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Dielectrics and Electrical Insulation, IEEE Transactions on

Issue 3 • Date Jun 2004

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Displaying Results 1 - 20 of 20
  • Relation between space charge accumulation and partial discharge activity in enameled wires under PWM-like voltage waveforms

    Page(s): 393 - 405
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    It has been observed that voltage waveforms generated by power electronic converters may affect significantly the reliability of electric motor insulation. Since partial discharges are considered to be the main cause of the reliability loss, new enamel insulations for magnet wires are being developed in order to withstand better stress amplification. The electrical characterization of these insulating materials is often carried out through aging tests which may provide estimation of life under different stress levels and conditions. However, deeper investigation of aging phenomena due to supply voltage waveforms is needed, especially regarding the relation between aging factors and stress conditions. This paper deals with this topic, showing experimental evidences of relation between partial discharge quantities (e.g., inception voltage, repetition frequency, amplitude) and electrical properties, associated with charge accumulation, which can be directly evaluated through space charge measurements. Characterization of insulating materials and comparison of materials candidate for application in power electronic waveform environment can be carried out resorting to the methodology proposed here. This approach can provide, therefore, a useful feedback to wire manufacturers regarding, e.g., the choice of additive nature and enamel components for magnet wires in power-electronic controlled motors. View full abstract»

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  • Numerical simulations and experimental study of frequency-dependent dielectric properties of composite material with stochastic structure

    Page(s): 379 - 392
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    Results of a computer modeling and analytical estimations of frequency-dependent dielectric properties of a composite material with stochastic structure in the frequency range from 1 mHz to 1 kHz are presented and are compared with experimentally obtained parameters. The studied composite was a mixture of materials having considerably different properties, where the inclusion phase with the volume fraction of 0.31 was distributed randomly in the host material forming a complex three-dimensional structure. For such composite dielectric, the applicability of bounds on the effective complex permittivity and different known mixing formulas for estimating of the effective parameters is examined. The numerical simulations performed using measured frequency-dependent characteristics of the constituents and the reconstructed three-dimensional stochastic structure of the composite, yielded values of the effective dielectric permittivity which were in good agreement with the measured ones. Frequency variations of the computed distributions of the microscale electric field and energy losses in the bulk of the studied composite dielectric are presented and discussed. View full abstract»

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  • Can water cause brittle fracture failures of composite non-ceramic insulators in the absence of electric fields?

    Page(s): 523 - 533
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    It was postulated by J. Montesinos et al. (see ibid., vol.9, p.236-43, 2002), based on experimental evidence, that brittle fracture failures of composite (non-ceramic) HV insulators could be caused by water and mechanical stresses. It was also claimed therein that the brittle fracture process was more likely to happen with water than acids. This postulation could be of major importance as its ramifications might affect the entire composite insulator technology and, in particular, the usage of glass fiber polymer matrix composites in HV applications. Such an important statement should not be left without an independent verification. Therefore, attempts have been made in this research to initiate this process in unidirectional E-glass/modified polyester and E-glass/vinyl ester composites, used in non-ceramic insulators, by subjecting them to water under four-point bending conditions. This was done to independently verify the main conclusion of J. Montesinos et al. that water may be more damaging to unidirectional E-glass/polymer composites than acids. It has been clearly shown in this work that water, in the absence of electrical field, cannot cause stress corrosion cracking of unidirectional E-glass/polymer composites and thus brittle fracture of composite non-ceramic insulators. Thus the main results of J. Montesinos et al. could not be independently reproduced. View full abstract»

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  • Dielectric and viscoelastic properties of cross-linked polyethylene aged under multistressing conditions

    Page(s): 406 - 417
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    Different measurements were performed in cross-linked polyethylene (XLPE) employed as insulating material in coaxial cables that were field-aged and laboratory-aged under multistressing conditions at room temperature. Samples were peeled from the XLPE cable insulation in three different positions: just below the external semiconductor layer (outer layer), in the middle (middle layer) and just above the internal semiconductor layer of the cable (inner layer). The imaginary part of the electric susceptibility showed three peaks that obey the Dissado-Hill model. For laboratory-aged XLPE samples peeled from the inner and from the middle positions the peak at very low frequency region increased while in samples from the outer position a quasi-DC conduction process was observed. In medium frequency range a broadening of the peak was observed for all samples. Viscoelastic properties determined through dynamic mechanical analysis suggested that the aging generates processes that promoted changes of the crystallinity and the cross-linking degrees of the polymer. Fourier transform infrared spectroscopy (FTIR) measurements revealed an increase of oxidation products (esters), evidence of polar residues of the bow-tie tree and the presence of cross-linking by-products (acetophenone). Optical and scanning electronic microscope (SEM) measurements in aged samples revealed the existence of voids and bow-tie trees that were formed during aging in the middle region of the cable. View full abstract»

