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Dielectrics and Electrical Insulation, IEEE Transactions on

Issue 5 • Date Oct. 2002

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Displaying Results 1 - 21 of 21
  • Our past quarter-century archived

    Page(s): 635 - 637
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    Freely Available from IEEE
  • Kerr electro-optic measurements of space charge effects in HV pulsed propylene carbonate

    Page(s): 838 - 844
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    The Kerr electro-optic field mapping technique has been used to study space charge effects in HV pulsed propylene carbonate (C4H6O3) using stainless steel parallel-plane, aluminum blade-plane, and aluminum point-plane electrodes. Measurements presented here were taken using a circular polariscope with aligned polarizers at room temperature (T ∼ 20 to 27°C). Average peak space charge free electric field strengths were E0 ∼ 52 kV/cm for the parallel-plane electrodes, E0 ∼ 210 kV/cm at the blade electrode tip and E0 ∼ 240 kV/cm at the point electrode tip. The measurement times ranged from 10 μs to 1 ms. For the parallel-plane electrodes, the light intensity pictures were analyzed along a line between electrodes in the center of the electrode gap and for the blade-plane and point-plane electrodes the light intensity pictures were analyzed both from the tip of the blade and point, to the plane, and along the plane surface. From the light intensity distribution for the parallel-plane and blade-plane electrodes, the electric field and space charge density were calculated as a function of position and time. The calculated space charge distributions show both positive and negative charge injections from the electrodes as well as bulk charge dissociation and recombination. The light intensity was recorded on Polaroid film for the parallel-plane, blade-plane and point-plane electrode measurements and also with a CCD camera for the point-plane electrodes. A CCD camera was used for the point-plane electrodes to resolve more accurately the gray-scale light intensity distribution because of the short optical path length. All the HV Kerr electro-optic measurements showed significant space charge effects in propylene carbonate because the light intensity distributions differed significantly from the calculated Kerr effect patterns from numerical solutions to Laplace's equation under space-charge free conditions. View full abstract»

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  • Aging and polarization phenomena in PE under high electric fields

    Page(s): 697 - 703
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    The influence of high electrical DC fields (>20 kV/mm) on aging, polarization and on the morphology of polyethylene (PE) is discussed. Infrared and positron annihilation spectroscopy measurements as well as capacitance measurements tend to suggest that the polymer morphology is modified by high fields. The author shows that the accelerated electrical aging characteristics of PE are linked directly to the morphology changes induced by the field. Below a so-called critical field, the activation volume of the aging process is dependent on the field-induced strain. Above the critical field, the amorphous phase is deformed significantly, and weak van der Waals bonds are broken, leading to another, faster, aging regime. There is an excellent agreement between the proposed model and experimental data obtained with various PE samples. The possible relation between the submicrocavity formation proposed in his aging model and various polarization measurements is discussed. It is his contention that strong charge injection occurs only after submicrocavity formation, i.e. after weak bond breakage. As is well known, the polarization currents obtained under high fields are controlled by space charges. It seems that the wave packets and the negative resistance observed at >100 kV/mm in PE are associated with a steady state in field-induced defect formation. This suggests that space charges are related to the formation of submicrocavities and, therefore, are a consequence, not a cause, of high field aging. View full abstract»

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  • History of the EI magazine

    Page(s): 651 - 654
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    The history of the Electrical Insulation Magazine, first published by the DEIS in September 1985, is outlined. The people involved in editing the magazine are listed as well as the history of the various features found in the magazine. View full abstract»

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  • History of the Dielectrics and Electrical Insulation Society (update)

    Page(s): 666 - 667
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    This is an update on the paper published under the same title in the Transactions on Electrical Insulation, Vol. 25, pp. 3-16, 1990, by the same author. That issue celebrated the 25th year of publication of this journal. The current update shows the Tables of the DEIS officers and an extended Table of the DEIS Awards. View full abstract»

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  • Linear and nonlinear data fitting for dielectrics

    Page(s): 845 - 849
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    The author discusses some of the problems associated with data fitting, particularly the case of uncertainties in all the variables, the possibly misleading results of algorithmic convergence, and also the limitations imposed by some commercial software. He suggests that the presence of local minima in the fitting function means that the parameters derived from the fitting may be subject to much larger uncertainty than often is suggested. He also addresses the difficulty of making accurate numerical Laplace transforms, even when regularization techniques are employed. His general conclusion is that the parameters derived by modeling dielectric data are liable to have considerable uncertainty. View full abstract»

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  • Dielectric mixtures: electrical properties and modeling

    Page(s): 809 - 828
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    A review of the current state of understanding of dielectric mixture properties, and approaches to use numerical calculations for their modeling are presented. It is shown that interfacial polarization can yield different non-Debye dielectric responses depending on the properties of the constituents, their concentrations and geometrical arrangements. Future challenges on the subject are also discussed. View full abstract»

