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Conduction and Breakdown in Solid Dielectrics, 1995. ICSD'95., Proceedings of the 1995 IEEE 5th International Conference on

Date 10-13 July 1995

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  • Proceedings of 1995 IEEE 5th International Conference on Conduction and Breakdown in Solid Dielectrics

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  • Relaxations in the mesophase of side chain liquid crystalline polymers: thermally stimulated discharge currents studies

    Page(s): 74 - 77
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    The aim of the present work is to give a contribution to the discussion of the nature, at the molecular level, of the relaxations above Tg observed in the TSDC studies of side-chain liquid crystalline polymers and, at the same time, to try to establish some kind of correspondence between those relaxations and the δ and α peaks observed by dielectric relaxation spectroscopy View full abstract»

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  • Conduction current and space charge formation in XLPE insulation

    Page(s): 144 - 148
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    The purpose of this article is to measure the space charge formation and the conduction current in cable grade XLPE and correlate the two measurements to identify the controlling conduction mechanism and hence the major source of space charge. The charge formation and conduction current is measured as a function of dc stress View full abstract»

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  • An interpretation of electroluminescence of polyolefins based on the similarity between electro- and plasma-induced luminescence spectra

    Page(s): 701 - 705
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    We discuss the possible nature of the luminescent centres involved in electroluminescence (EL) emission by comparing EL and plasma-induced luminescence in which the charges are brought to the surface of the polymer by a cold plasma View full abstract»

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  • A model for bipolar charge transport in insulators

    Page(s): 319 - 323
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    Failure of electrical cable insulation is still a major problem for the electricity generation and supply industries. Under high field conditions (>108 Vm-1), space charge and the concomitant electric field dynamics are involved in the initiation of dielectric breakdown. Space charge is established either by charge transferred across electrode-insulator interfaces, or by field assisted ionisation of centres within the bulk of the dielectric. The action of high fields upon charge provides mechanisms by which electrical energy is transformed into potentially destructive mechanical energy. Measurements of the dynamic space charge distribution within plane parallel samples of insulators contained between aluminium electrodes under high voltage DC stress have been previously obtained using a pulsed electro-acoustic (PEA) apparatus. The pulsed electro-acoustic technique has been developed to provide a high resolution and reliable method of measuring the space charge density dynamics within insulators. It is a flexible alternative to the pressure wave propagation method. In this paper, experimental data for space charge dynamics within degassed cross-linked polyethylene (XLPE) is compared to a simple numerical simulation, which has been derived from concepts first utilised in semiconductor physics View full abstract»

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  • Dielectric characterization of CVD diamond thin films

    Page(s): 433 - 437
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    The dielectric properties of diamond films deposited by CVD techniques onto p- and n-type silicon substrates have been measured in the frequency range from 0.1 to 103 KHz, at different temperatures. The interpretation of the data has been made on the basis of the many body theory of Dissado and Hill (1980) for the dielectric relaxation in solids. The parameters n and m calculated from this analysis have been correlated with the structure and content of the carbon phases in the films View full abstract»

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  • Surface resistance behaviour of insulating materials due to SF6 decomposition products

    Page(s): 600 - 604
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    The object of this work is to identify the decomposition products of SF6 in the presence of PTFE and nylon insulating materials and to investigate the influence of these products on its surface properties. For these studies, two experimental chambers were used. The presented results refer to the influence of energy dissipated by the system, the water content, and the type of material of the samples and contacts View full abstract»

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  • Ageing behaviour of contaminated complex insulation

    Page(s): 467 - 471
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    Composite insulating materials play an important role in the electrical equipment industry because of their balanced mechanical and electrical properties. Composite materials are totally homogenous and contain an organic material as binder and an inorganic material as reinforcing material. Any inhomogeneity is probably due to contaminations. In this study we deal with the type of contaminant resulting from chemical changes due to the reactions between the system constituents. Efforts were previously made to study the ageing behaviour of complex insulating materials. However, no major work has been done in the field of internal contaminants subjected to electrical stresses. This paper deals with investigations to determine the response of an internally contaminated composite due to voltage stressing. Ageing implies deterioration due to various types of stressing; electrical, environmental, thermal or mechanical, no matter what the type or stressing more or less all the properties get affected View full abstract»

