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Dielectrics and Electrical Insulation, IEEE Transactions on

Issue 5 • Date October 2007

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  • Table of contents - Oct. 2007 Vol 14 No 5

    Page(s): c1
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    Freely Available from IEEE
  • IEEE Dielectrics and Electrical Insulation Society - Executive Committee

    Page(s): c2
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  • Industrial Applications of Pulsed Power Technology

    Page(s): 1051 - 1064
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    A review of mainly the past two years is undertaken of the industrial applications of pulsed power. Repetitively operated pulsed power generators with a moderate peak power have been developed for industrial applications. These generators are reliable and have low maintenance. Development of the pulsed power generators helps promote industrial applications of pulsed power for such things as food processing, medical treatment, water treatment, exhaust gas treatment, ozone generation, engine ignition, ion implantation and others. Here, industrial applications of pulsed power are classified by application for biological effects, for pulsed streamer discharges in gases, for pulsed discharges in liquid or liquid- mixture, and for material processing. View full abstract»

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  • Diagnostic Methods for Outdoor Polymeric Insulators

    Page(s): 1065 - 1080
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    Composite insulators are considered mature products and a broad range of insulator types is nowadays available, including line insulators, hollow-core insulators and apparatus insulators, for applications ranging from distribution voltages to the highest transmission voltages. This development has created a need to elaborate diagnostic methods and tools for determining the quality of composite insulators. A review on recognized insulator faults and methods for their detection is provided. View full abstract»

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  • Some Recent Topics of Non-equilibrium Discharge Plasma Technologies - Their Widespread Use from Low Pressure to Atmospheric Pressure

    Page(s): 1081 - 1087
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    Non-equilibrium discharge plasmas have been utilized in a variety of fields and are indispensable to material processing, nanotechnologies and biotechnologies besides conventional applications such as light sources. In this review, neutral beam etching, advanced oxidation, protein removal, combustion control and volume, non-equilibrium discharge generation at atmospheric pressure are chosen and summarized as the recent, typical applications of the non-equilibrium discharge plasmas generated from low pressure to atmospheric pressure. A brief introduction of non-equilibrium discharge plasmas is also given, which serves comprehensive understanding of the physics and chemistry behind the technology. View full abstract»

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  • Bioelectric Effects of Intense Nanosecond Pulses

    Page(s): 1088 - 1109
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    Electrical models for biological cells predict that reducing the duration of applied electrical pulses to values below the charging time of the outer cell membrane (which is on the order of 100 ns for mammalian cells) causes a strong increase in the probability of electric field interactions with intracellular structures due to displacement currents. For electric field amplitudes exceeding MV/m, such pulses are also expected to allow access to the cell interior through conduction currents flowing through the permeabilized plasma membrane. In both cases, limiting the duration of the electrical pulses to nanoseconds ensures only nonthermal interactions of the electric field with subcellular structures. This intracellular access allows the manipulation of cell functions. Experimental studies, in which human cells were exposed to pulsed electric fields of up to 300 kV/cm amplitude with durations as short as 3 ns, have confirmed this hypothesis and have shown that it is possible to selectively alter the behavior and/or survival of cells. Observed nanosecond pulsed effects at moderate electric fields include intracellular release of calcium and enhanced gene expression, which could have long term implications on cell behavior and function. At increased electric fields, the application of nanosecond pulses induces a type of programmed cell death, apoptosis, in biological cells. Cell survival studies with 10 ns pulses have shown that the viability of the cells scales inversely with the electrical energy density, which is similar to the "dose" effect caused by ionizing radiation. On the other hand, there is experimental evidence that, for pulses of varying durations, the onset of a range of observed biological effects is determined by the electrical charge that is transferred to the cell membrane during pulsing. This leads to an empirical similarity law for nanosecond pulse effects, with the product of electric field intensity, pulse duration, and the square root of the numb- er of pulses as the similarity parameter. The similarity law allows one not only to predict cell viability based on pulse parameters, but has also been shown to be applicable for inducing platelet aggregation, an effect which is triggered by internal calcium release. Applications for nanosecond pulse effects cover a wide range: from a rather simple use as preventing biofouling in cooling water systems, to advanced medical applications, such as gene therapy and tumor treatment. Results of this continuing research are leading to the development of wound healing and skin cancer treatments, which are discussed in some detail. View full abstract»

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  • Chemical, Physical and Electrical Properties of Aged Dodecylbenzene: Thermal Ageing of Mixed Isomers in Air

