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Electrical Insulation, IEEE Transactions on

Issue 6 • Date Dec. 1977

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Displaying Results 1 - 17 of 17
  • Table of contents

    Page(s): c1
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  • IEEE Electrical Insulation Group

    Page(s): c2
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  • A Study of Inception and Growth of Water Trees and Electrochemical Trees in Polyethylene and Cross Linked Polyethylene Insulations

    Page(s): 383 - 389
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    This paper presents an experimental investigation into the effect of different factors, such as contaminants, humidity content, temperature, field strength and frequency on water treeing in polyethylene (PE) and cross linked polyethylene (XLPE). For this investigation, model test specimens have been used to supplement cables for testing. Colored trees and their points of initiation have been analyzed for their content of impurity elements and always are found to contain sulfur and some metal. The results show that the relative humidity in the insulation must exceed approximately 70% to produce a significant number of water trees. The average size of the trees shows a very small dependence upon time and temperature and a slight decrease with increasing field strength. An increase in frequency from 50 to 5000 Hz approximately doubles the average size of the trees. The trees appear during the first 300 hours of voltage application, but since no growth rate can be observed at either frequency, it is not justified to establish a frequency acceleration factor in general. View full abstract»

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  • Insulating Characteristics of Dimethyl Silicone in Bare and Insulated Uniform Field Gaps

    Page(s): 389 - 394
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    Impulse and sixty-hertz breakdown tests were conducted on stationary and circulating 50 centistoke dimethyl silicone using bare and insulated uinform field elect-rodes. The electrode insulation materials used were polyamide paper, and Kraft paper thermally upgraded with dicyandiamide. The test results show that insulating the electrodes, significantly increases the sixty-hertz and impulse dielectric strengths of silicone. Under most conditions, the uniform field insulating characteristics of dimethyl silicone are comparable to those of conventional transformer oils; however, the bare electrode sixty-hertz strength of silicone is approximately 20% lower than that of transformer oil. View full abstract»

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  • About the Significance of Peroxide Decomposition Products in Xlpe Cable Insulations

    Page(s): 395 - 401
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    This investigation is concerned with voltage stabilizing effects of peroxide decomposition products, measured by electrical treeing resistance. Trees are filled with a liquid, consisting of decomposition products. These details and the relationship to the treeing phenomenon are described and explained. The treeing resistance efficiency of individual substances and their reliability over a prolonged period of time in EHV insulation is pointed out. View full abstract»

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  • Phenyl Methyl Silicone Fluid and Its Application to High-Voltage Stationary Apparatus

    Page(s): 402 - 410
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    Phenyl methyl silicone fluids of low phenyl radical concentrations and low viscosities are characterized by their extraordinary gasabsorbing property in high electric fields. Their physical, chemical and electrical properties were investigated and compared with those of dimethyl silicone fluids. The corona resistant characteristics and applied voltage vs. life expectancy relationships were studied, using model capacitors consisting of the silicone fluid and polypropylene film capacitor paper insulation system, and heatresistant transformer models consisting of the silicone fluid and Nomex Aramid paper. It was found that the phenyl methyl silicone fluids greatly improve the corona resistance property and the life expectancy in high voltage fields over the dimethyl silicone fluids, although both fluids are similar in their general characteristics. As a result, it is suggested that the phenyl methyl silicone fluids can be used to construct reliable high voltage stationary apparatus which is small in size. View full abstract»

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  • Growth of Water Trees in Polyethylene and Silicone Rubber by Water Electrodes

    Page(s): 411 - 416
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    In this paper, various experimental results are described of water trees obtained in polyethylene and silicone rubber, using the water electrode method. The mechanisms of initiation and growth of water trees are discussed. The growth of water trees depends upon the applied voltage, the frequency, and the water resistivity below 10 k¿·cm. No differences in the growth of water trees were found among NaCl, KC1 and BaC12 solutions having equal resistivity. It is concluded that Maxwell stress, exerted on polyethylene or silicone rubber by applying an alternating voltage, forms micro-cracks in the material. Water permeates into the polymer, because the dielectric constant of water is higher than that of polyethylene or silicone rubber. With a high electric field and a high frequency, vaporization of water due to dielectric heating may occur: vapors may permeate into the amorphous region, and micro-cracks are formed by the vapor pressure. View full abstract»

