Showing papers in "IEEE Transactions on Electrical Insulation in 1993"
TL;DR: For a long time, classification of partial discharges was performed by eye, by studying discharge patterns at the ellipse of an oscilloscope screen as discussed by the authors, and the introduction of digital processing techniques allowed automation of the recognition procedure.
Abstract: For a long time, classification of partial discharges was performed by eye, by studying discharge patterns at the ellipse of an oscilloscope screen. The introduction of digital processing techniques allowed automation of the recognition procedure. These procedures are reported and applied to a number of actual HV constructions which suffer from partial discharges. The results of these tests show that a quite satisfactory recognition of discharges takes place. >
311 citations
TL;DR: In this article, the authors present theoretical mechanisms of surface flashover and pertinent experimental results, as well as some specific techniques for improving the holdoff voltage of insulators are recommended.
Abstract: Reviews surface flashover of insulator, primarily in vacuum, although some comments are made about the effect of ambient gases on surface flashover. It presents theoretical mechanisms of surface flashover and pertinent experimental results. The holdoff voltage of insulators depends upon many insulator parameters, such as material, geometry, surface finish, and attachments to electrodes, but also on the applied voltage waveform (duration, single pulse or repetitive), the process history of the insulator operating environment, and previous applications of voltage. Several suggestions are made regarding choice of the material, geometry, and processing when selecting an insulator for a particular application. Some specific techniques for improving the holdoff voltage of insulators are recommended. >
294 citations
TL;DR: In this article, the authors present the fundamentals of phenomenological aging theory and life modeling and give electrical and combined-stress life data for different materials, showing either linear or curvilinear behavior.
Abstract: The authors review aging phenomenology and life modeling; illustrate different approaches, showing their advantages and applicability limits; and raise problems relevant to practical applications of models and evaluation of material endurance. They present the fundamentals of phenomenological aging theory and life modeling and give electrical and combined-stress life data for different materials. Electrical, thermal and multistress life models valid for insulating materials and systems, showing either linear or curvilinear behavior are presented. Particular attention is given to threshold-life models under combined thermal-electrical stresses. General aging equations for single and multiple stresses are presented, and the life surface for combined thermal-electrical stresses is introduced. Generalization to N-stress life and aging models is discussed. Statistical processing of data and determination of model parameters are mentioned, and graphical methods for material characterization are proposed. >
220 citations
TL;DR: In this article, three different neural networks (NNs) were applied to the recognition of partial discharge (PD) patterns in industrial objects, and the results of PD measurements on simple two-electrode models were presented.
Abstract: The application of three different neural networks (NNs) to the recognition of partial discharge (PD) is studied. Results of PD measurements on simple two-electrode models, as well as on models of artificial defects in industrial objects, are presented. The PDs are measured using conventional discharge detection, and PD patterns are processed by previously developed statistical tools. Mathematical descriptors are used as input patterns for a backpropagation network, Kohonen self-organizing map, and learning vector quantization network. All three NNs recognize fairly well the PD patterns of those insulation defects for which they were trained. On the other hand, the NNs could misclassify those PD patterns for which they were not trained. The classification of PD patterns by NNs can be influenced also by the structure of the particular NN, the value of the convergence criterion, and the number of learning cycles. >
210 citations
TL;DR: In this paper, a previously developed method of partial discharge recognition is used to evaluate PD in HV devices using conventional discharge detection (bandwidth approximately 400 kHz), the PD patterns are studied.
Abstract: A previously developed method of partial discharge (PD) recognition is used to evaluate PD in HV devices. Using conventional discharge detection (bandwidth approximately 400 kHz), the PD patterns are studied. By means of unambiguous statistical operators like skewness, kurtosis, number of peaks, etc., quantitative information about the discharge source can be obtained. In the case of an unknown defect, a combination of these operators is compared to the same set of operators for a known configuration. In this way, a statement can be made on the character of a discharge source. The use of this technique in evaluating different discharges in HV cable and in 400 kV SF/sub 6/ insulation confirms the usefulness of the new approach. >
191 citations
TL;DR: In this paper, a dynamic model that computes the flashover voltages of polluted insulators energized with DC voltage is presented, which takes into account the configuration of the insulator profile at every instant.
