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Electrical Insulation, IEEE Transactions on

Issue 2 • Date April 1986

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Displaying Results 1 - 25 of 26
  • Table of contents

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

    Page(s): c2
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  • Sensitive Detection of By-Products Formed in Electrically Discharged Sulfur Hexafluoride

    Page(s): 105 - 110
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    A new method, based on fluoride ion exhcange reactions, for detecting many of the by-products of electrically discharged SF6 is described. The technique employs an ion-molecule reaction cell and a mass spectrometer capable of detecting negative ions from a high pressure gas (up to P=100 kPa). Because of the high rate constants (k> 10-10 cm3 s-1) for processes of the type SF6- + X ---> XF-~ + SF5, where X is a molecule having a high fluoride ion affinity such as SOF4, SiF4, SF4, WF6, etc., concentrations below 1 ppb (part per billion) of selected by-products are detectable. Results are shown for a sparked sample of SF6, analyzed by this technique, and they are compared with the standard positive ion-electron impact mass spectral analyses. Increased detection sensitivity via the addition of specific materials, to SF6 gas insulated high voltage equipment, to enhance the production of certain by-products is discussed also. View full abstract»

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  • Neutral Decomposition Products in Spark Breakdown of SF6

    Page(s): 111 - 120
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    The formation of decomposition by-products produced by electrical spark discharges in SF6 has been investigated by quadrupole mass spectrometry. The by-product SF4 was found to be a precursor to many of the long-lived decomposition by-products identified (SOF2, HF, SO2, and SiF4). The amount of SF4 formed was measured by "in situ" detection, utilizing a "threshold" technique for monitoring the SF4 ion (SF+3) in an SF6 background. The rate constant for the hydrolysis of SF4 was measured (at 350 K) and found to be ~2×10-19 cm3s-1. In addition to moisture, the effects of SiO2 and electrode material have been briefly examined. Quantification of the amounts of long-lived by-products of spark discharge in SF6 yielded the following ranking: SOF2 > SOF4 > SiF4 > S02F2 > SO2. The energy and pressure dependences in the ranges of 0.5 to 14.5 J/spark and 40 to 233 kPa respectively, of the amounts of the various by - products were examined. View full abstract»

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  • A Model for High Field Conduction in a Dielectric

    Page(s): 121 - 127
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    Simple models of a solid dielectric are set up for calculating current-voltage characteristics. For ideal trap-free dielectrics the characteristics for an electrode with a given injection function are compared with those for ohmic electrodes. Approximate power laws are shown to be valid for a set of assumed material parameters. View full abstract»

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  • Effects of Short-Time, High-Current Faults on Aged, Insulated Wire

    Page(s): 129 - 132
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    Several previous studies of short-time, highcurrent faults on electrical distribution conductors have been made by the author. These studies are meant to simulate conditions where wire, properly protected by circuit breakers or fuses, suffers bolted short circuits. As usual in performance tests, unaged wire was used. The present study was initiated to determine how the damage done to wire insulation varies with age of the wire. The results how that the ability to resist damage by bolted short circuit is enhanced by the aging of the wire. This improvement continues until cracks form which partially penetrate the insulation. View full abstract»

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  • The Analysis of Insulation Breakdown Probabilities by the Up-And-Down Method

    Page(s): 133 - 136
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    This paper discusses the assessment of breakdown probability by means of the up-and-down method. The Dixon and Mood approximation to the maximum-likelihood estimate is compared with the exact maximum-likelihood estimate for a number of response patterns. Estimates of the 50D probability breakdown voltage and the scale parameter of the breakdown probability function are considered, and the estimation bias is investigated. View full abstract»

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  • Morphology and Electrical Properties of Biaxially-oriented Polypropylene Films