    Page(s): 1113 - 1124
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    A commercial dodecylbenzene (DDB) cable oil was aged at temperatures between 90 and 135degC in air and was analyzed using various analytical techniques including optical and infra-red spectroscopy and dielectric analysis. On ageing, the oil darkened, significant oxidation features were found by infra-red spectroscopy and the acid number, water content and dielectric loss all increased. Ageing in the presence of paper or aluminum did not affect the ageing process, whereas ageing was significantly modified by the presence of copper. An absorption at 680 nm ("red absorbers") was detected by ultra-violet/visible spectroscopy followed by the production of an opaque precipitate. A reaction between copper and the acid generated on ageing is thought to produce copper carboxylates, and X-ray fluorescence confirmed that copper was indeed present in both the aged oil and the precipitate. Significantly, once red absorbers were detected, the dielectric loss increased to catastrophically high values and, therefore, the appearance of these compounds may serve as a useful diagnostic indicator. The development of acidity on ageing appears to be key in initiating the destructive copper conversion reaction and hence the control of oil acidity may be key to prolonging the life of DDB cable oils. View full abstract»

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  • Electrical Breakdown Studies on Electro-active Paper

    Page(s): 1125 - 1132
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    The concept of using cellulose as a smart material for preparing electro-active paper (EAPap) has been a land mark discovery, since it exhibits an impressive magnitude of actuation at relatively modest voltages. Considering the small thickness of cellulose samples (35 mum) and smaller depth of electrodes (100 nm), even at relatively low operating voltages (7 V), high electrical stresses can exist at pointed asperities on electrode surface, non-uniform locations in cellulose structure and at triple points joining electrode, cellulose and air. This paper reports the results of our AC and DC breakdown tests on cellulose samples carried out according to ASTM standards. The variation of breakdown strengths with relative humidity levels has been investigated and the results are explained with the aid of Maxwell-Wagner effect. View full abstract»

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  • Electrical Energy Density and Discharge Characteristics of a Poly(vinylidene fluoride-chlorotrifluoroethylene)Copolymer

    Page(s): 1133 - 1138
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    The high electric displacement (D>0.1 C/m2) and breakdown field (600 MV/m) in polyvinylidene fluoride based polymers suggest high electrical energy density in this class of polymers. By defect modifications which reduce or eliminate the remnant polarization in the polymer, a high electrical energy density can indeed be obtained. This paper shows that in properly prepared P(VDF-CTFE) copolymer film capacitors, an electrical energy density ~25 J/cm3 can be obtained with a breakdown field higher than 600 MV/m. The dielectric and discharge behavior of the polymer films were investigated. The results reveal that there are strong frequency dispersions in both the dielectric and discharge behavior. The dielectric constant decreases with frequency and the discharged energy density is also reduced at shorted discharge time (~1 mus) due to increased ESR for fast discharge. The results indicate the potential of this class of polymers for high energy density capacitors and suggest the need for further tuning of the polymer compositions to reduce the frequency dispersion. View full abstract»

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  • Microwave Measurements of Dielectric Properties Using a Closed Cylindrical Cavity Dielectric Resonator

    Page(s): 1139 - 1144
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    Microwave measurements of the dielectric constant and loss tangent of homogeneous isotropic samples in rod form, using a closed cylindrical cavity resonator, are described. The measurements are made at the resonant frequency of the TE01delta is mode. A new simple field model of the resonator is developed. This model provides a very simple and clear description of the field distribution within the resonator. The dielectric properties are computed from the resonant frequency, sample dimensions and unloaded quality factor of the resonator. The effect of conductivity losses within the metal cavity is examined. The measurement accuracy is assessed by comparing the results with those obtained using other well-known techniques. View full abstract»

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  • The Shielding Effectiveness of Composite Media - a Parametric Analysis Supporting an Engineering Perspective

    Page(s): 1145 - 1153
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    This paper is presented as an example of a parametric approach that may be applied to engineering the radio and microwave properties of composite materials in the context of providing electromagnetic shielding capability. In this case, the composites are formed by a conductive filler component embedded within an insulating material. The effective electromagnetic (permittivity) properties of the composite are modeled under the quasistatic approximation using the McLachlan general effective medium model, which enables the impact of the percolation (insulator-conductor) transition to be explored. Composites within the transition region exhibit a power-law nature to their effective material properties. The power-law exponents may take a range of values above a limiting value set by the dimensionality of the filler particle network within the composite and with the assumption of a perfectly random distribution of filler particles. In practice, the values of the power-law exponents depend on the chemical interactions between the constituents, the processing conditions and the nature of the inter-particle charge transport. The paper demonstrates the implications of different values of power-law exponent in the context of the trade-off between shielding effectiveness and composite thickness. View full abstract»

