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: Sunday, 23/Jun/2019|
|4:30pm - 7:30pm||Registration|
|7:00pm - 8:30pm||Welcome Reception|
|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|
|Date: Tuesday, 25/Jun/2019|
|8:00am - 5:30pm||Registration|
|8:15am - 10:00am||S3: Special Session on Synthetic and Natural Esters in TSO-DSO Transformer Applications|
Session Chair: Massimo Pompili, University of Roma "La Sapienza", Italy
Session Chair: Kevin James Rapp, Cargill, United States of America
ID: 1355 / S3: 1
Assessment of Oxidative Stability and Physical Properties of High Oleic Natural Esters
1University of Missouri, United States of America; 2SEA MARCONI TECHNOLOGIES S.a.s.; 3University of Roma "La Sapienza"
Natural esters (triglycerides) possess desirable attributes such as the higher fire points and better environmental compatibility relative to petroleum-derived insulating mineral oil, as a result, the use of such natural esters is on the rise as insulating and heat transfer fluids in electrical devices such as transformers. However, natural esters differ significantly in chemical composition from mineral oils and are more prone to oxidation than mineral oils. High susceptibility of natural esters can be addressed in part through the use of natural esters with higher monounsaturated fatty acid-high oleic natural esters. Recently several high oleic acid soybeans have been introduced commercially. These include Plenish® (Pioneer / Dupont) Vistive Gold® (Monsanto / Bayer) and Soyleic® (Missouri Soybean Association). Both Plenish® and Vistive Gold® are obtained from GMO soybeans, while Soyleic® has been developed through more traditional plant breeding. The oleic acid content of the three natural esters was found to be 79%, 71%, and 81% respectively. While polyunsaturated fatty acid (linoleic and linolenic) contents of the three natural esters were found to be 10.3%, 22.5%, and 7.8% respectively. High oleic soybean oils along with canola oil with oleic content of 75% and polyunsaturated fatty acid content of 17.2% and generic soybean with oleic content of 24.5% and polyunsaturated fatty acid content of 60.0% were subjected to accelerated aging under conditions outlined in IEC 62770 2013. Test results showed that natural esters with higher oleic and lower polyunsaturated acid contents were more stable than the natural esters with lower oleic and higher polyunsaturated content. This stability was reflected in little or no increase in kinematic viscosity and little increase in dissolved acidity. These natural esters are therefore more suitable for dielectric applications where long-term stability is of paramount concern.
ID: 1135 / S3: 2
Increasead Lodability of Transformers Immersed in Natural Esters
TERNA RETE ITALIA, Italy
Mineral-base oil has been the main insulating liquid for filling power transformers since the 1900’s due to its ready worldwide availability, low cost and good properties. Anyway, in recent times the new desires for a safer nonflammable, an environmental acceptable and a less impacting on sustainable common resources fluid has driven many users in the research and use of alternative fluids to mineral oil. Despite the availability of other fluids, the synthetic and natural (from vegetable seeds) esters (NE) represent the major alternative to mineral insulating oils. Terna as Italian Transmission System Operator (TSO) in according to European Union Directive 2001/42/EC should aim at guaranteeing high levels of environmental protection and safety, so Terna is also aware of its responsibility towards the community and has translated this into a single strategy: to find the right balance between the country's energy needs, nature conservation and the safeguarding of Italy's cultural heritage. In addition to the environmental and fire safety benefits, the review of the possible advantages of natural ester-filled transformers allowed identifying alternative design criteria with relevant financial benefits. The TERNA goal was to increase the loading ability of their transformers, mainly by enhancing a much higher limit for overloading in comparison to traditional transformers. For this prototype TERNA selected a 400/135 kV 250 MVA autotransformer, a standard practice for their network. To explore the superior thermal class of the new insulation system, the transformer manufacturer confirmed the possibility of designing this transformer with a “permanent additional capacity”. Five autotransformers with NE are already in service and in its next-2-years strategic plan Terna has planned the installation of more than 20 new power autotransformers filled with natural ester
ID: 1318 / S3: 3
Experience of Synthetic Ester Filled Transformers in SP Energy Networks
SP Energy Networks, United Kingdom
A fire in an embedded substation triggered a policy change in SP Energy Networks (SPEN) which led to the use of synthetic ester filled transformers in 11kV distribution embedded substations. Driven by improved understanding from research and increased experience in operating synthetic ester filled transformers, the use of synthetic ester then expanded to 33kV primary and 132kV grid transformers. This paper charts the increased use of synthetic ester filled transformers in SPEN along with sharing the benefits realised from adopting synthetic ester applications. Factory acceptance test and condition monitoring data are also presented which indicated the suitability of synthetic ester filled transformers as viable alternatives to conventional mineral oil filled units.
ID: 1334 / S3: 4
Natural ester liquid-filled transformers power the Olympic Games
1Cargill, Plymouth, MN United States of America; 2Cargill China; 3Cargill Brazil; 4Sea Marconi, Turin, Italy; 5University of Roma-Sapienza
This paper will present natural ester transformer operating data with liquid test results from the units since installation. Various facts and experiences from transformers of two Olympic cities will be shared. The results of physicalchemical and electrical testing including dissolved gas analysis will provide the performance history in the field of a group of power transformers of 138 kV design and of unique designed submersible 10 kV distribution units filled with natural ester fluid, some in service for more than 4 years.
ID: 1307 / S3: 5
Investigation of the Total Flow Rates in Oil Natural Transformer Retrofilling Scenarios
1The University of Manchester, United Kingdom; 2M&I Materials; 3Cargill Bioindustrial- Global Dielectric Fluids Technology
Retrofilling transformers with a new liquid has been considered as an option for life extension and/or uprating purposes. The determination of the new total liquid flow rate is of vital importance in assessing the effect of retrofilling on flow and temperature distributions in the winding, especially for ON transformers. This paper presents the determination of flow rate ratios for four liquids—a mineral oil, a GTL oil, a synthetic ester and a natural ester—in ON transformer retrofilling scenarios. Flow rate ratios among different liquids are provided for a simplified condition of linear radiator oil temperature variation. For a more realistic exponential radiator oil temperature variation, the detailed transformer geometric information is needed to estimate the total flow rate. In addition, a hydraulic winding network model is established to prove that “minor pressure losses” due to change of flow directions is indeed minor for ON transformer liquid flow conditions, justifying neglecting the minor losses in the deduction of the total liquid flow rate.
ID: 1358 / S3: 6
Fire simulation tests of mineral oil and natural esters transformers
1Italian Ministry of Home Affairs National Fire and Rescue Service Dept., Italy; 2University of Roma "La Sapienza", Italy; 3Terna Rete Italia, Italy; 4Italian National Institute for Insurance against Accidents at Work (INAIL), Italy; 5e-distribuzione, Italy; 6ISPRA Dept. for Geological Survey of Italy
This paper describes the work carried out by the Italian Institutional Working Group on Natural Esters; this Group has been promoted by the University of Roma "La Sapienza", the National Firefighters Authority, the National Institute for Insurance against Accidents at Work (INAIL) and the Department for Geological Survey of Italy (ISPRA) with the objective of further validating the real possibility of risk mitigation for humans and environment through a more widespread use of a new generation of transformers insulated with natural ester liquids. A useful contribution to the activities of the Italian Institutional Group on Natural Esters has been also given by the participation of some of the major players in the electrical sector, such as: Italian TSO, main Distributors, Natural Ester producers and transformer manufacturers. The development of this Italian Group at international level has been the set-up of the CIGRE WG D1.68 “Natural and synthetic esters – Evaluation of the performance under fire and the impact on environment”, which is actually preparing a report on this subject. The present paper reports the main results of experimental comparative fire simulations of both mineral oil and natural esters distribution transformers.
|10:00am - 10:30am||Coffee Break|
|10:30am - 12:30pm||S4: Special Session on Synthetic and Natural Esters in TSO-DSO Transformer Applications|
Session Chair: Russell Martin, M&I Materials, United Kingdom
Session Chair: FABIO SCATIGGIO, TERNA RETE ITALIA, Italy
ID: 1227 / S4: 1
Smoke Tests of Natural Esters and Mineral Oils under Transformer Fire Conditions
1A&A Fratelli Parodi Spa, Italy; 2Terna Rete Italia, Italy; 3INAIL, Italy; 4Università di Roma "La Sapienza", Italy
In the framework of the activities of the Italian Institutional Working Group on Natural Esters, smoke production under controlled fire conditions of such innovative insulating liquids has been studied in comparison with that released by traditional mineral oil, normally used in electrical power transformers. This comparison has been made in terms of solid particulates, carbon monoxide (CO), Total Organic Carbon (TOC), Polycyclic Aromatic Hydrocarbons (PAH), Volatile Organic Compounds (VOC) and Aldehydes in different conditions of greater or lower presence of atmospheric oxygen. The main results are reported in this contribution.
ID: 1288 / S4: 2
Oxidation Stability of Insulating Liquids by Rapid Small Scale Oxidation Test
1Central Power Research Institute, Bengaluru,India; 2JSS Science and Technology University,Mysore,India
Insulation materials are an important component of transformers; the life of the electrical equipment depends on the quality of solid and liquid insulating materials used. Mineral insulating oils, synthetic esters and natural esters are different types of liquid insulating materials. During prolonged service in electrical apparatus these oils undergo deterioration, mainly due to continuous oxidation. Hence, the long- term performance of insulating oils depends on the stability to oxidation. This behaviour is usually termed as resistance to the oxidation process or oxidation stability. Oxidation stability test as per test method IEC 61125 and ASTM D2112 are familiar methods to test the oils. According to IEC 61125 (Method C) the insulating oil, is conditioned at 120°C, with copper catalyst and by bubbling zero air over a duration of 48 for natural esters, 164 hours for uninhibited oils and synthetic esters, 500 hours for Inhibited oils. Rotating Pressure Vessel Oxidation Test method (RPVOT) as per ASTM D2112 requires copper catalyst and oxygen pressure of 620 kpa is allowed to oxidize the oil sample at 140°C. Oxygen bubbling method assesses the oil based on measurement of dissipation factor, acidity and viscosity for natural esters and sludge development for mineral insulating oils and synthetic esters. RPVOT method measures the induction period. Although the IEC 61125 is conventional, it is time consuming and the RPVOT curve for natural esters cannot be distinguished due to the poor stability characteristics of natural esters.This paper details experiments that have been carried out to measure oxidation stability by using a new method named as Rapid Small Scale Oxidation Test (RSSOT) as per ASTM D7545, using petroxy equipment to measure the induction period. Oxidation stability test has been carried out on mineral insulating oils, synthetic esters and natural esters. The results are compared to assess the suitability of the rapid small scale method for evaluating the stability of insulation oils. It is found that the rapid small scale method is suitable to measure the oxidation stability and the results are comparable to the conventional methods. Further, natural ester and synthetic ester was analyzed both with copper catalyst and without catalyst. It was found that presence of copper catalyst accelerates the rate of oxidation of both synthetic ester and natural ester. RSSOT has the advantage of being a rapid method, simple and easy to use, and where only a small quantity of sample is needed, thereby reducing the risks to safety and waste sample disposal problems.
ID: 1234 / S4: 3
Kraft and diamond dotted paper thermally aged in mineral oil and natural ester: mechanical characterisation
University of Cantabria, Spain
Oil-immersed transformers, whose lifespan is defined by cellulose insulation’s lifetime, utilize frequently mineral oil. However, this insulating fluid is being replaced by alternative liquids such as natural and synthetic esters. This replacement requires to guarantee a similar behavior of solid insulating materials immersed in them. Although there are different authors who have concluded that Kraft paper reduces its deterioration rate when it is immersed in biodegradable fluids, there are few works that have analyzed the effect of insulation liquids on the mechanical properties of other cellulosic materials such as diamond dotted paper (DDP) during laboratory tests. This paper shows a comparative analysis of four paper/oil specimens (a standard Kraft paper and a diamond dotted paper aged in both mineral oil and natural ester) under controlled laboratory accelerated thermal ageing. This work focuses on changes in mechanical properties such as the energy consumed per unit volume of the failure zone (ER), rupture strength (σR) and strain under ultimate strength (εcm).
ID: 1233 / S4: 4
Preliminary Studies on Soluble and Colloidal Decomposition Products in Ester Filled Transformers
ViAHT - UQAC, Canada
Esters dielectric fluids are found to be prominent replicate for mineral oil based insulation systems. Explicit studies on aging performance of these new insulating oils improve existing knowledge on the actual performance and degradation process. In this work, degradation of synthetic ester and natural ester has been investigated in comparison to mineral oil. Investigation is aimed at understanding the generation rate of soluble and colloidal particles in different oils with aging. Thermal aging is carried out as per ASTM D 1934 with a controlled aging history at different durations in presence of cellulose. Later, separation of colloidal particles is carried out as per ASTM D 1698 to study the comparative degradation rate of oils. Turbidity of oil and Particle counter measurements are performed before and after centrifuge to identify the growth of decay contents with aging in oils. A significant difference in the evolution of decay contents has been identified between esters fluids and mineral oils. The impact of colloidal particles on degradation of ester fluids is almost negligible whereas the degradation in mineral oils majorly governed by colloidal particles.
ID: 1248 / S4: 5
Influence of Pressure in Sealed Tube Ageing Test
1Weidmann Electrical Technology Inc.; 2M&I Materials Inc
This article discusses about the differences in results from an experiment that was performed on ageing of thermal upgraded Kraft (TUK) insulation system with mineral oil and ester liquids under different pressure conditions. When sealed tube ageing studies are conducted as per the IEEE C57.100 test standard, there are no requirements per the standard on the type of ageing vessels to use or the pressure limits. The experiment was conducted using metal vessels and glass vessels with pressure relief devices installed to control the pressure during ageing. The results from the ageing test showed that controlling the pressure in the ageing vessel does affect the rate of acceleration of the solid insulation and the ageing rate of TUK is slower in esters in comparison to mineral oil.
ID: 1253 / S4: 6
Fundamental study on the application of natural esters on intrument transformers
Trench Italia, Italy
Esters are nowadays very popular among high voltage power transformers manufacturers, because of their outstanding advantages in terms of thermal performance of extended overload possibilities. Instruments transformers manufacturers, on the contrary, have not started investigating their possible use yet, because of the lack of immediate performance increase, being low power machines. A starting testing campaign is described in this paper and aimed at verifying the feasibility of the ester liquids replacement in instrument transformers without affecting the current design where the dominant insulating fluid is mineral oil. High voltage current and voltage transformer prototypes were designed, dried and impregnated with Envirotemp FR3 and their performance was assessed by dielectric routine and type tests. An interesting polarity effect was noticed during the lightning impulse tests and currently under investigation, together with the endurance tests aimed at assessing the long term performance of the units.