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  • Advancements during the past quarter century in on-line monitoring of motor and generator winding insulation

    Page(s): 746 - 751
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    Electrical insulation plays a critical role in the operation of motor and generator rotor and stator windings. Premature failure of the insulation can cost millions of dollars per day. With advancements in electronics, sensors, computers and software, tremendous progress has been made in the past 25 yr which has transformed on-line insulation monitoring from a rarely used and expensive tool, to the point where 50% of large utility generators in North America are now equipped for such monitoring. This review paper outlines the motivation for online monitoring, discusses the transition to today's technology, and describes the variety of methods now in use for rotor winding and stator winding monitoring. View full abstract»

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  • Deterministic chaos in breakdown. Does it occur and what can it tell us?

    Page(s): 752 - 762
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    It is shown that the electrical breakdown mechanisms have a generic form that can exhibit deterministic chaos at sub-breakdown stresses, given a suitable parameter range. Calculation of temperature fluctuations in the thermal runaway mechanism is used to illustrate the behavior, and show the trends that may occur. Electrical tree propagation is used to outline the characteristics of deterministic chaos and to demonstrate its identification in an experimental sub-breakdown mechanism. The way in which this identification has been used to guide the development of a deterministic physical model for tree propagation is discussed. Some speculations are also made as to the possibility of using the properties of deterministic chaos for prediction, and on the relationship of deterministic chaos to cessation of activity prior to failure. View full abstract»

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  • Polyethylene under electrical stress

    Page(s): 717 - 729
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    Fifty years ago, the concept of an intrinsic electric strength for insulating solids was fashionable. It was supported by the sophisticated theoretical models of von Hippel, Frohlich and others for the interaction of electrons with crystal lattices in an electric field. The models came to be applied, rather implausibly perhaps, to polymers such as semi-crystalline polyethylene (PE). In that climate, the work of van Roggen on the high-field conductivity of single lamellar crystals of PE was notable. Since then, the picture of the insulating properties of PE has had to be painted with an increasingly complex palette in which the electrical elements have had to be supplemented by mechanical, chemical, and optical ones. The present review of the conducting properties of the polymer considers these other features, but concludes that the fundamental characteristics of the lamellar PE crystal are still the determining factors. View full abstract»

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  • Predicting electrical breakdown in polymeric insulators. From deterministic mechanisms to failure statistics

    Page(s): 860 - 875
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    Breakdown theories yield a specified time to breakdown for fields exceeding a critical value, whereas experiment shows that times-to-breakdown and breakdown fields are different on a sample-to-sample basis. This has forced the use of a statistical approach to failure, often without a clear physical understanding of the pertinent parameters. A general methodology that allows failure statistics to be derived from a given breakdown mechanism is presented. A number of case studies are used to illustrate the way in which mechanistic features can be related to the parameters of the failure statistic. In particular it is shown that the Gumbel statistic and not the Weibull function is the one appropriate to failure initiation by random defects. Both the formative stage and initiation stage of breakdown are considered, and it is shown that features can be identified in the failure statistic related to known thresholds in the active breakdown mechanism. Aging is examined through the three main control features: activation energy, field enhancement factor, and threshold factor. It is shown that distributions in each of these parameters could give rise to the observed statistics above the estimated characteristic threshold field. However, distributions in the material variables that define the local threshold value allow some failures to occur in the sample set, even at fields below the characteristic threshold level, whereas distributions in activation energy do not. The possibility of predicting the lifetime of individual specimens is briefly addressed in closing. View full abstract»

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  • EI Group/Society memoirs, 1975 to 1978

    Page(s): 668 - 670
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    An account is given of the time when the International Symposium on Electrical Insulation (ISEI) was inaugurated, the Group on Electrical Insulation was elevated to Society status, Dr. van Roggen was appointed as Editor of the Transactions upon the retirement of E. J. McMahon, the Scientific Achievement award was established in honor of Dr. Dakin, and when, much to the consternation of many, discussions began on the transfer of the Conference on Electrical Insulation and Dielectric Phenomena (CEIDP) from it aegis of the NAS/NRC to a more humble abode, namely that of the Electrical Insulation Society (EIS). View full abstract»

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  • Aging of polymeric and composite insulating materials. Aspects of interfacial performance in aging

