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Electrical Insulation, IEEE Transactions on

Issue 1 • Date Feb 1991

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Displaying Results 1 - 16 of 16
  • Influence of insulation morphology, impurities and oxidation on some electric properties of cables

    Page(s): 140 - 145
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    It is shown that the AC breakdown strength and dielectric loss of unaged and field-aged transmission and distribution cables vary with insulation crystallinity, contamination, and oxidation. It is also shown that the influence of these parameters is particularly important near the conductor shield and varies with aging. The influence of curing on cable properties is briefly discussed. The sample preparation, crystallinity, impurity, oxidation, AC breakdown, and dielectric loss measurements are described View full abstract»

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  • Effect of electrode shape on particle-initiated breakdown in SF6 gas under DC voltage

    Page(s): 156 - 170
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    Three methods are presented for improving the particle-initiated breakdown voltage of a spacer in sulfur hexafluoride (SF6) gas: the metal insert, recessed electrode, and shield ring methods. To find the basic method for improving the withstand voltage of the spacer, electrode shapes are changed and electric field calculations on these shapes are performed by using a cylindrical spacer. The distribution of charge accumulation on its surface was observed using the dust figure technique. The effect of electrode shape on the flashover voltage when a metallic particle is located on the spacer in SF6 gas under DC voltage was investigated. Experimental investigations show that the change of electrode shape leads to improvement of breakdown voltages by 30.9% in the metal insert method, 33.8% in the recessed electrode method, but very little in shield ring method View full abstract»

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  • An approximate calculation of the permittivity of aerogels as fractal-like objects

    Page(s): 53 - 56
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    An approximate calculation of the permittivity of a physical fractal (like aerogel of silica, which has a porosity of up to 99%) is performed, based on a self-similar model suggested by the Sierpinski gasket construction. It is shown that in some cases the polarizability of the units forming the homogeneous macrostructure tends to have a mathematical fractal behavior. The Sierpinski gasket and the first and succeeding stages of the model are described View full abstract»

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  • The hydrostatic piezoelectric coefficient of PVDF/PMMA blends

    Page(s): 78 - 84
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    The piezoelectric coefficients of polyvinylidenefluoride (PVDF) are known to be strictly dependent on the strength of the applied load. For hydrostatic piezoelectricity, it is shown that this nonlinearity is mainly due to the pressure dependence of the bulk compressibility and that blending with polymethyl methacrylate (PMMA) causes a change of sign of the intrinsic electric moment contribution to the overall piezoelectricity. PMMA molecules deteriorate the orientation correlation between the PVDF electric moments in the interface between the amorphous and crystalline phases, and this activity is enhanced by compression. The theoretical background of piezoelectric coefficients is reviewed, and the sample materials, high-pressure investigations, and X-ray and infrared measurements are discussed View full abstract»

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  • The electrically ruptured area of crosslinked polyethylene

    Page(s): 171 - 177
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    The electrically ruptured areas of failed crosslinked polyethylenes have been investigated using optical microscopy and Fourier transform infrared spectroscopy (FTIR). The formation of well-defined banded spherulites was observed around the ruptured areas. Since spherulites do not occur in crosslinked polyethylenes, the formation of spherulites in failed specimens is considered to be related to breakage of the network during the breakdown process. FTIR results are shown to support this suggestion, revealing that more than oxidation occurred during the breakdown process. This observation contradicts some well-established breakdown mechanisms, such as thermal breakdown. It is also shown that, if the initiation of electrical breakdown involves network rupture, the properties of crosslinked polyethylene could be enhanced by designing less reactive crosslink points View full abstract»

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  • Mechanism of charge storage in electron-beam or corona-charged silicon-dioxide electrets

    Page(s): 42 - 48
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    Thermally-stimulated-discharge (TSD) measurements performed to investigate the electret charges on 1-μm-thick, wet-grown SiO2 are discussed. Charge decay curves at room temperature for a time period of more than three years are given. Influences of charging methods and substrate doping on charge stability are also discussed. Measurements of charge decay in short- and open-circuit TSD experiments show interesting phenomena that are interpreted, including discharge current peaks at temperatures >250°C that were found in positively charged samples. An unexpected current reversal was observed in these experiments, and an explanation for this reversal is given. The generation by irradiation of traps in the bulk of SiO2 with an electron beam is described. The Sessler method is used to calculate the traps' mean-spatial depths View full abstract»