ID: 1310 / S4: 7
Effect of Field Uniformity on Positive Streamer Characteristics of a Synthetic Ester under Lightning Impulse
The University of Manchester, United Kingdom
This paper presents a study on the influence of electric field uniformity on the streamer characteristics of a synthetic ester under positive lightning impulse. Streamers were experimentally investigated under both needle-plane (NP) nonuniform field and plane-needle-plane (PNP) semi-uniform field. At the same gap distance, streamers under PNP semi-uniform field showed less branched structure and restrained more in the axial direction compared to those under NP non-uniform field. In this paper, field inhomogeneity factor (field factor) was used to describe the degree of the non-uniformity of various field geometries. It was found that as the field factor decreases indicating more uniform field, the streamer propagation is greatly facilitated. At the same stopping length, streamers under fields with higher degrees of non-uniformity have larger areas, which quantitatively indicate a more branched structure. As a consequence, a transition from propagation-dominated process to initiation-dominated process of streamer development as field factor decreases was well evidenced.
|12:30pm - 1:00pm||Conference Group Photo|
|1:00pm - 2:15pm||Lunch|
|2:15pm - 4:00pm||S5: Measurement, Monitoring and Diagnostic Techniques in High Voltage Equipments|
Session Chair: Abderrahmane Beroual, University of Lyon, Ecole Centrale de Lyon, AMPERE Lab CNRS, France
Session Chair: Bruce Pahlavanpour, Nynas, United Kingdom
ID: 1364 / S5: 1
Stirring effect in dielectric liquids breakdown voltage determination
1BAUR GmbH, Austria; 2University of Roma "La Sapienza", Italy; 3University of L'Aquila, Italy
The latest version of the standard IEC 60156 “Insulating liquids - Determination of the breakdown voltage at power frequency - Test method” was published in August 2018 as Edition 3.0. This standard follows the two previously published versions in 1963 and 1995. The test method described in practically all IEC 60156 versions defines a procedure in which the insulating liquid is subjected to an increasing AC electrical field until breakdown occurs and it is used for both acceptance testing on unused liquids at the time of their delivery and for establishing the condition of samples taken in monitoring and maintenance of equipment. In this paper the experimental results of 50 Hz breakdown voltages of both mineral and natural ester liquids performed following the tests methods described in the new edition of IEC 60156 are shown. The tests were performed also with the use of different stirring systems.
ID: 1296 / S5: 2
Investigation on Gassing Behavior of Various Insulation Liquids in Power Transformers
Leibniz Universität Hannover IfES Schering-Institute, Germany
Under normal operating conditions hermetically sealed power transformers undergo load cycles resulting in pressure and temperature variation. With decreasing pressure, the dissolved gases diffuse out of the insulation liquid and accumulate in gas phase. This gas leakage may be diagnosed as a fault in transformer by monitoring systems. However, it should be differentiated from a fault decomposing the insulation material. It is known that the conventional insulating liquid exhibit to some extent a different degassing behavior in comparison to the new alternatives. In addition to the erroneous fault indication, the gassing properties as well as the solubility of gasses influence the accuracy of the dissolved gas analysis. By determining the concentration of key gases and specific ratios among them, the type of fault can be classified. The gassing behavior of various liquids depends on many factors, such as pressure, temperature and of course the type of the insulation liquid. Therefore, the specification of the gassing and degassing behavior of new alternative insulating fluids is of critical importance. In this study, two different test vessels were built to determine the different gassing characteristics under laboratory conditions. On the one hand a simple arrangement with glass vessels was constructed to represent a kind of gas trap and on the other hand a scaled model of the transformer tank with a long diffusion way and a small contact to the gas phase above the liquid. The tests were performed at different pressure and temperature values by using a vacuum oven. To analyze the influence of these parameters on the gassing behavior, the pressure was kept at three different values: 800 mbar, 900 mbar and 950 mbar. Furthermore, the measurements were performed at various temperatures namely, 40 °C and 80 °C. A synthetic ester, an uninhibited mineral oil and a gas-to-liquid (GtL) oil were investigated. Before and after each test a dissolved gas analysis was performed. Moreover, the time, in which gas bubbles appeared, were registered.
ID: 1167 / S5: 3
Diagnosis of transformers based on vibration data
1Politecnico di Milano, Italy; 2RSE, Italy; 3Trafoexpert,Switzerland
Transformers with loose or deformed windings can fail during an external short circuit with loss of service and heavy maintenance costs. The transformers’ tank vibration technique potentially offers a decisive solution for an on line continuous assessment of the integrity of structural elements in transformers. In this paper, the influence of sensor location on tank vibration measurements is addressed by means of Support Vector Machine (SVM) algorithms. Laboratory tests have been carried out in different points of the tank, on a typical oil filled power transformer under two extreme conditions, tight and loose windings. Preliminary results of SVM analysis of tank vibration spectra showed that it is possible to correctly identify winding looseness during repetitive sensor installation.
ID: 1214 / S5: 4
Partial Discharge Defect Recognition in Power Transformer using Random Forest
1PLN, Indonesia; 2State Key Laboratory, Xi’an Jiaotong University, China; 3Bandung Institute of Technology, Indonesia
Partial Discharge (PD) diagnostic become more important for high voltage (HV) equipment condition monitoring. PD phenomenon in power transformer could indicate insulation aging or degradation, which in long term could reduce the integrity of the insulation and leading to transformer failure. High accuracy of recognition rate for different PD defect is necessary for a successful PD diagnostic. This paper presents Random Forest (RF) method for PD defect recognition in power transformer. RF is one of supervised learning algorithm in machine learning. RF known as an ensemble classifier build using many decision trees. The majority vote of each three will determine the PD type. There are three defects used in this paper, protrusion, floating metal, and void. A commercial PD measurement system and detecting impedance was used to record the phase resolved partial discharge (PRPD) patterns of different defects. 8 PD statistical features extracted from PRPD patterns to identify each defect. To calculate the accuracy of RF method, different amount of PD features was use for recognition and then compare with other methods.
ID: 1365 / S5: 5
FT IR and X-Ray Photoelectron Spectral(XPS) Evidence for interaction between Natural Ester and Cellulose paper
SAVITA OIL TECHNOLOGIES LIMITED, India
Several researchers have claimed that Natural Esters enhance the thermal stability of insulation paper. It has been claimed that the chemical interaction accounts for slowing down of ageing of paper and enhancement of insulation life. The enhancement of paper life translates to transformer asset life enhancement. We have conducted aging studies at 120 °C on normal Kraft paper (NKP) as well as thermally upgraded Kraft paper (TUK). The results showed unambiguous development of carbonyl structure on the paper surface – both normal Kraft paper and thermally upgraded paper. These results are further corroborated with X-ray photoelectron spectroscopy (XPS) which lends further support to the formation of carbonyl structure on the paper surface. The results are interpreted in terms of transesterification reaction taking place between cellulosic hydroxyls and the carboxylate of oil.
ID: 1155 / S5: 6
High frequency permittivity measurements of dielectric liquids with a new technique of coplanar waveguides
1USTHB, University of Science and Technology Houari Boumediene, Algeria; 2University of Lyon, Ecole Centrale de Lyon, Ampere Laboratory CNRS UMR 505
In this study, we propose a new approach for broadband measurement of the relative permittivity of dielectric liquids in the microwaves frequency domain. This can be useful in the process of diagnosis and monitoring of electrical equipments where liquid dielectrics are used for insulation. The achieved sensor consists of a micro-strip coplanar waveguide CPW free of substrate operating in the microwave frequency domain and whose characteristics are very sensitive to the electromagnetic properties of the medium in which it is placed (more specifically the relative permittivity). Two methods are investigated. The obtained results by using the first method show good agreement between the simulation and measurements. The experimentally obtained average results are close to the relative permittivity of the liquid over a broad band frequency.
|4:00pm - 4:30pm||Coffee Break|
|4:30pm - 6:00pm||S6: Partial Discharges|
Session Chair: Maks Babuder, Elektroinštitut Milan Vidmar, Slovenia
Session Chair: Nelly Bonifaci, G2E.lab, France
ID: 1110 / S6: 1
Prebreakdown and Breakdown in Liquid Nitrogen under Pulsed Heating for Superconducting Applications
1SuperGrid Institute, 23 rue Cyprian, 69628 Villeurbanne, France; 2Univ. Grenoble Alpes, CNRS, Grenoble INP, G2Elab, 38000, Grenoble, France
ID: 1228 / S6: 2
Partial Discharge Measurements on Dibenzyltoluene for High Temperature Encapsulant Application up to 350°C
1Université Grenoble Alpes, CNRS, Grenoble INP, G2Elab, France; 2PLN Indonesia, Indonesia; 3Institut Teknologi Bandung (ITB), Indonesia
ID: 1127 / S6: 3
Partial Discharge Characteristics caused by Metallic Particles under DC voltage on Oil Immersed Insulation
Mitsubishi Electric Corp., Japan
ID: 1160 / S6: 4
Comparison of Dissolved Gases in Natural Ester under Partial Discharges
King Mongkut’s Institute of Technology Ladkrabang, Thailand
ID: 1229 / S6: 5
Streamer Generation and Propagation in Dibenzyltoluene and Ester Liquids under High Temperature
1Université Grenoble Alpes, CNRS, Grenoble INP, G2Elab, France; 2PLN Indonesia, Indonesia; 3Institut Teknologi Bandung (ITB), Indonesia
|Date: Wednesday, 26/Jun/2019|
|8:00am - 4:00pm||Registration|
|8:15am - 10:00am||S7: Electrical Discharges and Breakdowns|
Session Chair: Pawel Rozga, Lodz University of Technology, Poland
Session Chair: Stefan Tenbohlen, University of Stuttgart, Germany
ID: 1332 / S7: 1
Structure analysis of streamers in transformer liquids under impulse voltages
Shanghai University of Electric Power, China, People's Republic of
It is well known that the performance of streamers in transformer liquids are closely related to the test conditions, e.g. liquid nature, voltage polarity, voltage level and field configuration. The differences in streamer phenomena under various test conditions can be reflected by the evolution of streamer shapes. However, the conventional parameters such as stopping length, average propagation velocity and apparent area cannot quantitatively describe the degree of structural complexity of streamers. In this paper, multi-fractal analyses were performed for 2-D projected streamer images captured in a mineral oil under impulse voltages. The multifractal spectrum shape, spectrum shift alone vertical axis and maximum value on the spectrum curve were estimated in order to describe the changing trend of streamer main branches and side branches, the distribution of streamer branches and the complexity of overall streamer morphology, respectively. Variations of these parameters with changes in test conditions including voltage polarity and voltage level were evaluated.
ID: 1164 / S7: 2
Lightning impulse withstand of insulating liquid in terms of unified weak-link theory
Končar D&ST, Croatia
Paper investigates the applicability of newly proposed weak-link model to lightning impulse breakdown measurements for different electrode geometries. Applicability has been confirmed on both positive and negative polarity impulses, and a functional relation of lightning impulse with AC breakdown withstand in terms of field non-uniformity has been established.
ID: 1222 / S7: 3
Impedance Analysis of Underwater High Current Pulse Discharge
1State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan, Hubei Province, China; 2School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan, Hubei Province, China; 3Key Laboratory of Pulsed Power Technology, Huazhong University of Science and Technology, Ministry of Education, Wuhan, Hubei Province, China
The liquid-electric effect has been widely used in the fields of petroleum deblocking and crystal crushing. In order to specifically investigate the characteristics of high current pulse discharge arc impedance in water, the arc development process of pin-plate electrode discharge with gap voltage of 30kV and different gap distances was studied. The high current liquid gap test platform in water, and the optical platform were used. The entire test phenomenon was taken frame by frame. The curve of time-varying resistance under different gap discharges is obtained, and the experimental value of arc resistance per unit length under the discharge condition is given as 0.008-0.01Ω/mm. Combined with the relevant theoretical models, the value is simulated and discussed. It is believed that the conclusions obtained are highly reliable and can promote the understanding of the discharge arc plasma in water, so as to better regulate the energy of the liquid-electric effect.
ID: 1168 / S7: 4
On polarity effect of underwater impulse breakdown
Chongqing University, China, People's Republic of
In this paper, the impulse breakdown tests of conductive water (350 μS/cm) were carried out under different experimental conditions (25-1500μs and 0.5-100mm). The polarity effect of underwater impulse breakdown was investigated, and the classification and region definition methods for polarity effect were proposed. The results showed that there are three kinds of polarity effect variation point and four kinds of polarity effect. The motion trail of polarity effect variation points varied with experimental condition can be used to define the region of specific polarity effect.
ID: 1255 / S7: 5
AC Breakdown Performance Analysis of SF6/N2 and SF6/CO2 Gas Mixtures for Ring Main Unit (RMU) Switchgear Application
1Universiti Teknikal Malaysia Melaka, Malaysia; 2Universiti Tun Hussein Onn Malaysia, Malaysia; 3Indkom Engineering Sdn. Bhd.
In high voltage applications, sulphur hexafluoride (SF6) gas has been utilized as the electrical insulation and/or current interrupter due to its strong electronegative properties. However, SF6 owns unfavorable impact to the environment since it was listed in Kyoto Protocol 1997 as a potent greenhouse gas. As one of the alternatives to minimize the usage of pure SF6, the breakdown behavior of SF6/N2 and SF6/CO2 gas mixtures at 10 % SF6 content are investigated under non-uniform field at pressure level between 0.11 MPa to 0.15 MPa, which focusing for ring main unit (RMU) switchgear application. In this study, the AC breakdown voltage test on both SF6 gas mixtures were conducted inside a pressure vessel using R6-plane electrode configuration, where the gap distances between the electrode were varied between 5 mm to 30 mm. The results show that the AC breakdown voltage of SF6/N2 and SF6/CO2 at 10 % amount of SF6 is above 40 % as relatives to pure SF6, throughout all gap distances and pressure levels. Moreover, it is also found that the AC breakdown voltage of SF6/CO2 is higher than SF6/N2 when the electrode gap is increased above 15 mm, suggesting the significant role of electrode gap distances in suppressing the breakdown streamer in SF6/CO2.
|10:00am - 10:30am||Coffee Break|
|10:30am - 12:30pm||S8: Electrical Discharges and Breakdowns|
Session Chair: Olivier Lesaint, CNRS / Grenoble Electrical Engineering Lab G2Elab, France
Session Chair: Zhongdong Wang, The University of Manchester, United Kingdom
ID: 1139 / S8: 1
Creeping Discharges at Liquid/solid and Gas/Solid Interfaces: Analogies and Involving Mechanisms
University of Lyon, Ecole Centrale de Lyon, AMPERE Lab CNRS, France
This paper is a synthesis of acquired results by my group on creeping discharges at fluid/solid interfaces during the last two decades. It aims to evidence the analogies between the characteristic parameters of surface discharges propagating on liquid/solid and gas/solid interfaces (namely, shape, stopping length, current/electrical charge, fractal dimension) and the dependency of these characteristics on the same physical parameters. It also evidences the influence of the capacitive effects on these characteristics under different types of voltage waveforms namely AC, DC and lightning impulse voltages.
