamer head while conditions in the channel determines the stopping length of non-breakdown streamers.
ID: 1131 / S1: 7
Infrared Cathodoluminescence of Xe2 Excimers in Xe-He and Xe-N2 Dense Gas Mixtures
1University of Padua, Italy; 2INFN Sez. Padova, Italy
Multiple scattering effects influence the transport properties of excess electrons in gaseous and fluid dielectrics but also affect the energy levels of electrons in delocalized molecular orbitals and can be investigated by carrying out spectroscopic observations. We have measured the infrared cathodoluminescence of the Xe2 excimer in dense Xe gas, and in Xe-He, and XeN2 mixtures. The large orbital characterizing the weakly bound, optically active electron of Xe2 encompasses several surrounding atoms and allows us to study their effects on the electron energy. In particular, the Coulomb force screening on the electron due to the atoms polarizability and the mutiple scattering effects described by the quantum scattering length are discussed and a gas density dependence of the Xe2 energy levels is predicted. A good agreement with the experimental density dependent wavelength shift of the infrared Xe2 excimer band is found
ID: 1216 / S1: 8
Excitation processes as a pathway for electron solvation in non-polar liquids
1Australian National University, Australia; 2James Cook University, Australia
The possibility for solvation of an electron in a nonpolar liquid by an excitation collision is considered in the context of capture into natural fluctuations. We focus on liquid methane as input data is readily available, although our method is easily extended to other species. We adapt our previous work, which found that sound mode excitations in atomic fluids could allow for trapping of electrons in weak fluctuations, to consider incoherent excitations as the trapping mechanism. These excitations present opportunities for solvation to occur at higher energies, around the threshold energies of the excitation processes. The rates we obtain for solvation in liquid methane are weak, due to the low abundance of fluctuations supporting bound states. The formalism presented here is aimed at providing an ab-initio energy-discriminant description, in contrast to an empirical timescale, for modelling solvation of electrons in applications such as plasma exposure of water or biological bodies.
|1:00pm - 2:15pm||Lunch|
|1:00pm - 2:15pm||IAC Lunch/Meeting|
Only by invitation
|Room of the Frescoes|
|2:15pm - 3:45pm||S2: Special Session on Electro-hydrodynamics|
Session Chair: Christophe LOUSTE, P' institute University of Poitiers, France
Session Chair: Pedro A Vazquez, Universidad de Sevilla, Spain
ID: 1200 / S2: 1
PIV flow measurements of conduction pumping flow created by nine pairs of asymmetric surface electrodes
1P' institute University of Poitiers, France; 2Dpt. Fisica Aplicada III E.T.S.I., Unversidad de Sevilla; 3Department of Mechanical Engineering Worcester Polytechnic Institute
In this paper, the electrohydrodynamic flow generated by nine electrode pairs of asymmetric electrodes is experimentally investigated. Electrodes are flushed into a cavity wall and a DC voltage is applied to the electrodes in order to set the liquid in motion. The liquid flow patterns are recorded by the use of a particles velocity Image system. Flows have been recorded during more than 500s and time variations are presented. According to the theory the flow over each electrode pair is most of the time directed from to small electrode to the large one but unpredicted flow patterns have also been obtained. It can be noticed that an unexpected reversed flow has even been observed in some configurations. In order to explain these behaviors, a joint analysis of both flow patterns and measured electric current is made. This last point is more particularly discussed in the last part.
ID: 1133 / S2: 2
A Non-destructive Thermal Stimulus Method as a Tool for studying the Electrical Double Layer
1IES, Université de Montpellier, CNRS, MONTPELLIER, FRANCE; 2Institut Pprime, CNRS - Université de Poitiers - ISAE-ENSMA, POITIERS, FRANCE
When a liquid is put into contact with a solid, two charge layers of opposite signs appear at the interface. This Electrical Double Layer (EDL) is the result of electrochemical reactions occurring in the region separating the liquid and the solid. A bottleneck in understanding and quantifying the EDL and its behavior is the availability of direct methods allowing to fully measure the EDL charge and distribution. This paper concerns the use of the Thermal Step Method (TSM) as a tool for characterizing the EDL to complete the flow electrification method. Several dielectric liquids (cyclohexane, mineral oil and silicon oil) are subjected to thermal step measurements. The obtained results are analyzed and discussed with respect to literature and to numerical simulations.
ID: 1344 / S2: 3
Mapping the thickness of falling liquid films under ionic wind by a light absorption technique
DESTEC, University of Pisa, Italy
The paper shows the development of a photometric technique for mapping the thickness of liquid films, subject to corona wind. The phenomenon of light absorption through a layer of dyed liquid is used to evaluate its thickness. The layer receives a back-illumination from the wetted wall and the transmitted intensity of light is measured by means of a digital camera. Non-uniformities in the original intensity field suggest building a calibration curve for each measurement point. The filtering and interpolation algorithm needed for transforming the intensity field into the thickness field is described in detail. In addition to being non-intrusive and inexpensive, the technique can determine the local film thickness with an accuracy lower than 10 % of its measuring range amplitude. Application to mapping the thickness of falling liquid films under ionic wind in different regimes and at different waviness is illustrated. It is particularly interesting to study this phenomenon, since an ionic wind, with electrical currents lower than 1 mA, can create additional waves and ripples on the liquid/gas interface, thus, in practical applications, it increases mass and heat transfer between the two phases with a negligible energy expense. Falling film thickness is measured with and without the generation of corona wind by a thin wire. The pattern of surface ripples can be observed over the entire illuminated area and the beneficial effect on surface waviness can be evaluated at both polarities of the applied high voltage.
