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Electrical Insulation, IEEE Transactions on

Issue 1 • Date Feb. 1982

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Displaying Results 1 - 19 of 19
  • Table of contents

    Page(s): c1
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  • IEEE Electrical Insulation Society

    Page(s): c2
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  • Flashover of a Liquid Conducting Film Part 1: Flashover Voltage

    Page(s): 10 - 14
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    We have studied the phenomenon of flashover in a configuration related to that of flashover of high voltage insulators under polluted conditions: a glow discharge is struck at the surface of a liquid, and if the applied voltage is above a critical value, flashover occurs. The flashover voltage Uc is dependent upon source capacity through two competing phenomena, the source voltage drop and liquid heating. The theoretical analysis shows the existence of a limiting value for Uc. The flashover voltage is also dependent upon the current constriction in the liquid at the liquid discharge interface and upon the influence of the liquid on discharge V(i) characteristic. Taking into account these parameters, a reasonable agreement is reached between experimental and theoretical results. View full abstract»

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  • Flashover of a Liquid Conducting Film Part 2: Time to Flashover - Mechanisms

    Page(s): 15 - 19
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    A dc glow discharge at atmospheric pressure is struck at the surface of a liquid. If this dc voltage exceeds a critical value, flashover occurs, resulting in a short circuit of the liquid. Curves of time to flashover as a function of applied voltage for different liquid resistivities are given. For low resistivities, the curves show a progressive decrease as voltage is raised. For higher resistivities a discontinuity is observed which results in a sudden l0x reduction in time to flashover for a given voltage value. We propose the existence of two different mechanisms governing flashover, corresponding to both parts of the curve. One of these mechanisms is identified as the action of an electrostatic force on the discharge. The second mechanism is probably a breakdown phenomenon. View full abstract»

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  • The Study of Apparent Negative Value in Measuring Dielectric Loss

    Page(s): 20 - 26
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    The measurement of the dielectric loss of insulating material or electrical apparatus with the Schering bridge at power frequency is one of the most fundamental dielectric tests for evaluating insulation behavior. It has been pointed out that a negative error or even an apparent negative reading of tan¿ may result if there is a tee network of interference present in the measuring circuit or within the test sample itself, but this problem has not yet been investigated fully. The purpose of our investigation is to find the origin of such phenomena. In this paper we discuss such phenomena occurring in three-terminal measurements of dielectric materials, and draw a conclusion that the negative error of tan¿ reading at power frequency is not due to the presence of resistance in the guard electrode circuit as conventionally supposed. We suggest a possible model of the tee network of interference present inside the sample itself and also point out the fact that another form of the tee network interference, the induction effect through electric field, may also cause a negative increment of the tan¿ reading. View full abstract»

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  • Natural Convection Cooling of an Electrical Conductor Wire

    Page(s): 27 - 33
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    The conductor wire connected to an electrical device generates and dissipates heat. For the successful design of the device, therefore, it is essential to analyze thermal response of the conductor wire in conjunction with the device. In this study, an approximate analytical method for the steady state wire temperature distribution is presented. Also, a finite difference solution for the transient behavior is given. For the steady state solution the conductor wire alone can be analyzed in a decoupled manner, but not for the transient case. The agreement between the steady solution and the transient solution at t=¿is excellent. View full abstract»

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  • The Determination of the Diffusion Rate of SF6 into Nitrogen

    Page(s): 34 - 38
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    Although gaseous mixtures of SF6 and N2 show particular dielectric characteristics, the diffusion process of SF6 into N2 has not been investigated in detail. This paper describes such an investigation using the variation in the sparkover voltage between spark gaps to determine the diffusion rate of SF6 into N2. It was found that the local sparkover voltage increases gradually with time when SF6 diffuses into N2 and this increase corresponds to an increase of the local SF6 content measured with a gas chromatograph. This diffusion process was also calculated using the binary gas-phase diffusion coefficient proposed by Fuller. This diffusion coefficient uses the hard sphere model. It was found that changes in the calculated local SF6 content is nearly equal to the measured local SF6 gas content for low SF6 concentrations. View full abstract»

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  • Pressure Dependence of DC Breakdown of Contaminated Insulators

    Page(s): 39 - 45
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    The effect of pressure on dc breakdown voltage of contaminated porcelain insulators and glass models was investigated in the range of 13 to 100 kPa. The study revealed that flashover voltage decreases nonlinearly with lowering of pressure. Arc characteristics under different pressure conditions were studied and the theoretical basis of low pressure flashover is discussed. View full abstract»

