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Electrical Insulation, IEEE Transactions on

Issue 4 • Date Aug. 1987

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Displaying Results 1 - 25 of 34
  • Table of contents

    Publication Year: 1987 , Page(s): c1
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    Freely Available from IEEE
  • IEEE Dielectrics and Electrical Insulation Society

    Publication Year: 1987 , Page(s): c2
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  • A Model for the Current-Voltage Chatacteristics of a Dielectric between Spherical Electrodes

    Publication Year: 1987 , Page(s): 353 - 356
    Cited by:  Papers (4)
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    Current-voltage characteristics and electric field strength distributions are investigated for a dielectric containing thermally generated, low mobility carriers. Spherical electrode geometry is used (as a reasonable approximattion to the more practical point-plane systems) with carrier emission from the electrode of smaller radius. Under some conditions, the injected charge may reduce the maximum field strength (for a given voltage) by almost an order of magnitude; additionally, the maximum field strength occurs at some distance from the smaller electrode. Fast electrons undergoing collision ionization within the dielectric would then cause maximum energy deposition at some point between the two electrodes rather than immediately adjacent to one electrode. View full abstract»

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  • Charging and Discharging of Non-Ideal Capacitors

    Publication Year: 1987 , Page(s): 357 - 359
    Cited by:  Papers (1)  |  Patents (4)
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    Analytical expressions are given, it is believed for the first time, for the Laplace transforms of the time-dependent currents and voltages associated with step-function charging and discharging of lossy, i.e. dispersive capacitors through a series impedance. The capacitors are described by their characteristic response functions f(t) in the time domain. The expressions obtained provide the basis for carrying out inverse transformations into the time domain, which in general have to be obtained numerically, although analytical solutions are given for some limiting cases. View full abstract»

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  • Energy Losses in Charging and Discharging of Capacitors

    Publication Year: 1987 , Page(s): 361 - 364
    Cited by:  Papers (2)
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    Analytical expressions are derived for the energy loss incurred in charging and discharging of lossy, i.e. dispersive capacitors under nearly step-function voltage, such as might be expected in the presence of a finite series resistance and with step-function rise and fall of the voltage. It is shown that the energy loss in the process of charging and discharging may amount to a large fraction of the total stored energy in the capacitor and this may give rise to a significant amount of heating. A physically realistic characteristic function is assumed for the capacitor, corresponding to a frequency-independent pendent loss over a large range of frequencies, such as might be obtained in many low-loss materials. View full abstract»

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  • The Influence of Cure Method on the Sol Content and Physical Structure of Crosslinked Polyethylene Insulation

    Publication Year: 1987 , Page(s): 365 - 372
    Cited by:  Papers (2)
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    A series of transmission cables insulated with crosslinked polyethylene have been studied. The cables were cured using a variety of heat transfer methods, but were all based on the same resin system. Insulation cured with steam or dry gas gave approximately constant sol fractions across the wall thickness. Cables cured using an experimental heat transfer method gave rise to a sol fraction which increased across the wall thickness as the conductor was approached. Correlations exist between sol fraction, swelling ratio, and melting data. It is suggested that a simple melting curve determination can be used to estimate both sol fraction and crosslink density for low density polyethylenes crosslinked using dicumyl peroxide. View full abstract»

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  • A Study of the Behavior of a Uniaxially Oriented Polyethymene Tape/Oil Insulating System Subjected to Electrical and Thermal Stresses

    Publication Year: 1987 , Page(s): 373 - 382
    Cited by:  Papers (3)
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    The occurrence of discharges in an insulation system consisting of lapped uniaxially oriented polyethylene tapes impregnated with dodecylbenzene oil and the behavior of air bubbles injected into the structure have been investigated. This insulation system should be suitable for use in power transmission cables because the tape is generally compatible with the oil and has suitable mechanical properties for cable manufacture in a conventional cable taping machine. The behavior of bubbles in the systems was monitored with a transparent electrode and a video system. An electronic protection system was used to remove the applied voltage just before breakdown so that the damage done by discharges to the tape structure could be measured. The discharge inception voltage was found to decrease with increasing butt gap depth and with increasing temperature. Bubbles were found to divide repeatedly and eventually to disperse at stresses above discharge inception. The rate of dispersal increased with increasing applied stress and temperature. Examination of the damage done to tapes showed a high level of correlation between the total energy of discharges in the insulation structure and the total surface area of visible damage. Measurement of the total discharge energy appears to be a promising diagnostic tool. View full abstract»

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  • Impregnant-Polypropylene Interactions in the All-Film Capacitor Configuration