ID: 1175 / S8: 2
Experimental Discharge Initiation Study for Paper and Pressboard Insulated Electrodes in Mineral Oil and Synthetic Ester Fluid
1ABB AG, Bad Honnef, Germany; 2ABB Corporate Research, Västerås, Sweden
Ester insulating fluids have different properties compared to commonly used mineral oils and for application in power transformers adequate design rules are needed. For dielectric design, parameters describing discharge initiation, propagation and breakdowns are relevant and need to be quantified. Some of them are defined and measured within this study. The discharge initiation lightning impulse voltages are measured for two test object types reflecting typical geometries of power transformers construction (oil gap and oil wedge configuration) and for two fluid types (mineral oil and synthetic ester). Furthermore, the discharge delay time is evaluated as well as the nature of discharge propagation.
ID: 1308 / S8: 3
Effects of Moisture and Oil Flow on White Mark Propagation on Pressboard in an Ester Liquid
The University of Manchester, United Kingdom
Surface tracking can cause irreversible damages to the pressboard and result in a weakened dielectric performance. Surface tracking with white mark generally occurs on the surface of pressboard immersed in the transformer oil. This paper presents an experimental research on the effects of moisture in the pressboard and oil flow on the propagation of white mark along an ester liquid/pressboard interface under AC stress. The moisture contents in the pressboard were controlled at three levels, i.e. 1%, 2% and 4%. The oil flow rate ranged from 0 to 4 L/min, and the corresponding oil velocity was from 0 to 0.2 m/s. The needle to plane electrode configuration and a composite pressboard structure were employed to perform the tests. It was found that different moisture contents in the pressboard resulted in different periods for the white mark to propagate. The decrease of the moisture content resulted in a longer initiation time for the white mark. In addition, the increasing oil flow rate could decrease the growth velocity of the white mark and extend the time needed for the white mark to reach the final stage.
ID: 1198 / S8: 4
Discharge Characteristics with Impulse Voltage Application in Ester Oil/Pressboard Composite Insulation System
1Kyushu Institute of Technology, Japan; 2Mitsubishi Electric Corporation, Japan
Partial discharge characteristics as well as breakdown phenomena in a power transformer insulation, i.e. oil and paper insulation, has to be clarified for miniaturization of the apparatus. In recent years, environmental-friendly transformers using ester oil, which shows excellent biodegradability, receive much attention due to the worldwide growing environmental awareness. Considering this, researches on fundamental characteristics of discharge phenomena within the ester oil are required. Although various papers on discharge characteristics in the ester oil have been published by many researchers, there are still few reports on these researches using ester oil and pressboard (PB) composite insulation system. In this paper, the discharge inception field and starting point in the ester oil and PB composite insulation configuration are investigated and the results are compared with those in the mineral oil to discuss the detailed discharge mechanisms.
ID: 1303 / S8: 5
Assessing the Production and Loss of Electrons from Conduction Currents in Mineral Oil
KTH Royal Institute of Technology, Sweden
The evaluation of the high-field generation and loss of charged carriers is a key step to simulate any prebreakdown process in a dielectric liquid. Currently, the electron generation in mineral oil has been widely described in terms of “electric-field-dependent molecular ionization” and the electron loss is estimated using a fixed attachment time constant. This paper reports our next step towards the quantitative characterization of the production and loss of electrons in mineral oil. In this step, the electrical conduction measurements are performed in mineral oil for a needle-plane configuration (tip radius ~3 μm) and submicrometric gap distances (ranging between 10 to 100 μm). Conduction currents in negative polarity are reported from 10-12 to 10-7 A, from the ohmic to the spacecharge limited regimes. In order to check the validity of existing simulation models for mineral oil, computer simulation is used to calculate the VI characteristic in the liquid considering electrohydrodynamic (EHD) motion. It is shown that the active zone where electrons are produced in front of the needle is around 10 μm long. Furthermore, it is found that electrons travel a similar distance before they attach into ions. It is also shown that the currents are grossly misestimated when parameters proposed in the literature to model generation and loss of electrons in mineral oil are used.
ID: 1187 / S8: 6
Effects of Discharge Patterns and Pulse Width on Hydrogen Peroxide Formation by Pulsed Electrical Discharge in Water
State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an, Shaanxi, P.R. China
Active species generated during the underwater discharge process play a pivotal role in the application fields. The electrical parameters including voltage amplitude and voltage pulse width make various contributions to the generation of active species. In this paper, we investigate the influences of discharge patterns (streamer and spark discharge) and voltage pulse widths on hydrogen peroxide (H2O2) generation. The experimental results show that the production rate and energy yield of H2O2 increases with the rise of applied voltage in streamer discharge region. While after spark discharges occur, the energy yield shows a saturated trend and the production rate even decreases in the spark discharge region. The increase of voltage pulse width also makes a positive contribution to improving the production rate of H2O2. While the energy yield of H2O2 production is independent on the variation of voltage pulse width. Besides, it is inferred that the generation of H2O2 mainly occurs during the wave tail time instead of rising time.
ID: 1162 / S8: 7
Three-Parameter Weibull Distribution Curves for LIBV of Pressboard Samples Impregnated with Natural Ester and Mineral Oil
Lodz University of Technology, Poland
The studies presented in this paper were focused on comparative analysis of Weibull distribution curves determined for lightning impulse breakdown voltages of 1 mm thick pressboard samples impregnated with natural ester and mineral oil respectively. The analysis of the results was made using threeparameter Weibull distribution function with location parameter V0 (theoretical zero probability) meaning the threshold value of voltage below which breakdown does not happened. The curves obtained within the studies are in general similar in shape with some benefits in direction of curves connected with pressboard impregnated by natural ester liquid. Quantitatively the difference between the considered cases was found as very small (around 2 kV when comparing the V0 obtained). The reason for this may be the difference in electrical permittivity of pressboard impregnated by ester, which is a little bit higher in comparison with pressboard impregnated by mineral oil. The studies confirmed also that the applied three-parameter Weibull distribution is an excellent statistical tool for determination of threshold electrical strength of liquid-solid insulation systems.
|12:30pm - 1:45pm||Lunch|
|1:45pm - 3:45pm||S9: Applications and Performances of Dielectric Liquids in High Voltage Equipments|
Session Chair: Yves BERTRAND, EDF R&D, France
ID: 1224 / S9: 1
Non-standard PD inception voltage testing of liquid dielectrics used in transformers
1Elektroinštitut Milan Vidmar, Slovenia; 2Nynas, Sweden
This paper reports on experience learned from PD research testing on 7 various new mineral oil and natural ester liquids. Samples of different chemical composition and condition (impurities), alike to those in operating transformers with known condition parameters (differing water and cellulose particle content) were tested. Tests were done using PD inception voltage testing cell applying steady electrical stress. PD testing arrangement and test protocol are described. Results of PD inception voltage of different oil samples are presented and evaluated with respective conclusions. The aim of this research was to enable distinguishing between insulating liquids regarding their ability to prevent or suppress partial discharges (PD) when the liquids are submitted to high electrical stress. Implementing and meticulously considering the IEC standard procedure for PD inception voltage testing, several questions arose: - Is the so obtained characteristic relevant and enough to understand the PD phenomena in oil impregnated paper, - Are the dried and filtered samples representative to help evaluating the behaviour of the insulating liquid in operation during the whole lifetime of an insulation and - May the PD current true recording help in assessing of oil samples from operating transformers. And besides, one may have some doubts whether such a high field stress, which is necessary to produce the standard PD threshold values (above 100 pC), can represent a realistic situation in a concrete case of a power transformer HV oil-paper insulation.
ID: 1153 / S9: 2
Time and Space Transition of DC Electric Field Distributions in Oil-Pressboard Composite Insulation in AC/DC Converter Transformer
1Aichi Institute of Technology; 2National Institute of Technology, Niihama Collage; 3Nagoya University
It is necessary to enhance an HVDC electrical insulation performance for further introduction of DC electric power systems. In AC/DC converter transformers under DC application, the electric field distributions are distorted due to the deposited charge on pressboard (PB). However, DC electric field stress in oil-PB composite insulation has not yet been clarified in detail. In this paper, we investigated the time and space dependent characteristics of DC electric field stress in oil from DC-on (initial state) to DC steady-state in oil-PB composite insulation systems. As a result, we quantitatively clarified that DC electric field stress strongly depends on the elapsed time and the location in the electric field space in oil. In particular, it was found that the most severe electric field stress in oil for the electrical insulation performance may emerge during the time transition process between initial DC-on to DC steady-state, using an insulated conductor lead and an actual AC/DC converter transformer model.
ID: 1210 / S9: 3
The conformity of DGA interpretation techniques: Experience from transformer 132 units
King Mongkut’s Institute of Technology Ladkrabang, Thailand
Dissolved gas analysis (DGA) is an important method and widely used for assessment the conditions of transformer insulations. The dissolved gas interpretation is one of the most significant procedures to identify the failure causes. The objective of this paper is to represent diagnosis of the dissolved gas techniques i.e. IEC ratio, Duval Triangle and Duval Pentagon for interpretation. The data of dissolved gas is received from Metropolitan Electricity Authority (MEA), Thailand during 2016. The DGA test results obtained from 132 transformer units. Due to the transformers have various rated power so providers have made a classification of results by rated transformer power rated of 40, 60, 250 and 300 MVA respectively. Overheating at high temperature is generally found. The results of the data analysis by using Duval Triangle method is the most similar result from observation work. Moreover, the Duval Pentagon method is interested for gas interpretation. However, it needs more research work to guarantee and support this method.
ID: 1161 / S9: 4
Studies for the Use of a Dielectric Liquid as Insulator in a Wireless High Voltage Generator
1Padova University, Italy; 2INFN, Sez. di Padova, Italy; 3INFN, Laboratori Nazionali di Legnaro, Italy
We investigated the possibility to use a liquid as insulator in a High Voltage generator which is wireless powered by a laser system. The liquid must be transparent to the laser light wavelength, must not attack the control circuits, which are immersed in it, and the support materials. An adequately performing liquid was identified and we characterized the liquid performance in intense electric field, by measuring its breakdown voltage and the leakage current, and checked its optical and thermal behaviour.
ID: 1327 / S9: 5
Comparison of X-Wax Formation in Different Insulation Liquids
Leibniz Universität Hannover, Germany
The formation of solid wax-like ageing products in mineral oil under high voltage stress is known for almost a century. It was observed in oil-impregnated cables, bushings and capacitors. Its formation was generally attributed to high field strength and partial discharges. Since these types of equipment do not rely on oil flow for cooling the wax formation was seen as a sign of wear and not by itself as threat to the equipment. With the improvement of materials and design tools, the field strength in transformers increased. In recent years there was a significant number of outages in distribution transformers, which were related to partial discharges and wax formation. The purpose of this research is to understand how this wax is formed and how different insulation liquids behave in regard to the wax formation. Observations from the investigation of faulty transformers are compared to a lab experiment. A scaled model of the high voltage insulation of a distribution transformer was designed and build to investigate the influence of temperature and partial discharges on the generation of waxlike substances in the laboratory. Different insulation fluids, such as synthetic and natural esters and silicone fluids are investigated as well as a mineral oil for comparison. They are stressed with partial discharges for a duration of 200h. The partial discharges are monitored to allow a comparison between the PD energy and the amount of wax formed during the experiment. The tests are performed at different temperatures, as previous investigations have shown a significant influence of the temperature.
ID: 1163 / S9: 6
Experimental Evaluation and Tests on Ester oil for Non-vacuum Tap Changer
CTR MANUFACTURING INDUSTRIES LIMITED, India
Ester oil filled On Load Tap Changers (OLTC) are introduced in Indian power systems since the last four years. A series of focused experiments done at the authors’ R&D Laboratories prove that ester oil has superior dielectric strength in both uniform and nonuniform fields, considering both prebreakdown and breakdown processes, when compared with mineral oil. Special test cell and special electrodes were designed to create varying nonuniformities for studying the effect of nonuniformity on the voltage breakdown characteristics. The results indicated satisfactory performance of ester oil filled OLTC for nonuniformities that normally exist in every high voltage product. The current and service duty tests done on many ester oils filled OLTCs indicated satisfactory performance. The paper discusses the experimental study conducted on the natural ester oils and also on the ester oil filled OLTC & concludes that a well-designed OLTC with ester oil provides good performance in the field.
ID: 1354 / S9: 7
Corrosions & PCBs: Inventory, Diagnostics and Treatments of Oils and Transformers
SEA MARCONI TECHNOLOGIES S.a.s., Italy
This paper describes the “State of the Art” for inventory, diagnostic, prognostic and integrated treatment of electrical equipment and insulating liquids containing DBDS/Corrosions & PCBs (Tech Pathologies).
The Corrosions determine a functional risks for transformers and equipment filled with mineral insulating oils: C1-DBDS &Corrosive Sulfur; C2-NOT DBDS &Corrosive Sulfur; C3-.SCBP &Corrosive Sulfur; C4-NOT Corrosive Sulfur &Metal Dissolution.
The PolyChlorinatedBiphenyls (PCBs) are a “Persistent Organic Pollutants” (POPS), as “Class 1.Cancerogenic to humans (IARC 2013) and determine risks for workers, public health and environment.
The oils & transformers integrated treatments, PCBs dehalogenation technique (“DMU & CDP Process” patented by Sea Marconi) and DBDS Selective Depolarization, in continuous mode through a closed circuit process are the sustainable solutions (Therapies) based on “circular economy”.
