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Dielectrics and Electrical Insulation, IEEE Transactions on

Issue 4 • Date Aug. 2005

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Displaying Results 1 - 25 of 26
  • IEEE Transactions on Dielectrics and Electrical Isulation

    Page(s): 0_1
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    Freely Available from IEEE
  • Excecutive committee

    Page(s): 0_2
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    Freely Available from IEEE
  • Editorial

    Page(s): 627 - 628
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    Freely Available from IEEE
  • Polymer nanocomposite dielectrics-the role of the interface

    Page(s): 629 - 643
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB) |  | HTML iconHTML  

    The incorporation of silica nanoparticles into polyethylene increased the breakdown strength and voltage endurance significantly compared to the incorporation of micron scale fillers. In addition, dielectric spectroscopy showed a decrease in dielectric permittivity for the nanocomposite over the base polymer, and changes in the space charge distribution and dynamics have been documented. The most significant difference between micron scale and nanoscale fillers is the tremendous increase in interfacial area in nanocomposites. Because the interfacial region (interaction zone) is likely to be pivotal in controlling properties, the bonding between the silica and polyethylene was characterized using Fourier transformed infrared (FTTR) spectroscopy, electron paramagnetic resonance (EPR), and x-ray photoelectron spectroscopy (XPS). The picture which is emerging suggests that the enhanced interfacial zone, in addition to particle-polymer bonding, plays a very important role in determining the dielectric behavior of nanocomposites. View full abstract»

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  • Charge transport and dissipative processes in insulating polymers: experiments and model

    Page(s): 644 - 654
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    Electroluminescence in insulating polymers signs the existence of potentially harmful excited states because the excess energy can be released through degraded pathways, opening the way to chemical degradation. Excitation mechanisms involve impact excitation/ionization by hot carriers or bi-polar charge recombination. In order to discuss the relative contribution of these processes to light emission in polyethylene, we introduce a numerical model of charge transport postulating a recombination-controlled electroluminescence. Model outputs and experimental measurements are compared for three different protocols of DC voltage application considering especially the simulated recombination rate and the measured light emission. A fairly good agreement is found between model and experiment when considering electroluminescence under constant DC stress. The model fails to describe the measurement under time-varying DC stress suggesting that excitation by hot carriers should be taken into account. View full abstract»

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  • Model for electrical tree initiation in epoxy resin

    Page(s): 655 - 668
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (277 KB) |  | HTML iconHTML  

    A model for electrical tree initiation in epoxy resins is presented in which the process is driven by the generation of new charge traps as a result of energy transferred to the polymer via charge recombination processes. The electroluminescence intensity expected from the model is computed and shown to be in agreement with the experimental data. In particular it is shown how the initial emission due to recombination can change to an emission arising from impact excitation in a natural way when the trap density reaches a level sufficient for the high electric field of the tree initiation region to connect shallow traps to form conducting filamentary paths in the form of percolation clusters. This result allows the electroluminescence behavior to be correlated with the observed onset of filamentary damage. The model is also shown to be able to explain the decrease in emission intensity observed at the time of transition between the two mechanisms for luminescence. View full abstract»

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  • Proposal of a multi-core model for polymer nanocomposite dielectrics

    Page(s): 669 - 681
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    A multi-core model, i.e. a simplified term of a multi-layered core model, is proposed as a working hypothesis to understand various properties and phenomena that polymer nanocomposites exhibit as dielectrics and electrical insulation. It gives fine structures to what are called "interaction zones". An interfacial layer of several tens nm is multi-layered, which consists of a bonded layer, a bound layer, and a loose layer. In addition, the Gouy-Chapman diffuse layer with the Debye shielding length of several tens to 100 nm is superimposed in the interfacial layer to cause a far-field effect. Nano-particles may interact electrically with the nearest neighbors each other due to this effect, resulting in possible collaborative effect. Such a multi-core model with the far-field effect is discussed, for example, to explain partial discharge (PD) resistance of polyamide layered silicate nanocomposites, and is verified to demonstrate its effectiveness. View full abstract»

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  • The mystery of the missing joules

    Page(s): 682 - 689
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    A liquid dielectric exhibiting Debye behavior can be represented by a series RC circuit. It is evident that if this circuit is energized by a constant DC source, when the capacitor is fully charged the amount of energy stored in it is equal to the amount of energy expended as heat in the resistor. Nevertheless, the variation of power with time delivered to each element is not the same. In his analysis, Debye ignores the inertia of the molecular dipoles, and it follows that the total torque acting on each of them must always be zero. He therefore equates the driving torque on each dipole created by the applied field to the retarding torque, proportional to dipolar angular velocity, caused by inner molecular friction. However, it is evident that following DC charging, the energy which is returned on discharge must have been stored in the dielectric. It is shown that this energy storage can be attributed to the work done against another retarding torque in addition to the frictional torque. Although such a torque was not introduced explicitly by Debye into his analysis, his method produces the same result that he would have obtained if he had done so. View full abstract»