ID: 1118 / S2: 4
Conditions for explosive growth of free surface perturbations for a dielectric liquid in a normal electric field in confined axisymmetric geometry
1Institute of Electrophysics, UB RAS, Russian Federation; 2Lebedev Physical Institute, RAS, Russian Federation
We consider the behavior of the free surface of an ideal dielectric liquid in an applied normal electric field for the case of confined axisymmetric geometry of the system. The quadratic nonlinear amplitude equation which describes the evolution of the boundary is derived in the framework of the Hamiltonian formalism. According to this equation, the hard regime of excitation of electrohydrodynamic instability is always realized. Also, it is shown that the part of the potential energy functional which is responsible for the higher-order nonlinearities is negatively defined if the dielectric constant of the liquid is sufficiently large, 𝜀 > 2.78. Under this condition, the growth of surface perturbations has an explosive character.
|3:45pm - 4:15pm||Coffee Break|
|4:15pm - 5:45pm||P1-1: Poster Session on Basic Properties and Fundamental Studies|
Session Chair: Edward Casserly, Ergon, United States of America
Session Chair: Alexey Khrapak, Joint Institute for High Temperatures RAS, Russian Federation
ID: 1317 / P1-1: 1
Time-dependent dielectric behavior of mineral oil under the influence of different DC voltage conditions
1FHWS University of Applied Sciences Würzburg-Schweinfurt, Germany; 2TU Dortmund University, Dortmund, Germany; 3Siemens AG, Nürnberg, Germany
This contribution contains extensive studies about the time-dependent dielectric behavior of mineral oil. Therefore, different measurement systems are used in order to investigate several dielectric phenomena of a 5 mm oil gap. Polarization and depolarization current measurements, as well as electro-optic Kerr-effect measurements, verify the significant influence of space charges on the time-dependent electrical conductivity and the electric field. In addition, a simulation model, based on the drift and diffusion theory, is presented. Therefore, all the gained knowledge about the charge carrier processes, which are measured with the two different test setups, are included in the simulation model.
ID: 1125 / P1-1: 2
15 min DC breakdown tests with liquid nitrogen
The dielectric strength of liquid nitrogen is an important design issue for numerous cryogenic high voltage apparatus. In some cases the design must consider gas bubble occurrence caused by resistive heating, e.g. during activation of a resistive superconducting fault current limiter. The objective of the FASTGRID project is to support a liquid nitrogen cooled superconducting fault current limiter solution for DC grids. The high voltage test facility Fatelini 2 allows DC testing of liquid nitrogen up to voltages of 325 kV. A high voltage electrode with the shape similar to a bell and a ground plane electrode were used. A heater was installed within the ground plate in order to allow bubble generation which was verified via video observation. A one hour voltage stress was performed as an initial voltage step without activation of the heater. The test was continued with a duration of 15 min with the same voltage but including five 500 W heating impulses of 10 s duration, each. In case of no breakdown the test was followed by about 10% voltage increases for subsequent steps of 15 min DC operation including 5 heating impulses, each. The maximum examined gap length was 96 mm for negative polarity only. In most cases the breakdown occurred during bubble generation. An outliner with a very low disturbed voltage waveform did also occur. The breakdown voltage values obtained by these tests are lower than for test series which were performed without operation of the heater.
ID: 1136 / P1-1: 3
Suspension Stability of Transformer Oil-based Nanofluids
Xi'an Jiaotong University, People's Republic of China
The transformer oil-based nanofluids (TNFs) formed by adding nanoparticles into the pure transformer oil not only can improve the heat exchange properties but also can enhance the dielectric withstand characteristics of transformer oil, which show a wide prospect of application. Investigation on the suspension stability is of great significance to guiding the design and preparation of stable nanofluids system. In this paper, the effects of ultrasonic oscillation time, dispersant and temperature on stability of TNFs were analyzed by ultraviolet-visible spectrophotometry (UV-vis) and dynamic light scattering (DLS) methods. In addition, the molecular dynamics simulation was adopted to study the stability mechanism of TNFs, which provides a new perspective in guiding the preparation of TNFs. The experimental results indicate that there is an optimal ultrasonic shock time for the preparation of stable nanofluids, and the addition of dispersant can improve the long-term stability. But the increase of temperature will make the stability worse. By molecular dynamics simulation, it can be found that the main reason for improving the stability of transformer oil-based nanofluids by ultrasonic oscillation time is to reduce the diffusion coefficient of nanoclusters by reducing the particle size of nanoclusters. The dispersant increases the distance between the particles and reduces the van der Waals attraction potential between the particles
ID: 1314 / P1-1: 4
Influence of the Electrode Surface Roughness on the Electrical Conductivity of Pure Paraffin
1Hochschule für angewandte Wissenschaften Würzburg-Schweinfurt, Germany; 2Julius-Maximilians-Universität Würzburg, Germany; 3Technische Universität Ilmenau, Germany
A comprehensive theory of the conduction processes in dielectric liquids is needed to describe their behavior from low to high field strengths. To investigate the conductivity of dielectric liquids a paraffin with low self-conductivity and well-defined chemical structure is used. Particularly at higher field strengths the material and surface of the electrodes has to be considered as well. It is shown, that ground and polished electrodes of stainless steel reveal different behavior during current measurements. Furthermore, particularly at high field strengths long-time measurements are needed to reach steady state conditions. The current measurement employing polished electrodes shows great scattering. Due to the polishing process several surface irregularities became apparent. Hence, for current measurements the electrode material and surface treatment of the electrodes are of great importance.
ID: 1338 / P1-1: 5
Impact of Oil-Based Nanofluids on Partial Discharge Activity
1Tanta University, Egypt; 2Minoufiya University, Egypt
Oil-based nanofluids have an enhanced breakdown strength compered to mineral oil. However, their partial discharge (PD) characteristics under non-uniform fields need more investigation. In this study PD activity of oil based nanofluids was studied and compared to that of base oil. The selected nano modifier was Titanium oxide (TiO2) with low weight fraction. The nanofluids sample was prepared via ultrasonic processing. Regarding the PD measuring system, a needle-plane electrode was manufactured with an oil gap spacing of 3mm. The comparison includes both partial discharge inception voltage (PDIV) and PD propagation at different levels of applied voltage. First, the probability of the measured PDIV was evaluated using Weibull distribution and average inception was calculated. Then, the number of PD pulses was calculated for both negative and positive polarity of applied voltage. In addition, the phase appearance of PD pulses was analyzed. Moreover, the time transition of PD pluses for 10 min time domain was depicted. It was found that partial discharge pulses appear around the peak of the applied voltage for both nanofluid and base oil. Based on the obtained results, the role of nanoparticles in PD activity is discussed based on the initial electron generation and propagation.