These solutions are based on the use of Smart Decontamination Modular Units (DMUs) and a solid reagent, consisting of a higher molecular weight glycol compounds, a mixture of bases and radical promoter or other catalyst on a high surface area particulate support. These processes normally run at 80-100 °C and have the capability to decontaminate equipment on-site through continuous circulation of the oil in a closed system (without draining the oil or using auxiliary tanks), using the solvent capability of the oil for continuous extraction of PCBs and DBDS from solid materials inside the equipment (according IEC 60422 art. 11.4.4).
International experience of diagnostic, prognostic and integrated treatments are presented according to IEC & CENELEC include On -Load treatments in power transformers and shunt reactors, in several countries.
|4:00pm - 7:45pm||Visit Sistina Chapel|
|Bus Meeting Point|
Only by invitation
|Date: Thursday, 27/Jun/2019|
|8:00am - 4:00pm||Registration|
|8:15am - 9:45am||S10: Special Session on Alternative gasses on SF6 having much less greenhouse impact|
Session Chair: Carlo Mazzetti, University of Roma "La Sapienza", Italy
Session Chair: Chuanyang Li, University of Bologna, Italy
ID: 1343 / S10: 1
SF6 Gas Replacement in Pulsed High Voltage Coaxial Cables
Several fast pulsed high voltage kicker systems at CERN use coaxial cables with SF6 gas as dielectric. Leak detection systems are installed and for interventions, the gas is recuperated and re-circulated, reducing emissions to a minimum. Nevertheless due to the high global warming potential of SF6 gas and the efforts of the European Union and CERN to reduce fluorinated greenhouse gas emissions to a minimum, a replacement strategy for the SF6 gas filled coaxial high voltage cables is being developed. New pulse generator technologies as well as different SF6 gas substitutes and also new conventional PE insulated cables are being studied. This paper gives an overview of the studies carried out to replace these cables. A comparison of possible alternatives with liquid, solid and gas dielectrics is given. The properties of the cables with alternative dielectrics are outlined, by either measurement, simulation or calculation. Especially the important parameters for kicker systems are evaluated and compared: breakdown voltage, low attenuation and low impedance change. Possible dimensions and tolerances are given, the expected costs and environmental impact are outlined. In addition an overview of different dielectric liquids used in the complete pulse generator as well as the operational experience, performance and limitations is given.
ID: 1292 / S10: 2
Insulation Characteristics of Spacer Filled with Different Gas insulating mediums Under Superimposed Voltage of DC and Impulse
1State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University, Beijing 102206, China; 2State Grid Beijing Electric Power Co., Ltd. Chaoyang Power Supply BR, Beijing 100124, China
The analysis of the influence of different dielectric gases on the flashover characteristics of insulators under DC voltage superimposed impulse voltage is mainly performed in this paper. In the experiment, the spacer surface charge is saturated by applying DC voltage under working temperature in advance. The flashover experiments were conducted with and without linear metal particle in pure SF6, C4F7N/CO2 (4%/96%) and SF6/N2 (20%/80%) gas mixtures. At the same time, the surface potential distribution was measured and analyzed. The results show that the type of the gas medium is not the dominant factor of potential distribution without particle, and there is little difference in different gas environments. When metal particle defects appear on spacer surface, it will cause severe potential distortion and these regions are located around the tip of the particle and coincide with the flashover path. It also has proved that the gas insulating medium has influence on the surface charge accumulation in this circumstance. In C3F7CN/CO2 mixture, the minimum potential value is - 9954.86V, which is lower than that of others, and the decline percentage of flashover voltage is 16.82%. These indicate that C3F7CN/CO2 is better than SF6 and its mixed gas in some respects.
ID: 1179 / S10: 3
Electron transport coefficients and negative streamer dynamics in CF3I-SF6 gas mixtures
1Institute of Physics Belgrade, Serbia; 2Serbian Academy of Sciences and Arts, Serbia; 3Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México
A multi term theory for solving the Boltzmann equation and a Monte Carlo simulation technique are used to calculate electron transport coefficients in the mixtures of CF3I and SF6 as a function of the applied electric field. The calculated transport coefficients are then used as an input in the fluid equation based models to investigate the transition from an electron avalanche into a streamer and streamer propagation. Electron transport coefficients are also calculated in radio-frequency electric and magnetic fields crossed at arbitrary phases and angles. A multitude of kinetic phenomena induced by the synergism of the magnetic field and electron attachment is observed and discussed using physical arguments.
ID: 1321 / S10: 4
Prediction of breakdown voltage value in SF6-N2 gases mixture under DC voltage with the influence of conducting particles by analyzing experimental data using ANN
Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University, Beijing 102206, China
Sulphur hexafluoride (SF6) is the most commonly used dielectric gas in electrical systems, DC-GIL is considered as a new type of transmission lines has the potential to replace the overhead lines and cables in the future for use in DC distribution networks. It deserves great concern that abundant amount of SF6 use in the earth’s atmosphere because this gas is known to be a kind of “greenhouse gas”. Also, metal particles inevitably appearing in the pipeline of DC GIL which may do damage to GIL and cause a serious threat to its insulation safe and reliable operation. This paper aims to focus on experimental study on the difference in insulation strength of SF6 gas and the mixture of two gases (SF6 and N2) with and without using conducting particle under DC voltage in the ball-bowl electrode arrangement. Moreover, spherical conducting particle is selected to simulate metal particle defects in GIL and they are set to the floating position. Breakdown characteristics of SF6 gas and (SF6 -N2) gas mixtures have been measured in non-uniform electric field when the SF6 gas mixture ratio (70%, 50%, 30% and 20%) and the pressure is between 0.1MPa and 0.5MPa under the positive and negative polarity of DC voltage.The experiment results show that DC negative polarity is more severe as compared with positive polarity. In addition, it is found that there is no significant increase in breakdown voltage when the pressure is more than 0.3MPa in the presence of particle but the growth trend is clear without particle. The equivalencies between the breakdown voltage of SF6 and SF6-N2 gas mixtures were analyzed with and without the presence of conducting spherical particle and tried to predict the improved breakdown voltage SF6-N2 gases mixture using Artificial Neural Network technique.
ID: 1281 / S10: 5
Calculation of Thermodynamic Physical Properties of C4F7N-CO2 Mixed Gas
1School of Electrical Engineering,Shenyang University of Technology, China, People's Republic of; 2Department of Electrical Engineering and Electronics, University of Liverpool
Recent studies have shown that a mixture of C4F7N-CO2 can be used as an environmentally friendly alternative to SF6. In this paper, the saturated vapor pressure of C4F7N-CO2 mixed gas is calculated by Antoine vapor pressure equation and gas-liquid equilibrium law, and the liquefaction temperature of the mixed gas in different states is obtained. According to the molecular structure characteristics, the C4F7N-CO2 mixed gas compression factor, constant pressure specific heat capacity and viscosity were calculated by P-R (Peng Robinson) equation of state, Joback group contribution method and Thodos method, respectively. The calculation results show that if the liquefaction temperature of the insulating medium is not higher than 253K when the GIS and GIL are operated at 0.5MPa, the proportion of C4F7N in the mixed gas should not exceed 10, the ratio of the GWP (Global Warming Potential )of the mixed gas is 694, which is about 2.95% of SF6, and the corresponding compression factor is close to 1, and the mixed gas tends to be in an ideal gas state. The constant pressure specific heat capacity and viscosity of C4F7N-CO2 mixed gas increase with the increase of temperature at the same pressure, and increase with the increase of pressure at the same temperature. At the same pressure and temperature, the specific pressure specific heat capacity and viscosity of the mixed gas are less than SF6, such as the specific heat capacity and viscosity of 5% C4F7N-95% CO2 at 273K and 0.5MPa are about 43.37% and 85.62% of SF6, respectively.
ID: 1324 / S10: 6
Study on Electric Strength and Synergistic Effect of C3F7CN-CO2 Gas Mixture by Steady State Townsend Method
North China Electric Power University, China, People's Republic of
To replace SF6 in electric power system, C3F7CNCO2 gas mixture was put forward and thought as the most promising substitute. However, there is a lack of swarm parameters of C3F7CN-CO2 gas mixture. In this study, the effective ionization coefficients of C3F7CN-CO2 gas mixture at different C3F7CN mole ratios were measured by Steady State Townsend (SST) method, over an extended range of density normalized electric field, from 150 to 1050 Td. The density normalized critical electric fields of C3F7CNCO2 gas mixture showed nonlinear increase with different C3F7CN mole ratios, from 0% to 100%. The synergistic effect increases sharply at first with the increase of C3F7CN mole ratio, and then decrease slowly. It shows greater synergistic effect of C3F7CN-CO2 gas mixture at low C3F7CN mole ratio.
|9:45am - 10:15am||Coffee Break|
|10:15am - 12:15pm||S11: Applications and Performances of Dielectric Liquids in High Voltage Equipments|
Session Chair: Alfredo Ortiz, University of Cantabria, Spain
Session Chair: Tim Gradnik, EIMV, Slovenia
ID: 1149 / S11: 1
Investigation on Heating Aging Mechanism of Cellulose Paper for Oil-Immersed Transformer Main Insulation
1Jiangxi University of Science and Technology, China, People's Republic of; 2Electric Power Engineering, Chalmers University of Technology, Sweden; 3School of Electrical Engineering, Shenyang University of Technology, China
Power transformer plays a vital role in maintaining reliable and efficient electricity supply. However, in service is increasing and growing older, much and much attention has been paid on their aging condition and life assessment than ever. The aging and degradation of transformer insulation will determine the life-time of its operation. The intensities of these depend on mechanical, thermal and environmental stresses that act on the insulations. Due to the temperature rise, the lifetime of insulation material will be shortened. The accelerated thermal aging method is often adopted to do some evaluation on the oil-paper insulation materials under different temperature for the thermal lifetime model. According to existing aging test, both insulation paper and mineral oil were aged at the same temperature. In this paper, the thermal aging experiments were implemented on the transformer main insulation model made with modified and unmodified insulation paper. The accelerated thermal aging tests were finished, and the superior electric characteristics of the nano-TiO2 and cellulose composition insulation were validated.
ID: 1203 / S11: 2
Potential Usage of Magnetic Liquids in High Voltage Test Devices
University of Maribor, Slovenia
The paper provides a basic theoretical and technical framework for implementing a magnetic-liquid into a high-voltage coil in order to achieve a continuously variable and saturable inductor. Such design, implemented to the Glaninger extension, has a favorable effect on the tail time compensation when the lightning impulse is applied to the low inductive transformer’s winding. The numerical investigation of the voltage response over the winding has been performed by using a magnetic liquid and an air core based coil in the Glaninger extension. Comparison of results exposes the advantages and disadvantages that arise by involving the magnetic liquid into the Glaninger extension.
ID: 1366 / S11: 3
Global footprint of free breathing transformer with Natural ester
Cargill India Pvt. Ltd, India
Natural ester dielectric fluid is being adopted at an accelerated speed globally. Even use of IEC 60076 part 14, 2013 Annexes C.2 table is being referred and used as guideline for design. Most of transformers with natural ester are sealed from external oxygen and water by various means. Manufacturer of natural ester do not advise to use natural ester fluid in free breathing application. Even On Load Tap Changer (OLTC) manufacturer has limited study with natural ester but few Asian OLTC manufacturers have done significant study and proved increased contacts life & significantly less maintenance when OLTC are filled with natural ester fluid. Here author collected all global data & did detail on site case study of transformer running successfully with OLTC in free breathing application in India. This transformer is monitored for fluid performance every year by original equipment manufacturer (OEM) of transformer. This paper presents case study of monitoring and validation of results for Free breathing transformers with Natural ester fluid. Electrical Parameters monitored.
ID: 1252 / S11: 4
Effect of maghemite nanoparticles on insulation and cooling behaviour of a natural ester used in power transformers
University of Cantabria, Spain
In this paper, an experimental research was conducted to study the effect of the presence of Fe2O3 nanoparticles over cooling and dielectric performance of a natural ester used in power transformers. Different concentration samples of nanofluid have been characterized to find an optimal one, focusing on viscosity, thermal conductivity and dielectric strength. A monitored experimental platform has been used to observe the temperature increases during operation while being cooled. This includes a single-phase distribution transformer, working at three different load levels, C=0.7, C=1 and C=1.3. Both natural ester base fluid and optimal nanofluid have been used as cooling fluid. At first sight, the nanoparticles seem not to affect neither thermal conductivity nor viscosity at the concentrations used. On the contrary, breakdown voltage of base fluid experiments an enhancement at some of them. The cooling capacity of the nanofluid has also shown an improved behavior.
ID: 1156 / S11: 5
Transient Thermal Condition of Natural Oil-cooled Disc-type Winding
University of Stuttgart, Germany
The degradation of solid insulations in windings of a power transformer is most often due to thermal stresses. In this contribution, Computational Fluid Dynamics (CFD) is used to predict the hot-spot and top-oil temperatures by applying various boundary conditions during transient states following, which are validated with temperatures measured from an experimental setup. The experimental model, which consists of a disc-type winding with 20 discs and four turns, is divided into 3 passes and equipped with PT-100 temperature sensors. Heating cartridges are installed into each conductor of the winding model to supply the electrical heat losses in the winding turns. In order to consider, the variations of the thermal characteristics of oil, its properties are changed at each time step by increasing the temperature. This investigation takes into consideration the transient thermal behaviour of natural cooling method inside winding model at various starting oil temperatures 40 °C and 80 °C. Transient curves of top - oil and hot - spot temperatures are compared to identify the time constants. On evaluating the measurement data, the locations and the temperature time constants of hot - spots at different starting oil temperature are found to be the same. Moreover, it is observed that there is no flow reversal or blockage caused by separation eddies, which can be attributed to low oil flow rate through horizontal channels. Finally, it is noted that the average volume temperatures of conductors and top-oil temperature reach steady state thermal condition over time.
