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Epoxy insulators in gas insulated switchgear and gas insulated transmission lines tend to accumulate surface charges, leading to insulation flashover. Improving the surface trap characteristics of epoxy materials, which can accelerate the... more
Epoxy insulators in gas insulated switchgear and gas insulated transmission lines tend to accumulate surface charges, leading to insulation flashover. Improving the surface trap characteristics of epoxy materials, which can accelerate the surface charge dissipation of epoxy insulators, is a promising method to improve the surface insulation performance. The surface trap characteristics of epoxy materials are strongly influenced by the chemical groups in the acid anhydride molecules. In this work, by quantum chemical calculations and isothermal surface potential decay tests, taking six organic anhydrides that differ only in the methyl and carbon–carbon double bonds, we find the modulation laws of methyl and carbon–carbon double bonds on the charge trap depth within and between molecular chains. The regulation mechanism is revealed from the microscopic perspectives of electron energy structure and electron cloud offset. The changes of surface charge trap depth of epoxy materials are primarily attributed to the changes in the spatial distribution of the electron cloud density between and on the valence bonds caused by the interaction between the electron-donating methyl group and the electron-absorbing carbon–carbon double bond.
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This work addresses the repeatability of PD Inception and Extinction Voltage (PDIV and PDEV respectively) measurements obtained on different configurations of aeronautic wires following the practical testing procedures described in... more
This work addresses the repeatability of PD Inception and Extinction Voltage (PDIV and PDEV respectively) measurements obtained on different configurations of aeronautic wires following the practical testing procedures described in different existing standards. We show that substantial differences in the results can be obtained according to sample configuration and according to the actual implementation of the standardized test procedures by different laboratories carrying out the experiments. see also: T. Hahner, P. Rybsky, I. Cotton, R. Lowndes, L. Albert, C. Thomas, S. Dinculescu, G. Teyssedre, "<em>A round-robin test study of Partial Discharge inception voltage in aeronautic cables</em>", Proc. 9th International Symposium on Electrical Insulating Materials (ISEIM), Waseda University, Tokyo, Japan, 13-17 Sept. 2020 (held as a virtual conference), pp. 1-7, 2020. <strong>Work carried out in the frame of the European H2020-CleanSky2 Project Hivacs, under ...
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Les polymeres et composites a matrice polymere sont aujourd'hui tres largement repandus pour des fonctions d'isolation electrique et de stockage d'energie dans le domaine de l'electrotechnique. Ils le sont notamment pour... more
Les polymeres et composites a matrice polymere sont aujourd'hui tres largement repandus pour des fonctions d'isolation electrique et de stockage d'energie dans le domaine de l'electrotechnique. Ils le sont notamment pour des raisons liees entre autres a leurs qualites intrinseques, a la variabilite des proprietes selon leur nature, aux conditions de mise en œuvre, aux evolutions des architectures des systemes eux-memes et a des considerations economiques. L'objectif de cet article est de presenter les specificites de ces materiaux en termes de performances et de durabilite vis-a-vis des exigences et des contraintes electriques et environnementales rencontrees dans l'electrotechnique.
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The objective of this study is to investigate the impact of thermoelectrical stress compared to thermal stress on the properties of HVDC model cables. To do so, electrical and physico-chemical characterizations have been performed as a... more
The objective of this study is to investigate the impact of thermoelectrical stress compared to thermal stress on the properties of HVDC model cables. To do so, electrical and physico-chemical characterizations have been performed as a function of ageing time that extends over several months. Electrical characterizations show that the thermoelectrical ageing tends to decrease the conductivity compared to the thermal ageing. The same conclusion holds for space charge, where more charges are observed during characterization for a thermally aged cable, compared to an electro-thermally stressed one. Physico-chemical characterizations do not show significant differences between thermoelectrical and thermal ageing. Both ageing conditions show an increase of the carbonyl index with ageing time.
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Cross-linked polyethylene finds application in the insulation of high-voltage cables, constituting a high demanding domain in terms of electrical performances. High-quality XLPE grades are now produced for insulation under high-voltage... more
Cross-linked polyethylene finds application in the insulation of high-voltage cables, constituting a high demanding domain in terms of electrical performances. High-quality XLPE grades are now produced for insulation under high-voltage direct current (HVDC) stress. Luminescence techniques have constituted original techniques along the development of such materials, particularly as regards the role of defects and residues in the behaviour of materials in terms of electrical charges stabilization. Luminescence provides a family of extremely sensitive techniques, though limited to substances with unsaturated groups: in materials like XLPE only additives, residues and defects are optically active. After recalling the grounds of luminescence principles in organic materials, we explain the implemented techniques, mainly based on photoluminescence and on an analysis of optical emissions related to charge traps into materials. The main results obtained with the identification of the role of...