ID: 1238 / P1-1: 6
Investigation of Temperature Effect on Conductance Characteristics of Transformer Oil-based Nanofluids
Xi'an Jiaotong University, China, People's Republic of
Adding some nanoparticles to the transformer oil can improve its heat exchange properties as well as its dielectric withstanding characteristics, which has attract more and more attentions in the world. The conductance characteristics of transformer oil-based nanofluids (TNFs), especially at different temperatures, will help to understand the modification theory. The charge carrier transport processes at different electric fields can be divided into three stages: Ohmic, tunneling and space charge limited current (SCLC), respectively. In Ohmic stage at a very low field, the addition of nanoparticles increases the carrier number density, thus the conduction current is increased. In tunneling stage at medium to high electric field strengths, the main charge carriers in the transformer oil change from ions and colloidal particles to electrons emitted from the electrodes. The addition of nanoparticles increases the barrier thickness at the metalliquid interface, which reduces the amount of electrons passing through the interface region. Therefore, the field strength required for electron transport is enhanced, and the dielectric strength is improved. In the space charge limited current stage at a very high electric field, the large trap density of TNFs lowers the carrier mobility, suppressing the discharge. In addition, as the temperature increases, the accelerated movement of the carriers increases the conduction current in the transformer oil. However, the electron tunneling process in the tunneling stage is little affected by the change in temperature.
ID: 1305 / P1-1: 7
New equation for calculating electronic polarizability using refractometry
1Institute for Systems Analysis, FRC CSC RAS, Russian Federation; 2Murmansk State Technical University
The determination of the electronic polarizability of molecules is carried out by quantum-mechanical, refractometric and spectrometric methods. Refractometry is the simplest and most reliable method, since to determine the values of the electronic polarizability, it is required to have data on the absolute refractive index, substance density (molar volume) and the theoretical relation relating these parameters to electron polarizability. The Lorentz-Lorenz equation is currently used as such a relation. In this paper the justification of the new equation for determining the electronic component of the isotropic polarizability of molecules is given. From the experimental data on the density and absolute refractive index of a substance, the values of the average electronic polarizability of 62 different molecules were determined. The calculation was performed for the condensed state of a substance at 293.15K.
ID: 1304 / P1-1: 8
The theoretical study of dielectric properties of water using the modified Onsager-Kirkwood-Fröhlich theory
1Institute for Systems Analysis, FRC CSC RAS, Russian Federation; 2Murmansk State Technical University
In the work, we present the new method for calculation dielectric properties for Water in the wide temperature range. We use the modified Onsager-KirkwoodFröhlich theory, which makes it possible to calculate the polarization characteristics without using the static permittivity. We assumed that the dielectric is an isotropic medium consisting of molecules that do not interact with each other and are located in molecular electric fields. It allows us to use the average cosine of the angle between local electric field vectors and the dipole moment vectors of molecules in a medium as the average measure of the local orientation of the dipoles. This approach also makes it possible to equate the value of the energy of the interaction of dipoles with molecular fields to the value of the internal interaction energy if the energy of the interaction of the dipoles with external fields used for the experimental determination of the value of static permittivity is much less than the energy of the interaction. The calculated values of the dipole moment agree with the modern quantum mechanical calculations, and the results of calculating the values of permittivity are in practical agreement with experiment in the wide range of 123.15K - 573.15K. The method allows to calculate the static permittivity of water in various aggregate states: ice Ih in the range from 123K to melting point, supercooled water in the range from 238K to melting point, water at the saturation line from the melting point to the precritical region.
ID: 1157 / P1-1: 9
Comparative Dielectric properties of 1,2-dichloroethane with n-methylformamide and n,n-dimethylformamide using Time Domain Reflectometry Technique
1Research Scholar, Maharashtra Udayagiri Mahavidyalaya, Udgir-4137517, Latur, Maharashtra, India, India; 2Principal, Sunderrao Solanke Mahavidyalaya, Majalgaon-431131, Beed, Maharashtra, India
The study of dielectric relaxation properties of polar liquids in the binary mixtures has been carried out at 10, 15, 20 and 25ºC temperatures for eleven different concentrations using picoseconds time domain reflectometry technique. The dielectric properties of a solute-solvent mixture of polar liquids in the frequency range of 10 MHz to 30 GHz give the information regarding formation of monomers and multimers and also an interaction between the molecules of the mixture. The dielectric parameters viz. static dielectric constant and relaxation time has been obtained by the least squares fit method using the Debye equation characterized by a single relaxation time without relaxation time distribution.
ID: 1319 / P1-1: 10
Effect of Cumyl Alcohol in Multilayer Dielectric on Space Charge Build Up
1Bandung Institute of Technology,Indonesia; 2Université Paul Sabatier, LAPLACE, France; 3PT. PLN (Persero), Indonesia
One of the issues of using cross-linked Polyethylene (XLPE) in DC insulation systems is the propensity of crosslinking byproducts to promote charge buildup inside the insulation, leading potentially to insulation failure. Field-induced ionization of the molecules, like in insulating liquids, is thought to be one of the processes of charge generation. In this paper, space charge measurement is realized to probe the effect of cumyl alcohol as one of the crosslinking byproducts. Low Density Polyethylene (LDPE) is used as polymer matrix, and soaked in cumyl alcohol. We show that polyethylene naphthalate (PEN) layers constitute efficient barriers to the evaporation of cumyl alcohol from LDPE films. The space charge behavior of soaked LDPE is compared to that of reference LDPE with PEN. Significant charge build-up occurs at the LDPE/PEN interfaces due to the conductivity gradient. PEN appears not suited for such analysis as the field is concentrated in the layer and is weak in the bulk LDPE.