ID: 1104 / S11: 6
Analysis on Extending Service Life of Aged Transformers by Oil Replacement with Novel 3-Element Mixed Insulation Oil
1Chongqing University, China, People's Republic of; 2State Grid Chongqing Electric Power CO. LTD. Chongqing Electric Power Research Institute, China, People's Republic of; 3State Grid Henan Electric Power CO. LTD. Henan Electric Power Research Institute
Oil-paper composite insulation is the key parameter affecting the overall performance and service life of transformers, and it gradually ages with the operation time. In order to extend the aging lifespan of transformers, scholars all over the world have spared no effort to delay the aging rate of the insulation paper. Recently, our group has proposed a novel 3-element mixed insulation oil, whose main parameters meet the current IEC 60296-2012 standard for mineral oil, indicating the novel 3-element mixed insulation oil can be used for replacing mineral oil directly. In this paper, different oilpaper systems which consist of 3-element mixed insulation oil, mineral oil and Kraft paper, were used for accelerating thermal aging test at 130 °C. In the middle aging period, aged mineral oil in some samples was replaced with new mineral oil and 3-element mixed insulation oil respectively, and then the accelerating thermal aging test continued. Comparison on thermal aging rate and AC breakdown of oil shows that the 3- element mixed insulation oil could not only keep excellent insulation property in aging process after oil replacement, but also indeed decrease the thermal aging rate of aged insulation paper. Oil replacement with 3-element mixed insulation oil increases 1.5 times aging lifespan of insulation paper in the thermal aging experiment, which suggests that the service life of aged transformer may be extended by oil replacement with the novel 3-element mixed insulation oil.
ID: 1329 / S11: 7
In-service ageing comparison study of natural ester and mineral oil filled distribution transformers
1Guangdong Electric Power Grid Co. Guangzhou, China; 2Xianyang Power Supply Bureau of Shaanxi Power Grid Co., Ltd; 3Cargill, China; 4Cargill, Plymouth, MN United States of America; 5State Key Lab -Xi'an Jiaotong University, Shaanxi Xi'an, China
In 2011, Shaanxi Power Grid Corporation, a Chinese utility, launched the first batch of natural ester-filled transformers in China to investigate the effectiveness of environmentally friendly insulating liquid in operating transformers. After 7 years continuous operation, two healthy 10kV 200kVA units were selected for study, one is filled with a soybean based natural ester liquid, Envirotemp™ FR3™ Fluid, the other is filled with mineral oil. These two distribution transformers (DT) were operating in the same city for about the same time period. Each transformer is made by a different manufacturers but have similar designs, however, their loading profiles differed significantly. The transformers were taken off the grid in June of 2018. Routine tests of the transformers and oils show that the transformers are in good condition. In January of 2019, both transformers were disassembled to test the oil and winding paper insulation samples. The oil condition, degree of polymerization and water content of paper samples from both units were compared. The details of the teardown and laboratory analysis are presented in this paper. In view of this in-service 7 year test, the compatibility of NE liquid with transformer construction materials under normal loading rate condition is confirmed. Also, the results offer useful status information about oil-paper insulating system for performance diagnosis in daily operation.
|12:15pm - 1:15pm||Lunch|
|1:15pm - 2:45pm||P2-1: Poster Session on Synthetic and Natural Esters|
Session Chair: Qiang Liu, The University of Manchester, United Kingdom
ID: 1122 / P2-1: 1
The analysis of cellulose particles bridging in natural ester oil under DC voltage
North China Electric Power University, China
ID: 1256 / P2-1: 2
Determination of Epoxy Resin in Transformer Oils by FTIR Method and the Study of Its Damage
Electric Power Research Institute of Guangdong Power Grid Co., Ltd., China, People's Republic of
ID: 1241 / P2-1: 3
Analysis of Water Solubility in natural-ester based nanodielectric fluids.
Universidad Carlos III de Madrid, Spain
ID: 1202 / P2-1: 4
Analysis of Particle Size Distribution and Other Parameters of Nanoparticles in Natural Ester Oil
1University of West Bohemia, Czech Republic; 2University of Žilina, Slovakia
ID: 1235 / P2-1: 5
Impregnation processes of insulation rigid components of cellulose in synthetic ester and mineral oil
1University of Cantabria, Spain; 2Repsol Technology Center, Spain
ID: 1128 / P2-1: 6
Investigation on the Compatibility of Transformer Construction Materials with Natural Ester
1Xi’an Jiaotong University, China, People's Republic of; 2Electric Power Research Institute of Guangdong Power Grid Corporation, China, People's Republic of
ID: 1340 / P2-1: 7
Mobility of Charge Carriers in Dielectric Liquids
University of Strathclyde, United Kingdom
ID: 1165 / P2-1: 8
Interturn insulation characteristics for transformer windings using three ester types under lightning impulse voltage
1Kanazawa Institute of Technology, Japan; 2Meidensha Corporation
ID: 1280 / P2-1: 9
Study on Bubble Formation of Different Moisture Content Oil-immersed Cardboards in Natural Ester Oil
North China Electric Power University, China, People's Republic of
ID: 1207 / P2-1: 10
Analysing the impact of Moisture on the AC Breakdown Voltage on Natural Ester Based Nanodielectric Fluids
Universidad Carlos III de Madrid, Spain
ID: 1185 / P2-1: 11
Synthesis of Trimethylolpropane Esters as Potential Insulating Oil Base Stocks
Chongqing University, China, People's Republic of
ID: 1291 / P2-1: 12
Thermal and Dielectric Properties of Processed Mahuva Oil
1Central Power Research Institute, India; 2JSS Science and Technology University,Mysore,India
ID: 1312 / P2-1: 13
Investigation of AC breakdown strength and frequency varied dielectric response of the non-conventional vegetable oil
1IIT Guwahati, India; 2RTL, Central Power Research Institute Guwahati
ID: 1349 / P2-1: 14
Moisture Effects on Partial Discharge Inception Voltage in Natural Esters
University of Douala, Cameroon
ID: 1350 / P2-1: 15
Temperature Effects on Partial Discharge Inception Voltage in Natural Esters
University of Douala, Cameroon
ID: 1370 / P2-1: 16
Behavior of Transformers Interconnecting Microgrid and Prosumers
1University of L'Aquila; 2University of Roma "La Sapienza", Italy
ID: 1360 / P2-1: 17
Life Cycle Management of Natural Esters &Transformers according to IEC Standards: Case History of Envirotemp FR3 Fluid & TransfoClean Solution in Brasil
1SEA MARCONI TECHNOLOGIES S.a.s., Italy; 2Cargill Bioindustrial, United States of America; 3University of Missouri, United States of America; 4University of Roma "La Sapienza"
|1:15pm - 2:45pm||P2-2: Poster Session on Nanoparticles, applications in insulating fluid and measurements|
Session Chair: Issouf Fofana, ViAHT - UQAC, Canada
ID: 1289 / P2-2: 1
Nanoparticle Polarization Effect on the Permittivity of the Dielectric Liquid
Indian Institute of Technology, Guwahati, India
Nanofluids (NFs) are being increasingly used to improve the heat transfer and dielectric capabilities of the electrical equipment and enhance their life expectancy. Preparation of a stable NF and its superior thermophysical and electrical properties is expected to lead to a much lower life-cycle cost of a power/distribution transformer. This paper intends to analyze the effect of polarization of the nanoparticles (NPs) on the improvement of relative permittivity when they are dispersed in TO. To validate the existing theories about it, experiments are carried out to determine the values of the relative permittivity of both the fresh mineral oil (MO) and vegetable oil (VO), and also the MO-NF and VO-NF. The VO used for this study is the pongamia pinnata oil. In this work, different volumetric concentrations of 0.01, 0.05 and 0.1 wt.% of exfoliated hexagonal boron nitride (Eh-BN) NP dispersed in both MO and VO are considered to understand the variation in the permittivity measurements and a comparative analysis is carried out. This study recognizes the effects of using NPs in both MO and VO and how significantly it influences the dielectric behaviour of the liquid. The results show enhanced permittivity for the NFs as compared to the base fluids. The mechanism behind the change in the relative permittivity is understood by the impact of polarization effects in the Eh-BN NPs added to the oil.
ID: 1150 / P2-2: 2
Suppression Mechanism of TiO2 for the Partial Discharge of Oil-paper Insulation in Intensive Electric Field
1Jiangxi University of Science and Technology, China, People's Republic of; 2Electric Power Engineering, Chalmers University of Technology, Sweden; 3Sanbian SCI-TECH Co. LTD Taizhou, China
With the rapid development of modern HVDC transmission technology, higher insulation properties are put forward on the oil-paper insulation system of the transformer, which determine the transformer service life to a certain extent. Traditional transformer oil-paper insulation is becoming increasingly difficult to meet the demands of insulation system with large capacity and miniaturization at ultra-high voltage level. In order to improve the insulation strength of oil-paper system, the insulation cellulose paper modified by TiO2 nanoparticles of different diameters (5 nm, 10 nm, 20 nm, 30 nm) were prepared, in addition, each of modified cellulose paper has different mass fraction of TiO2 nanoparticles (1%, 3%, 5%, 7% wt.). The partial discharge (PD) detection platform was established, and the partial discharge inception voltage (PDIV) values of the oil-paper insulation system with and without nanoparticles were measured. To investigate the PD characteristics, the PD waveforms and PD frequency spectrums of modified cellulose paper and the unmodified were obtained. The suppression mechanism of TiO2 nanoparticles on PD was explored through scanning electron microscope (SEM) observation. All the experiment results indicate that adding nano-TiO2 is beneficial to enhance the insulation properties of oil-paper insulation, and the optimum diameter and mass fraction of TiO2 nanoparticles to suppress oil-paper PD were obtained.
ID: 1309 / P2-2: 3
Research on DC Breakdown Performance of Nanofluid-impregnated Pressboard Based on TiO2 Nanoparticles
North China Electric Power University, China, People's Republic of
UHVDC has been applied widely since it possesses technical advantages in transmission electric power in long distance and large capability, leading to the severe test for the insulation performance of converter transformer. Oilimpregnated pressboard (OP) is one of the key insulating components in converter transformer due to its high mechanical strength and dielectric property, and its electrical performance is strictly related to the phenomenon of space charge accumulation. Recent experiments have shown that the insulation nanofluid has attracted a great deal of attention due to its considerable dielectric performance. Meanwhile, TiO2 semiconductor nanoparticles are considered to be the best choice owing to their low dielectric loss induced and considerable modification effect. However, the relation among particle sizes, dc breakdown voltages and space charge characteristics of nanofluid-impregnated pressboard (NP) based on TiO2 nanoparticles remains largely uncertain, which limits the performance improvement of oil/pressboard insulating system. In this paper, the modification effect on dc breakdown strength of oil-impregnated pressboard based on TiO2 nanoparticles with various sizes has been investigated. Moreover, the accumulation characteristics of OP and NPs were also studied by use of Pulsed Electro Acoustic Method (PEA). According to the the experimental results and analysis, the relation among particle sizes, dc breakdown performance and accumulation characteristics of space charge was clarified and a possible modification mechanism has been proposed.
ID: 1240 / P2-2: 4
Streamer simulation in nano-based dielectric fluids at different Fe3O4 nanoparticle concentrations
1Universidad Politécnica de Madrid (UPM) Escuela Técnica Superior de Ingeniería y Diseño Industrial (ETSIDI) Departamento de Ingeniería Eléctrica, Electrónica, Automática y Física Aplicada Ronda de Valencia 3, 28012, Madrid, Spain; 2Universidad Carlos III de Madrid Departamento de Ingeniería Eléctrica Avenida de la Universidad 30, 28911, Leganés, Madrid, Spain
Nano-based dielectric fluids (NDF) seem to be a good alternative for improving dielectric and thermal characteristics of conventional liquid dielectric systems used in power transformers. Fe3O4 (magnetite) nanoparticles (NP) is one of the most investigated type of NP. Some experiments have shown that with its addition to mineral oil (MO) and ester, increases in breakdown voltage (BV) can be achieved applying both AC and DC voltages. This kind of NP have the advantage that can be handled and synthesized safely and easily using a two-steps method. Besides, streamer propagation can be reduced or avoided introducing Fe3O4 NP in dielectric fluids. These NP act as electronic traps and behave like slow-moving charged particles in the NDF. This behaviour as well as other dielectric characteristics such as resistivity, permittivity and loss tangent, depend on the type, size and concentration of NP. In this work, comparisons and analyses of thermal and dielectric performance of NDF with different Fe3O4 NP concentration are made taking into account the evolution and behaviour of streamers. It has been found that temperature in streamer tip, its length and speed depend on the Fe3O4 NP concentration and the BV is affected because of changes in streamer speed. The most adequate concentration for controlling the streamer has been obtained through simulations and comparisons with experimental results showing good agreement.
|2:45pm - 3:15pm||Coffee Break|
|3:15pm - 5:00pm||P3-1: Poster Session on Applications and Performances of Dielectric Liquids in High Voltage Equipments|
Session Chair: Luigi Calcara, University of Roma "La Sapienza", Italy
ID: 1251 / P3-1: 1
Cooling performance of different dielectric fluids containing nanoparticles in a transformer winding
University of Cantabria, Spain
This work presents a study where the thermal performance of different nanofluids is tested in a transformer winding model. A 2D axisymmetric non-isothermal CFD model has been used to compare temperature and velocity distribution of the proposed fluids. The fluids tested consists of eight different mixtures manufactured from two different nanoparticles and two different concentrations, using a mineral oil and a natural ester as base liquids. The comparison has been carried out between each nanofluid and their base fluid to observe the thermal impact of nanoparticles. The temperature dependent properties have been determined to include them in the simulation model. Two different inlet velocities were selected as inlet conditions, representing Oil Natural and Oil Directed Cooling. The analysis has been carried out using ANSYS Fluent® in a two pass winding model. The average and maximum disc temperatures and mass flow distributions are obtained for all the cases. The results obtained show that the temperature in the seven discs of the considered winding increases when the nanoparticles are added to the natural ester, between 3 and 7%. On the other hand, in the case of mineral oil, the addition of nanoparticles reduces the temperature in the discs between 0.3 and 3%.
ID: 1346 / P3-1: 2
Insulating and aging properties of transformer oil-based nanofluids
NORTH CHINA ELECTRIC POWER UNIVERSITY, China, People's Republic of
A transformer oil based nanofluid has been prepared by dispersing Alumina nanorods (NRs) into mineral oil to improve insulating properties of the host oil. The AC and lightening impulse breakdown voltage characteristics of fresh and aged samples were measured according to IEC standard methods. The results indicated that breakdown strength of nanofluids under all test voltages were increased as compared to that of the base oils. The possible modification mechanisms of Alumina NRs on the insulating properties of fresh and aged transformer oil was discussed depending on the trap characteristics of the host oil and nanofluids.
