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).
|Location: Cloister Courtyard|
|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|
|10:15am - 10:45am||Coffee Break|
|1:00pm - 2:15pm||Lunch|
|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.
|Date: Tuesday, 25/Jun/2019|
|8:00am - 5:30pm||Registration|
|10:00am - 10:30am||Coffee Break|
|1:00pm - 2:15pm||Lunch|
|4:00pm - 4:30pm||Coffee Break|
|Date: Wednesday, 26/Jun/2019|
|8:00am - 4:00pm||Registration|
|10:00am - 10:30am||Coffee Break|
|12:30pm - 1:45pm||Lunch|
|Date: Thursday, 27/Jun/2019|
|8:00am - 4:00pm||Registration|
|9:45am - 10:15am||Coffee Break|
|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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