ID: 1186 / P1-1: 11
Electrothermal Coupling Simulation of Termination Insulation of Superconducting Energy Pipeline
Xi'an Jiaotong University, China, People's Republic of
Superconducting DC energy pipeline realizes the mixed transportation of electric energy and liquid natural gas, which is a high efficiency and low energy consumption method of redistribution of energy. Superconducting DC electric termination is one of the cores equipment of superconducting DC energy pipelines which bears various extreme conditions such as electric field, large temperature gradient, mechanical stress, etc. Under the influences of multiphysics, the electrical and thermal properties of the terminal materials will change to varying degrees, and these changes will cause distortion of the physical field in turn. Therefore, in the design of the terminal structure, multiple physical interactions and mutual cooperation methods need to be considered. Under the two-way coupling of multiphysics and terminal material parameters, the physical simulation model of superconducting energy pipeline is established, and the electric field distortion in this model are analyzed. In this article, the physical model of superconducting energy pipeline terminal is established by COMSOL. And we find that the change rule of the material conductivity with temperature counts a great deal in the distribution of the electric field thermal field in the terminal. At the same time, the cooling power of liquid nitrogen influences the temperature distribution, thus affect the electric field indirectly to a certain extent. Therefore, in the optimization design of the terminal, selection of insulation materials, how to control the heat generation should take into consideration. This study provides theoretical support for the insulation optimization design of superconducting energy pipeline terminals.
ID: 1249 / P1-1: 12
DC breakdown and space charge characteristics of mineral oil impregnated thermally upgraded paper with different ageing conditions
State Key Laboratory of Power Equipment & System Security and New Technology College of Electrical Engineering Chongqing University, China, People's Republic of
Oil-paper insulation is widely used as the insulating material in transformers. Temperature is one of the major factors causing mineral oil-paper insulation system ageing. In order to relieve mineral oil-paper insulation’s thermal ageing problem, the thermally upgraded paper is used as the insulation system. In this paper, a thermal ageing experiment had been conducted on the thermally upgraded paper impregnated in mineral oil. Samples were collected on different days, then the space charge characteristic test was performed using pulsed electro acoustic method (PEA method). DC breakdown tests were conducted with and without pre stressing. A ramp test was conducted to determine the space charge injection threshold voltage. From the experiment result, the space charge injection threshold voltages for mineral oil-thermally upgraded paper at each thermal ageing state are attained. Thermal ageing of the insulation will not influence the space charge injection threshold voltage, but with further deterioration, the higher the corresponding voltage will be. The space charge injection for the samples is homo charge injection. The more the deterioration, the easier it becomes for the injection. Thermal ageing does not influence the DC breakdown voltage significantly. Pre stressing will increase samples’ DC breakdown field strength. The more the deterioration of the sample, the more apparent the increase will be.
ID: 1178 / P1-1: 13
Electron transport and propagation of negative streamers in liquid-phase xenon
1Institute of Physics Belgrade, Serbia; 2Serbian Academy of Sciences and Arts, Serbia; 3James Cook University, Australia
The Monte Carlo method, initially developed for charged particle swarms in neutral dilute gases, is extended and generalized to investigate the transport processes of electrons in liquid-phase noble gases by accounting for the coherent and other liquid scattering effects. Electron transport coefficients, including the electron mobility, diffusion coefficients and ionization coefficient, are calculated as a function of the reduced electric field in liquid-phase xenon. Calculated transport coefficients are then used as an input in the classical fluid model to investigate the dynamics of negative streamers. Using the language of the contemporary kinetic theory of plasma discharges, in the present work among many important points, we investigate how various representations of inelastic energy losses in inelastic scattering events affect the electron transport and the macroscopic streamer properties.
ID: 1219 / P1-1: 14
Influence of Polarity Effect and Internal Impurity on the Breakdown Voltage of Palm Oil under Inhomogeneous Electric Field
Universitas Brawijaya, Indonesia
This paper presents the research results on the effect of internal impurity of palm oil and needle electrode polarity on the breakdown voltage. The electrodes used in this research were in an arrangement of needle-plate with the needle sharpness angles used were 45o and 60o. A DC high voltage has been used as the testing voltage during experiment with the spark gap between the needle and plate electrodes was 2.5mm and 5mm. Breakdown testing has been done using two polarities on the needle electrodes, which were positive and negative polarities. Before the exposure to electric field, microscopically an unused palm oil looked clear and did not reveal any impurity. The solid impurities started to appear in the oil once it was exposed to electric field. It was originated from the fat contained in the palm oil. Under the influence of electric field, the impurities were moving and gathering around the tip of the needle electrode, the part with the highest field intensity. The largest amount of internal impurities around the needle tip has been found during the experiment with the needle sharpness angle of 60°, meaning that sharper the needle point, larger would be the amount of impurities gathered around. Considering the two spark-gap distances and the two needle sharpness angles used in the research, it was found that the level of breakdown voltage at positive polarity is smaller than the breakdown voltage level at negative polarity.
ID: 1218 / P1-1: 15
Breakdown Voltage of Palm Oil under Inhomogeneous Electric Field
Universitas Brawijaya, Indonesia
This paper presents the results of research on the breakdown voltages of palm oil under the influence of an inhomogeneous electric field distribution. The field distribution has been obtained using an arrangement of needle-plate electrodes. Three levels of needle sharpness have been considered, by using the sharpness angle of 0o, 45o, and 60o . The high voltage AC and DC with the distance between electrodes of 2.5mm and 5mm have been used during the experiment. The homogeneity of the electric field has been examined through simulation using the free FEMM 4.2 software. The results show that at a certain distance of electrodes considered, the heterogeneity level increases with the increase of the sharpness angle of the needle electrode. The field efficiency of the needle-plate electrodes arrangement with the sharpness angles of 0o, 45o, and 60o were respectively 40.6%, 18.6% and 11.4%. The experiments on the breakdown voltage of the spacing gap using the same sharpness angles indicate that the obtained peak values of the AC breakdown voltage were respectively 25.5kV, 22.0kV, and 19.7kV, whereas for the DC breakdown voltage the values were 41.0kV, 31.1kV, and 27.2kV respectively.
ID: 1174 / P1-1: 16
SPACE CHARGE EFFECT ON THE ELECTROPHYSICAL CHARACTERISTICS OF LIQUID DIELECTRICS
Prydniprovska State Academy of Civil Engineering and Architecture, Ukraine
Liquid dielectrics are extensively used as an insulating and heat transfer agent in electrical apparatus. The electophysical properties of these insulating liquids are of vital importance to the service life of electrical equipment and have become increasingly important as operating voltages have increased to 500 kV and above and internal equipment spacing has decreased. We initially studied the current time characteristics of benzene, toluene and carbon tetrachloride under dc electric stress. The results demonstrated that the current decreased with the time, what could be explained by the creation of space charge near the electrodes. Current-voltage characteristics were constructed for different times of electrical field application. We have also conducted measurements of discharge currents, which led to obtaining the values of diffusion coefficient and space charges. From the reversal currents investigations it is possible to calculate the mobility of charge carriers. We added also the new data about reversal currents in hydrolique liquids. The model explaining the dependence of the resistivity on the distance between the electrodes is proposed.