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  • Partial Discharges in Cavities in Insulation Impregnated with Supercritical Helium

    Page(s): 46 - 52
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    Apparatus has been designed and constructed to evaluate the high voltage parameters of assemblies of flat discs of insulation incorporating artificial voids or cavities impregnated with supercritical helium for pressures up to 1.5 MPa (15 bar) and for temperatures down to 4.2 K. The materials studied are possible insulations for a superconducting cable and are high density polyethylene and Valeron(R) (cross laminated polyethylene film). These were selected on previously published parameters related to mechanical properties, lappability, and low loss (tan¿< 2 × 10-5). Polyethylene terephthalate also was investigated because its permittivity is higher than that of polyethylene. The variation of inception stress (1 pC and 5 pC) with helium density for various pressures is obtained for circular and square section cavities and the relevance of the results to the design of insulation for a superconducting cable is discussed. View full abstract»

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  • Thermal Endurance Data for Solid Insulating Materials

    Page(s): 53 - 63
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    The Arrhenius plotting procedure has been used as the base for extensive international standardization of the International Electrotechnical Commission (IEC) Publication #216. Thermal endurance data for approximately 50 insulating materials, tested and evaluated according to IEC #216 have been made available from Swiss and German laboratories. The data have been collected and used for the determination of the ¿Thermal Endurance Profiles¿ (TEP) which are in addition to the ¿Temperature Indices¿ (TI), a fairly new format in IEC-Publication 216, for describing the life time-temperature relation. These TEP's have been achieved by testing the thermal capability with different criteria and different endpoints. Additionally, the regression coefficient representing the slope of the Arrhenius curve respectively (the activation energy of the Arrhenius equation), has been recorded in the form of a doubling (or halving) endurance temperature interval. The reported data are discussed in respect to: the reproducibility of the test procedures; the feasibility of certain instructions; the lack of equivalence of TEP results when different criteria and/or different endpoints were selected; the importance of presenting the slope of the Arrhenius plot; and the problem of identifying accurately the insulating materials. The complexity of material reactions on thermal stresses and consequently the variety of verified thermal endurance predictions has to be recognized. Such considerations lead to the conclusion that single-point representation of thermal endurance should be avoided. View full abstract»

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  • Frequency Acceleration Characteristics in Internal Discharge Endurance Tests by a Glass-Covered Electrode System

    Page(s): 64 - 69
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    Discharge endurance life tests were conducted at frequencies from 50 Hz to 5 kHz using a partially ventilated void with a glass barrier on one side and the plaque of the insulating material on the other. This system produces reproducible results, and, with certain reservations, the number of cycles of voltage to failure is seen to be constant. That is, frequency acceleration can be used. The upper frequency limit depends on the material and the oxygen content of the discharge space. Materials which strongly absorb oxygen have low upper frequency limits. Temperature rise due to discharge had negligible effect on lifetime at frequencies below the upper limit. Despite the insensitivity of lifetime (in cycles to failure) to frequency, tests of luminosity of the discharge, of visual observation of degradation patterns, and of discharge magnitude indicate that frequency effects are present. View full abstract»

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  • Calculation of Sparking Potentials of SF6 and SF6-GAS Mixtures in Uniform and Non-Uniform Electric Fields

    Page(s): 70 - 75
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    A simple formula is developed to predict the sparking potentials of SF6 and SF6-gas mixture in uniform and non-uniform fields. The formula has been shown to be valid over a very wide range from 1 to 1800 kPa·cm of pressure and electrode gap separation for mixtures containing 5 to 100% SF6. The calculated values are found to be in good agreement with the previously reported measurements in the literature. The formula should aid design engineers in estimating electrode-spacings and clearances in power apparatus and systems. View full abstract»

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  • Communication Some Observations on Tree Patterns in Pmma Under Alternating Voltages

    Page(s): 76 - 80
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    Observations of the development of electrical trees in polymethy-lmethacrylate (PMMA) using a single needle plane ground electrode system and 50 Hz voltages are reported for both voidless samples and samples having an artificial void. The temporal changes in the tree pattern from branch-like to bush- or fan-like observed in the voidless specimens are intimately associated with the occurrence of localized cracks. No change in pattern and no cracks occur in samples with an artificial void. The results support the theory that a gaseous discharge occurs in the various hollow channels of the branch-like tree pattern. View full abstract»

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  • Meetings

    Page(s): 88
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  • IEEE Electrical Insulation Society

    Page(s): 88-a
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  • Information for authors

    Page(s): 88b
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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