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  • Determination of space charge distributions in polyethylene samples submitted to 120 kV DC voltage

    Page(s): 57 - 62
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    The measurements of charge distribution evolutions in polyethylene samples subjected to an applied voltage of ⩽120 kV are discussed. To apply significant voltage gradients to plates or cables having an insulator thicknesses ranging from 5 to 10 mm, the large applied voltage was necessary. The possibilities offered by this equipment are illustrated by results obtained with 6-mm-thick plates. A comparison of the behaviors of 2-mm-thick plates and 6 mm thick plates made of the same materials and submitted to the same field is presented. The results indicate that increasing the thickness of the insulator does not increase the charge densities which develop under the applied field and that the observed space charge is localized at the vicinity of the electrodes, in a region extending over 0.7 mm, in which the diffusion of impurities from the semiconducting electrodes is very important View full abstract»

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  • Laser-intensity modulation method (LIMM)-an analytical and numerical modification

    Page(s): 63 - 68
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    An analytical method that has been used with the laser intensity modulation technique for the determination of polarization and space-charge distributions in electrically stressed low-density polyethylene is described. A numerical method and data analysis are presented. In the analysis, a specific model of spatial distributions of space charge and polarization has been assumed that appears to provide reasonable agreement between the experimentally observed and the expected results View full abstract»

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  • Electron emission from electron-irradiated dielectrics

    Page(s): 18 - 25
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    Two methods for the measurement of the electron emission currents and the secondary electron yields for electron-irradiated dielectrics are discussed. Experimental results indicate that the dynamic measurement method for the secondary emission yield δ provides yield curves that are significantly lower than those obtained by conventional methods, at least in the region in which δ goes through a maximum. This effect is believed to be due to a recombination between the electrons undergoing emission and the positive surface charges which the dielectric acquires during the continuous irradiation to which it is exposed in the dynamic method. A modified method that replaces the continuous radiation by pulse radiation and eliminates the formation of charges on the dielectric is described. It is shown that, at beam energies well beyond the energy Em of the maximum yield, both methods give similar results. The pulse method was used to determine the yield curves of a variety of polymers and to confirm that these curves can be represented in the form of a universal curve when δ/δm is plotted against E/Em. It was found that the positive and negative charges generated on the dielectric by the electron irradiation remain surface charges and do not drift into the bulk of the material View full abstract»

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  • Biographies of contributors to the early investigation of electrical phenomena

    Page(s): 85 - 130
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    The biographies of William Gilbert, Otto von Guericke, Stephen Gray, Francis Hauksbee, John Theophilus Desaguliers, Willem Jacob 's-Gravesande, Petrus van Musschenbroek, Christian August Hausen, Charles-Francois de Cisternay Dufay, Jean-Antoine Nollet, Ewald Georg von Kleist, Johann Heinrich Winckler, Benjamin Franklin, Leonhard Euler, Robert Symmer, Rudjer J. Boskovic, William Watson, Giambatista Beccaria, John Canton, Franz Ulrich Theodosius Aepinus, Henry Cavendish, Johan Carl Wilcke, Joseph Priestley, Charles-Augustin Coulomb, Georg Christoph Lichtenberg, Alessandro Giuseppe Antonio Anastasio Volta, Pierre-Simon Laplace, and Tiberius Cavallo are presented View full abstract»

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  • Pulse withstand capability of self-healing metalized polypropylene capacitors in power applications

    Page(s): 146 - 155
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    Experiments performed on the end-edge contacts of polypropylene capacitors to determine whether the thermal effect is the main cause of their degradation are described. Current pulses with different wave-shapes but with the same value of the Joule integral were applied to the contacts, and the degradation levels were ascertained by measuring the tan δ variation, since degradation of the contacts results in an increase of the equivalent series resistance of the capacitor. The results obtained show only a partial dependence of the degradation level on thermal stress, revealing a contribution from the electrical and mechanical stresses View full abstract»