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  • TSDC characteristics of extruded polymer insulated cables

    Page(s): 33 - 37
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    Four XLPE and TRXLPE insulated 15 kV cables were characterized using the thermally stimulated discharge currents (TSDC) technique in order to investigate the effect of the roughness and cleanliness of the semiconductive shield/insulation interface. The XLPE cables, Cable A and Cable B, had nominally the same compound formulation. However, the materials were reportedly cleaner for Cable B compared to Cable A. The cables were tested in the 0 to +/-140 kV voltage range. Cable B, gave a lower TSDC at all voltages when compared to Cable A, at positive and negative polarization. In addition, two 15 kV TRXLPE cables were tested. Cable C has a conventional conductor shield compound while cable D had a supersmooth conductor shield. Some possible interpretations of the TSDC responses are presented View full abstract»

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  • Fundamental approach to the storage of energy in dielectrics

    Page(s): 324 - 328
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    The classic approach to the storage of energy in dielectrics and their degradation does not consider the fact that charge injection and charge trapping always occur in capacitors subjected to high electric fields. In fact, when a charge is trapped in an insulating material and localized at an atomic scale, a quasi static polarization is induced, producing a local increase of the internal energy of the order of 5 to 10 eV. This change of the internal energy affects all the thermal properties of the material. Under certain circumstances this energy reaches a level so high that it constitutes a reservoir of energy sufficient to produce irreversible damage of the material when it is released after charges are detrapped View full abstract»

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  • Interpretation of atomic force microscope (AFM) signals from surface charge on insulators

    Page(s): 408 - 412
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    The surface of an insulator can accumulate charge by a variety of means. There is a need for good experimental procedures to measure these surface charge densities. The most promising new method is to use an atomic force microscope (AFM). The vastly improved resolution compared with the previous methods, coupled with use in the ambient atmosphere, mean that this method will become widely used. The observed signals show a spatial spreading and a temporal decay. In this paper we show how these measurements can be related to the physical mechanisms causing charge motion on the surface and within the bulk of the sample. A patch of charge having a radius a of about 100 nm is deposited on the surface of a dielectric. It is then monitored by an AFM probe which is scanned across the charged zone at a height h, also of order 100 nm. Either the force gradient or the force can be obtained, but we consider only the force in this paper. This force is due to the vertical electric field of the charge patch, which we need to calculate. A typical sample thickness of 25 μm is much larger than the size of the patch of charge, so the grounded surroundings are effectively at infinity. This view is confirmed by the elementary calculation of Stern et al. (1988), which agrees with experiment View full abstract»

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  • Dielectric breakdown of SiO2 formed by plasma-enhanced chemical vapor deposition of tetraethoxysilane

    Page(s): 656 - 660
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    In the present study, in order to estimate the intrinsic breakdown strength precisely, the self-healing technique was used with 1 μs-width pulse voltages. The effect of point defects on the intrinsic breakdown strength is discussed based on the knowledge of optical properties obtained with synchrotron radiation View full abstract»

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  • Study on application of wavelet analysis for degradation diagnosis of partial discharge in a void

    Page(s): 371 - 375
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    Waveforms of partial discharge (PD) current and sound wave emission by PD are measured in a void between a polyethylene terephthalate (PET) film and an electrode. The measured waveforms of PD current and sound wave are transformed by Gaussian and Mexican hat wavelets. The relation between the obtained results and degree of insulation degradation is discussed. As a result, it was clear that wavelet analysis results could be used in degradation diagnosis of an insulator View full abstract»

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  • Dielectric relaxation in medium-voltage cable insulation