    Page(s): 137 - 144
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    BO-PP films have fairly different morphologies to those of non-oriented PP films. These morphological differences were found to originate from the orientation of the crystalline and amorphous phases. The orientation of the amorphous phase causes a pronounced decrease observed both in ionic conduction and in dielectric loss. Two types of BO-PP films were found to have fairly different morphologies: the tubular type seems to exhibit a network structure made of oriented crystalline zones which are linked with slightly entangled amorphous chains, while the tenter type shows a spherulite-deformed structure made of a highly oriented cyrstalline phase connected with elongated and highly oriented amorphous chains. Despite their dissimilar structures, the two BO-PP films studies were found to have generally the same dielectric behavior except for the activation energy of the conduction and the dielectric relaxation processes. View full abstract»

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  • Charging of Insulators in a surface Discharge Switch

    Page(s): 145 - 150
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    Surface discharge switches, which have exceptionally low inductance, are of interest for fast switching of electrical energy. This paper describes experimental data on the residual electric field and spatial charge distribution measurements on three insulators, namely, G-10, Delrin, and Lucite used in a surface discharge switch. The insulators were subjected to different numbers of shots in the switch and the measurements were carried out after the applied field was turned off. The G-10 samples exhibit positive charging with 1/e decay times ranging from 3.8 to 7.4 h, and show a great deal of structure in the charge distribution patterns. Delrin specimens exhibit negative charging with considerably longer decay times than those of G-10, and the charge patterns are not well defined. Lucite, on the other hand, shows quite different results, i. e. no detectable charge decay after fifteen hours and no definite charge patterns. The results are qualitatively discussed and are related to the resistivity of the dielectricts and the switch operating characteristics. View full abstract»

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  • Volt-Time Characteristics in Air, SF6/AIR Mixture and w2 for Coaxial Cylinder and Rod-sphere Gaps

    Page(s): 151 - 155
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    This paper reports volt-time characteristics of air and air mixture with 1% SF6 additive for a 1.25 5.2 cm coaxial-cylinder gap. The surge voltages used included waveshapes of 0. 260 Ps, 1.25660 ps impulse voltages as well as 1511200 ps, 275/2500 , us switching surge voltages. The experimental pressure ranged from 100 to 500 kPa (absolute) Additional tests were conducted using rod-shpere gaps in dry air and nitrogen. For steep-fronted impulses the breakdown values decreased with increasing the rate of rise of voltage. The effect depended upon the polarity of the voltage, the pressure, and the nature of the gas. View full abstract»

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  • Breakdown in Compressed HE/SF6 Gas Mixtures in Uniform Field

    Page(s): 157 - 160
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    The breakdown strengths in uniform field were calculated for helium/SF6 mixtures at pressures up to 300 kPa for smooth electrodes, and compared with measured values. The effect on discharge thresholds in He/SF6 mixtures due to the polarity of an artificial protrusion and due to irradiation of the gap was investigated. The results obtained from this study show that the calculation of the breakdown levels in He/SF6 mixtures from the pure gases has not given satisfactory agreement with measured values. An empirical equation which expresses the limiting value of Ep (E= electric field, p=pressure) for the mixtures was derived as a function of the ratio of the partial pressures of He and SF6. View full abstract»

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  • An Automatic Device for the Measurement of the Growth of Water Trees

    Page(s): 161 - 164
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    An automatic device for the measurement of the growth of water trees as a function of time is described. The system is based on video camera signal processing of the images of water trees through a microscope. Water trees are grown in laboratory specimens using the water needle method. At regular intervals, specimens under test are successively placed under the microscope and any change in light transmission along the axis of the water tree is detected and stored in a memory device. Several examples of results obtained with the device are presented. Due to its high sensitivity it allows new observations such as, for example, residual growth of water trees after the voltage switched off. The device allows study of the growth mechanisms of water trees as well as comparisons of the resistance of translucent materials to water treeing. View full abstract»

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  • Design of Field-Controlled Multi-Layer Insulation System