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  • Correlation between thermal expansion and Seebeck coefficient in polycrystalline Co3O4

    Page(s): 49 - 52
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    Characteristics of the cobalt-oxide spinel Co3O4 are described. Spinel is the name for a certain crystal structure that is built up out of three sublattices; one sublattice contains, in this case, only oxygen ions, and the other two sublattices, tetrahedral and octahedral, contain the metal cobalt (Co). Co3O4 is shown to exhibit an abnormally high thermal expansion above 750 K. This expansion is explained by an electronic transition of the nonmagnetic smaller trivalent Co ion to the magnetic larger trivalent Co ion. Seebeck effect measurements reveal that the number of charge-carriers also changes with temperature, which is explained by a charge-disproportionation reaction on octahedral sites. Both electronic processes are linked by the decrease of the bandgap, which is drastically reduced by the high expansion View full abstract»

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  • Constant-current corona charging of Teflon PFA

    Page(s): 35 - 41
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    Experiments in which 25-μm-thick films of tetrafluoroethylene-per-fluoromethoxyethylene copolymer (Teflon PFA) were charged positively and negatively with a constant-current corona at different temperatures and subsequently discharged are discussed. The time behaviors of surface potential, total current, and conduction current during constant-current and constant-voltage charging are compared. The mean charge depth is found to increase with negative constant-current and constant-voltage charging at elevated temperatures. It is shown that, compared with constant-voltage charging, constant-current charging leads to a more prominent mean-charge-depth shift towards the back electrode and to an improved charge stability in Teflon PFA, since a large amount of the deeper bulk traps is being filled View full abstract»

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  • Polarization dynamics of VDF-TrFE copolymers

    Page(s): 69 - 77
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    The polymer polyvinylidenefluoride (PVDF) and its copolymers with trifluoroethylene (TrFE) exhibit a strong piezoelectric effect after poling in high electric fields (100 MV/m). HV impulses of definite duration have been applied to the polymer in order to study the dynamics of the poling process. The dielectric displacement during the HV impulse was recorded. After the impulse, the remanent polarization under short-circuit conditions was also measured. It was thus possible to obtain the minimum poling time dependent on the applied field strength necessary to stabilize the remanent polarization. Comparing the time development of the dielectric displacement with the corresponding remanent polarization revealed a time delay between the orientation of the dipoles and their stabilization. It is concluded that the process of orientation of the dipoles itself is not sufficient to lead to a remanent polarization and that an additional interaction between the trapped charges and the oriented dipoles can explain the stability of the remanent polarization and the observed time delay View full abstract»

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  • Models for the decay of radiation-induced conduction

    Page(s): 26 - 34
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    The diffusion-limited recombination and tunneling-controlled recombination theories that account for the decay of insulator conductivity following irradiation are described. The diffusion-controlled recombination with a Coulomb or other long-ranged interaction shows a time-dependent reaction rate, but does not agree with experimental results. The tunneling model with first-order kinetics does agree with experimental results. A comparison of the two models and the experimental data obtained for the radiation-induced conductivity of a polyethylene sheet are presented View full abstract»

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  • A critical evaluation of analytical. techniques for the characterization of extruded dielectric cables

    Page(s): 131 - 139
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    Various analytical techniques used to characterize cables are reviewed. It is shown that cable morphology can be evaluated simply by density and differential-scanning-calorimetry (DSC) measurements and that oxidation is best evaluated by Fourier-transform-infrared (FTIR) spectroscopy. Elemental contamination is best evaluated by neutron activation analysis and proton-induced X-ray emission (PIXE) measurements, whereas ions can be detected by ionic chromatography. It is shown that the water content of cables can be reliably measured by commercial instruments relying on coulometry and Karl-Fischer titration View full abstract»

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Aims & Scope

This Transactions ceased production in 1993. The current retitled publication is  IEEE Transactions on Dielectrics and Electrical Insulation.

Full Aims & Scope