ID: 1148 / P3-1: 3
Optimization of Mass Fraction and Particle Size of TiO2 Additives in Application of HVDC Transformer Insulation
1Jiangxi University of Science and Technology, China, People's Republic of; 2Electric power engineering, Chalmers university of technology, Sweden
With the fast development of high voltage direct current (HVDC) transmission technology, higher electrical insulation properties are demanded in application of HVDC converter transformers. The nano adding in the cellulose insulation is a kind of effect method to enhance their electrical insulation properties. In this paper, nano-TiO2 particles with four different diameters (5 nm, 10 nm, 20 nm and 30 nm) and four different loading ratios (1 wt%, 3 wt%, 5 wt% and 7 wt%) are added during preparation of the insulation cellulose paper. To evaluate their dielectric properties, DC breakdown test, partial discharge inception voltage test, the accumulating properties of the surface charge dynamics and trap distribution characteristic are performed on the prepared nano-TiO2 modified paper samples. The experimental results show that the DC breakdown voltage and the partial discharge inception voltage of oil-immersed composition insulating paper are significantly improved by adding nano-TiO2 particles. According to the testing data, the optimum combination of 10 nm particle size and 5 wt% mass fractions were obtained, and the modification mechanism of nano-TiO2 of the nano-composition insulation were presented in the paper.
ID: 1205 / P3-1: 4
Study on temperature distribution in oil-immersed inverted current transformer
1JiangSu Electric Power Company, Nanjing, China; 2Jiangsu Electric Power Company Research Institute, Nanjing, China; 3Chongqing University Chongqing, China
Oil-immersed inverted current transformer, as an important electrical equipment in power grid, is mainly used in power plants and substations. Accidents caused by oilimmersed inverted current transformers are generally accompanied by explosions, which not only reduce the amount of electricity delivered, but also damage other nearby equipment in the substation and even cause casualties. Therefore, it is very necessary to detect and evaluate the operation status of oil-immersed inverted current transformer and study the fault prevention technology to reduce the probability of accidents. According to the common faults of oilimmersed inverted current transformer, this paper firstly analyzed the parts and components with high fault rate of current transformer. Combined with the operating condition of current transformer and its internal insulation structure, the internal temperature field simulation model of current transformer and the temperature calculation model of key parts were established. It was found that the temperature near the winding of the oil-immersed inverted current transformer was the highest, while the temperature rise at the lower part far from the heat source was very small. The simulation results were basically consistent with the experimental results, and it was found that the temperature distribution on both sides of the primary conductor in the head region of the current transformer was symmetrical.
ID: 1295 / P3-1: 5
The effect of interface of electrode and liquid on space charge injection in transformer oil under impulse voltage
1State Grid Sichuan Electric Power Researche Institute, Chengdu, China, People's Republic of; 2State Key Laboratory of Power Transmission Equipment &SystemSecurity and NewTechnology, Chongqing University, Chongqing, China, People's Republic of
Electrode have an important influence on the breakdown of liquid dielectrics. The interface of electrodes and liquid dielectrics may affect the injection and distribution of space charge in liquid dielectrics, and thereby affecting the breakdown of liquid dielectrics. To find experimental evidence, the Kerr electro-optic method was used to observe the space charge in transformer oil under different electrode materials (Brass, Aluminum). With the use of array photodetector, the space-time evolution of space charge in liquid dielectrics can be directly measured under a single impulse voltage. The results show that when impulse voltage was applied to the electrodes, the Br (+)-Br (-) electrodes injected unipolar positive space charges, the Al (+)-Al (-) electrodes injected unipolar negative space charges, the Br (+)-Al (-) electrodes injected bipolar homo-charges, and the Br (-)-Al (+) didn’t inject significant space charges. The reason of this phenomenon may be the different properties of electric double layer formed by different electrodes and transformer oil. Considering that the homocharge injection can weaken the electric field near the electrode, the breakdown voltage under Br (+)-Al (-) should be highest, which is consistent with other researchers’ conclusions. This study provides an experimental basis for selecting a suitable electrode combination to strength the breakdown voltage of transformer oil.
ID: 1195 / P3-1: 6
Dielectric Response Analysis of Mineral Oil Immersed Transformer, Natural Ester(FR3) Immersed Transformer, and Palm Oil Immersed Transformer
King Mongkut’s Institute of Technology Ladkrabang, Thailand
Currently alternative liquid insulation such as natural ester (FR3) is widely used as distribution transformer insulation because it provides outstandingly dielectric characteristics and natural friendly including highly affordable fire safety. Besides, palm oil is interesting liquid insulation for such transformers because of its distinguish dielectric properties. To analyze the dielectric properties of insulating material, polarization and depolarization current (PDC) measurement is one of the widely accepted non-destructive test technique. This paper presents the dielectric response analysis for the insulation system of a mineral oil immersed transformer, a natural ester (FR3) immersed transformer, and a palm oil immersed transformer by analyzing PDC test results. Three identical single phase transformers with 22kV/460V 30 kVA rated were designed and constructed. The first transformer was fully filled with mineral oil. The second and the third transformer was fully filled with natural ester (FR3) and palm oil respectively. After finishing the construction process, PDC measurement technique was applied for these transformers. The PDC measurement were performed for three case studies as follows: 1) dielectric response for the insulation between high voltage winding and low voltage winding, 2) dielectric response of high voltage winding insulation and low voltage connected to ground 3) dielectric response of high voltage and low voltage winding insulation by which the high voltage lead was connected to the low voltage lead. From the test results, it can be concluded that the dielectric response of the insulation system of the mineral oil immersed transformer was obviously different compared with that of the natural oil (FR3) immersed transformer and the palm oil immersed transformer. Moreover, the PDCs obtained from the tests were also analyzed and reported in this paper.
ID: 1362 / P3-1: 7
A study on a high-reliability electromechanical undervoltage relay immersed in natural ester oil: application in mutual aid system for gensets using
Sapienza University of Rome, Italy
The paper focuses on the reliability of an undervoltage electromechanical relay suitable for critical industrial applications. The specific application underlined in this paper is a mutual aid system for gensets: the relay is able to actuate the parallel of the batteries in case of failure of the starting-up of the genset. A particular “Plunger-type” electromechanical device, with redundant contacts, has been proposed in order to maximize the MTBF parameter; electronics devices have been rejected in according with on-filed statistic surveys about the relative failure rates. The relay is equipped with a natural ester oil delaying system (dashpot): physical and dielectric characteristics of natural ester oil can assure better delaying system performances and insulating level. Other advantages obtainable by using insulating ester oil into the relay are also highlighted.
ID: 1239 / P3-1: 8
Experimental Study on The Motion Law of Solid Particles in Oil under Electric Field
1Chongqing University, China, People's Republic of; 2Jiangsu Electric Power Company Research Institute, Nanjing, China
The irregular movement of solid particles in insulating oil is caused by the influence of oil flow and electric field. During the movement of solid particles, the distribution of electric field in insulating oil will change, leading to the high electric field area in the inner part of transformer, which will lead to the discharge accident of transformer. Therefore, the experimental research work on the movement law of solid particles in oil under electric field is carried out. The main research contents are as follows: An experimental platform for the trajectory of solid particles in insulating oil was built. The experimental study on the effects of voltage type, electric field strength and particle concentration on the trajectory of solid particles was studied. The experimental results show that the solid particles always aggregate in the high electric field to form particle clusters. When the number of solid particles is large enough, a solid particle bridge will be formed through the electrode; it is difficult to form a continuous solid particle bridge under AC voltage, DC voltage and obvious small particle bridges can be observed under AC and DC composite voltage; voltage type and particle concentration are the key factors affecting the formation of small bridges of solid particles.
ID: 1109 / P3-1: 9
Gas Production Characteristics and AC Breakdown of a New Three-element Mixed Insulation Oil
1Chongqing University, People's Republic of China; 2State Grid Chongqing Electric Power CO. Chongqing Electric Power research institute
A novel three-element mixed insulation oil (mineral, soybean, and palm oil) was successfully developed (76 v.% mineral oil + 19 v.% soybean oil + 5 v.% PFAE oil + 0.2 wt% T511 + 0.2 wt% L06) by our team. This mixed insulation oil combines the advantages of mineral oil and natural esters, and its parameters could satisfy the requirement of IEC 60296:2012. This novel three-element mixed insulation oil could be used in power transformers as a substitute for mineral oil without changing the structure of transformers. In this study, firstly, the gas generation characteristics of the three-element mixed insulation oil and mineral oil under thermal condition 150 °C -750 °C were measured and compared. Secondly, the breakdown and gas generation characteristics of the two kinds of oils after being AC breakdown 20, 40 and 60 times were analyzed. Gas production analysis under overheating condition shows that the law of concentration and percentage of dissolved gases in the two oils is similar. When the temperature exceeds 450 °C, CH4, C2H4, C2H6 increase significantly with the increase of temperature. The Concentrations of hydrocarbon gases (C2H2, C2H4, C2H6 and CH4) dissolved in insulation oil increase rapidly with breakdown time, especially in the new mixed insulation oil. C2H2 and H2 can be used as characteristic gases to diagnose the AC breakdown fault in three-element mixed insulation oil.
ID: 1254 / P3-1: 10
The Application of Polyhedral Oligomeric Silsesquioxanes on Vegetable Insulating Oil Modification
Chongqing University, China, People's Republic of
Vegetable insulating oils, as promising substitutes for mineral insulating oils, have gained a lot of researches on their modification. Polyhedral Oligomeric Silsesquioxanes (POSS), a hybrid organic-inorganic nanoparticle, is of great prospect in vegetable insulating oil modification based on its remarkable dispersion property in organic liquids. In this research, the test material of vegetable oil (FR3, to be specified) was mixed with OctaMethyl-POSS (OM-POSS) in several different concentrations 0, 0.001, 0.004, 0.007 and 0.01 wt.% to make modified dielectric nanofluids. The AC breakdown strength and dielectric properties (relative permittivity, electrical conductivity and dissipation factor) of POSS-based oils were investigated. The experimental results showed that the AC breakdown strength of POSS-based nanofluids increased in a proper concentration range, while the permittivity, conductivity and dissipation factor of tested samples exhibited a reduction with proper POSS concentrations, where the model of interfacial zone was applied to explain the mechanism.
ID: 1316 / P3-1: 11
Heat Transfer Characteristics of Environmental-friendly Insulation Gas Mixtures
1North China Electric Power University, China, People's Republic of; 2Anhui Electric Power Research Institiute of SGCC Hefei, China
SF6 is widely used insulating gas , which has a strong greenhouse gas with a high global warming potential （ GWP ） and a long atmospheric lifetime of the order of 3000 years. . Therefore, the concept of environmental friendly GIL/GIS equipment is proposed. SF6/N2 and C3F7CN/CO2 are promising alternatives to environmental friendly gas insulating media. The heat transfer performance of substitute gases is a key aspect relating to the current-carrying capacity and the safety of the equipment. Because of the different specific heat, thermal conductivity and dynamic viscosity, the heat transfer performance of the gases will be different. Aiming at the influence of heat dissipation performance of alternative gases in the application of gas insulated transmission equipment, the heat transfer characteristics of SF6 gas, SF6/N2 gas mixture and C3F7CN/CO2 gas mixture are obtained by temperature rise experiment. Compared with SF6, the heat dissipation capacity of SF6/N2 and C3F7CN/CO2 decrease 11.3% and 19.7%, respectively. It hopes the research results of this paper can provide a reference for the further application of environmentally friendly alternative gases.
ID: 1264 / P3-1: 12
Compatibility of construction materials used in HVDC Transformer with naphthenic inhibited insulating oil
Apar Industuries Limited, India
With the changing technologies and design factors of Transformers as well as the higher rating and the AC / HVDC modes of Power Transmission, the use of good material compatible to the mineral insulating oil is becoming of paramount importance. For understanding this aspect an extensive study was conducted to evaluate the effect of various transformer construction materials used in high voltage direct current (HVDC) transformer on the physicochemical and electrical properties of mineral insulating oil under heating. The test specimens were prepared as per ASTM D 3455-11 standard and the compatibility test was carried out according to the procedure specified in this test method. The oil samples were analyzed after this ageing test for physicochemical and electrical properties. The test results obtained on the oils containing the test specimens of construction materials were compared with the reference blank oil specimen to determine any differences in the properties. The parameters that showed variation after this mineral oil compatibility testing with different materials were Dissipation factor , Resistivity at 90 o C and Interfacial tension. The compatibility of the construction materials with the insulating oil was decided based on the minimum acceptance criteria of ASTM D 3455 – 11 and internal control limit of Resistivity requirement. This study helped to identify the construction materials that are compatible and those that are not compatible with the naphthenic inhibited mineral insulating oil used in the HVDC transformer application.
ID: 1183 / P3-1: 13
The Polarization and Depolarization Current Characteristics of Mineral Oil, Natural Ester (FR3), Palm Oil, and Liquid Impregnated Pressboard
King Mongkut's Institute of Technology Ladkrabang, Thailand
Polarization and Depolarization Current (PDC) measurement is a non-destructive dielectric testing method used to determine the electrical properties of transformer insulation. Nowadays, natural ester has been used as alternative liquid insulation in transformers because it can be easily decomposed, highly flammable, resistant to moisture, and prolong of pressboard (solid insulation in a transformer) compared with mineral oil. Furthermore, palm oil is also an interestingly alternative insulating liquid. This paper presents the PDC characteristics of mineral oil, natural ester (FR3), and palm oil under various temperatures. All received liquid specimen were dry in the controlled temperature oven at 70°C under 200 mbar and then they were cooled down to ambient temperature around 25-30°C. The liquid samples were investigated for three cases as follows: 1) moisture content measurement according to ASTM D1533, 2) dielectric dissipation factor measurement as per ASTM D924, and 3) polarization current and depolarization current measurement at liquid temperature of 30°C, 50°C, and 70°C respectively. The PDC characteristics of mineral oil impregnated pressboards and natural ester impregnated pressboards were also investigated. The PDC test results were analyzed. It was found that the dielectric response of mineral oil was significantly different from natural ester (FR3) and palm oil. Besides, it was clearly that the conduction current of liquid insulation increased with increasing liquid temperature. Moreover, the pressboard impregnated with natural ester provided better insulation characteristics such as lower conduction current than that of the pressboard impregnated with mineral oil.