    Publication Year: 1987 , Page(s): 383 - 388
    Cited by:  Papers (8)
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    Having reviewed the main parameters which control the swelling of polypropylene (PP) film, the authors describe three different approaches for its quantification in the situation of a real capacitor. The first method consists in following the height increase of a stack of flat all-film capacitor windings at different temperatures. The behavior of a large variety of fluids has been studied, allowing an easy ranking of the swelling ability of these different fluids. The influence of the nature of the film in connection with the temperature has also been determined. The second method is even more representative of the capacitor configuration since in this case the geometry of the winding was not permitted to change. In this method the internal pressure within the winding stack was recorded, the variation being the result of the swelling of the film. Large differences of behavior were pointed out. Various PP films showed different abilities to flow under the effect of the pressure induced by the swelling itself. In the third method, the capacitance variations were determined. The mathematical treatment of these variations displayed the different steps of the film swelling, each one having a well defined speed. From these different approaches of the swelling evaluation, some interesting conclusions were drawn indicating the leading role played by the nature of the film in the film-liquid association. View full abstract»

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  • A Stusy of the Dielectric and Mechanical Property Interactions of Glass-Cloth/Epoxy Composites

    Publication Year: 1987 , Page(s): 389 - 395
    Cited by:  Papers (3)
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    Some dielectric properties of a commercially produced epoxy resin reinforced by two layers of glass cloth are investigated as a function of mechanical stress in order to study the basic dielectric characteristics of composite insulating materials. Because of voids and delaminations, the dielectric strength of the composites are noticeably affected by applied mechanical stresses. It is also shown that for equal levels of tensile stress, the extent of changes in dielectric strength depends on the orientation of the glass yarns with respect to the axis of the applied forces. View full abstract»

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  • Electric Strength of Small Insulating Distances

    Publication Year: 1987 , Page(s): 397 - 404
    Cited by:  Papers (4)
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    The capabilities of modern materials and new technologies allow significant size reductions to be achieved particularly in the field of low-voltage equipment. The limits encountered are often due not so much to technical or physical factors, but to widely varying safety requirements determined in many cases by earlier technological capabilities and the limits and specifications based thereon. This paper reports further results obtained from an extensive research project. Exposure of a large number of test specimens to various environmental conditions has proved conclusively that spacings on the surfaces of insulating materials are affected only if contamination is significant. Under heavy contamination these so-called creepage distances form tracks leading sooner or later to failure. Comparatively clean creepage distances however are not affected by tracking and should therefore only be dimensioned on the basis of their short-term electric strength. The results of this extensive series of tests are a statistically verified basis for the dimensioning of rather clean, small creepage distances (>10 mm). They can be incorporated directly into the relevant standards. Other results from the research project will be reported on conclusion of current investigations. However, it is expected that this work will not be completed before 1988. View full abstract»

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  • Oxidation and Water Tree Formation in Service-Aged XLPE Cable Insulation

    Publication Year: 1987 , Page(s): 405 - 412
    Cited by:  Papers (45)
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    The insulation from six 5 kV power cables, which has been in service underground for 6 to 8 years, was examined by infrared (IR) spectroscopy and oxidation induction time (OIT) analysis. Sections of insulation containing water trees were found to contain high levels of ionic contaminants. All insulation samples showed evidence of oxidative degradation in service and frequently there was a higher than average level of oxidation in the treed regions of the insulation. Sections of the insulation containing water trees had appreciably shorter OIT's than untreed regions, indicating that they were more prone to subsequent oxidative degradation. A model for water tree formation and electrical breakdown of the insulation is described where oxidative degradation during prolonged service reduces the ability of the insulation to withstand stress concentrations at defects, and water trees are initiated. Some localized oxidation may accompany the tree propagation step. Extensive localized oxidation then takes place in the treed regions, catalyzed by ionic contaminants, and insulation failure occurs. View full abstract»

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  • Determination of the Zero-Field Position in an Insulating Film by Thermally Stimulated Surface Potential Measurement in the Presence of a Temperature Gradient

    Publication Year: 1987 , Page(s): 413 - 417
    Cited by:  Papers (1)
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    A new technique for measuring the zero-field position in an insulating film is proposed. The technique consists of thermally stimulated surface potential measurement in the presence of a constant temperature gradient (TG-TSSP measurement) and it does not depend on sample thickness. Using a low-density polyethylene (LDPE) film having thickness d= 0.3 mm, the zero-field position vs. collecting voltage characteristic was measured and the electric field in the sample was determined. View full abstract»

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  • Analysis of Space Charge in Insulating Materials under Non-Uniform Electric Fields

    Publication Year: 1987 , Page(s): 419 - 424
    Cited by:  Papers (6)
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    A simple technique to calculate the charges induced on electrodes by space charges distributed in a dielectric is presented. The technique is based on Green's theorem and does not depend on the type of electrode system. A needle-plane electrode system is analyzed and the charges induced on each electrode are calculated. Experimental results of thermally stimulated current measurements usinig a needle-plane electrode system have been analyzed and the mean location of trapped charge has been determined. View full abstract»