Abstract: A dynamic model that computes the flashover voltages of polluted insulators energized with DC voltage is presented. The salient feature of this model is that it takes into account the configuration of the insulator profile at every instant, which plays an important role in the flashover process of the DC polluted insulators. A number of practical insulator geometries have been studied, and the validity of the model is verified by comparing the computed results with the experimental results of previous researchers. >
157 citations
TL;DR: The effects of long exposure of epoxy resin surfaces to partial discharges under AC field stress were examined in this article, where the use of electrical pulse measuring techniques in conjunction with light emission measurements using a photomultiplier tube, which allowed simultaneous detection of both spark and glow discharges, permitted the establishment of a definite transition from spark to glow discharging.
Abstract: The effects of long exposure of epoxy resin surfaces to partial discharges under AC field stress were examined. The use of electrical pulse measuring techniques in conjunction with light emission measurements using a photomultiplier tube, which allowed simultaneous detection of both spark and glow discharges, permitted the establishment of a definite transition from spark to glow discharges. Spark discharges were found to be responsible for the initial surface modification leading to increased surface conductivity, which favored the transition to a pulseless glow type discharge within the cavity. The latter form of discharge was found to prevail over the major portion of the remainder of the exposure period. >
137 citations
TL;DR: In this article, a Weibull statistical analysis of breakdown voltages of thin polyethylene-insulated power cable slices is performed on large populations, and it is shown that a data set described by a two-parameter Weibell distribution contains additional statistical dispersion factors which may or may not yield information on the insulation itself.
Abstract: A Weibull statistical analysis of breakdown voltages of thin polyethylene-insulated power cable slices is performed on large populations. Computation of confidence intervals implies that the statistically correct description is a three-parameter Weibull distribution, i.e., with a nonzero location parameter. It is shown that a data set described by a two-parameter Weibull distribution contains additional statistical dispersion factors which may or may not yield information on the insulation itself. In other words, a zero location parameter, always results from inhomogeneities in the sampling. Comparative testing is used to discriminate between the various sources of inhomogeneity. When it is obtained under carefully controlled experimental conditions, the location parameter value can be considered a true quality factor of the system under test. The statistical analysis of data collected in routine breakdown tests provides a very sensitive tool to investigate small changes in electrical insulation when performed on extensive data sets. >
113 citations
TL;DR: In this paper, two different methods for classifying partial discharge (PD) phenomena by a personal computer-aided system are described, one concerned with common minimum distance classification, using statistical data on pulse quantities such as apparent charge, energy and phase.
Abstract: Two different methods for classifying partial discharge (PD) phenomena by a personal-computer-aided system are described. The first is concerned with common minimum distance classification, using statistical data on pulse quantities such as apparent charge, energy and phase. Applying the correct algorithms and features, such a system is able to discriminate between unknown defects using conventional discharge patterns. Classification with neural networks, which offers the possibility of classifying the shape of the PD pulses without using statistical tools for data reduction, is also discussed. Examples of diagnostic decisions are shown for a gas-insulated-switchgear system with several artificially introduced defects. The reliability of the diagnosis is estimated for both time-resolved detection evaluated by neural networks and classic phase-resolved PD evaluation. A two-step strategy of time-resolved preclassification and automated phase-resolved evaluation is introduced. >
99 citations
TL;DR: In this paper, the partial discharge pattern recognition capability of a neural network, employing the multilayer perceptron technique with data input based on five discharge pulse form parameters, is examined.
Abstract: The partial discharge (PD) pattern recognition capability of a neural network, employing the multilayer perceptron technique with data input based on five discharge pulse form parameters, is examined. Simple discharge sources, consisting of artificially created cylindrical cavities with metallic and dielectric electrodes, are employed. The PD pattern discrimination capability is tested using cavities of equal depth but with different electrodes, and cavities of varying depths but with similar electrodes. Preliminary test results are positive. >
94 citations
TL;DR: In this article, the authors compared experimentally obtained partial discharge pulse forms with those derived theoretically, using a mathematical model of a short gap, and showed that the apparent absence of the protracted ion current tail in the overall pulse form is due to the large excess of the electron current component generated by strongly enhanced cathode emission by the photo effect and other phenomena.