    Page(s): 165 - 174
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    A novel method is proposed and validated experimentally to increase the breakdown voltage of an insulating system for applications in the electrical insulation of large power equipment. The method relies on controlling the electric field within a multilayer insulation system. The insulation system is constructed from n layers of insulation and m very thin conducting strips placed between successive insulating layers. The conducting strip at each layer is symmetrically shifted by a constant distance determined from a shifting factor which is calculated to maximize the withstand voltage of the insulation. The potential distribution within the composite insulation is determined from the solution of the Laplace equation for different design parameters, and it is shown that the field can be reduced for a proper choice of the dimensions of the system. A composite insulation system based on the proposed method has been fabricated and tested for ac (60 Hz) and impulse voltages. Substantial improvements in the withstand voltage are obtained over an identically sized system without the conducting strips, thus validating the analysis presented in this paper. View full abstract»

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  • A Comparative Study of Polymer Insulating Materials Undern Salt-Fog Conditions

    Page(s): 175 - 182
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    This paper describes the performance of the widely used polymeric insulating materials for outdoor insulation - high temperature vulcanized (HTV) silicone rubber, ethylene-propylene rubber (EPR) and epoxy resins with a commonly used inorganic filler, alumina trihydrate, under salt-fog conditions. The role of the filler and the effect of the filler concentration in imparting track resistance to the materials is investigated. Various methods to describe the surface aging of polymer materials such as the peak and the average of the leakage current, the cumulative charge, the weight loss and the flashover voltage have been investigated. The results show that at moderate concentrations of filler, 105 to 130 parts per hundred (pph) of polymer, there is little difference in the performance of silicone rubber and EPR materials. At low concentrations of filler (30 pph), the EPR samples track whereas the silicone rubber samples erode. The epoxy materials exhibit inferior properties when compared to silicone rubber and EPR. The results also indicate that monitoring the weight loss, the reduction of the flashover voltage, and the peak of the leakage current are better methods to characterize aging of insulators than the average of the leakage current or the cumulative charge. View full abstract»

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  • A FIlter for Optimal Temporal Resolution in Partial Discharge Measurements

    Page(s): 183 - 188
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    In partial discharge measuring instruments, a band-pass filter is always incorporated for noise reduction. Both narrow-band and wide-band filters may be used. Narrowband filters usually give a better output signal-to-noise ratio, but the output pulse width is greater so that a rapid sequence of input pulses may appear as overlapped and distorted waveforms at the output, making it impossible to resolve the individual pulses. The temporal resolution of the measurement system is thus degraded. For broad-band filters, the temporal resolution is better, but the output SNR is worse. Hence there is a trade off between SNR and temporal resolution. In this paper, the problem of optimizing the temporal resolution in the presence of noise is analyzed and a Wiener filter is proposed as the solution. Methods to implement the filter are given and results of computer evaluation studies are presented. View full abstract»

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  • Improvement of Flashover Strength and Reduction of Surface Charge-induced Field Enhancement of Insulating Material

    Page(s): 189 - 195
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    ac surface flashover voltage in air (ACFOV) and the effect of surfactant-painting are studied with several polymeric tubular insulators which have a back-side (inner) electrode. The insulating materials used are Nylon-6 (NY), Polymethyl - methacrylate (PMMA), Polyvinylchloride (PVC), Polypropylene (PP), Polyethylene (PE), and Polytetrafluoroethylene (PTFE). The surfactant used is alkyl-benzenesulfonate. ACFOV chareristics for non-painted specimens can be classified into two types according to the insulating material used: With PTFE, PE, and PP specimens (A-type), the diagram of the relation between ACFOV and electrode distance does not have an extremely saturated curve and a definite minimum; these are characteristics of the B-type specimens: PVC, PMMA, and NY. ACFOV of the A-type is higher than that of the B-type. When the surfactant is painted on the B-type, ACFOV increases, and the ACFOV characteristics are similar to those of the non-painted A-type: The extreme saturation and the definite minimum cannot be seen. With the painted A-type, ACFOV and the characteristics are similar to those of the original non-painted. These experimental results can be explained by the condition of the electric field enhancement due to the accumulated surface charge. View full abstract»

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  • Corona Current and Field Profile Underneath Vertical Bipolar HVDC Lines with Bundle Conductors

