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Electrical Insulation, IEEE Transactions on

Issue 4 • Date Dec. 1973

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Displaying Results 1 - 16 of 16
  • Table of contents

    Page(s): c1
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  • IEEE Electrical Insulation Group

    Page(s): c2
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  • Editorial

    Page(s): 117
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  • Fluctuations of DC Conduction in Mineral Oil under High Electrical Fields

    Page(s): 118 - 122
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    Pulses of conduction current in transformer oil under high electrical fields were studied by recording them on magnetic tapes and then subjecting them to pulse-height analysis. It was found that for the degassed oil, small-magnitude pulses increased, whereas large-magnitude ones decreased with the duration of the stress conditioning period. With air dissolved in the oil, pulses of all magnitudes decreased during stress conditioning. The electrode material affected the current pulses only at relatively low stresses. The pulses were found to be sensitive to hydrostatic pressure only for relatively large gaps at high applied fields. The results support the theory that a gaseous phase is involved at some stage in the breakdown process of liquids. View full abstract»

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  • DC Electric-Field Modifications Produced by Solid Insulators Bridging a Uniform-Field Vacuum Gap

    Page(s): 122 - 128
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    The results of measurements of the electric field near the surface of stainless-steel electrodes in vacuum are described. It is found that the field is modified by a solid insulator bridging the interelectrode gap. The extrapolated cathode field is enhanced sufficiently to equal the value considered necessary to initiate break-down in a plane vacuum gap. The measured fields are greater than the applied field and consistent with the accumulation of positive surface charge on the solid insulator. Analysis of the data suggests that the surface charge results from bombardment of the surface by electrons emitted at the insulator-cathode junction. View full abstract»

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  • Thermal Breakdown of Silicone Liquids under Pulsed High-Frequency Field

    Page(s): 128 - 133
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    The effects of the pulse duration of applied field and electrode geometry on the thermal-breakdown phenomenon have been studied by applying pulsed high-frequency field (1-10 MHz) with variable duration (10-1000, ¿s) to the silicone liquids immersed in the rod-plane electrodes (approximate uniform field) and the needle-plane electrodes (extreme nonuniform field), considering the temperature dependence of the electrical conductivity of silicone. It has been found that the thermal breakdown due to dielectric heating occurs when the field is applied for less than a millisecond. Thermal breakdown explains the experimental results in which the breakdown strength decreases in the rod-plane electrodes with increasing pulse duration and electrode separation, but is little influenced in the needle-plane electrodes by these same variables. View full abstract»

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  • The Resistivity of MgO Powder at Elevated Temperatures

    Page(s): 133 - 136
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    A simple apparatus is described for the measurement of resistivity of dielectric powders at elevated temperatures. MgO powder is tested in the range of temperatures from room temperature to 500°C. A large decrease of resistivity is observed at about 50°C, which is in contrast to a previously reported decrease of resistivity in single crystals of MgO at much lower temperatures. The iron content in the samples of typical purity is sufficient to cause a significant lowering of the activation energy for conduction in MgO, but it is not clear why the increased conduction occurs in a narrow range of temperatures. View full abstract»

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  • Influence of Field Nonuniformity on the Breakdown Characteristics of Suliur Hexafluoride

    Page(s): 136 - 142
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    A methodical variation of the radius of curvature of the electrode reveals interesting electrical breakdown properties of the sulfur hexafluoride (SF6) which may be useful to the designer of high-voltage apparatus. The pressure range under consideration was 1-5 kg/Cm2 absolute. The tests were performed under 60-Hz voltages. For a given electrode configuration and a specified operation voltage, there exists a region for the value of the radius of curvature within which flashover occurs. At high pressures this region may be restricted to a narrow zone of low values of the radius of curvature. Very sharp electrodes usually lie outside of this region. The field in the hemispherically capped rod-plane is analyzed by the finite-element method for values of d/r between 0.8-40. The critical field was found, at high pressures, to tend towards a constant value, which is that prevailing under uniform-field conditions irrespective of radius of curvature. View full abstract»

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  • Corona Inception and Electrical Breakdown in a Coaxial Cylindrical Geometry

    Page(s): 142 - 148
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    The corona inception and the sparking potentials of dry air are measured in the pressure range 25×10-3-760 torr using two separate coaxial electrode systems. The similarity theorem for the sparking potential is obeyed when the central electrode is made to have a positive-voltage polarity over the range 10-3 < pR1 < 0.3 torr m. For the negative polarity of the inner electrode, the similarity theorem is found not to hold. The measured coronainception potential is compared with the values obtained from the theories of Werner and Townsend. It is found that the Townsend theory for calculating the corona-inception potential gives better agreement with the experimental results, as it makes no restrictive assumptions concerning the discharge parameters. At a fixed gas pressure, the sparking potential for the positive wire is higher than that for the negative polarity of the same electrode in the range 100-375 torr. As the pressure is increased further, the positive breakdown potential decreases below the corresponding value for the negative breakdown. This phenomenon is shown to be due to the role of the negative-ion space charge which is present when the central electrode is made negative. View full abstract»

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  • Contributors

    Page(s): 149 - 150
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  • Author index

    Page(s): 150a - 150b
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  • Subject index

    Page(s): 150b - 150c
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  • A Look to Your Future IEEE Can Help You Stay Current Technically Through Groups and Societies

    Page(s): 150-d
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  • Membership application

    Page(s): 150-e
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  • Editorial policies and criteria

    Page(s): 150-f
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  • Information for authors

    Page(s): 150g
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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