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  • The Deterioration and Breakdown of Solid Dielectrics by Internal Discharges at Cryogenic Temperatures

    Page(s): 417 - 423
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    An investigation of internal discharge phenomena in artificial air-filled cavities in impregnated-paper, polyethylene, and polypropylene over a temperature range from 90 to 343 K is described. The technique used for the detection and measurement of internal discharges has a high resolution and sensitivity, and incorporates a multi-channel, pulse-height analyzer. It has been demonstrated that when the temperature is lowered, the repetition rate and the magnitude of internal discharges under direct voltages are greatly reduced. In addition, considerable improvement in the electric strength of the insulation is obtained with alternating, surge and direct-voltages, and with voltages with polarity reversal. The improvement measured with direct voltages is particularly marked. Higher working stresses might therefore be used for the insulation of electrical apparatus operating at cryogenic temperatures. View full abstract»

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  • Schottky Injection Currents in Insulators: The Effect of Space Charge on the Time Dependence

    Page(s): 424 - 428
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    When a particle current is injected into an insulator, and the charge is trapped in the insulator, the field at the injecting electrode decays with time t. Consequently, both the particle current and the total current density j also decay. If the trapping is complete, the time dependence is hyperbolic, i.e. j ¿ (t + ¿)-1, where ¿ is a time constant. We show that this holds both when the traps are distributed in space, and also when the potential maximum of the Richardson-Schottky barrier lies within this space charge region. Therefore it is not possible to discriminate between the effect of spatially distributed traps and of an idealized thin sheet of traps. We suspect that this also holds even when the trapping is incomplete. View full abstract»

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  • Influence of Dielectric Stress Concentration on Voltage Endurance of Epoxy-Mica Generator Insulation

    Page(s): 428 - 434
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    The structure and shape of the coils in high-voltage apparatus have a pronounced effect upon their electrical life expectancy because of the dielectric stress concentration at the edges and corners of the conductors. In these regions, as a rpsult of the high dielectric stress, accelerated damage to the insulation can occur due to the partialtial discharges on the surfaces and in minute voids created during manufacture or in service. The extent of the influence of these increased stresses on the electrical life expectancy of several types of epoxy-mica insulation for large electrical machines was investigated. The partial discharges on surfaces and artificially-created voids were applied to a combination of mica splittings and mica paper with various backing fabrics and types of epoxy-resin bonding materials. The discharge intensity was amplified by means of sharp pin-electrodes and the resulting life-expectancy d, ata were compared with those obtained from tests on actual machine insulation. The test results on generator coil replicas insulated with epoxy-bonded mica splittings demonstrate that the electrical strength can be improved by means of favorable geometry of the coil cross section. A specially designed coil-edge contour is shown to assure a considerably longer life expectancy of this type of mica insulation for large turbogenerators. View full abstract»

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  • High Speed Laser Schlieren Studies of Electrical Breakdown in Liquid Hydrocarbons

    Page(s): 435 - 442
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    The events occurring just prior, during, and after electrical break-down in liquid hydrocarbons have been photographed using 15 ns laser pulses produced with a ruby laser, to illuminate the space between two parallel plate electrodes, and schlieren optics. In this manner it was possible to obtain experimental evidence of the density gradients produced by the movement of charge carriers during prebreakdown and the energy released during and after breakdown. Bysplitting the laser beam and delaying one half by 40 ns with respect to the other, the events occurring in the electrode gap could be studied as a function of time. Attempts to use the light emitted prior to breakdown as trigger signal for the laser were not successful. The initiation and propagation of breakdown are discussed in the light of the available photographic evidence. View full abstract»

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  • A Mass Spectrometric Study of Dielectric Breakdown

    Page(s): 442 - 445
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    The volatile degradation materials from a polyimide insulation on magnet wire was studied under thermal stress alone and in the presence of both thermal and electrical stress. Both types of experiments were carried out under vacuum with the apparatus connected directly to a mass spectrometer. The combination of thermal and electrical stress led to a different mass spectrometric pattern than that for thermal stress alone. The most marked difference was the sharp increase in water peaks. The possible interpretations are discussed. View full abstract»

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  • Editorial

    Page(s): 448
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  • Author index

    Page(s): 448a - 448b
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  • Subject index

    Page(s): 448c - 448e
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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