    Page(s): 197 - 204
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    For the cases of monopolar and horizontal bipolar coronas, the corona equations are solved for vertical bipolar geometry without restrictions with regard to the number of subconductors. The variation of ion mobility with lifetime, as well as the change of corona onset voltage from point to point around each subconductor, are taken into account. The lateral distribution of the field intensity and current density calculated and compared with those measured experimentally. These profiles also are compared with those for a horizontal bipolar test line. The effect of applied voltage, number of subconductors and the surface factor is studied. View full abstract»

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  • Numerical Method to Calculate Corona Profiles at Ground level and underneath Monopolar Lines as Influenced by wind

    Page(s): 205 - 211
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    In this paper, the monopolar corona equations are solved numerically in flowing air for HVDC transmission lines with bundle conductors. The lateral distributions of the corona current density and field intensity over the ground surface and underneath monopolar HVDC models are calculated and compared with those measured experimentally. View full abstract»

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  • Analysis of Electric Stress Distribution in Cavities embedded within Dielectric Structures

    Page(s): 213 - 219
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    Electric stress distribution within dielectric cavities are studied using the finite-element numerical technique. The results indicate that the electric stress is enhanced within a gas-filled cavity embedded in the dielectric. The amount of stress enchancement and the electric field distribution within the dielectric are significantly influenced by the dielectric permittivity, the dimensions of the cavity, the number of cavities in series within the dielectric gap, the cavity orientation, the dielectric thickness (electrode spacing), the contour of the edge of the electrodes, and the presence of floating electrodes near electrode edges. The effect of various parameters on the stress distribution within a dielectric is important in the design, fabrication, and testing of devices made of multi-layered dielectric/electrode film structures. View full abstract»

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  • Niew Apparatus for Detecting Transformer Faults

    Page(s): 221 - 229
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    A diagnostic apparatus for detecting gases dissolved in transformer oil is described, in which a tetrafluoroethylene-perfluoroalkylvinylether copolymer membrane is used to separate H2 CO, CH4, C2H2, C2H4, and C2H6 from the oil. These gases are detected with a new gas detector, which consists of a catalytic gas sensor and a gas chromatograph using air as the carrier gas. Using the gas concentration, the apparatus automatically determines whether a transformer is operating normally or not and, in the latter case, what kind of fault may have occurred. By the above diagnostic apparatus, a transformer could be diagnosed simply and inexpensively. This apparatus should prove useful for identifying what kind of fault may have occurred. View full abstract»

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  • Meetings

    Page(s): 230 - 238
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    Freely Available from IEEE
  • Optical Electric Field Assessment in a Dielectric Liquid

    Page(s): 231 - 232
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    A new experimental method is described in which the electrostrictive effect in a liquid is made visible. A real-time interferometer employing a Q-switched ruby laser was used to record transient optical disturbances. When a pulse voltage, synchronized with the laser pulse, was applied to the test object, interference fringes were produced in the viewing plane that could be recorded on photographic film. Experimental results are presented, together with a model for interpretation. View full abstract»

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  • Influence of Water and Silanol Contents on Some Electrical Properties of Silicone Oil

    Page(s): 233 - 237
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    The precise measurement of water in silicone oils is difficult owing to the reaction of water with siloxane to give silanols. In this paper we report kinetic and equilibrium measurements of the water and silanol content in 50 cSt silicone oils from different manufacturers. Using various techniques, we show that the water content in silicone oil varies linearly with relative humidity. The silanol content was deduced and is never less than 80 to 150 ppm in dry oil; it increases nonlinearly with RH. The influence of water and silanols on several electrical properties of silicone oil is also discussed. View full abstract»

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  • IEEE Dielectrics and Electrical Insulation Society

    Page(s): 240-a
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    Freely Available from IEEE

Aims & Scope

This Transactions ceased production in 1993. The current retitled publication is  IEEE Transactions on Dielectrics and Electrical Insulation.

Full Aims & Scope