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  • Determination of the Polarity of Carrier Traps in Gammairradiated Polyethylene by Thermally Stimulated Current Measurements Using a Temperature Gradient

    Publication Year: 1987 , Page(s): 425 - 429
    Cited by:  Papers (4)
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    The thermally stimulated current measurement using a temperature gradient has been applied to the determination of the polarity of carrier traps in ¿-irradiated low density polyethylene films. A method for determining the polarity of carrier traps has been analyzed theoretically and it was found experimentally that carrier traps in the films were electron traps. Further, we found that there was no space charge field in the films. View full abstract»

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  • Spacer Involvement in Conducting-Particle-Initiated Breakdown in Compressed Gas Insulated Systems

    Publication Year: 1987 , Page(s): 431 - 438
    Cited by:  Papers (7)
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    This paper describes the results of an investigation into conducting particle initiated breakdown in a 76/250 mm coaxial electrode configuration, representative of a 145 kV gas insulated transmission line (GITL) or gas insulated substation. A free moving particle is known to initiate breakdown through a sequential two-stage process. The involvement of an epoxy disk spacer in such a breakdown, when the particle is at a distance from the spacer, is studied through specially designed experiments. For 6.4 mm long, 0.45 mm diameter aluminum particles it is observed that the discharge path may involve the spacer surface even when the particle is several centimeters away from the spacer surface. However, the 60 Hz ac breakdown voltages for discharge paths involving the spacer surface are not significantly different from those without spacer involvement, if the particle-to-spacer distance is greater than 3 mm. View full abstract»

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  • Performance Improvement of Insulators in a Gas-Insulated System

    Publication Year: 1987 , Page(s): 439 - 446
    Cited by:  Papers (3)
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    The solid-electrode-gas interface has a critical influence on the withstand voltage of the insulating gap. The geometrical shape of the insulator plays a major factor in the enhancement of the electric field and therefore determines the withstand voltage capability of the dielectric. A concave shaped insulator, suitable for GIS, has been examined theoretically to determine the best contact angle between the dielectric and the conductor to yield an improved withstand voltage. An experimental verification has been conducted by extensive measurements of the surface flashover in sulphur hexafluoride and in nitrogen. It is found that the withstand voltage capability can be increased by up to 20%, at high gas pressure, compared to a rectangular cylindrical insulator post. View full abstract»

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  • Degradation Due to Wet Hydrogen Firing on the High-Voltage Performance of Alumina Insulators in Vacuum Applications

    Publication Year: 1987 , Page(s): 447 - 452
    Cited by:  Papers (6)
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    The HV characteristics of plain and doped alumina ceramics fired under air and air plus wet hydrogen conditions were tested in a uniform field vacuum gap using dc excitation. Wet hydrogen firing of doped alumina ceramics considerably degraded voltage hold-off as compared to air firing. Baking hydrogen-fired samples in vacuum did not improve their performance and the V-I curves remained unaltered. Gap currents measured for plain and doped air-fired samples were essentially the same (~1 to 10 nA), however, for wet hydrogen-fired samples the currents were much higher for doped than for undoped alumina samples. In general, the non-resistive current component obtained from the V-I curves was found to follow the Fowler-Nordheim equation only in the high-field region (> 60 kV/cm) for air-fired alumina samples. Processing the wet-hydrogen-fired samples by subsequent firing in an atmosphere of dry hydrogen revived the voltage hold-off of the doped alumina ceramics; the currents being comparable to that of wet-hydrogen-fired samples in the low voltage range (< 50 kV). View full abstract»

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  • Prebreakdown Cathode Processes in Liquid Hydrocarbons

    Publication Year: 1987 , Page(s): 453 - 458
    Cited by:  Papers (21)
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    Measurements are presented of the initiation of prebreakdown streamers at a point cathode in liquid hydrocarbons. Using a computer implementation of the method of images, the electric field is computed for selected geometries to confirm that the field strengths in the vicinity of these streamers are probably high enough so that electron multiplication processes can occur. High magnification photographs of streamer initiation show that the initial streamer velocity is (2.8±0.4) x 104 cm/s in toluene. View full abstract»

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  • Temperature Dependence of Ion Injection by Metallic Electrodes into Non-Polar Dielectric Liquids

    Publication Year: 1987 , Page(s): 459 - 465
    Cited by:  Papers (4)
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    This study deals with the influence of temperature on the electrical conduction of solutions of electrolytes in n-decane. The temperature dependence of the ion mobility deduced from transit time measurements is due to the viscosity variation. The activation energy for the ion creation is rather well foreseen from the Fuoss model of dissociation of ion-pairs and from the assumption that the distance between ions in an ion-pair decreases with temperature. From the injection current density, we deduce that the charge density qA at the distance xA of closest approach from the metal follows the relation qA/qo= exp[ eo/16¿¿xLKT] whatever the liquid conductivity (a= 2Kqo) and the temperature, and is entirely determined by the interactions of an ion with its image. This observation, in agreement with our previous ones, supports the assumption of a charge-transfer step involving only the electrolyte. View full abstract»