    Page(s): 103 - 107
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    This paper describes dielectric relaxation in 11 kV and 33 kV cables. Relaxation is measured by discharging the insulation from a steady D.C. potential and recording an absorption-current transient, which persists after discharge of the geometric capacitance. The technique is attractive as a simple means of in situ assessment of degradation in underground cables. With appropriate transformation the transient may be interpreted in terms of the physical processes that govern the relaxation and the structure in which they occur. The aim of the present work is to characterize relaxation in the impregnated-paper and polymer systems used in medium-voltage cables, and to identify features that indicate the degree of ageing View full abstract»

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  • Role of electrode material in partial discharge chemistry

    Page(s): 605 - 610
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    The work reported shows that the electrode material will affect the chemistry of the discharge atmosphere. It is demonstrated that the complex chemical reactions occurring at the surface of metallic electrodes is material dependent. This variation in the gaseous reactions with electrode material adds to the difficulty of identifying the degradation reactions and the development of a generic reaction scheme for degradation processes under partial discharge stressing View full abstract»

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  • On effects of variation of polarizing temperature and additive content on space charge formation and electric field distribution in plain LDPE and LDPE doped with BaTiO3 additive: evidence from measurements using the thermal step method

    Page(s): 288 - 292
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    A thermal step method was used to investigate the effects of polarizing temperature and additive content on space charge formation and electric field distribution in relatively thick samples (~2 mm) of plain low density polyethylene (LDPE) and LDPE doped with 5 wt% barium titanate (BaTiO3). Space charge was formed using dc field of about 26 kV/mm at two different polarizing temperatures: 25°C and 50°C. Results indicate that for plain LDPE the remanent space charge density and electric field increase with increasing the polarizing temperature from 25°C to 50° C. The addition of 5 wt% BaTiO3 to plain LDPE appears to have remarkably reduced the amounts of the remanent space charge and electric field and changed their distribution patterns when compared with the corresponding values for the plain material. The maximum values of the remanent electric field reached in plain LDPE and doped LDPE are about 85% and 15% of the external applied field respectively. Moreover, the distribution patterns of the remanent space charge and electric field for the doped material appear to be more sensitive to variations of polarizing temperature than those for the plain material. Whereas in plain LDPE, the observed distribution patterns of the remanent space charge exhibit a homocharge at the cathode and a heterocharge at the anode for both polarizing temperatures, for the doped material, the rise of the polarizing temperature from 25°C to 50°C appears to have a considerable effect on the distribution pattern of the remanent space charge in this case: at 25°C, the remanent space charge distribution exhibits a heterocharge at the anode and homocharge at the cathode while at 50°C the remanent space charge distribution pattern is reversed showing a homocharge at the anode and a heterocharge at the cathode View full abstract»

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  • Digitally aided recognition of partial discharges in insulating materials and systems as a diagnostic tool

    Page(s): 264 - 268
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    The author shows that in spite of many problems, computer aided digital measurement techniques may be applied as an effective tool in the recognition of internal defects inside the complex insulating system, but thorough investigations of the prebreakdown state and a correct analysis of collected data are required. The best results can be obtained by defining the exact model for each insulating system View full abstract»

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  • On chaotic aspects of trees

    Page(s): 185 - 189
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    All things degrade and breakdown, and we live in degraded circumstances or we use such things, for example, as electrical insulating materials in electrical engineering etc. Thus it is very important to study and estimate these degradation processes. Almost all cases of solid degradation processes, which are a kind of branching process, have been very difficult to analyze, due to their nonlinearity and complexity, until recent developments of computer and analysing methods such as fractal wavelet, chaotic concepts etc. were proposed. Under such conditions, fractal properties of tree phenomena which are a kind of degradation process of solid insulating materials have been studied and various characteristics obtained. As for the tree phenomena which is a typical branching process, we report some chaotic aspects based on Takens's reconstruction theorem. Thus, the trajectories reconstructed from a series of discharge current pulses accompanied with tree developments are discussed. In this work a different tree pattern from the previous are discussed and further study is based on wavelet analysis, thus, the trajectory of time dependent wavelet coefficients was reconstructed as well as current pulse data View full abstract»