    Page(s): 704 - 716
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    Aging of polymeric and composite materials is reviewed mainly from the standpoint of their interfacial performance. Insulating materials can be divided into simple polymers and composites. Polymers for power cables, transformers, insulators and rotating machines consist of thermoplastics such as PE, PET and PPS, elastomers such as silicone, EPR and EPDM, and thermosets such as epoxy. Composites for GIS, rotating machines and insulators comprise epoxy/glass, epoxy/silica/alumina, and epoxy/mica systems. Aging processes are complicated in general, and take place under simultaneous multiple stresses such as electrical, thermal, mechanical and environmental stresses. Some of the phenomena covered in this paper are associated with the degradation by tracking and erosion and the loss of hydrophobicity in case of surface properties, and with PD, electrical treeing, water treeing and combined phenomena. The quality of cable insulation such as XLPE has been improved extensively from the standpoint of design electric strength. Interfacial problems will emerge for modification of cable joints. It is expected that polymers for outdoor use and filled epoxy resin systems should be improved from their environmental stability and from their design stress enhancement, respectively. View full abstract»

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  • Partial discharges. Their mechanism, detection and measurement

    Page(s): 763 - 808
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    Different partial discharge (PD) detection and measurement procedures suitable for use on cables, capacitors, transformers and rotating machines are examined and compared. Both narrow and wide bandwidth PD detectors are considered; particular attention is given in regard to their suitability to different types of electrical apparatus and cable specimens under test as well as their applicability to discharge site location and their capability to detect different forms of PD. A rather substantial portion of the discussion is devoted to the use of intelligent machines as applied to PD pattern recognition in terms of either PD pulse-height/discharge epoch (phase) distributions or discharge pulse shape attributes. View full abstract»

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  • Fleeting paradigms in dielectrics and electrical insulation. A personal point of view of recent TDEI history

    Page(s): 638 - 646
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    An overview is given of the drastic changes in both measurement technology and interpretation of the obtained data, related to the fields of dielectrics and electrical insulation in general. A history is given of the Transactions on Dielectrics and Electrical Insulation (TDEI), mainly of the last quarter century, with tables indicating individual contributions by many people, many members of the sponsoring society, the DEIS. View full abstract»

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  • Progress in electrothermal life modeling of electrical insulation during the last decades

    Page(s): 730 - 745
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    This paper has the purpose of highlighting the achievements during the last decades in life modeling under electrothermal stress. Phenomenological and physical models are examined, considering also a statistical approach, with applications to experimental results. View full abstract»

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  • CEIDP recollections, 1965-2001

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    The author briefly outlines his recollections of the Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), mentioning the changes in direction that have occurred and the changes in personnel during the review period. View full abstract»

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  • Less can be more. Holes in polymers lead to a new paradigm of piezoelectric materials for electret transducers

    Page(s): 850 - 859
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    The review begins with a very brief history of electrets and of piezo and pyroelectricity in nonuniform space charge electrets. The development of cellular propylene as an electret-transducer material since the mid-eighties is described, and the accompanying research into the origins of (quasi-)ferro-, pyro- and piezoelectric effects in voided polymer electrets is discussed in some detail. In this context, the most relevant charging and measuring techniques for piezo and pyroelectric polymer-foam electrets are introduced. Porous fluoropolymer electrets and their investigation as single or multiple-layer piezoelectrics are considered in view of their better thermal and temporal stabilities. Finally, some proposed or demonstrated applications of voided polymer electrets are briefly mentioned. View full abstract»

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  • History of the electrical insulation conference

    Page(s): 655 - 665
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    The Electrical Insulation Conference (EIC) Was organized in 1958. Four conferences were held before the establishment of the IEEE. Starting with the fifth conference in 1963, IEEE became a co-sponsor for this conference. The history of the various awards and recognitions sponsored by the EIC are listed. Efforts at expanding the scope of the technical activities and the interactions with related groups are discussed. View full abstract»

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  • Relaxation. The quantitative application of time-domain techniques to dielectrics

    Page(s): 829 - 837
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    Results are demonstrated that show that for a given time-domain measurement of a relaxational system to given accuracy, it is possible to compute the equivalent frequency-domain response to comparable accuracy. The computation is well defined, numerically stable, and is independent of any assumed functional form. The error propagation is given by explicit analytical results that allow for experimental design for a given desired level of precision. For the numerical transformation of analytically defined functions, it provides an efficient numerical integrator with prescribed numerical accuracy. View full abstract»

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  • Electric fields and electrical insulation

    Page(s): 672 - 696
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    The adoption of a field-theoretical approach to problems arising in the framework of electrical insulation is discussed with reference to six main topics, which have been addressed over the last 30 years. These include uniform field electrodes, Green's differential equation, electrode surface roughness, induced charge, electrostatic probes, and partial discharge transients, together with several follow-on aspects. Each topic is introduced and thereafter the progress achieved through the use of a field-theoretical approach is reviewed. Because the topics cover a wide spectrum of conditions, it is amply demonstrated that such an approach can lead to significant progress in many areas of electrical insulation. View full abstract»

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Aims & Scope

IEEE Transactions on Dielectrics and Electrical Insulation contains topics concerned with dielectric phenomena and measurements with development and characterization of gaseous, vacuum, liquid and solid electrical insulating materials and systems.

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Editor-in-Chief
Reuben Hackam