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Electrical Insulation, IEEE Transactions on

Issue 6 • Date Dec. 1988

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Displaying Results 1 - 20 of 20
  • Continuum properties from interdigital electrode dielectrometry

    Page(s): 897 - 917
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    Using a modal approach, a model is derived that makes the interdigital electrode microdielectrometer developed by S. D. Senturia et al. (J. Adhesion, vol.15, p.69-90, 1982) applicable to measuring continuum parameters in a wide range of heterogeneous media. In this so-called imposed omega -k technique, the medium is excited at the temporal (angular) frequency omega by means of an interdigital electrode structure having a spatial periodicity length lambda =2 pi /k and hence a dominant wavenumber k. Given the surface capacitance density C( omega , k) of any linear system having property gradients perpendicular to the plane of the electrodes, the model predicts the complex gain, taking into account the properties, geometry, and terminal configuration of the interdigital electrode structure. This capability can then be used with an appropriate parameter estimation strategy to determine the continuum properties and/or geometry of the medium. Examples illustrating the application of the technique are presented.<> View full abstract»

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  • A numerical method for the determination of first-order kinetics relaxation time spectra

    Page(s): 919 - 927
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    A numerical method is developed for computing relaxation-time spectra from time-domain measurements. The method starts with an assumed spectrum. This spectrum is altered and adjusted by comparing the data calculated from the assumed spectrum with the measured data. The approach is essentially an inverse Laplace transformation for the measured data. The method is suitable for broad spectra as well as for narrow relaxation-time spectra. Measurements performed on polyimide and aluminium oxide illustrate the capabilities of the method. The stability against noise in the data is investigated, and a smoothing procedure is described.<> View full abstract»

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  • Analysis of electronic conduction pulses produced in liquid ionization chambers by high-energy radiation

    Page(s): 937 - 940
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    The electron pulse shape produced by the passage of an ionizing particle through a liquid-filled ionization chamber is analyzed theoretically. In addition, the authors discuss the effect of an electric field on the observed pulse height Q/sub e/(t/sub d/), where t/sub d/ is the electron drift time. The analysis of the pulse shape yields information on the type of particle and on the purity of the liquid. For reliable operation, a condition of the liquid characterized by tau >>t/sub d/ (where tau is the electron lifetime) has to be achieved. A plot of the pulse peak height as a function of the electric field strength for cosmic ray particles can be used to deduce the electron lifetime.<> View full abstract»

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  • Streamer generation and propagation in transformer oil under AC divergent field conditions

    Page(s): 941 - 954
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    Prebreakdown phenomena in transformer oil are studied under AC voltage in different field configurations, ranging from very divergent point-plane geometry to quasi-uniform fields produced by rods or spheres. A detailed study of phenomena in both polarities is presented, and the minimum conditions required for streamer breakdown voltage measurements under AC are established. In negative polarity, the generation of a microscopic gas bubble ( approximately 10 mu m in diameter) immediately precedes the development of streamers. In the case of bushlike streamers, it is concluded from energetic considerations that the vaporization of the liquid constitutes the main process of streamer growth. In positive polarity, similar conclusions are drawn for slow bushlike streamers, whereas in the case of fast filamentary streamers, it is observed that the conductivity of filaments determines their propagation.<> View full abstract»

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  • Behavior of streamers in liquids under step voltages in point-plane geometry

    Page(s): 955 - 959
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    An attempt to identify gases generated during the propagation phase of streamers and to measure their volume is presented. The method used consists of producing a large number of streamers (thousands) in liquids (a blend of mono- and dibenzyltoluene, and phenylxylylethane) previously saturated with nitrogen and measuring the total electric charge, from which the mean energy of a streamer can be evaluated. The liquid samples are analyzed afterward by chromatography. This analysis shows the presence of decomposition products such as H/sub 2/, CH/sub 4/. C/sub 2/H/sub 2/, C/sub 2/H/sub 4/, and C/sub 2/H/sub 6/. The different mechanisms that could be involved in the prebreakdown phase are discussed. It is shown that fast streamers need much more energy to propagate, and their propagation seems to be governed mainly by dissociation and ionization in the liquid phase. Slow streamers seem to result from the vaporization of the liquid by heating. These results are confirmed by spectroscopic studies of the light emitted by streamers.<> View full abstract»

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  • Effect of electrode polarity and additives on the direct breakdown voltage of silicon oil under highly non-uniform fields

    Page(s): 961 - 970
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    The direct breakdown voltage versus gap length (50 to 900 mu m) characteristics were obtained using point-sphere electrodes for degassed silicone oil, oxygen-saturated oil and oil containing varying concentrations (0.005 to 1.0 molar) of 1-methylnaphthalene as additive. The characteristics of degassed and oxygen-saturated methylnaphthalene were also obtained. The shape of the characteristics for both polarities of the point depended on the material of the sphere electrode, the presence or absence of oxygen, and the nature of the liquid itself. In silicon oil the crossover gap length, at which the breakdown voltage is the same for both polarities of the point electrode, was increased greatly by the presence of oxygen, whereas oxygen greatly reduces this gap in hydrocarbon liquids. In both degassed and oxygen-saturated oil the presence of the additive caused a shift in the crossover gap to smaller lengths.<> View full abstract»