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  • Mechanism of high field electroluminesence and determination of the space charge limited field in polymeric dielectrics

    Page(s): 690 - 699
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    The mechanism of electroluminescence under inhomogeneous field conditions is investigated, as is the use of electroluminescence for determination of the space charge limited field. The latter investigation indicates that if the volume of polymer within the space charge limited field region is too small, the photon flux can be too low to permit accurate determination of the space charge limited field. Further, no means is available to assure that the photon flux is sufficient to assure accuracy. View full abstract»

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  • Correlation between DC polarization and failure characteristics of XLPE and EPR aged with AC voltage in a wet environment

    Page(s): 700 - 708
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    Polarization and depolarization currents obtained at a low DC field for two different brands of XLPE and EPR insulation subjected to water treeing were correlated with the insulation breakdown characteristics to assess the diagnostic value of various polarization/depolarization current parameters. It is shown that for all three materials the polarization currents change more consistently with aging than do the depolarization currents. It is also shown that although the RC time constant and the area under the polarization current curve change consistently with the aging time for all three materials tested, the consistency and the diagnostic value of the information they provide about impending insulation failure depends very much on the type of material. View full abstract»

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  • Kohlrausch relaxations: new aspects about the everlasting story

    Page(s): 709 - 718
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    For transient, time dependent polarization processes stretched exponential functions and power laws referred to as Kohlrausch relaxations are often observed in disordered dielectrics. These relaxations can be distributed in time or frequency over more than 12 decades. Among the various existing models for an interpretation two of them based on similar mathematics but different physical grounds are repeated. In these models charges, either electrons or protons, hop between adjacent sites. The distances between the sites are distributed resulting in a distribution of relaxation times. Then two new models which emerged in the last years are discussed. (I) It is shown that the dipolar interaction between dipoles of the same kind, i.e. without a distribution of any property, can result in Kohlrausch relaxations. (II) In solid electrolytic capacitors charges can be attracted by their images in the electrode. After application of an external voltage this charge attraction leads to an external current with a power law time dependence. View full abstract»

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  • Breakdown strength at the interface between epoxy resin and silicone rubber-a basic study for the development of all solid insulation

    Page(s): 719 - 724
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (241 KB) |  | HTML iconHTML  

    As a key component for a future power substation system entirely consisting of solid insulating materials, a special connection system between different pieces of power equipment has to be developed. A soft dielectric such as silicone rubber and a hard one such as epoxy resin are to be used for this connection. This paper describes the interfacial breakdown strength between silicone rubber and epoxy resin using two types of model samples on which the electric field can be applied in parallel or perpendicularly to their interface. Partial discharge characteristics at the interface and the effect of air penetration on the breakdown voltage along the interface are discussed. View full abstract»

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  • Computer modeling of interaction of gas discharge plasma with solid dielectric barriers

    Page(s): 725 - 735
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    A computer model describing charge transfer in a system consisting of two parallel-plate metallic electrodes covered with solid dielectric barriers immersed in gas medium is proposed. The material of the barriers is supposed to be a non-ideal insulator whose properties correspond to polyethylene and air is considered as a gas phase. The model is based on continuity equations for fluxes of charge carriers and accounts for their drift and diffusion and also for different sources of their generation and losses in different media. The continuity equations are coupled with Poisson's equation for computing electric fields affected by temporal and spatial variations of space charges in the system. Results of the computer simulations are obtained for the case when the applied field in the gas exceeds its breakdown threshold, i.e. charge transfer in the gas phase takes place in the form of an electrical discharge (electron avalanche and streamer). Evolution of generated discharge plasma is analyzed taking into account conditions on gas-solid interfaces and in the bulk of the solid dielectric barriers. View full abstract»

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  • A novel technique for partial discharge and breakdown investigation based on current pulse waveform analysis

    Page(s): 736 - 744
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    A novel technique for partial discharge (PD) measurement and analysis (PD-CPWA; PD current pulse waveform analysis) is developed and introduced in this paper. PD-CPWA is expected to be utilized to discuss PD mechanisms and physics in electrical insulating materials, focusing on the PD current pulse waveform and its time transition from PD inception to breakdown (BD). In this paper, the concept and principle of PD-CPWA are described, and the applications of PD-CPWA to (1) epoxy spacer samples under thermal and electric combined stresses in GIS, (2) creepage PD on epoxy spacers in SF6 gas and (3) liquid nitrogen/polypropylene laminated paper composite insulation system for high temperature superconducting cables are introduced and discussed. View full abstract»

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  • Electrical conductivity and space charge in LDPE containing TiO2 nanoparticles

    Page(s): 745 - 753
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (418 KB) |  | HTML iconHTML  