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Dielectric nanocomposite materials are now involved in a large panel of electrical engineering applications ranging from micro-/nano-electronics to power devices. The performances of all these systems are critically dependent on the... more
Dielectric nanocomposite materials are now involved in a large panel of electrical engineering applications ranging from micro-/nano-electronics to power devices. The performances of all these systems are critically dependent on the evolution of the electrical properties of the dielectric parts, especially under temperature increase. In this study we investigate the impact of a single plane of silver nanoparticles (AgNPs), embedded in a thin silica (SiO2) layer close to the surface, on the electric field distribution, the charge injection and the charge dynamic processes for different AgNPs-based nanocomposites and various temperatures in the range 25°C – 110°C. The electrical charges are injected locally by using an Atomic Force Microscopy (AFM) tip and the related surface potential profile is probed by Kelvin Probe Force Microscopy (KPFM). To get deeper in the understanding of the physical phenomena, the electric field distribution in the AgNPs-based nanocomposites is computed by ...
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Secondary and backscattered electron emission from solids submitted to electron-irradiation is of considerable interest in many fields of science and technology: electron beam analyses techniques, electron lithography, study of the... more
Secondary and backscattered electron emission from solids submitted to electron-irradiation is of considerable interest in many fields of science and technology: electron beam analyses techniques, electron lithography, study of the behavior of satellite charging processes in orbit submitted to irradiation, field emission display technologies, Hall Effect Thrusters (HET), dielectric breakdowns. Regardless the specific area of interest, the knowledge of the electron emission yield (EEY) is highly requested. The EEY is the number of emitted electrons (secondary and backscattered) with respect to the incident electrons number. The properties of the emitted electrons in metals (number, angular distribution and energy) mainly depend on electron-electron interactions. For dielectric materials, the trapping of the injected charge due to the poor conductivity, affects significantly the electron emission. In this work, the charging effect on the electron emission was investigated and analyzed. For this purpose, the electron emission yield of very thin thermal SiO2 layers with different thicknesses deposited on Si-substrates where measured in order to link the space charge and the resulting inner electric field with the electron emission properties. The obtained EEY was compared with the one measured for a plasma elaborated SiO2 thin layers in which the density of structural defects is higher.
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ABSTRACT Whereas synthetic materials have been used for long in the insulation of HVAC cables, their use in the case for HVDC applications is still pending due to a lack of knowledge on the behaviour of space charge and on their impact on... more
ABSTRACT Whereas synthetic materials have been used for long in the insulation of HVAC cables, their use in the case for HVDC applications is still pending due to a lack of knowledge on the behaviour of space charge and on their impact on the reliability of cables. As volatile cross-linking by-products are known to have an impact on space charge accumulation, it is important to control the optimum outgassing conditions in respect to such application. In this work, the accumulation of space charge in cross-linked polyethylene (XLPE) samples is investigated under dc electrical fields at room temperature using the pulsed electroacoustic (PEA) method. Organic semiconducting screens were attached on both sides of the dielectric during the cross-linking procedure and were used as electrodes. Five different degassing conditions were studied. The samples degassed at room temperature developed heterocharges. Conditioning by holding at 50degC for 2 days decreased the accumulation of heterocharges. Surprisingly, no heterocharges were observed in some fresh samples and heterocharges only changed sign (the density remained almost the same) when the applied voltage was reversed. These results appear consistent with space charge build up resulting from a spatially inhomogeneous distribution of permanent dipole molecules, like crosslinking by-products, present in the material. A model, based on diffusion of volatile cross-linking by-products and polarization orientation features, was developed to describe the heterocharges formation in XLPE. Simplified assumptions (one dimensional infinite sample, desorption phenomenon) were adopted in order to obtain a simple expression of the polarisation charge density. Theoretical results predict, basically, that the heterocharges move in time from the electrodes into the bulk due to the permanent dipole gradient. The magnitude of the polarization charge is also affected by the temperature and the initial dipoles concentration.
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Charging of insulators modifies local electric field distribution and increases potential threat to the safety of the gas insulated equipment. In this paper, surface charge tailoring techniques are classified and reviewed by introducing a... more
Charging of insulators modifies local electric field distribution and increases potential threat to the safety of the gas insulated equipment. In this paper, surface charge tailoring techniques are classified and reviewed by introducing a Dam-flood model. Technical solutions of different charge tailoring methods are compared and discussed. The outlook of potential solutions to suppress charge accumulation is recommended and discussed based on industrial consideration. This paper serves as a guide handbook for engineers and researchers into the study of charge tailoring methods. Meanwhile, we hope that the content of this paper could shed some lights upon charge-free insulators to promote the industrial application of HVDC GIL/GIS.