ID: 1335 / P1-1: 17
The effects of TiO2 nanoparticles on insulation and charge transport characteristics of aged transformer oil
1NCEPU, China, People's Republic of; 2Tianjin Power Company of State Grid Tianjin, China
The insulation property of transformer oil is prone to decreasing due to insulation aging caused by the heat, electricity and other factors under the long-term operation, which is vital to the safe operation of power equipment. It has been reported that nanoparticles can improve the insulation properties of transformer oil. However, there has been no evidence showing the effect of nanoparticles on insulation properties of aging transformer oil, and the modified mechanism of nanoparticles is not clear. To reveal the modified mechanism of nanoparticles on aging transformer oil, this paper presents the effects of TiO2 nanoparticles on the insulating properties, space charge characteristics and trap characteristics of aged transformer oil. The results show that the insulation properties of transformer oil with different aging degree are improved by adding TiO2 nanoparticles. The AC breakdown voltage of aged nanofluid is increased significantly to the one of non-aging transformer oil. The lightning impulse breakdown voltage is increased by 30%~40%. Besides, the partial discharge inception voltage is increased by 12%. Moreover, the space charge characteristics measuring by the pulse electro-acoustic technique show that the charge dissipation rate of the aged transformer oil is increased by 57% with the presence of TiO2 nanoparticles, which reduces the accumulation of space charges. The thermally stimulation current shows that more traps with shallower energy level are induced by TiO2 nanoparticles. The charge trapping and de-trapping process in shallow traps are beneficial to the rapid dissipation of charges and restrains the accumulation of space charges. Therefore, TiO2 nanoparticles can effectively modify the charge accumulation and dissipation characteristics in aging transformer oil and significantly reduce the distortion of electric field, resulting in the improvement of the insulation property.
ID: 1220 / P1-1: 18
Influence of Water Contaminants on the Breakdown Voltage and Leakage Current of Palm Oil under Inhomogeneous Electric Field
Universitas Brawijaya, Indonesia
The impurity because of water presence in a palm oil under an inhomogeneous electric field has been investigated in this paper. The inhomogeneous field condition has been produced during the experiment using an arrangement of needle-plate electrodes with three different sharpness angles, namely 0o, 45o, dan 60o. An AC high voltage has been taken as the testing voltage while the gap between the needle and the plate electrodes used was 5 mm. Two levels of impurity in the palm oil have been considered, which were 2000ppm and 4000ppm. The experiment results showed that in a new and uncontaminated palm oil it was found that the more pointed the needle electrode was, the smaller would be the leakage current level. It implied that less uniform the electric field intensity between the electrodes, the smaller would be the leakage current level. The experiment results also showed that the water content in the palm oil decreased the breakdown voltage level significantly, and the more pointed needle electrode caused a decrease in the level of breakdown voltage of palm oil with water contaminants. It has also been observed during the experiments that the water droplets in the electric field were broken apart into smaller water droplets.
ID: 1143 / P1-1: 19
Temperature dependence of the shear viscosity of mineral oils and natural esters
1DIAEE-Dept of Astronautical, Electrical and Energy Engineering, Sapienza University of Rome, Italy; 2CNIS-Research Center on Nanotechnology Applied to Engineering, Sapienza University of Rome, Italy
Over the past years, there has been an increasing interest in natural ester insulating liquids for application in power transformers, thanks to their higher environmental compatibility and lower fire point, as compared to conventional mineral oils. The main function of a transformer oil is its ability to dissipate heat, while ensuring electrical insulation. Among the various influencing parameters, it is well known that heat exchange in a liquid is also affected by its viscosity. Thus, the temperature dependence of the viscosity of an insulating oil should be carefully considered in the design of the cooling system of a power transformer. In this study the variation of the dynamic viscosity with temperature of commercially available natural esters and mineral oils is compared. Steady state rheological measurements are carried out, through a controlled shear rate rotational rheometer, in the 20°C÷100°C temperature range, under isothermal conditions. Temperature ramps are also performed, while fixing the shear rate, with the aim of investigating the variation of the steady shear dynamic viscosity over the whole temperature range. Results demonstrate that the viscosity of natural esters, though being higher at low temperatures, compared to mineral oils, strongly decreases for higher temperatures, thus favouring heat transfer and reducing the risk of hot-spots, which might lead to insulation-failures.
ID: 1132 / P1-1: 20
Studies on the Criteria for the Classification in Complementary Predictive Techniques applied in the Analysis of the Insulation System of Power Transformers
1ENEL Distribution Goiás; 2Federal Institute of Goiás; 3School of Electrical, Mechanical and Computer Engineering - Federal University of Goiás
This article presents studies on various predictive techniques (referred to herein as complementary) related to the insulation system. In combination with other existing techniques, these complementary techniques, whose test classification criteria are demonstrated by scores ranging from “A” (excellent) to “E” (very poor), are important for the diagnosis of power transformers. These techniques are particle counting (particles suspended in the insulating mineral oil) based on the level of the electrical voltage of the device; degree of polymerization of the insulation paper (cellulose polymer); dibenzyl disulfide content (formation of copper sulfide in windings); partial discharges determined by the acoustic emission method, and analyis of their correlation with the loading. These criteria complement existing studies and express the rigor required to analyze transformer insulation systems, in combination with maintenance engineering criteria, thus modeling the analyses performed by specialists and assisting them in decision-making about possible interventions in these devices, which are essential components of electrical.