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  • Correlation of damage, dry band arcing energy, and temperature in inclined plane testing of silicone rubber for outdoor insulation

    Page(s): 424 - 432
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    Silicone rubber samples, filled with 30% alumina trihydrate, subjected to the ASTM inclined plane test, show good correlation between the measured harmonic power components of dry band arcing and the surface temperature recorded with a thermovision camera. The simultaneous study of the low frequency fast Fourier transform and variations in temperature shows that when the temperature rises above 100°C there is a well defined increase in the low frequency harmonic components of the measured power; however, this trend is not verified by the fundamental component. The eroded mass of the samples is measured independently by a laser approach and a model to rank the tested samples using the inclined plane test is developed. The model is validated by applying it to both the recorded harmonic power components and temperature, resulting in the correct ranking of damage on the samples tested in the inclined plane test. View full abstract»

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  • More accurate breakdown voltage estimation for the new step-up test method in the Weibull model

    Page(s): 418 - 423
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    The estimation problems for the conventional step-up method (the observed breakdown voltages are not given at all) and the new step-up method (some of the observed breakdown voltages are given) are analyzed when the underlying probability distribution is assumed to be a Weibull model. This paper is a consecutive research of the case that the underlying probability distribution is assumed to be a normal model. Similarly to the normal model, the new step-up test method, in the Weibull model, also has advantages compared to the conventional method: (1) the confidence intervals of the estimates become smaller and (2) the estimates can be obtained with higher probability. The bias observed when sample size is small can be reduced by using the bootstrap method. View full abstract»

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  • Atmospheric pressure of nitrogen plasmas in a ferroelectric packed-bed barrier discharge reactor. Part II. Spectroscopic measurements of excited nitrogen molecule density and its vibrational temperature

    Page(s): 491 - 497
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    For pt.I see ibid.(vol.11 no.3 p.481-90, 2004). In order to validate a nonthermal plasma model using nitrogen in a ferroelectric packed-bed reactor, the number density of the excited nitrogen molecules has been investigated by spectroscopic measurements. Experiments were conducted at applied voltages from 0 to 20 kV, 60 Hz and gas flow rates from 1 to 5 L/min in pure nitrogen gas. The results show that the number density for excited N2 molecules increases with increasing applied voltage and dielectric constant and agrees qualitatively with the numerical modeling results at lower applied voltage. The vibrational temperature of the C3Πu (v') state of N2 has been calculated from the light intensity emitted by the 2nd positive band. The vibrational temperature decreases with increasing gas flow rate and no significant effects of the applied voltage and dielectric constant were observed. View full abstract»

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  • Nanosecond streak photography of discharge initiation on ice surfaces

    Page(s): 450 - 460
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    This paper presents an exploratory experimental study of discharge initiation on surface of ice. The phenomena underlying these processes are, as yet, poorly understood. To elucidate the initiation process in particular, ultra high-speed streak photography was used to observe and analyze the first visible discharges and a number of parameters were investigated. It could be shown that ambient temperature, conductivity of ice surface and the presence of imperfections on the ice surface influence not only the critical voltage for discharge initiation, but also the velocity of discharge development. Some parameters could be identified, which should be investigated further. The present paper is the first stage of a long-term research effort in this new field. This study should enable further experimental investigations and mathematical simulations to gain better understanding of ice surface discharges, specifically in the context of electrical insulation integrity of support insulators in power systems operating under severe atmospheric conditions. View full abstract»

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  • Water diffusion into and electrical testing of composite insulator GRP rods