ID: 1154 / P3-1: 14
New Approach to Molded Case Circuit Breakers Maintenance System Using Nanoparticles
1Suez University, Egypt; 2Port Said University
Molded case circuit breaker (MCCB) is used to operate and protect electric devices and therefore, the maintenance process is very important and should be made regularly. Maintenance is made via removing the dust by an air blower. This process cleans the MCCB from the outer body only so, the contact points were located at the inner part is dusty. In thus, during the operation, the carbon is formulated on the contact points. Due to the repeat of operations, the contact points become invalid and should to replace by another new one. Maintenance of the (MCCB) was made by a newly proposed maintenance technique. In the proposed maintenance technique, the nanoparticles (NPs) are used and dissolved in the transformer oil. Then the nano oil is prepared. The nano oil leaks into the internal contact points of MCCB and absorbs carbonate. In addition, the nano oil is used to lubricate the internal mechanical parts of MCCB. An electrical test of the MCCB is performed after treatment to ensure the benefits of the new proposed method. The test results of proposed maintenance processes are compared with the traditional method according to the IEC Standards 60947. The results are studied using statistical analysis and explained substantial differences when using nanoparticles. MCCB has raised the efficiency and prolonged life span.
ID: 1353 / P3-1: 15
AC Breakdown Voltage Behavior of Deionized Water
1Leibniz Universität Hannover, Institute of Electric Power Systems, Germany; 2Siemens AG Corporate Technology Taufkirchen, Germany
This study presents investigations aiming at substituting conventional air or oil insulated enameled wires with water-filled ones for ac supplied applications. In this regard, twisted enameled pairs were prepared. Accordingly, ac breakdown voltage of the samples immersed in insulating oil, tap water and deionized water was measured and compared with those tested in atmospheric condition. This investigation was performed for two types of magnet wires differentiating in insulation thickness. The experimental results manifested the enhanced breakdown voltage of the hybrid system containing water. The simulation revealed the decrease in electric field in water surrounding the magnet wire in comparison with in air and oil medium, which indicates the excellent immunity of this system against partial discharge outside the coating layer. In contrast, the electric field is intensified in solid insulation as a consequence.
ID: 1276 / P3-1: 16
Moisture in power transformers DFR analysis – real cases studies on site
ELMA Servizi Industriali srl, Italy
Dielectric Frequency Response Test (DFR) – FDS- Frequency Domaine Spectroscopy) of power transformers is a diagnostic tool used to assess the dielectric properties as moisture in insulating system paper and oil , power factor, oil conductivity , etc..) in the frequency range from 0.05 mHz to 1 kHz. In this paper we have selected some real case studies on some power transformers that presented problems in the insulating system during the monitoring phase on the one hand, and on the other hand, we have studied the restoration of such anomalies with targeted corrective actions aimed at improving the residual life of the transformer. In particular the following case studies are reported: - two twin transformer of 150 MVA with high furanics compounds ( 2FAL); - an autotransfo of 5 MVA after coils replacement in manufacturer workshop. - a transformer of 8 MVA – 132/6 kV with high moisture ( 6%) in paper and high dissipation factor–under vaccum reconditioning up to moisture in paper about 3 %. The advantages / effectiveness of the DFR analysis compared to the analysis of the oil standard (Karl Fisher method): Determines the water content in the solid-paper insulation without opening the transformer Eliminates the problem related to the interpretation of moisture in the oil and solid insulating part (active part) of the transformer. Allows the monitoring of the paper moisture treatment, its extraction (% by weight), and the limit below which to stop the treatment
ID: 1257 / P3-1: 17
XEMIS2: A liquid xenon Compton camera to image small animals
1SUBATECH, IMT Atlantique, CNRS/IN2P3, Université de Nantes, 44307 Nantes, France; 2INSERM, UMR1101, LaTIM, CHRU Morvan, 2 avenue Foch, Brest, 29600, France; 3Centre Hospitalier Universitaire de Nantes, 1 place Alexis-Ricordeau, 44093 Nantes, France; 4INSERM U892 équipe 13, 8 quai Moncousu, 44000 Nantes, France; 5LS2N, Ecole Centrale de Nantes, CNRS/Inp, Université de Nantes, 44307 Nantes, France
An innovative Xenon Medical Imaging System, XEMIS2, designed for small animal 3γ preclinical imaging, has been constructed and it is currently under test and qualification at the SUBATECH laboratory. It consists of a Compton camera, containing nearly 200 kg of liquid xenon, whose main goals are the precise three-dimensional localization of the 44Sc radioactive emitter used to image the small animal and the reduction of the administered radio-pharmaceutical activity in cancer diagnosis. The active volume of the XEMIS2 camera is surrounded by a set of PhotoMultiplier Tubes (PMTs) to measure scintillation light. The read-out anodes are segmented in 20000 pixels to measure ionization charges. In order to reduce the electronics dead-time during continuous data taking, a novel DAQ system specifically designed for XEMIS2 has been realized and recently tested. It consists of two independent synchronized scintillation and ionization signal detection chains. The self-triggered scintillation light detection chain has been recently tested and calibrated in XEMIS1, whose experimental results showed a good performance. XEMIS2 will be soon installed at the Center for Applied Multimodal Imaging (CIMA) in the Nantes University Hospital for further preclinical studies. To safely manage a large amount of xenon in a hospital center, a recovery and storage cryogenic subsystem called ReStoX has been conceived, successfully commissioned and already installed at CIMA.
ID: 1181 / P3-1: 18
Dielectric Response Analysis of Mineral Oil Immersed Transformer Insulation during Manufacturing Process
King mongkut's institute of technology ladkrabang, Thailand
Polarization and Depolarization current (PDC) method is one of non-destructive insulation testing methods that can be used for diagnosis the insulation conditions of high voltage equipment. This paper presents the PDC analysis of an oil immersed distribution transformer measured during the manufacturing process. A 22 kV, 30 kVA single phase transformer was designed and constructed. During manufacturing process, the polarization current and depolarization current of the transformer insulation were measured for 6 case studies as follows: 1) paper insulation between iron core and low voltage (LV) windings before dry and vacuum in the oven, 2) paper insulation between LV and high voltage (HV) windings before dry and vacuum in the oven, 3) paper insulation between iron core and LV windings after dry and vacuum in the oven, 4) paper insulation between LV and HV windings after dry and vacuum in the oven, 5) oilpaper insulation between iron core and LV windings after dry and impregnation process and 6) oil-paper insulation between LV and HV windings after dry and impregnation process. Then, PDC test results were analyzed. It was found that the moisture content in the paper insulation clearly affected the capacitance at power frequency, and PDC shapes. Besides, the impregnation process had a good effect on the capacitance ratio and dielectric dissipation factor. Moreover, the current difference of dry paper insulation between HV and LV windings presented the nonlinear characteristic both before and after impregnation process.
ID: 1112 / P3-1: 19
Microsecond Break Arcs During or After Commutation of Current in a Hybrid DC Switch
Tokyo Institute of Technology, Japan
Hybrid DC switches have been intensively studied because of the increasing demand for DC power distribution systems. A hybrid switch consists of high-speed mechanical contacts, semiconductor power devices, and metal– oxide varistor elements. Make arcs are suppressed from occurring by turning on the power device connected in parallel before closing the contacts. In the opening period, the contact voltage increases and microsecond make arcs occur intermittently during the rise of contact voltage exceed the boiling voltage of the contact material. The arc voltage turns on the power device and subsequently the circuit current commutates from the contacts to the power device. The DC current is interrupted by the power device with varistors. Although the duration of make arcs was a few 10 s, the contact surface was degraded and the insulation strength decreased up to 20% in 1 kA DC commutation.
ID: 1108 / P3-1: 20
DC Characterization of Liquid Silicon Insulation Material
1Van Oord ofshore wind projects B.V., Netherlands, The; 2Deme offshore services B.V.; 3Delft university of Technology; 4Lovink Enertech B.V.
Increasing use of Direct Current (DC) in medium and high voltage electrical networks is demanding new research in the existing as well as new insulating materials. The electric field under DC is complex because it is dependent on the conductivity and temperature, which leads to formation of space and surface charges in the insulation material. The formation of space and surface charges in the insulation material can lead to premature breakdown of the insulation material. Several studies are being carried out around the world to use the existing alternating current (AC) infrastructure under DC conditions. To study the feasibility of using any equipment under DC conditions, it is therefore important to investigate the conductivity and space charge behavior of the insulation material and their dependence on the temperature and the electric field, which are not predictable yet. In this study, an attempt has been made to study the conductivity and its dependence on temperature and the electric field of liquid silicon insulation material. This liquid insulation material has a unique property of turning into solid state once exposed to moisture. In this paper, conduction Current measurements has been performed in liquid as well as solid state to investigate their conductivity values and study its dependence on the temperature and the electric field. From the results obtained, an indication of the electric field threshold value, above which space charge starts accumulating in the solid silicon insulation material is found out. These parameters then were used for performing simulations using finite element analysis software to study the behavior of insulation material under DC conditions. Due to the complex conduction phenomenon observed and the complexity in the measurement set up, it was not possible to study the electric field threshold values in liquid silicon insulation. A comparison between XLPE and solid silicon insulation under DC conditions is then studied. The electric field inversion is observed in both the insulation materials. In addition to this, it is observed that, because of the high electric field dependency on the conductivity a solid silicon insulation equalizes the inverted electric field distribution and thus reducing the magnitude of maximum electric field.
|3:15pm - 5:00pm||P3-2: Poster Session on Measurement, Monitoring and Diagnostic Techniques in High Voltage Equipments|
Session Chair: Lars Lundgaard, SINTEF Energy Research, Norway
ID: 1171 / P3-2: 1
Extraction and analysis on oil immersed paper's obscured low frequency polarization based on Frequency Domain Spectrum
Xi'an Jiaotong University, China, People's Republic of
Frequency domain spectrum is regarded as a reflection of insulation material’s dielectric process such as conductance and polarization which provides non-destructive insulation diagnosis on power equipment nowadays. Theories and explanations on this method are controversial with plenty of arguments, which limits its further application. Traditionally, low frequency range of oil-impregnated paper’s curve was treated as a conductance-dominant band where polarization contributes little to the dielectric loss. However, based on the motion characteristics and classic models of charges’ conductance and polarization process, this paper proposes for the first time that a polarization process with rather long relaxation time, which differs from the low frequency dispersion phenomenon, is supposed to exist in oil impregnated paper’s broadband dielectric response but is mainly obscured by large conductance loss. Meanwhile, the dielectric losses caused by this type of polarization under series of temperatures are quantified, which indicates that the polarization loss is comparable with conductance loss under some certain frequencies. The temperature characteristic and its explanation theory for this extracted polarization are further presented, by which the polarization’s barrier height, one of the polarization’s intrinsic parameters, is able to be obtained.
ID: 1290 / P3-2: 2
Research on the Overheating Fault of HVDC Wall Bushing and its Dignosis Strategies Based on CFD
1Xi'an Jiaotong University, China, People's Republic of China; 2Department of Electrical, Electronic, and Information Engineering University of Bologna; 3Southern Electric Power Research Institute Guangzhou, People’s Republic of China
Resin impregnated paper (RIP) wall bushing is the only channel connecting the valve hall to the outdoor DC field. It carries full voltage, full current and strong mechanical stress in long-term operation. Long-term thermal expansion and contraction causes the electrical contact wear of the outdoor part to be very serious, and it is prone to overheating failure. The local overheating will accelerating the fretting wear and corrosion, which will decrease the insulation and mechanical performance of RIP core. The byproduct also may fall out and distort the electrical field. Therefore, it is vital to maintain the overheating faulted bushing in time. In this paper, firstly the 3- dimentional finite element model of ±500kV DC wall bushing including connect structure was established. Then the thermal field distribution of wall bushing with the contact fingers with different degrees of deterioration were simulated. The correspondence between the temperature of the fault point and the temperature of the sheath were established. Finally, the correspondence were successfully applied to maintain a faulted wall bushing before destructive overheating fault occurs. This research can provide a basis for monitoring the overheating fault of the bushing with an infrared camera.
ID: 1209 / P3-2: 3
Effect of Moisture on Low Frequency Relaxation of Oil-Paper Insulation
State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, China, People's Republic of
The insulation performance of oil-paper insulation power equipment is seriously affected by moisture in oil and pressboard, but the current dielectric response diagnosis technologies are difficult to distinguish the effect of moisture and aging. In order to seek an effective moisture assessment method based on dielectric response technologies, the low frequency relaxation of oil-impregnated pressboard is tested and analyzed. Firstly, oil-impregnated pressboard samples of different moisture contents were prepared; then the frequency dielectric responses were tested, and the low frequency relaxation curves were obtained; finally, the effect of moisture on low frequency relaxation was discussed. The test results show that, the relaxation peak increases by moisture content, while the characteristic frequency of the peak remains the same. Besides, a new relaxation peak appeared at higher frequency range when moisture content is above 4%, which is considered to be caused by free water in oil-impregnated pressboard.
ID: 1287 / P3-2: 4
Moisture Detection in Transformer Oil Impregnated Paper Using High-Frequency Depolarization Current Measurements
NRC Metrology, National Research Council Canada, Ottawa
Moisture in transformer paper insulation is one of the most important parameters to be monitored in order to assess the useful life of the transformer. Time domain spectroscopy based on polarization and depolarization current measurements is one of the methods that can be used for detection of moisture content in the transformer paper insulation. However, these measurements could be influenced by thermal transient during the application of voltage, which may lead to an inaccurate interpretation of the insulation condition. In this paper, a novel method is proposed in order to avoid this thermal transient effect by using the high frequency component of the of depolarization current acquired during the measurement. Preliminary results show a correlation between the high frequency component of the depolarization current waveform and the moisture content in the paper insulation within a moisture content range of about 3 %. At higher moisture content, a resistive leakage current seems to have a negative effect on the measured depolarization current.
ID: 1225 / P3-2: 5
FTIR-Spectroscopic and Electrical Analysis of Thermally Stressed Liquid Dielectrics
Glasgow Caledonian University, United Kingdom
Mineral oils are employed as liquid dielectric insulators in many high voltage transformers. It is recognised that the dielectric properties of these oils degrade over time with continued exposure to high voltages and thermal stress. This breakdown can be monitored using FTIR spectroscopy or electrical techniques. In this work the mineral oils have been thermally stressed by exposure to 120oC over a prolonged time period with changes to the electrical breakdown voltage and FTIR spectra measured at frequent intervals. Different samples of oil were prepared with some exposed to Kraft paper, copper or a combination of the two. The ratio of oil: copper: Kraft paper was consistent with that commonly found in transformers. Results show that the growth of the carboxylic acid peak can be correlated with a total acid number (TAN) through a calibration process which is less time consuming, won’t overestimate TAN and is an alternative to titration.