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  • Internal Field-Assisted Thermal Ionization

    Publication Year: 1987 , Page(s): 467 - 472
    Cited by:  Papers (1)
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    The bulk-limited electronic transport due to field-assisted thermal ionization of coulomb trapping centers is considered, taking into account the internal electric field contribution. Previous theories of the effect are presented and compared with the present model which is in agreement with the experimental electrical current characteristics obtained over a wide range of temperature and applied field in several differently doped CdF2 crystals and in SiO films. Possible origins of the internal electric field are discussed and a theoretical evaluation based on the electron-phonon interaction is given. View full abstract»

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  • Pre-Breakdown Currents Due to Filamentary Thermal Breakdown in Polyimide Films

    Publication Year: 1987 , Page(s): 473 - 477
    Cited by:  Papers (9)
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    Pre-breakdown currents in polyimide (PI) films were measured under the application of dc ramp voltage (30 V/s) and the breakdown mechanism is discussed on the basis of the results. A steep current increase was observed from about 10-3 before the breakdown and was ascribed to a thermal runway which results in a filamentary thermal breakdown path. An analytical solution of the pre-breakdown current was obtained on the basis of this filamentary thermal breakdown with a constant filamentary path; it deviated from the experimental data, suggesting a decrease in the effective radius of the filamentary path with time. A numerical calculation of the pre-breakdown current has been carried out for the filamentary thermal breakdown with a temperature distribution in the filament. The calculated pre-breakdown current agrees well with experimental results, and the effective radius of the filament also decreases as observed. From these results, we conclude that filamentary thermal breakdown occurs in PI at high temperatures. View full abstract»

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  • Impulse Voltage Breakdown Characteristics of Teranry Gas Mixtures in A Coaxial Cylinder Gap

    Publication Year: 1987 , Page(s): 479 - 484
    Cited by:  Papers (1)
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    Impulse breakdown characteristics for ternary gas mixtures were studied using a coaxial cylinder geometry. The experimental mental pressure ranged from 100 to 600 kPa. The mixtures comprised SF6 with an additive C-C4F8 and various proportions of "buffer" gases including N2, C02, CO, and dry air. For 50% flashover voltages, mixtures containing CO exhibited highest dielectric strength for pressures up to 500 kPa. The studies also showed that for a coaxial cylinder geometry the breakdown strength is not affected significantly by increasing the amount of the additive gas C-C4F8 but is determined by the total percentage of the electronegative gas component. View full abstract»

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  • Cable Life Expectancy Calculation - A Practical Approach

    Publication Year: 1987 , Page(s): 485 - 487
    Cited by:  Papers (2)
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    Cable life expectancy calculations can yield much better results if based on actual, rather than rated or extreme, load and environmental conditions. Activation energy at 60% retained relative elongation and realistically assessed service conditions should, in most cases, result in a 40-year life with sufficient built-in safety margin. A sample calculation with fluctuating current load and temperature is presented. View full abstract»

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  • Partial Discharge Characteristics in Barium Titanate Multi-Layered Structures: Effect of Material and Structural Parameters

    Publication Year: 1987 , Page(s): 489 - 495
    Cited by:  Papers (2)
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    The partial discharge characteristics of barium titanate multi-layer ceramic capacitors were investigated under 60 Hz voltage excitation. For capacitor specimens which were specifically fabricated for this study, the partial discharge characteristics were found to depend strongly on such para, meters as dielectric film thickness, relative permittivity, porosity and void size distribution. View full abstract»

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  • An Electric Stress-Pulse Technique for The Measurement of Charges in A Plastic Plate Irradiated by an Electron Beam

    Publication Year: 1987 , Page(s): 497 - 501
    Cited by:  Papers (40)
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    The distribution profile and quantity of charges in insulators have been studied by various methods, some of them utilizing thermal, mechanical, and electrical stimulations. A new method, incorporating pulse electric stimulations and pulse acoustic detection, is reported here along with preliminary results of the measurement of the amount and approximate distribution profile of charges in electron-beam irradiated polymethyl methacrylate (PMMA) samples. The amount and the mean penetration depth of charges in the sample are obtained from the height of the first acoustic signals produced in response to a HV impulse applied to the sample. A 5 mm thick PMMA plate irradiated with a 1 MeV electrons at 0.5 to 3.0 Mrad was found to trap charges of approximately -0.3 ¿C/cm2 at a mean depth of about 2 mm. 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