    Electrical conductivity (DC) and space charge accumulation were studied in samples of low density polyethylene to which nano-sized and micro-sized TiO2 (anatase) particles and a dispersant had been added. Sample thicknesses were in the range 150-200 μm. At applied field strengths of 10 and 20 kV/mm, the conductivity at 30 °C, measured in vacuum in samples containing 10 % w/w nano-sized TiO2, decreased by 1-2 orders of magnitude relative to samples with dispersant but without TiO2, and by three orders of magnitude at 70 °C. In air at 30 °C the corresponding decrease was an order of magnitude at 10 kV/mm, and a factor of four at 20 kV/mm. In samples containing 10 % w/w micro-sized TiO2 the conductivity increased in air and in vacuum, but only by factors in the range 2-10 depending on temperature and field. Space charge profiles were obtained using the laser-intensity-modulation-method (LIIMM), irradiating both surfaces of the sample. The micro-sized TiO2 particles are associated with increased charge injection from the electrodes and increased charge trapping in the sample bulk, increasing the conductivity overall. The nano-sized particles generate very little charge in the sample bulk, but render the electrodes partially-blocking and so lower the conductivity. View full abstract»

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  • Space charge phenomenology in polymeric insulating materials

    Page(s): 754 - 767
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    Topics related to space charge phenomenology, particularly the origin of space charge and its interaction with the host insulating polymer, have been widely discussed in recent years. Due to the development of reliable techniques for direct observation of space charge it is now possible to obtain, besides obvious indications on space charge and electric field magnitude and location, quantities that provide additional information on space charge accumulation and depletion rate, apparent mobility and trap depth distribution. Therefore, commonly debated topics such as the nature of charge carriers, the conduction mechanism, the charge dynamics at interfaces and the relation with nanostructure can be re-examined on the basis of space charge observation and this is, indeed, the purpose of this paper. View full abstract»

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  • Thermal instability of electromechanical films of cellular polypropylene

    Page(s): 768 - 778
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    An investigation has been undertaken into the thermal instability of electroactive, cellular polypropylene, in particular concentrating on the interaction between mechanical and electrical properties. A range of mechanical and electrical techniques have been applied including, dynamic mechanical analysis (DMA), thermo mechanical analysis (TMA), thermally stimulated currents (TSC) and admittance spectroscopy. Evidence is presented which indicates that the initial stages of a TSC spectrum is dominated by thickness changes in the foam. Changes in mechanical dimensions correlate well with temperature-induced changes in resonator parameters. View full abstract»

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  • Non-linear ferroelectric composite dielectric materials

    Page(s): 779 - 790
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1252 KB) |  | HTML iconHTML  

    The use of ferroelectric fillers in polymers can allow the formulation of a composite material which possesses enhanced AC currents at elevated electrical field strengths. This non-linear characteristic can be utilised as a stress relieving mechanism in applications with non-uniform electric fields. The enhanced characteristics are achieved through electrical field dependent permittivity mechanisms, which are occurring within the composite material. These stress relieving materials have distinct advantages over previous stress relieving polymer composites, using conductive or semi-conductive fillers, however, stress relief is only realisable under AC fields. The ferroelectric material used in these investigations is barium titanate, which has been used as a filler in an acrylic base resin system. The experimental results show how both the AC and DC conductivities are influenced by the electrical field strength, at a variety of filler concentrations. The research has also looked into how the AC and DC characteristics change as the degree of cure of the resin system is increased and how the particle size of the barium titanate influences the behaviour of the material. View full abstract»

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  • Influence of electro-mechanical stress on electrical properties of dielectric polymers

    Page(s): 791 - 800
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    The influence of high electrical fields on water treeing, electrical treeing, relaxation, conductivity and charge mobility in various polymers is reviewed within the context of a molecular model. The real value of the AC field acting on water trees is questioned and it is shown that the strain induced by very large fields may affect the water tree growth in solutions with large dielectric constant. A model based on simple electrostatic and molecular parameters describes most water treeing results. Light emitted during electrical tree growth could be associated with the field-induced strain at the tip of the electrode. The strain in PET is also related to the Maxwell stress due to high DC field. The log of the charge stored in some polymers varies with the square of the field suggesting that there same phenomenon might influence charge formation under high fields. The significance of a constant mobility value is discussed in light of experiments showing that it is not constant at moderate fields in various polymers. It is shown that the only constant parameter under varying high fields is the activation volume typical of a given sample. Future work is pointed out, especially regarding the nature of the trapping sites and the influence of sample size on the activation volume. View full abstract»