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  • Experimental setup for measurements of light emission and electrical parameters during the dc interfacial breakdown on contaminated electrolytic surfaces

    Page(s): 224 - 228
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    The authors have realized an experimental laboratory set up designed to observe and analyze the electric flashover on a slightly conductive surface modelled by a ditch filled by an electrolyte. They emphasize the following features of the work: This device allows one to record nearly at the same time and in one event, the evolution of electrical and optical parameters. The first results confirm the complexity of the phenomena; it seems that the the discharge type could be varied during its lengthening. Modelling work is needed to explain these observations View full abstract»

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  • Space charge and dielectric breakdown in polypropylene

    Page(s): 641 - 645
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    This report deals with the results of breakdown-strength measurements and laser induced pressure pulse (LIPP) measurements on polypropylene (PP), and the effects of space charge on breakdown is mainly discussed View full abstract»

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  • Charge formation in PE/EVA laminates and blends

    Page(s): 283 - 287
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    The authors show that large amounts of charge accumulate near the interface in the laminate samples, resulting in an increase of the electric field in the PE layers. This may enhance homocharge injection in the PE layer. The heterocharge in PE/EVA blends decreases as the VA content of blends increases, which was attributed by the enhancement of homocharge trapping at the interface and/or by the enhancement of negative charge injection via an increased electric field in the PE component View full abstract»

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  • Modelling of streamer discharges between insulating and conducting surfaces

    Page(s): 350 - 355
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    Two types of discharge configurations are discussed: (1) small spherical voids embedded in a dielectric (small cavities with one metal electrode) which both have in common that the radial spread of a surface discharge is negligible; (2) oblate inclusions embedded in a dielectric or with one metal and dielectric boundary. In these cases a radial surface discharge propagation (perpendicular to the electric field) predominantly determines the discharge process. The authors present a simplified physical model for partial discharge quantities based on the streamer theory serving to analytically estimate, for example, apparent charge, pulse phase/pulse height distribution, inception voltage for the two cases mentioned View full abstract»

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  • Effects of addition of silicone fluid on electrical performance of RTV silicone rubber coatings

    Page(s): 616 - 620
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    The room temperature vulcanizing (RTV) silicone rubber was formulated without and with addition of 10% silicone fluid by weight. The addition of silicone fluid to the RTV formulation is made in an attempt to explore the factors and extend the lifetime of the coating. The average leakage current and the leakage current pulse counts were determined as a function of time of exposure to combined electrical stress and salt-fog. Examination of the surface using attenuated total reflection (ATR) Fourier Transform Infrared (FTIR) spectroscopy coupled with the determination of the surface micro-roughness using a Scanning Electron Microscopy (SEM) and a high resolution roughness detector were carried out to characterize the RTV performance under salt-fog condition for different formulations of coatings. The content of the silicone fluid in the RTV coating was determined before and after salt-fog test, at different locations on the surface, and for different RTV formulations, using an extraction technique in an analytical hexane. The contact angle of a droplet of water on the surface, indicating the quality of hydrophobicity, was also determined View full abstract»

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  • Recognition of phase resolved partial discharge patterns for internal discharges and external corona activity

    Page(s): 386 - 392
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    A laboratory investigation of discharge pattern evolution as a function of electrical aging has been carried out for internal partial discharge (PD) and external corona activity. The setup was composed of three stator bars. The groundwall insulation of only one bar was exposed to high voltage. A second bar was not exposed directly to high voltage but was crossing over the first bar in the end arm region. From the evolution of the phase resolved discharge pattern, monitored over 3000 hours, internal discharges were easily distinguishable from end arm corona. The phase angle at which both types of activity occurred revealed some difference indicating that different discharge mechanisms were involved. A third bar used as an antenna was not subjected to any discharge activity and was monitored to determine the amount of electromagnetic coupling occurring at different frequencies. Some of the information found can be extrapolated to rotating machine monitoring to determine the presence of end arm corona View full abstract»

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