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Space charge accumulation and changes in the nature of trapping sites are investigated going from low density (LDPE) to cross-linked (XLPE) polyethylene. Two different types of techniques were used: the pulsed electro-acoustic (PEA)... more
Space charge accumulation and changes in the nature of trapping sites are investigated going from low density (LDPE) to cross-linked (XLPE) polyethylene. Two different types of techniques were used: the pulsed electro-acoustic (PEA) technique to detect the net space charge under dc stress and luminescence experiments to probe the trapping sites. It is found that the chemical and/or structural modifications introduced by the cross-linking process itself control the charge storage in XLPE.
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Avec l'expansion des technologies HVDC, il devient necessaire d'etudier la conduction des isolants non plus seulement pour la comprehension des phenomenes disruptifs, mais egalement pour predire la distribution des contraintes.... more
Avec l'expansion des technologies HVDC, il devient necessaire d'etudier la conduction des isolants non plus seulement pour la comprehension des phenomenes disruptifs, mais egalement pour predire la distribution des contraintes. Dans ce travail, l'effet Maxwell-Wagner dans des associations d'isolants est revisite, en considerant d'une part un modele avec une conductivite non lineaire en champ, et des mesures de charge d'espace donnant un acces direct a cette charge d'interface. Nous montrons que des mesures de charge d'espace permettent d'estimer la charge d'interface produite par effet Maxwell-Wagner entre deux dielectriques de nature differente. Incidemment, les mesures confirment que la distribution de champ electrique passe progressivement d'une distribution capacitive a une distribution resistive sous contrainte electrique prolongee.
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In this paper, proton irradiated fluorinated polymer films are investigated by physicochemical analysis, such as PhotoLuminescence (PL), FT-IR and Differential Scanning Calorimetry (DSC). It has been observed that proton irradiated... more
In this paper, proton irradiated fluorinated polymer films are investigated by physicochemical analysis, such as PhotoLuminescence (PL), FT-IR and Differential Scanning Calorimetry (DSC). It has been observed that proton irradiated fluorinated films have a positive charge accumulation in the bulk under DC stress. The origin of this charge storage seems to be due to molecular chain scission. Therefore, this paper focused on physicochemical analysis results obtained on ETFE and FEP irradiated films. From the data, the scission, oxidization and crosslinking phenomena have been confirmed.
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Conduction current measurements have been widely used to characterize charge transport behavior in insulating materials. However, the interpretation of transport mechanisms and more generally of non-linear processes from current... more
Conduction current measurements have been widely used to characterize charge transport behavior in insulating materials. However, the interpretation of transport mechanisms and more generally of non-linear processes from current measurements alone is not straightforward. For this reason, space charge measurements, on the one hand, and models of charge transport encompassing charge generation, trapping and transport have been developed. The completeness and accuracy of a model can be assessed only if a substantial range of stress conditions, being field and temperature for the current topics, is available. The purpose of this communication is to enrich the investigation of low density polyethylene - LDPE insulation material characteristic using conduction current measurement. Measurements were conducted on 250 μm thick LDPE samples, for DC fields in the range 2 to 50 kV/mm and for temperatures from 20 to 70°C. Experimental data, i.e. transient current in charge/discharge and quasi-st...
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The optical and electrical properties of aluminum oxide layers formed by Micro-Arc Oxidation (MAO) process for potential application in spacecrafts have been investigated. The operational conditions of the MAO process have been correlated... more
The optical and electrical properties of aluminum oxide layers formed by Micro-Arc Oxidation (MAO) process for potential application in spacecrafts have been investigated. The operational conditions of the MAO process have been correlated to the structural features of the coatings and to the optical properties. Results show that, although environnement tests (UV, particles and thermal cycling) remain to be done, by selecting appropriate electrolyte formulation, the measured thermo-optical parameters could fit the specification range of cold coatings. Furthermore, the electrical properties of such coatings have been investigated by means of surface and volume conductivity measurements as well as dielectric spectroscopy. Results highlight that materials exhibiting the best thermo-optical properties are those having the higher electrical conductivity, with values appearing favorable regarding the targeted application.
Charge injection and retention in thin dielectric layers remain critical issues due to the great number of failure mechanisms they inflict. Achieving a better understanding and control of charge injection, trapping and transport phenomena... more
Charge injection and retention in thin dielectric layers remain critical issues due to the great number of failure mechanisms they inflict. Achieving a better understanding and control of charge injection, trapping and transport phenomena in thin dielectric films is of high priority aiming at increasing lifetime and improving reliability of dielectric parts in electronic and electrical devices. Thermal silica is an excellent dielectric but for many of the current technological developments more flexible processes are required for synthesizing high quality dielectric materials such as amorphous silicon oxynitride layers using plasma methods. In this article, the studied dielectric layers are plasma deposited SiO x N y . Independently on the layer thickness, they are structurally identical: optically transparent, having the same refractive index, equal to the one of thermal silica. Influence of the dielectric film thickness on charging phenomena in such layers is investigated at nanos...