ID: 1158 / P1-1: 21
Influence of Location of Pressboard Barrier on the Development of Electrical Discharges in Synthetic Esters and Mineral Oil at Negative LIV
1Lodz University of Technology, Poland; 2Cargill - Dielectric Fluids
This article presents the results of an investigation to study the influence of the location of a pressboard barrier on electrical discharge development in synthetic esters and mineral oil under negative lightning impulse voltage (LIV). The measurements were conducted using as a base configuration a point-to-sphere electrode system at a distance of 25 mm oil gap. A 5 mm thick pressboard barrier was considered in the studies and the light emission detection was applied as the main experimental technique. Additionally, the studies were completed by an analysis of electrical field distribution using finite element method (FEM). The results showed that pressboard similarly for synthetic esters and mineral oil prevents against the appearance of breakdown within the considered range of testing voltage changed from 90 to 180 kV. This conclusion concerns all the pressboard locations taken into account in the studies. It is because the differences in the electrical field distributions are small both from the point of view of liquids used and location of the insulating barrier. Concerning the light emission, the studies confirmed previously made observations that in mineral oil the discharges develop with lower intensity of emitted light than in the case of synthetic esters.
ID: 1359 / P1-1: 22
Comparison of the charge trapping tendency between ester impregnated cellulose sheets and mineral oil ones
1Trench Italia, Italy; 2DEI Dipartimento di Ingegneria dell'Energia Elettrica, Bologna
Natural esters are nowadays attracting a lot of utilities which are thinking of installing (or have already installed) the first large power transformers with positive expectations in terms of thermal and long term performance. Instrument transformers manufactures are anyway still resilient to experiment with such fluids, because of the lower advantage-disadvantage ratio related to their application (higher costs not immediately translated into outstanding performance). In a previous investigation, we discovered an interesting so far unknown failure mechanism, which seemed not to be related to manufacturing errors, but to a possible charge trapping related phenomenon. Pulsed Electro-Acoustic measurements have been carried out on simple impregnated sheets samples to compare the different behavior between mineral oil and natural esters. Preliminary obtained results highlight a very low voltage injection thresholds in both cases, and a comparable injected charge, but the depolarization trends seems to be lower in the case of natural impregnated paper even if the investigation is still far to be considered concluded.
ID: 1140 / P1-1: 23
Influence of Conductive Nanoparticles on the Breakdown Voltage of Mineral Oil, Synthetic and Natural Ester Oil-based Nanofluids
1Department of Electrical Engineering, College of Engineering, King Saud University P.O. Box. 800, Riyadh 11421, Saudi Arabia; 2University of Lyon, Ecole Centrale de Lyon, AMPERE Lab CNRS, France
This paper deals with experimental study of the influence of magnetic nanoparticles namely (Fe3O4) at various concentrations on the dielectric strength of mineral oil, synthetic and natural esters (namely MIDEL 7131 and MIDEL 1204, respectively). A statistical analysis of experimental results is conducted using Weibull probabilistic law. The breakdown voltage with risk of 1%, 10%, and 50% probability are also estimated. Experimental findings reveal that this type of nanoparticles significantly improves AC breakdown voltage of mineral oil and synthetic ester. The enhancement is the highest for mineral oil; the breakdown voltage (BDV) can exceed twice that of mineral oil. With synthetic ester, the enhancement can reach 48%. While the improvement of breakdown voltage of natural ester based Fe3O4 nanofluids does not exceed 7%. The physicochemical mechanisms implicated in this improvement are discussed.
|4:15pm - 5:45pm||P1-2: Poster Session on Electro-hydrodynamics|
Session Chair: Igor Timoshkin, University of Strathclyde, United Kingdom
ID: 1274 / P1-2: 1
Study of the Dielectric Behavior of HFE-7000 in Function of Electric Field and Temperature Variations
1Institute Pprime, France; 2Worcester Polytechnic Institute, USA; 3University of Balamand, Lebanon
Nowadays, heat transfer enhancement devices are becoming very essential in many applications. Most of electronic devices, from the simplest to the most sophisticated, contain processors. Advanced processors require efficient cooling for an optimal performance. Due to the growing interest in faster and lighter devices, researchers always seek to innovate and optimize cooling strategies. In spatial applications, the use of typical cooling systems can cause complications due to the vibrations during takeoff and due to zero gravity effects. Electrohydrodynamic (EHD) pumping, which is based on the interaction of a dielectric liquid with an electric field, could present a solution to all these challenges. EHD pumps were considered a breakthrough in the field of cooling since they demonstrate many advantages over other types of pumps. EHD devices are less power consuming, lighter and cheaper. They don’t have moving parts and they are suitable for microgravity applications. The hydrofluoroethers (HFE) are dielectric liquids that could be ideally utilized in these pumps for many applications. Being dielectric fluids with eco-friendly properties, HFEs could replace CFCs, HFCs, HCFCs, and PFCs. Due to their promising EHD applications, studies must be done to investigate the variation of their dielectric behavior with electric field and with temperature. This work presents an experimental investigation of the dielectric characteristics of HFE-7000 with temperature variations. Understanding this aspect can help enhance and optimize the performance of EHD systems.
ID: 1330 / P1-2: 2
Computation the effective dielectric constant of nano-probe local surrounding by solvatochromic spectral shift measurement of organic dye molecule
Photochemistry Center FSRC “Crystallography Photonics” RAS, Russian Federation
Computer modeling the dielectric properties of the cucurbit uril (CB) cavity based on the OnsagerLiptay model was carried out by analyzing the solvatochromic shift of the absorption spectrum of 1- (3ammoniumpropyl) -4 - [(E) -2- (3,4-dimethoxyphenyl) ethynyl]pyridinium upon the formation of the inclusion complex with CB in a water solution. The CB cavity was considered as a polar environment into which the dye chromophore is placed. Positions of the maxima of the dye absorption spectra were measured experimentally in the following solvents: methanol, ethanol, i-propanol, n-butanol and water with known dielectric and optical properties. These values were used for parametrization of the Onsager-Liptay equation. Quantumchemical calculations were used to determine molecular structures, dipole moments of the ground and excited states, and polarizability of the dye. Theoretical value of the effective dielectric permittivity of the cavity is in good agreement with the literature data derived by another method. Thus, we propose a new method for investigation the dielectric constant both in bulk liquids and in very small liquid volumes, for example, into picoliter droplets.