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  • Correlation between Brightness and Channel Currents of Electrical Discharges

    Page(s): 1154 - 1160
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    Channel brightness of 500 mm long electrical discharges were measured by analyzing a set of digitized images taken by 3 cameras placed symmetrically around a discharge gap at a radial distance of 200 cm from the axis of the spark. The sparks were generated between a steel rod and a plane electrode. The distribution of the brightness across the channel represented a Gaussian distribution. A linear correlation was seen between the channel brightness measured by different cameras looking at the same spark channel. No correlation was seen between the channel brightness and the channel depth (direction perpendicular to the camera plane). The measured peak current and the brightness of the main spark channel show a high degree of correlation (R2=0.97). The sum of brightness of branches was equal to the brightness of the parent channel. One can use this result to calculate the relative distribution of branch currents in complex electrical discharges including natural lightning flashes. If the current in the parent channel is known, branch currents can be calculated by measuring the optical intensities using photographic techniques. View full abstract»

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  • Electromagnetic Wave Propagation in a Coaxial Pipe GIS Model

    Page(s): 1161 - 1169
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    Partial discharge (PD) detection using a UHF band signal is a well known advanced insulation diagnosis method in a gas insulated switchgear (GIS) and has been actively studied. Detailed investigation of detection principles and electromagnetic wave propagation inside the GIS tank is required for significant improvement in sensitivity and accuracy. As the wavelength of UHF-band signals is comparable to the GIS tank size, higher-order modes also appear in electromagnetic waves propagating inside at frequencies at or above a certain value, creating complicating phenomena. This study investigated these phenomena, focusing on experiments with a UHF sensor inside a coaxial pipe as a simplified model of GIS structure, while varying conditions such as sensor shape and installation position (both circumferential and longitudinal), the input method of a simulated PD signal, and the presence or absence of an insulating spacer. On the low frequency side (TEM mode only), the sensor output can be described by an equivalent electric circuit determined by the coupling capacitance between the sensor surface, the center conductor and the tank. At the cutoff frequency of the TE11 mode or above, resonance phenomena appeared, which were related to the pipe length. Further, it was found that installing an insulating spacer inside the coaxial pipe shifted the resonant frequency in a manner closely connected with the spacer position's relationship to the electric field distribution inside the tank. View full abstract»

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  • Structural Changes in EPDM Subjected to Ageing in High Voltage Transmission Lines

    Page(s): 1170 - 1182
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    This work presents a study of the structural changes in aged EPDM (ethylene-propylene-diene monomer) from outdoor high voltage transmission lines. Samples were taken from failed and non-failed insulators after up to ten years in service on a 33 kV line. Infrared absorption, hydrophobicity index, dynamical mechanical analysis (DMA) and dielectric relaxation (DR) were employed as experimental techniques. The same experimental techniques were also applied to new samples of EPDM that were subjected to high electric fields (up to 14 kV/mm) for several hours. Results from DMA and DR techniques are in good agreement and, together with previous results from neutron irradiation techniques, suggest that the experimental data obtained from outdoor-aged and laboratory tested samples may be explained by a decrease in the degree of crystallinity due to the interaction between electrical and mechanical effects in the dielectric. The proposed model is based on the disentanglement of the crystallites by forces originated in the interaction of the electric field with the polar groups located in the amorphous phase of the polymer matrix. An alternative explanation, based on a relaxation process appearing at the interfaces between the filler (ATH) and the polymer matrix conflicts with several experimental results presented in this work. View full abstract»

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  • Component Reliability Modeling of Distribution Systems Based on the Evaluation of Failure Statistics

    Page(s): 1183 - 1191
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    The procedures of asset-management have been developed into a central element of network operation and planning in liberalised electric markets of power supply for the present. The method of asset management considers all relevant life cycle cost related to the network equipment and provides strategies for reinvestment, maintenance and fault elimination. However, the method requires practical information about the available failure statistic from distribution networks, as well as about the reliability evaluation of equipment installed in distribution network. For the quantitative evaluation we collect failure record data of distribution networks in the special failure statistic. Furthermore, this paper represents the first attempt at modeling the component reliability for representative electrical components due to electrical stress, mechanical stress, temperature and time, which takes general aging mechanisms of insulating materials into consideration. Thus the proposed models provide reliability estimates, e.g. failure probability and failure rate for distribution systems. These models can be not only parameterized with a great deal of statistical data but also determined by aging tests and breakdown tests being available for the probabilistic assessment. Our results imply that the assessment approach for component reliability will motivate a need for reasonable and accurate data at an early decision-making stage in future deregulation of electric power market. View full abstract»