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  • A localized trace element analysis of water trees in XLPE cable insulation by micro-PIXE and EDX

    Page(s): 971 - 978
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    PIXE (proton-induced X-ray emission) with a focused proton beam of 30-or 220- mu m diameter and EDX (energy dispersive X-ray analysis) of water-trees in XLPE HV (cross-linked polyethylene high-voltage) cable insulation. The merits of these two methods are compared and discussed. It is shown that water-trees are more contaminated than the surrounding insulation. On a localized basis the impurity content of the untreed insulation varies considerably within a few square millimeters.<> View full abstract»

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  • Electrode-fall of local discharge on an electrolytic surface

    Page(s): 979 - 986
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    Presents experimental results on the electrode-fall of local discharge on electrolytic surfaces, which simulate the surfaces of wet polluted insulators. A rod-plane electrode system with the electrolyte layer on the plane electrode was used. This electrode system was set in a Pyrex glass chamber. The air pressure in the chamber was varied from approximately 6.67 to 101 kPa, and the resistivity of the electrolyte was varied from approximately 10 to 6600 Omega cm. The electrode-fall voltage was determined from simultaneous measurements of the applied voltage waveform and the discharge current waveform. It was found that the electrode-fall voltage remains at its high value regardless of the air pressure and increases with the resistivity of the electrolyte. From these results, it is deduced that the discharge mechanism in the local discharge between the rod electrode and the electrolyte surface is similar to that in a glow discharge.<> View full abstract»

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  • The chemistry of insulation tracking with copper electrodes

    Page(s): 987 - 991
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    The mechanism of insulation failure when copper electrodes are used for the comparative tracking index test was investigated. It was found that exothermic reactions initiated by the scintillation increase the intensity of the microarcs. The observation of color difference between test sites where failure occurred and test sites where there was no failure when using copper electrodes as well and increase in the brightness of scintillation when copper was used led to the hypothesis that Cu/sub 2/O released by the electrodes and spread out over the insulation surface is oxidized to CuO. This hypothesis was confirmed by performing tests in which platinum electrodes were used on insulation surface covered with a layer of commercially prepared Cu/sub 2/O.<> View full abstract»

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  • Degradation and breakdown of solid dielectric materials resulting from surface discharges in air and in insulating liquids

    Page(s): 993 - 998
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    An effort is made to identify some of the common aspects of the behavior of PDs (partial discharges) originating in different conditions and interacting with different solid dielectrics (SDs) in media of different density. Emphasis is placed on the behavior of PDs in the SD arrangement with a view to its use as a standard model system for testing the comparative resistance of various dry and impregnated solids to PDs appearing in flat and broad slits, such as those due to delamination and other defects which occur in many kinds of insulation. Observations were made on the propagation and intensity of the discharges as well as their effect on the solid dielectric surface. Results of measurements of light output in the optical range and of magnitude of the PDs are reported, and the resulting damage patterns and the breakdown probability characteristics are described.<> View full abstract»

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  • Electron avalanches influenced by detachment and conversion processes

    Page(s): 999 - 1008
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    The authors analyze the avalanche growth in electronegative gases which exhibit detachment and conversion processes in addition to ionization and attachment processes. The study is based on an evaluation of the model of H.F.A. Verhaart and van der Laan (1982). Humid air is taken as an example to demonstrate, with this model, the effects of detachments and conversion processes on the avalanche electron distribution across the gap and on the external current waveform. The model is also used to determine swarm parameters from fast swarm experiments. The results show that detachment and conversion affect the electron distribution in the avalanche and can thereby influence the streamer breakdown threshold. The neglect of these process in the analysis of swarm experiments results in measured values for the effective ionization coefficient that can may substantially differ from the true values.<> View full abstract»

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  • Formation of PCDF and PCDD in electrical discharges

    Page(s): 1009 - 1013
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    The formation of polychlorinated dibenzofurans (PCDF) and dibenzo-dioxins (PCDD) in electrical discharges in liquids containing polychlorinated biphenyls (PCBs) is examined. Little or no formation of these products was found in high-energy short-duration breakdowns or arcs in air-saturated trichlorobenzene (TCB), mixtures of TCB and PCB, or mineral oils containing small amounts of PCB. Low-energy partial discharges could not be sustained in air-saturated liquids. It is concluded that the formation of PCDF and PCDD within electrical equipment does no appear likely.<> View full abstract»

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  • DC contamination performance of station insulators