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Due to the rapidly increasing demand of electric power, insulating materials used in electrical components are pushed up to their limits, where their electronic properties are of fundamental importance. Electroluminescence provides an... more
Due to the rapidly increasing demand of electric power, insulating materials used in electrical components are pushed up to their limits, where their electronic properties are of fundamental importance. Electroluminescence provides an elegant way to investigate electronic properties, high field effects and electrical ageing of polymers although the emission spectrum is still poorly understood. Unlike in organic semi-conductors, electroluminescence spectra of large band gap polymers exhibit specific spectral features that cannot be interpreted on the basis of the photo-physical properties of the material. By irradiating polypropylene thin films with electrons up to a few keV and by analyzing the emitted light, we were able to isolate the elementary components of the emission and to reconstruct the electroluminescence spectrum. For the first time, a comprehensive study of electroluminescence in polymers is provided and the underlying mechanisms of the emission are discussed. The results herein provide an univocal demonstration that the electroluminescence from wide band gap polymers results in part from chemical reactions, opening the way to the diagnosis and prognosis of polymeric materials under electrical stress.
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ABSTRACT Thermo-stimulated depolarization current (TSDC) measurements and space charge measurements were performed on poly(ethylene naphthalene 2,6-dicarboxylate) (PEN), an aromatic and polar polyester. The aim is to develop an... more
ABSTRACT Thermo-stimulated depolarization current (TSDC) measurements and space charge measurements were performed on poly(ethylene naphthalene 2,6-dicarboxylate) (PEN), an aromatic and polar polyester. The aim is to develop an understanding of the dipolar and conduction processes at play in this material and in particular to understand the effects of temperature. For the TSDC measurements, when polarizing at 130 and 170 °C, the sub-glass transition and the glass transition relaxations are observed. However, in the case of a polarization temperature of 170 °C, one more current peak, labelled ρ peak, is observed at temperatures above the glass transition. This peak is not only of dipolar origin and could be associated with charge detrapping in the material. To unravel the mechanisms behind this process, a TSDC was combined with space charge measurements using the pulsed electroacoustic method (PEA) and the partial heating method was used. It is shown that the ρ peak is predominantly associated with the release of the negative charge build-up in the material.
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ABSTRACT The Pulsed Electro-Acoustic method (PEA) is widely used both in laboratory for fundamental research and in industry for components assessment and diagnosis. However, in most cases, the technique is used without paying enough... more
ABSTRACT The Pulsed Electro-Acoustic method (PEA) is widely used both in laboratory for fundamental research and in industry for components assessment and diagnosis. However, in most cases, the technique is used without paying enough attention for acoustic losses and dispersive effects, which render the interpretation of the material/product response somewhat uncertain, especially when dealing with relatively thick samples. Moreover, for cable systems, PEA signals are affected by the acoustic wave propagation in the material and the response of the measurement system. We developed a deconvolution technique that takes into account the divergent effects due to coaxial geometry and insulation thickness. The accuracy of the recovered charge profile depends on the system modeling (especially the estimate of the attenuation and dispersion coefficients). Furthermore, simulation results show that the recovered charge profiles can be affected, to some extent, by the Signal to Noise Ratio of experimental data. A comparison between experimental results on power cables with and without the deconvolution technique is reported and discussed.
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ABSTRACT An experimental setup that permits total electron emission yield and backscattered electron yield measurements was developed. To ensure its efficiency the experimental setup was modeled on a particle in cell model. Measurements... more
ABSTRACT An experimental setup that permits total electron emission yield and backscattered electron yield measurements was developed. To ensure its efficiency the experimental setup was modeled on a particle in cell model. Measurements of total electron emission yield and backscattered electron yield were performed on air-exposed technical silver. The results are in agreement with the literature.
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ABSTRACT A numerical model for describing charge accumulation in electron-beam irradiated low density polyethylene has been put forward recently. It encompasses the generation of positive and negative charges due to impinging electrons... more
ABSTRACT A numerical model for describing charge accumulation in electron-beam irradiated low density polyethylene has been put forward recently. It encompasses the generation of positive and negative charges due to impinging electrons and their transport in the insulation. However, the model was not optimized to fit all the data available regarding space charge dynamics obtained using up-to-date pulsed electro-acoustic techniques. In the present approach, model outputs are compared with experimental space charge distribution obtained during irradiation and post-irradiation, the irradiated samples being in short circuit conditions or with the irradiated surface at a floating potential. A unique set of parameters have been used for all the simulations, and it encompasses the transport parameters already optimized for charge transport in polyethylene under an external electric field. The model evolution in itself consists in describing the recombination between positive and negative charges according to the Langevin formula, which is physically more accurate than the previous description and has the advantage of reducing the number of adjustable parameters of the model. This also provides a better description of the experimental behavior underlining the importance of recombination processes in irradiated materials.