    Page(s): 506 - 522
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    This paper describes water diffusion into and electrical testing of unidirectional glass reinforced polymer (GRP) composite rods used as load bearing components in high voltage composite (non-ceramic) insulators. The tests were performed following ANSI standard C29.11 Section 7.4.2 that can be used to evaluate electrical properties of composites. The unidirectional composite rod materials based on either E-glass or ECR-glass fibers with modified polyester, epoxy and vinyl ester resins were investigated. Two types of ECR-glass fibers were considered, namely high and low seed (voids). The effects of composite surface sandblasting, mechanical pre-loading and nitric acid exposure on the electrical properties of the composites were studied. In addition to the required data of the ANSI standard, the specimen mass gain was also measured after boiling for 100 h. Most importantly, there was no correlation found between the mass gain and the leakage current for different composites. The materials with high seed ECR-glass fibers had much higher leakage currents and they absorbed less moisture than the composites based on either the low seed ECR-glass fibers or E-glass fibers. It was shown in this work that different types of sandblasting, as well as mechanical preloading with and without acid exposure had a negligible effect on the leakage currents and water mass gain of the composite specimens. View full abstract»

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  • Application of wavelet analysis to acoustic emission pulses generated by partial discharges

    Page(s): 433 - 449
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    The subject matter of this paper refers to the improvement of the acoustic emission (AE) method when used for detection, measurement and location of partial discharges (PDs) in oil insulation systems of power appliances. The detailed subject matter refers to the issues connected with the application of modern methods of digital processing of signals obtained during technical high-power measurements. The paper presents the results of measurements and analyses of the AE pulses generated in setups making the modeling of basic PD forms that can occur in oil insulations possible. The research concentrated mainly on the following types of PDs: point-plane, multipoint-plane, multipoint-plane with a layer of pressboard, surface, generated in gas bubbles and on the indeterminate-potential particles moving in oil. In each case, the acoustic pulses generated by PDs in both positive and negative half times of the voltage supplying the spark gaps under study were analyzed. The AE pulses measured were subject to the wavelet analysis. For each of the PD forms the continuous wavelet transform (CWT) was determined and the corresponding time-frequency distributions were drawn. Moreover, for the AE pulses generated by PDs of the surface and multipoint-plane types, the discrete wavelet transform (DWT) was calculated, the runs of the particular details for six frequency levels and the approximation run were presented. In reference to the DWT analysis for the particular details, the probability density functions (PDF) and the autocorrelation functions (ACF) were determined at the particular levels of decomposition. Also columnar diagrams showing the energy value that is transferred at the particular levels of decomposition were presented. Moreover, the energy density spectrum runs determined through a FFT were presented for comparison. The Morlet wavelet was used to determine the CWT, and the symlet wavelet was used to calculate the DWT. Next, the distributions obtained for the particular PD forms underwent a comparative analysis taking into account the voltage polarization. It was observed that different frequency structures occur for the particular PD forms. Also, a different time of coherent structure duration for the particular PD forms was observed. View full abstract»

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  • A displaced dipole model for a two-cylinder system

    Page(s): 542 - 550
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    In this paper, a displaced dipole model for two infinitely long dielectric cylinders in an applied uniform field is proposed. The displaced dipole moment and its displacement can be approximately obtained from the applied field values at the two poles of a cylinder. The electric potential distributions near the surface of cylinder calculated using the displaced dipole method are compared with those obtained with the finite-element method. The electric field distributions around the surfaces of cylinder calculated using the displaced dipole method are compared with those obtained with the finite-element method and the dipole-at-the-center approximation. The displaced dipole method is a good approximation, especially in the area between two cylinders when the displacement is less than 0.2 R. View full abstract»

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  • Measurement technique for high frequency characterization of semiconducting materials in extruded cables

    Page(s): 471 - 480
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    Knowledge on the dependence of wave propagation characteristics on material properties and cable design is important in establishing diagnostic methods for cable insulation. In this study, a high frequency measurement technique to characterize the semi-conducting screens in medium voltage cross-linked polyethylene (XLPE) cables has been developed. The frequency ranges from 30 kHz to 500 MHz. The influence of the experimental set-up, sample preparation methods, pressure and temperature are investigated. A dielectric function is developed for the semiconducting screens and this is incorporated into a high frequency model for the cable. The propagation characteristics obtained from the high frequency cable model are compared with those obtained from measurements made on the same cables. View full abstract»