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  • Study on Pollution Flashover Performance of Short Samples of Composite Insulators Intended for ±800 kV UHV DC

    Page(s): 1192 - 1200
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    Based on the artificial pollution tests, the effects of pollution and high altitude on the flashover performance of short samples of five kinds of UHV/EHV dc composite long rod insulators are analyzed. The exponent characterizing the influence of salt deposit density on the flashover voltage is related with the profile and the material of the insulator shed. The values of the samples' exponents vary between 0.24 and 0.30, which are smaller than those of porcelain or glass cap-and-pin insulators, namely, the influence of the pollution on the composite long rod insulators is less, relatively. Thus, the composite insulators have certain advantages in severe pollution regions. The best ratio of the leakage distance to the arcing distance is about 3.35. The exponent characterizing the influence of air pressure on the flashover voltage is related with the profile and the material of the insulator shed and the pollution severity, the values of the samples' exponents vary between 0.6 and 0.8, which are larger than those of porcelain or glass cap-and-pin insulators. Therefore, the dc composite insulator used in high altitude regions should have enough arcing distance. Based on the test results, if insulator sample Type E is selected for the plusmn800 kV UHV dc transmission lines, the basic arcing distance should be no less than 8.16 m and the basic leakage distance no less than 30.2 m. View full abstract»

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  • Influence of Algal Fouling on Hydrophobicity and Leakage Current on Silicone Rubber

    Page(s): 1201 - 1206
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    Polymer insulators made of silicone rubber (SIRs) can suffer from algal fouling in tropical and even temperate regions. The purpose of the present study was to understand the hydrophobic behavior and leakage current characteristics of algal- fouled SIR materials when exposed to wet and contaminated conditions. Salt-fog tests were conducted on SIR samples colonized with the treatable alga Chlorella vulgaris. SIR samples covered with non-soluble kaolin powder at a deposition density comparable to that for the alga-treated SIRs were also evaluated. Results show that algal fouling considerably reduced the SIR hydrophobicity compared to the kaolin powder, which resulted in the development of a large leakage current. A major component of the leakage current produced on algal-fouled SIR is dry-band discharge, which leads to material degradation involving tracking and erosion. View full abstract»

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  • Electrical Insulation Characteristics of Silicone and EPDM Polymeric Blends. I

    Page(s): 1207 - 1214
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    The typical parts of a polymeric insulator are core, metal end fittings and polymeric housing material. The housing is intended to protect the fibre glass rod from the environment and electrical surface discharges. Since the housing materials are made of organic polymeric material, its insulation characteristics need to be studied. Amongst the many different polymers available, this work focuses on silicone rubber and ethylene propylene diene monomer (EPDM). Blends of EPDM and silicone rubber are prepared in a two roll mixing mill. Dicumyl peroxide is used as vulcanizing agent. The blends consisting of various proportions of component polymers are prepared, compression moulded into sheets, and post cured. The blends are tested for their insulation characteristics as per IEC and ASTM standards. Volume and surface resistivity, dielectric strength, dielectric constant, tan delta, tracking resistance, arc resistance, comparative tracking index, tensile strength, and percentage elongation at break of the blends are studied and discussed. The test results show that the increasing proportion of silicone enhances the electrical insulation properties whereas increasing weight percentage of EPDM improves the mechanical strength of the blends. View full abstract»

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  • Degradation Dynamics of Polymeric Housing Materials Used for HV Line and Station Apparatus

    Page(s): 1215 - 1223
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    A combination of laser irradiation and thermogravimetric analysis has been utilized to understand the degradation dynamics of polymeric materials used for housings of outdoor high voltage (HV) line and apparatus insulators, namely, silicone rubber, ethylene propylene diene monomer rubber and cycloaliphatic epoxy. The induced temperature rise was calculated using laser photo-thermal models and the results were found to be in good agreement with experimental findings. It has been shown that there are significant differences in the degradation dynamics of silicone rubber when compared with ethylene propylene diene monomer and epoxy. It has also been shown that the laser irradiation technique can be used as an efficient method to rank polymers materials for arc tracking and erosion resistance, especially for present day materials that will easily pass the screening tests prescribed in the ASTM and IEC standards. View full abstract»