    Page(s): 1015 - 1023
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    The authors describe the results of an investigation of the contamination performance of equipment insulators under the application of a DC voltage. Artificial contamination tests on insulators with various shed profiles were carried out. In addition to total leakage distance, shed profile is found to play a role in determining the DC withstand voltage. Deep-rib-type insulators exhibit a superior DC contamination performance compared to other types of insulators. Anticontamination design criteria that are based on the results of the investigation are given for DC equipment insulators.<> View full abstract»

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  • Improvement of the DC voltage insulation efficiency of suspension insulators under contaminated conditions

    Page(s): 1025 - 1032
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    The authors describe the results of the research and development on a suspension-type insulator having a DC contamination withstand voltage 1.25 to 1.3 times higher than that of the standard DC fog insulator, as measured by the fog-withstand or the clean-fog method. Also described are the withstand voltage characteristics of the suspension insulator contaminated with soluble materials and nonuniformly contaminated, simulating natural-field conditions. Design criteria taking these results into account are also discussed.<> View full abstract»

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  • The effect of cable structure on space charge formation

    Page(s): 1043 - 1046
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    An experimental investigation of space charges in LDPE (low-density polyethylene) and XLPE (cross-linked polyethylene) cables with different semiconductor layers is presented. The space-charge distribution was investigated using the field probe technique as a direct method. It was found that the structure of the semiconducting layers as well as the voltage polarity of the conductor have a marked effect on the space-charge distribution. The results provide direct experimental evidence on the polarity of space charges formed in HVDC (high-voltage, direct-current) cables. Their distribution helps to explain the reduction of the breakdown voltage that occurs on polarity reversal.<> View full abstract»

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  • Measurement of arc energy during insulation ignition

    Page(s): 1047 - 1050
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    A digital arc energy meter was developed for insulation-ignition measurements. The meter takes 54 discrete samples of the current through, and voltage across, the electrodes during each 60-Hz cycle. It multiplies the values, sums the products, multiplies the sum of products by the sampling time (time between samples), and displays the result in Joules. The computation is accurate to 3%. The device is designed to handle arcs that last up to 300 ms, although the typical high-energy arc lasts approximately 75 ms. Tests were run on various NEMA-grade materials. It is concluded that the most satisfying result of the investigation is the consistency in the graphs of arc energies. In spite of the variation from cycle to cycle within the test, these graphs show that each grade of material has a detectable signature.<> View full abstract»

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  • The effect of different types of inclusions on PE cable life

    Page(s): 1051 - 1055
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    Experiments on polyethylene (PE) cable samples have shown that conducting inclusions are not as harmful as mineral particles, in particular glass. The consequences of this result for cable breakdown during type tests are discussed. The experiments suggest that about 50% of the cables polluted with glass will fail during a type test for medium-voltage cables (10 kV/mm, 24 h); all polluted cables will show a high failure percentage (>50%) at a type test for high-voltage cables (23 kV/mm, 24 h).<> View full abstract»

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  • Comments, with reply, on "Correlation of Arrhenius parameters: the electrotechnical aging compensation effect

    Page(s): 1057 - 1063
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    The commenter makes three particular comments concerning the work of P.K. David (see ibid., vol. 22, p.229-236, 1987). They relate to: (1) the question of whether different properties should be related to aging process in different ways, so that degradation of one property is not as sensitive to aging reactions as for another property; (2) the problem of the common point of intersection in a family of life lines pertinent to different failure criteria; and (3) the theoretical background and development of David's theory. The author's discusses the commenters points further.<> View full abstract»

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  • Polarity effect in DC withstand voltages of contaminated surfaces

    Page(s): 1033 - 1042
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    The characteristics of partial arcs on contaminated surfaces are believed to dominate the withstand voltage of a contaminated insulator. The structure of a DC partial arc on an experimental model of an insulator surface contaminated with sodium chloride is investigated using a still camera and an interferometric method. The results reveal a difference in the structure of the positive and the negative partial arcs, and make it possible to explain the cause of the polarity effect in the withstand voltage of a heavily contaminated DC insulator, namely, the negative withstand voltage is lower than the positive. It is concluded that knowledge of the structure of partial arcs can be used in constructing an advanced mathematical model of the flashover phenomenon on a contaminated surface View full abstract»

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  • A generalized analytical-numerical method for the calculation of 3-dimensional HV fields

    Page(s): 929 - 936
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    A generalized analytical-numerical method for computing electric fields in 3-dimensional geometries is introduced. It is based on the construction of an analytic function for the electric potential by the limited development of harmonic functions, using coordinate systems appropriate to the configuration studied. The harmonic functions correspond to particular solutions of the Laplace equation obtained by the separation-of-variables technique. Each solution is weighted by an originally unknown numerical factor; the satisfaction of Dirichlet boundary conditions for the potential leads to a system of linear equations for these numerical factors. Their solution first determines the value of the numerical factors; then the electric potential in any point in the region outside the conductors can be calculated by superposition. Applications of the method to two practical HV (high voltage) configurations are given 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