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  • A water treeing model

    Page(s): 801 - 808
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    A new model for water treeing is introduced. It assumes that when the field-induced stress applied on nano cavities filled with a liquid is larger than the yield strength of the polymer, bonds will be broken and the nano cavity will expand. The growth of the water trees is enhanced by the fatigue induced by the alternating electric field. The diffusion of the liquid is also a parameter affecting the water tree length. A simple equation relating the water tree length with field, time, frequency, and the nature of the solution is presented. A very good agreement between theory and experiments for a wide variety of results obtained with low density polyethylene (LDPE) tested under various fields, frequencies and ionic solutions is observed. This model also predicts the growth of water trees under DC fields after very long times or after many polarity reversals. Some aspects of this model requiring further refinements or experimental data are also pointed out. View full abstract»

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  • Novel numerical methods for measuring distributions of space charge and electric field in solid dielectrics with deconvolution algorithm

    Page(s): 809 - 814
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (455 KB) |  | HTML iconHTML  

    The deconvolution algorithm for measuring the distribution of space charge under DC by the pressure wave propagation (PWP) method is studied in this paper. A new Fredholm integral equation of the first kind, including a space charge distribution without a partial differential operator is presented. Numerical methods based on Tikhonov regularization for solving this integral equation and the original PWP equation are studied. Numerical simulation is studied for the effect of signal-to-noise ratio (SNR), and comparison with other algorithms is discussed. The numerical solution of an electric field distribution from measurements of a LDPE specimen is obtained successfully. View full abstract»

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  • Continuous monitoring of SF6 degradation in high voltage switchgear using Raman scattering

    Page(s): 815 - 820
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (498 KB) |  | HTML iconHTML  

    In high voltage SF6 insulated switchgear, the level of SF6 concentration needs to be monitored regularly because of its degradation by switching arcs and on-going partial discharges or coronas. In the work reported here, measurements of SF6 dissociation rate following 75 μA positive and negative coronas have been made using a mass spectrometer and Raman spectroscopy. The two sets of data correlate well, the rates of degradation of SF6 and production of gaseous by-products being shown to be proportional to the charge transported by the corona. SF6 provides a particularly strong Raman signal at 773.5 cm-1, and the results demonstrate the feasibility of using Raman scattering to monitor SF6 degradation in high-voltage switchgear. View full abstract»

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  • Comparison of two particle charging experiments for testing the JSC Mars-1 Martian regolith simulant against man-made materials

    Page(s): 821 - 826
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    NASA has great interest in testing the electrostatic charging of various materials due to the saltation process near the surface of Mars. As wind blows over the Martian regolith, particles are picked up, travel over a distance, and then fall back to the surface. These moving particles collide with each other and with any other materials present giving rise to a triboelectric charge transfer. Variables involved in this charge transfer include the number of particles, the frequency of collisions, and the particle velocities. It is necessary to know the extent of charging of man-made materials in this process in order to better plan future Mars missions. Two different methods for creating frictional charging between the regolith simulant and the materials in question are described. The first method utilizes a deflection board apparatus. The second uses a shaker box apparatus. The benefits and drawbacks of each experimental approach are listed. Some experimental data obtained through each method is provided but further study is required to fully characterize these charging processes. View full abstract»

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  • Experimental and numerical studies of dielectric properties of BaTiO3-platinum composites at microwave frequencies

    Page(s): 827 - 834
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    The conductor loading method has been used for creating a lossy dielectric material with a desired loss tangent. This method may also be applicable for developing high dielectric constant materials. In this paper, we will present the experimental results of the dielectric properties of BaTiO3 and BaTiO3 -platinum (BaTiO3-Pt) composites. These composite materials were designed to increase the real part of the effective dielectric constant at high frequency. Three different platinum volume fractions were used, 3, 5 and 10%, to make BaTiO3-Pt composites, in addition to a pure BaTiO3 material. To characterize the BaTiO3-Pt composites, microwave frequency measurements were conducted using the waveguide transmission technique. The experimental and numerical results verify that it is possible to increase the dielectric constant using the conductor loading method. View full abstract»

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  • Improvement of electromechanical actuating performances of a silicone dielectric elastomer by dispersion of titanium dioxide powder

    Page(s): 835 - 843
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (369 KB) |  | HTML iconHTML  

    This paper presents the first reported data on the embedding of highly dielectric ceramic inclusions in a rubbery host medium as a means to increase the electromechanical material response for dielectric elastomer actuation. The studied polymer/ceramic composite, consisting of a silicone matrix in which titanium dioxide powder was dispersed, exhibited, in comparison with pure silicone, a decreased elastic modulus, as well as an increased dielectric constant. The measured low frequency permittivity resulted in accordance with several classical dielectric mixing rules. The use of this material as elastomeric dielectric for planar actuators enabled a reduction of the driving electric fields, so that a transverse strain of 11% at 10 V/μm and a transverse stress of 16.5 kPa at 9 V/μm were obtained. These levels of strain and stress were respectively more than eight and four times higher than the corresponding values generated with the pure polymer matrix for analogous electrical stimuli. 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