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  • Quantification of Damage due to Surface Tracking

    Page(s): 1224 - 1231
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    Fractals have been very successfully used to address the problem of modeling and to provide a description of naturally occurring phenomena and shapes, wherein conventional and existing mathematical models were found to be inadequate. The geometrical patterns of dielectric breakdown like electrical trees, surface discharges, and lightning are known to be of fractal in nature. These fractal patterns can be analyzed numerically using fractal dimensions and lacunarity. Surface tracking occurring in HV insulation systems is a very complex phenomenon and more so are the shapes of tracking patterns. It has been fairly well established that the shapes and the underlying parameters causing tracking have a 1:1 correspondence and therefore methods to describe and quantify these patterns must be explored. This contribution reports preliminary results of such a study wherein 2D tracking patterns of gamma irradiated ethylene propylene diene monomer (EPDM) were analyzed and found to posses' fairly reasonable pattern discriminating abilities. View full abstract»

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  • A New Approach to the Statistical Enlargement Law for Comparing the Breakdown Performance of Power Cables. 1. Theory

    Page(s): 1232 - 1241
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    This paper, the first of two companion papers, describes a new approach to the application of the statistical "enlargement law" to power cable insulation. The results of this work allow for selecting better insulation for medium or high voltage cables. The selection is based on the results of dielectric strength tests performed on cable models or full size cables of a limited length. The relevance of the so-called crossing length, where one insulating compound performs better below it and another compound above this length, is discussed. The proposed theory was used to analyze the performances of two ethylene-propylene rubber (EPR) compounds and two cross-linked polyethylene (XLPE) compounds. The results are presented in the companion paper. View full abstract»

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  • Model of Inception and Growth of Damage from Microvoids in Polyethylene-based Materials for HVDC Cables. 1. Theoretical Approach

    Page(s): 1242 - 1254
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    A comprehensive physical aging and life model is presented for damage inception and growth in polymeric insulation, starting at the level of microscopic cavities, that are known to be one of the most severe factors limiting design electric field and life of cable insulation. Degradation within a polyethylene-based material for HVDC cables is considered as a hot-electron induced bond-breaking process that cumulates with time into the polymer matrix at microvoid-polymer interface, fed by subsequent electron avalanches generated in microvoids. By this way, a conductive pit is formed, that may exceed eventually a critical size for the start-up of a rapid failure mechanism, thereby leading ultimately to electrical breakdown. The model, essentially based on the physical and microstructural characteristics of the insulation, is virtually free from disposable parameters. It is shown to reproduce qualitatively the dependence of insulation time to failure on applied field, temperature and cavity size and to fit quantitatively experimental times-to-failure relevant to PE-based materials in typical working conditions for HVDC cables. The first part of this paper presents the theoretical background and the derivation of model equations, as well as their discussion. The second part deals with parametric investigation and data fitting. View full abstract»

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  • Model of Inception and Growth of Damage from Microvoids in Polyethylene-based Materials for HVDC Cables. 2. Parametric Investigation and Data Fitting

    Page(s): 1255 - 1263
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    A new, physical, aging and life model for damage inception and growth in polymeric insulation starting at the level of microscopic cavities has been presented in Part 1, by illustrating extensively its theoretical background and derivation. In the present paper a parametric analysis, relevant to a polyethylene-based compound, is carried out that illustrates the sensitivity of the model to technological and material parameters, first of all applied electric field, temperature, conductivity and cavity size. In addition, fitting to experimental times-to-failure relevant to HVDC cable insulation is discussed in order to confirm soundness and validity of the proposed approach. View full abstract»

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  • Analytic Solutions for Pulse Propagation in Shielded Power Cable for Symmetric and Asymmetric PD Pulses

    Page(s): 1264 - 1270
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    Shielded power cable can be considered as a lossy transmission line, the high frequency attenuation of which causes the PD pulse amplitude, as well as the pulse energy, to decrease as a function of distance propagated. We develop analytical expressions which characterize PD pulse propagation in a shielded power cable for both symmetric and asymmetric PD pulse waveforms for an attenuation constant which increases linearly with frequency. View full abstract»

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Aims & Scope

IEEE Transactions on Dielectrics and Electrical Insulation contains topics concerned with dielectric phenomena and measurements with development and characterization of gaseous, vacuum, liquid and solid electrical insulating materials and systems.

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Editor-in-Chief
Reuben Hackam