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  • Correlation between dielectric properties and sintering temperatures of polycrystalline CaCu3Ti4O12

    Page(s): 534 - 541
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    Dielectric properties of polycrystalline CaCu3Ti4O12 (CCTO) pellets sintered in the temperature range 1000-1200°C were evaluated with impedance spectroscopy at frequency range of 102 to 107 Hz from 90 K to 294 K. A correlation has been established between the pair values of low frequency limit dielectric constant and the total resistivity and the sintering temperature. For example, the sample sintered at 1100°C demonstrates higher value of low frequency limit dielectric constant and lower value of total resistivity, while the sample sintered at 1000°C demonstrates lower values of low frequency limit dielectric constant and higher value of total resistivity. This correlation has been successfully explained by relating with the difference in grain size and grain volume resistivities of these two polycrystalline CCTO samples. Further, it is suggested that donor doping of oxygen vacancies Vo' and Vo" may be the reason to cause the difference in the grain volume resistivities of these two samples. View full abstract»

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  • Atmospheric pressure of nitrogen plasmas in a ferroelectric packed bed barrier discharge reactor. Part I. Modeling

    Page(s): 481 - 490
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    Numerical modelling of ferroelectric packed bed nonthermal plasma reactor has been conducted to predict plasma parameters in a pure nitrogen environment. Simplified time averaged one-dimensional physical model based on Poisson's equation for electric field and transport equation for electrons was developed. The mean electron energy was obtained by a swarm relationship from calculated electric field profiles and plasma neutral conditions. For chemical model, N+, N2+, N3+, N4+, N*, N2* and electron were considered where N* and N2* are the total excited atoms and molecules, respectively. The results show that all the plasma parameters increase with increasing applied AC voltage and pellet dielectric constant. The numerical results also show that the dominant ion is N4+ and the metastable molecule density is much higher than radical and the electron densities at atmospheric gas pressure. View full abstract»

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  • Optical investigation of AC preflashover of alumina ceramic in vacuum

    Page(s): 498 - 505
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    Optical phenomena accompanying the preflashover along a planar metal-alumina-metal structure were investigated under stepped AC voltage in vacuum. Two kinds of electrode contacts with and without sputtered gold films were employed. For sputtered alumina, the luminescence became observable at ∼1 kVpeak, and revealed two stages depending on the amplitude of applied voltage. For non-sputtered alumina the optical emission appeared at a much higher voltage and presented irregular and discrete light pulses. The energy band at the metal-alumina interface for the two kinds of electrode contacts is responsible for the relevant optical mechanisms. For non-sputtered contact, the light emission was initiated by field electron emission from the triple junction. While for the sputtered contact, prior to the electron emission, electrons/holes could be injected from electrodes into the surface layer of alumina and electroluminescence phenomena occur due to the radiative electron-hole recombination. Injected electrons form a long-term negative space charge region away from each electrode and hence at a critical applied voltage, the trapped electrons are detrapped resulting in intense light emission. These processes play a significant role in the development of flashover. View full abstract»

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  • Extraction of high frequency power cable characteristics from S-parameter measurements

    Page(s): 461 - 470
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    A technique is developed for extraction of the wave propagation properties of power cables from S-parameter measurements. The method extracts the complex propagation constant and the characteristic impedance, as well as the LCRG telegrapher's equation parameters. The extraction process is developed after clarifying the effect of the connection between the measurement port and the power cable. It is concluded that treating the connection solely as a characteristic impedance change could lead to considerable errors in the parameter extraction. Furthermore, the method corrects for electrical lengths, which are not accounted for by the standard network analyzer calibration. The extraction is demonstrated for a medium voltage cross linked polyethylene (XLPE) cable over the frequency range 300 kHz to 300 MHz. The results are compared to a time domain short pulse propagation method for cable characterization. Both measurement methods are evaluated against a cable model. View full abstract»

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  • IEEE Transactions on Dielectrics and Electrical Insulation - Table of contents

    Page(s): 01
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  • IEEE Dielectrics and Electrical Insulation Society

    Page(s): 2
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  • IEEE Dielectrics and Electrical Insulation Society

    Page(s): 03
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  • IEEE Transactions on Dielectrics and Electrical Insulation

    Page(s): 04
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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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