ID: 1236 / P1-2: 3
Effect of Electric Nusselt number on Electro-Thermo-Convection in dielectric liquid subjected to unipolar injection
1Bulgarian Academy of Sciences, Bulgaria; 2P’ Institute of Poitiers, Department of Fluids, Thermal and Combustion Sciences, EHD Team, CNRS / University of Poitiers/ ENSMA ISAE Futuroscope, France.
In this article we analyse the results of a numerical simulation of an electro-thermo-convective flow induced in a dielectric liquid layer by the simultaneous action of an external electric field and a thermal gradient. A low conductivity liquid is placed between two horizontal electrodes and subjected to strong unipolar charge injection which set the fluid in motion under the combined action of Coulomb and buoyancy forces. The motion induced by the charge injection has a vigorous character and strongly increases the electric charge transfer and heat transfer between the electrodes. The full set of governing equations including Navier-Stokes equation, the conservation equations of electric charge and energy and Poisson equation for electric potential is solved by a finite volume method. We define an electric Nusselt number (Ne) as the ratio of the effective current and the current existing without liquid motion, number which can be considered as the analog of Nusselt number (Nu) for a pure thermal problem. The case of heating and strong injection of electric charges from lower electrode is considered. The variation of the electric Nusselt number Ne with electrical parameter T for different values of the non-dimensional parameter mobility number M and Rayleigh number is then analyzed. It is shown that the mobility number M is a parameter which plays an important role in the characterization of electro-thermo-convective flows and also that the physical mechanisms of the different instability regimes can be better understood considering the electric Nusselt number Ne.
ID: 1190 / P1-2: 4
Dielectric droplet on a superhydrophobic substrate in an electric field
1Novosibirsk State University; 2Institute of Hydrodynamics of Siberian Branch of RAS
A non-stationary electrohydrodynamic model of a dielectric droplet dynamics on solid substrate in surrounding gas is developed. The equations for electric field potential and fluid dynamics are solved together. Computer 3D simulations of liquid dielectric droplets on wettable and superhydrophobic surfaces are carried out. The dynamics of the pinned droplet is also simulated. The droplets tend to elongate in the direction of DC electric field. The droplet can jump over a superhydrophobic substrate after the electric field is applied.
ID: 1191 / P1-2: 5
EHD Pumping in Flexible Conic Nozzle
1Universidad de Sevilla, Spain; 2Worcester Polytechnic Institute; 3Institut PPRIME
When an external electric field is applied on a weakly conducting liquid, next to each metallic electrode two layers with a net electric charge of opposing polarity appears. These are called heterocharge layers. The electric field exerts a force on these layers. If the electrodes of different polarity have different geometric characteristics a net electric force is produced, creating a net flow. This is the basis of EHD conduction pumping. This technique has a great number of interesting applications, notably in heat exchange devices to be applied in satellites and aerospace systems. Here we consider a flexible EHD conduction pump. An array of symmetric electrodes is deployed on a flexible non-conducting substrate. This flexibility allows the pump to be installed in conduits of complicated geometries, increasing the applicability of the EHD conduction pumping concept. Specifically, we present the results of numerical simulations with a conic flexible pump with several pairs of electrodes. We discuss the structure of the fluid flow and of the heterocharge layers along the pump.
ID: 1232 / P1-2: 6
Experimental study and numerical simulation of partial discharges in deformed bubbles in transformer oil
1Lavrentyev institute of hydrodynamics of Siberian branch of russian academy of sciences, Russian Federation; 2Novosibirsk State Technical University
The experiments on partial discharges (PDs) in gas bubbles floating up in transformer oil and calculations of the characteristics of partial discharge (PD) in the bubbles were made. For floating up bubbles, it was shown that the PD did not occur even if the electric field was higher than that obtained from Pashen’s law. The experiments on inception of PD in bubbles with X-rays were performed. They confirmed our hypothesis that the absence of PDs can be explained by the lack of initial electrons in floating up bubbles at the conditions of low radiation background. The calculations of the “apparent” and “true” charges of PD in elliptic cavities in a condensed dielectric were performed. A good agreement of the simulations with our experiments was revealed. For the elliptic bubbles, the “apparent” charge is proportional to the bubble volume while the “true” charge is proportional to the surface of the bubble.
ID: 1339 / P1-2: 7
Heat Transfer Enhancement in a Dielectric Coolant by Electroconvection in Point-Plane Geometry
DESTEC, University of Pisa, Italy
The heat transfer performance of an ionic jet impinging on the upper surface of a heated plate is experimentally investigated. Ions are injected by a point electrode, set at high voltage. The working fluid is the spacequalified coolant H-Galden ZT 85. Different tests are performed on the working fluid, varying the composition, the shape and the polarity of the point, the applied voltage, the point-to-plane distance, and the imposed heat flux. The electrohydrodynamic technique produces heat transfer augmentation up to 230 % with respect to thermogravitational convection and heat transfer coefficients in the order of one kW/(m2·K). The electrohydrodynamic enhancing effect is obtained with very low power input. The ionic flow has remained active for 750 hours of continuous monitored operation. H-Galden ZT 85 performs better than other dielectric liquids, such as FC-72, HFE-7100, and Vertrel XF, tested in previous campaigns of electrohydrodynamic heat transfer enhancement reported in literature.
ID: 1284 / P1-2: 8
Analytical model of the flow electrification of a liquid under charging conditions
Laboratoire des Sciences de l’Environnement et de l’Energie (LS2E), Haiti
Flow electrification is a common phenomenon which has been widely studied for the last decades through different approaches. A very large scope of experimental work has proven that its properties are best understood when conditions are created to isolate the phenomenon’s occurrence from a maximum of environmental influences. For instance, high precautions are usually taken to relax all electrical charges inside the liquid before reaching the solid material test sample. In actual industrial processes or systems where flow electrification commonly takes place, it is practically almost impossible to find such occurrences as the liquid is usually flowing through a complex circuit where several different types of solid materials contribute to the overall electrification. Thus, results obtained from experimental studies isolating the streaming current resulted from individual solid/liquid couples are often insufficient to help understanding the actual manifestations observed in industrial environments. This paper develops an analytical approach which allows studying flow electrification taking into account the electrical charging history of the liquid. Even though such analytical model is developed for a simple geometrical configuration adapted to flat rectangular ducts, it broadens the scope of understanding of flow electrification properties to a scale situated between very idealistic laboratory and more pragmatic industrial cases.