ID: 1208 / P3-2: 6
Fault Diagnosis of Power Transformers Based on Comprehensive Machine Learning of Dissolved Gas Analysis
Xi'an Jiaotong University, China, People's Republic of
Currently, the commonly used fault diagnosis methods of power transformers are often difficult to deal with the ambiguity problems encountered in the troubleshooting process. Even with some artificial intelligent techniques already experimented, the results have not been not systematic compared and are far from real application. Therefore, this paper tries to make a thorough use of machine learning tools towards result data from dissolved gas analysis. This paper establishes a machine learning model based on dissolved gas analysis for internal fault diagnosis of power transformers, and makes a comparison between multiple machine learning methods. Firstly, an overall neural network model of transformer diagnosis based on the dissolved gas analysis is formed. Next, the performance of optimized BP neural network, probabilistic neural network (PNN), and decision tree algorithm is compared from the aspects of speed and accuracy. Furthermore, the case-based reasoning method based on the Euclidean distance and normalized energy intensity algorithm is employed to get the closest matching similar case to realize the transformer defect prediction and assistant decision-making. With actual examples verified, the case-based reasoning method can help detect the most likely abnormal causes of faulty transformers through providing the most similar matching case.
ID: 1337 / P3-2: 7
Optical Spectroscopy Analysis of Ester Oils under Thermal Aging Conditions
1Tanta University, Egypt; 2Egypt-Japan University of Science and Technology, Egypt
Ester oils have been proposed recently as alternative insulating liquids to mineral oils inside oil-filled power transformers. They are environmentally friendly, biodegradable and harmless to human body. During the operation of power transformers, the insulating oil is subjected to thermal and electrical stresses. Consequently, it is decomposed, and the aging by-products are generated. As a result, the properties of insulating oil are degraded. This study aims to investigate the impact of thermal degradation on ester oils during the operation of power transformer using UV-Vis optical spectroscopy technique. First, several aged ester oil samples were prepared using an accelerated aging experiment. In addition, aged mineral oil samples were prepared to compare the impact of aging on both. Then, these samples were tested using optical spectroscopy test. The obtained optical spectra have been investigated and the aging by-products could be evaluated. Furthermore, dissipation factor test was carried out on the aged samples to correlate between the thermal degradation and the dielectric properties. The obtained results have assured that ester oils have great potential to substitute mineral oils in the future.
ID: 1322 / P3-2: 8
Comparative Study of Furfural’s Raman Spectroscopy Detection in oil based on two kinds of Extractants
1State Key Laboratory of Power Transmission Equipment & System Security and New Technology, Chongqing University Chongqing, China; 2State Grid Zhejiang Electric Power Company, Zhejiang, China
How to accurately detect the concentration of furfural in transformer oil plays an important role in the analysis of the aging state of the transformer. As a fast and nondestructive detection method, Raman spectroscopy is the key to improving the sensitivity of Raman detection. In this paper, based on the extraction technique, the deionized water and methanol are used as extractants to carry out the comparative experiment of furfural Raman spectroscopy in oil. Firstly, the deionized water and methanol extract of furfural in oil are prepared and obtained. The Raman characteristic peaks of furfural are 1372 cm-1 and 1411 cm-1 and 1675 cm-1 by Raman detection, and qualitative analysis is discussed. The experimental results show that deionized water as an extractant has certain feasibility for Raman detection, and it has the lower limit of detection for Raman detection compared with methanol as extractant, which makes a certain contribution in order to improve the sensitivity of furfural Raman detection in transformer oil.
ID: 1333 / P3-2: 9
The History and Significance of the Carbon Oxide Ratio
GE Grid Solutions, United States of America
This paper describes the traditional interpretation of the CO2/CO ratio as it relates to dissolved gas analysis and what new research has revealed about the ratio in recent years. The industry at large has considered this ratio as a single number, for diagnostic purposes, at a given point in time. New information suggests that this is likely not the most beneficial position to take. Traditionally the ratio has been used as an indicator of the thermal decomposition of cellulose. More recent research of this topic has revealed that this ratio may even predict the deterioration of cellulose prior to any thermal acceleration.
ID: 1260 / P3-2: 10
Diagnosis of Moisture Content in Oil-immersed Paper Based on Dielectric Loss with Variable Voltage at Power Frequency
1State Key Lab of Electrical Insulation and Power Equipment, Xi’an Jiaotong University, Xi’an, China; 2State Grid Shaanxi Electric Power Research Institute, Xi’an, China
This paper studies the dielectric property of oilpaper in high electric field, especially the effect of moisture on the dielectric loss under variable voltage at power frequency in oil-immersed paper with different moisture content. Oilimmersed paper insulation model samples with different moisture content are prepared in laboratory. Afterwards, increasing voltage and decreasing voltage tanδ-U curves of samples with different moisture content were tested under different experiment condition and a non-linear phenomenon was observed. Test results show that the tanδ-U curve is influenced by the moisture content of oil-immersed paper and test temperature. When the moisture content in the oilimmersed paper is high, the tanδ value is gradually increasing with the increase of the voltage. And in the process of decreasing the voltage, the tanδ value gradually decreases but is greater than the value at the same voltage in the process of increasing the voltage. The decreasing voltage tanδ-U curve is above the increasing voltage tanδ-U curve while these two curves overlap at high voltage and have great separation at low voltage. Moisture content changes the overall shape of the curve and the area between the two curves by influencing the transfer of charge carriers in oil-immersed paper. As water is polar, energy level and density of the trap in the oil-immersed paper with different moisture content are different. Water provides more paths for free moving charge carriers so that the accumulation and dissipation velocity of the charge carriers in Oil-immersed paper vary. The temperature doesn’t change the overall shape of the tanδ-U curve. Based on the dielectric response, the tanδU curve of samples with different moisture content could be expounded and the moisture Content in oil-paper insulation equipment could be evaluated by the tanδ-U curve
ID: 1204 / P3-2: 11
Reliability Study of Furan Level Analysis for Transformer Health Prediction
1VUM Verfahren Umwelt Management GmbH, Austria; 2University of Graz, Austria; 3FH Joanneum GmbH, Austria
To determine the reliability of furan compound analysis for insulation-system health prediction, the furan level found in oil, paper and pressboard was monitored throughout a large-scale ageing study. Therefore, thermally upgraded and normal Kraft paper as well as transformer pressboard were immersed in 4 different types of insulation liquid (mineral oil, G-t-L oil, synthetic and natural ester) at 3 different ageing temperatures (110, 130 and 150°C) and studied throughout a 56 day ageing setup, resulting in 100 mixed samples and 300 furan analyses. While the evolution of furan compounds in each system was somehow steady, comparisons between different material mixes and temperatures show significant aberrations. For similar stages of wear, standard deviations of 100% and more are detectable for the total furan compound concentration in oil, while deviations in solid insulation materials can be even higher. Due to the complexity and high number of variables, irregular analysis intervals without supporting information seem to be highly arguable for transformer health prediction.
ID: 1283 / P3-2: 12
A SERS Substrate For Detecting Methanol In Transformer Oil
1State Key Laboratory of Power Transmission Equipment & System Security and New Technology, Chongqing University, Chongqing 400044, China; 2State Grid Zhejiang Electric Power Company
In the development of on-line monitoring technique for transformer aging status, detecting concentration of methanol dissolved in transformer oil by the method of surface enhanced Raman spectroscopy (SERS) is a novel and promising technique. By use of Raman spectroscopy technique, we can improve various shortcomings of traditional detection technology. In this paper, the concentration of methanol dissolved in 2 mL/L methanol-oil solution was effectively detected by surface enhanced Raman spectroscopy. In the first, Raman spectra of single methanol molecule and its SERS were simulated to analyze the Raman peaks of methanol. A SERS substrate was prepared with selective enhancement. Based on prepared SERS substrate, concentration of methanol dissolved in transformer oil with content of 2 mL/L have been effectively detected. This helped us to further study the lower concentration of methanol in oil and make quantitative analysis.
ID: 1269 / P3-2: 13
Effect of molecular structures of insulating oil on Stray Gassing
JXTG Nippon Oil and Energy Corporation, Japan
Reports from all over the world indicate that transformer oils can release large amounts of flammable gasses even at moderate operating temperatures. This phenomenon is termed ‘stray gassing’. However, there have been few studies on the relationship between the molecular structures of the oil and stray gassing. In this report some molecular structures were selected because they represent each carbon-type composition. They were subjected to stray gassing tests. It was found that the structures of each compound have different gas patterns under the stray gassing test conditions.
ID: 1145 / P3-2: 14
Research on Transformer Oil Multi-frequency Ultrasonic Monitoring Technology Based on Convolutional Neural Network
Electric Power Research Institute of Guangdong Power Grid Co., Ltd., China, People's Republic of
Facing the deficit of the effective measures to evaluate the insulation status of power transformers in service, this paper brought up a new method to estimate the physical and chemical properties of transformer oil through its transmission characteristics for ultrasonic signals under various frequencies. However, given the large volume of acquired ultrasound spectrum data by such technology, and the complexity as well as the variety of the transformer structures and conditions in which the transformer oil resides in, the interpretation of above data and the prediction of transformer health becomes enigmatic. Thus a recognition method was brought up by this paper to connect the ultrasonic spectrum to transformer oil conditions through Convolutional Neural Network. First of all, for the transformer oil test data, by using the density-based clustering method, the “standard oil” and other “degraded oils” approaching the standard are distinguished to achieve the purpose of distinguishing the quality of the transformer oil. Then, the principal component analysis is used to reduce the dimensionality of the ultrasonic spectrum data of the transformer oil. The dimensionality classification results of the reduced dimensional ultrasonic spectrum data and transformer oil test parameters are used as the input and output data of the algorithm model. The Convolutional Neural Network is established and the model parameters are trained. The final accuracy rate of the assessment model is 92%. Finally, a transformer oil condition detection method based on multi-frequency ultrasonic spectroscopy was established.
ID: 1325 / P3-2: 15
Study on Quantitative Analysis Method of Methanol Raman Spectra in Oil By Extraction Technology
1State Key Laboratory of Power Transmission Equipment & System Security and New Technology, Chongqing University; 2State Grid Zhejiang Electric Power Company, Zhejiang
Accurately detecting the concentration of methanol dissolved in transformer oil is of great importance for diagnosing the aging degradation of insulating paper. In this paper, acetonitrile were selected as extractants, and mixed with transformer oil samples containing different concentrations of methanol to complete the sample pretreatment work. The concentration of methanol in transformer oil samples was determined by Raman spectroscopy. The quantitative analysis method based on the principal component analysis of peak intensity of Raman spectra and the quantitative analysis method based on principal component analysis of peak area of Raman spectra were compared. The results show that the accuracy of fitting and error calculation using Raman spectral peak area as quantitative analysis parameter is higher, especially in the low concentration case concerned, it is helpful for us to detect trace methanol dissolved in transformer oil.
ID: 1180 / P3-2: 16
Pollution Degree Detection of Insulators based on Hyperspectral Imaging Technology
Xi'an Jiaotong University, People's Republic of China
Present researches prove that the pollution flashover of operating insulators still threatens the safe and reliable operation of power system. However, the traditional detection methods are difficult to achieve noncontact detection. The hyperspectral imaging technology is a nondestructive testing technology which combine image information and spectral information, therefore it has potential to become an important detection method for power device external insulation. In order to study the application of hyperspectral imaging technology in the detection of insulator pollution degree, a new data processing method is produced. On the one hand, the result of spectrum processing shows that there are corresponding relationships between the pollution degree and the reflectivity value, the reflectivity waveform and base material. On the other hand, the result of image processing proves that it can distinguish between the polluted and nonpolluted areas by using principal components analysis or Kmeans clustering algorithm. The result shows that the application of hyperspectral imaging technology in the detection of insulator's external insulation is feasible and it will have a broad application prospect.
ID: 1215 / P3-2: 17
Toward an optical monitoring of chemical markers in transformers insulating oil
1RSE,Dipartimento Tecnologie Trasmissione e Distribuzione, Italy; 2TERNA, Direzione Ingegneria,Italy; 3Università della Campania, Luigi Vanvitelli, Dipartimento Ingegneria, Italy; 4Università di Pavia, Dipartimento Chimica
An optical sensor for transformer oil monitoring is reported. It has been implemented in a plastic optical fibre which acts as optical platform for the sensing element, that is, a Molecular Imprinted Polymer layer, a robust, reproducible and low-price receptor for chemical marker also in the insulating oil matrix. This optical sensor has been assessed on the detection of a chemical byproduct of transformers’ paper degradation, the furfuraldehyde (2-FAL). The optical sensor performances have been tested on used insulating oil samples spilled from ex-serviced instrument transformers and compared with results of standard methods applied to the same samples. The achieved good agreement emerging by comparative analysis confirms the ability of the optical sensor of detecting low 2-FAL contents directly in mineral oil, without any treatment or dilution of the oil.
ID: 1361 / P3-2: 18
Advances in Measuring Partial Discharge in Insulating Liquids
1Omicron Electronics, France; 2University of Roma "La Sapienza", Italy
The IEC 61294 Technical Report, published in 1993, describes a simple test procedure to measure the PD Inception Voltage (PDIV) in insulating liquids and doesn’t cover any other items related to the PD patterns and their evolution at higher voltages. This simplified approach should be considered superseded when taking into account the several studies published [1-9] in the last decades concerning the PD detection in different dielectric liquids, with the aim to find a correlation between this phenomenon, breakdown event and liquid characteristics. It is well known that the origin of PDs is always due to imperfections or voids presence somewhere in the overall insulation. In the case of liquid dielectrics, the situation becomes much more complex because of such voids (bubbles) are not stable and form, grow, develop and collapse randomly under the action of the electrical field. In consequence of this dynamic, PDs in insulating liquids appear as fast event in terms of burst of rapid PD pulses of ascending magnitude which cannot be correctly detected with Narrow Band (NB) instruments and, for this reason, Ultra-Wide Band (UWB) detectors started to be employed [10,12]. Additionally, signals emitted from PD activity in insulating liquids may be of extremely low magnitude and, for this reason, it is crucial to use highly sensitive PD measurement equipment. This, however, results in a higher susceptibility to interference from external noise. These conditions can render the detection of PD patterns extremely difficult. Therefore, an important function of modern digital PD testing systems is to separate overlapping PD signal sources and to filter out noise [13-14]. This capability is neces¬sary for meaningful standardized PD detection in insulating liquids. Being nowadays in progress the preparation of an ASTM Standard on PD detection in dielectric liquids and being envisaged in the near future in IEC the revision of the existing Technical Report IEC 61294, the present paper reports some considerations on the measurements of the PD phenomena.
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