ID: 1119 / P1-2: 9
Conical structures on the surface of a liquid with ion current in the space-charge limited mode
1Institute of Electrophysics, UB RAS, Russian Federation; 2Lebedev Physical Institute, RAS, Russian Federation
Conical structures arising on the surface of a liquid with ionic conductivity in an electric field are considered taking into account the influence of both bulk and surface charges. It is demonstrated that the field distribution problem admits an exact analytical solution corresponding to the space-chargelimited current mode. The dependence of the saturation current through the conical formation on the cone apex angle, on the dielectric constant of the liquid, and on the mobilities of positive and negative ions is found. The current vanishes at zero and Taylor’s (49.3∘) cone half-angles, and reaches the maximum value between them. The maximum current is shifted to higher angles with increasing dielectric constant of the medium.
ID: 1126 / P1-2: 10
Numerical simulation of the wave breaking process on the surface of a dielectric liquid in a tangential electric field
Institute of Electrophysics, Ural Division of RAS, Russian Federation
This work is devoted to numerical simulation of the process of interaction between nonlinear waves propagating along the free surface of dielectric liquid in a strong tangential electric field. The model is based on two assumptions: (1) the strong field limit, for which the effects of gravity and capillarity are neglected, and (2) the smallness of nonlinear effects. Results of the numerical simulation show that singular points are formed at the fluid boundary. A sharp drop of the boundary curvature occur in the spatially narrow regions. The amplitude and slope angles of the boundary inclination remain small. The spectral functions of the surface of the liquid acquire a power dependence, namely, ∣𝜂𝑘∣ 2 ∼ 𝑘−5. Near the singularity, the boundary curvature demonstrates behavior typical for Moore’s singularities.
ID: 1103 / P1-2: 11
Experimental Investigation of the Influence of Electric Charge on the Behavior of Water Droplets in Electric Fields
Technische Universtität Darmstadt, High-Voltage Laboratories, Germany
High voltage insulators in electric power transmission and distribution must withstand extreme weather conditions like rain or snow without long-term degradation. One difficulty is the presence of water droplets residing on the hydrophobic silicone rubber surface of insulators, which locally alter the electric field and leads to ageing of the insulator's surface. The present contribution investigates the behavior of sessile water droplets exposed to strong electric fields with a highspeed camera. Electrically charged and uncharged droplets are generated under well-defined conditions and placed on a generic insulator model. The oscillation frequency of the droplet in resonance mode is investigated in detail with respect to the amount of charge, droplet volume, frequency of the electric field as well as the electric field strength. Significant changes in drop behavior are observed depending on the charge and the electric field strength. A regime map based on the experimental data as well as a mathematical model is developed to quantify the necessary conditions for the change of behavior. The performed experiments improve the understanding of droplets in electric fields as well as the ageing process of high voltage insulators. Index Terms—sessile droplet, electro-hydrodynamics, electric charge, composite insulator, droplet resonance, electric field, ageing.
ID: 1144 / P1-2: 12
The Streamer Discharge Simulation of Transformer Oil-based Nanofluid
Xi'an Jiaotong University, China, People's Republic of
Transformer oil plays an important role in the insulation of power equipment such as power transformers and bushings. Due to its good thermal conductivity and insulating properties, the transformer oil-based nanofluids (TNFs) have been received more and more attention as a new kind of liquid dielectric. In order to explore the modification mechanism of TNFs, a two-dimensional axisymmetric fluid dynamics model is established to simulate the streamer discharge behavior in it. In this model, the positive steamer discharge behavior in pure transformer oil and TNFs is studied with different electrode distances and addition of different kinds of nanoparticles in a needle-plate electrode. Modeling results indicate that by adding nanoparticles to the transformer oil, the development of streamer discharge is significantly slower, and the density of negative charges in the streamer channel apparently increases. When different kinds of nanoparticles are added, nanoparticles with a larger saturation charge can result in a slower streamer rate. It can be seen that the addition of nanoparticles effectively inhibits the development of the streamer discharge process. Because of the electric field, the negative electrons attach to nanoparticles in a short time and generate negative nanoparticles. In addition, the inhibition of the development of streamer is more pronounced by the nanoparticles with larger saturation charge, adsorbing more electrons in the same period of time. Therefore, the development of the streamer is slowed down and the insulation properties of the transformer oil are improved.
ID: 1192 / P1-2: 13
Numerical study of electrically induced flow by conduction mechanism in a blade-plane configuration.
1Institut PPRIME, France; 2Universidad de Sevilla, Spain; 3Worcester Polytechnic Institute, USA
In this study a full 3D numerical simulation of the flow induced by the dissociation of neutral molecules in a weakly conductive liquid between a blade shaped electrode and a vertical plane electrode is undertaken. It turns out that even in the conduction situation where neutral molecule dissociate into ions, although the flow is expected to be directed from the plane to the blade a reversed flow occurs after a transition when some circumstances are met. To the best knowledge of the authors, this intriguing phenomenon has never been reported. In this study, this unexpected behavior is analyzed, and an explanation is proposed. The conditions leading to this particular flow inversion pattern are examined and highlighted.
ID: 1193 / P1-2: 14
Numerical investigation of EHD pumping through conduction phenomenon in a rectangular channel.
1Institut PPRIME, France; 2Universidad de Sevilla, Spain; 3Worcester Polytechnic Institute, USA
This study aims to demonstrate the capability of simulating the flow induced by the dissociation of neutral molecules in a weakly conductive liquid in a full 3D channel. We investigate numerically the EHD pumping through pure conduction phenomenon in a 3D rectangular channel. It is important to verify if the assumptions allowing us to consider that the flow remains 2D are always valid and in which circumstances some 3D phenomena may occur ? Not very surprisingly it is observed that while increasing the electric Reynolds number in increasing the electric potential difference between the two electrodes makes the flow becoming turbulent. In such situation 2D computations are not anymore valid.
|Bus Meeting Point|
Contact and Legal Notice · Contact Address:
Privacy Statement · Conference: IEEE ICDL 2019
|Conference Software - ConfTool Pro 2.6.128
© 2001 - 2019 by Dr. H. Weinreich, Hamburg, Germany