Abstract: Experimentally obtained partial discharge pulse forms are compared with those derived theoretically, using a mathematical model of a short gap. The calculations indicate that, with overvolted short gaps, the apparent absence of the protracted ion current tail in the overall pulse form is due to the large excess of the electron current component generated by strongly enhanced cathode emission by the photoeffect and other phenomena. Under conditions of high overvoltage the ion-impact-induced emission, the ion fluxes and, consequently, the ion current component are greatly reduced as compared to the electron current. The long ion current tail, representing not more than a few percent of the total current, passes undetected. Pulseless and pseudo-glow discharges are considered. Preferred terms to designate the different forms of partial discharges are suggested. >
TL;DR: An attempt was made to use hidden Markov models (HMM) to classify partial discharge (PD) image patterns and the performance of the HMM approach is shown to exceed that of neural networks.
Abstract: An attempt was made to use hidden Markov models (HMM) to classify partial discharge (PD) image patterns. After an introduction to HMM, the methodology and algorithms for evolving them are explained. The selection of the model and training parameters and the results obtained are discussed. The utility of the approach is evaluated by applying it to five types of actual PD image patterns. The performance of the HMM approach is shown to exceed that of neural networks. >
TL;DR: In this paper, it was shown that elastic and quasi-elastic scattering of hot electrons in dielectrics can be described in terms of band structure parameters, whereas inelastic scaling is often governed by the formation of transient anions, which can decay by stabilization, by producing vibrationally and electronically excited molecules, or by dissociating into stable anion and a neutral radical.
Abstract: The author points out that hot electrons generated in dielectrics subjected to high electrical field strengths can produce highly reactive chemical species which contribute to the aging process. The study of the interaction of such low energy (0 to 15 eV) electrons near the surface of dielectrics in experiments combining cryogenic thin film deposition and high-resolution low-energy electron-beam techniques is discussed. Examples of the results obtained with thin film atomic and molecular solids are used to illustrate the basic mechanisms which control the electron-dielectric interactions and provide a description of the basic degradation processes involved during electronic aging. It is shown that elastic and quasi-elastic scattering of hot electrons in dielectrics can be described in terms of band structure parameters, whereas inelastic scattering is often governed by the formation of transient anions. These anions can decay by stabilization, by producing vibrationally and electronically excited molecules, or by dissociating into a stable anion and a neutral radical. These latter species usually initiate other reactions with nearby molecules, causing further chemical damage. >
TL;DR: In this paper, a quasi-simultaneous detection and location of internal defects in power transformers is presented, where the response of the insulating system to PD signals injected at least at three different sites of each winding (top, center, bottom) is calculated, or measured at the signal tap-off points (i.e., bushings).
Abstract: With the development of fast, and low-cost analog-digital converters (ADCs) and new mathematical procedures for waveform description, e.g., time encoded signal processing and recognition (TESPAR), novel approaches to detect and locate internal defects in the insulation of power transformers become feasible if the following requirements are fulfilled: the equivalent circuit of the insulating system, suitable for the fast partial discharge (PD) signals with risetimes of approximately 10 ns, is known; the response of the insulating system to PD signals injected at least at three different sites of each winding (top, center, bottom) is calculated, or measured at the signal tap-off points (i.e., bushings); and the pattern matrix of all calculated or measured signals exists: e.g., encoded and signal processes with TESPAR as a reference. The above mentioned requirements are examined for quasi-simultaneous detection and location of internal defects in power transformers. The method is applied to PD measurements on power transformers. >
TL;DR: A critical study of the performance of several digital filters for rejecting discrete spectral interference in partial-discharge (PD) testing is reported, and the nonadaptive methods are found to be stable against impulsive disturbances, while adaptive methods are unstable.
Abstract: A critical study of the performance of several digital filters for rejecting discrete spectral interference (DSI) in partial-discharge (PD) testing is reported. The filters are evaluated with particular reference to distortion introduced on successive PD pulses. A digital filtering method based on a cascaded second-order IIR lattice notch filter is proposed. The study shows that, for similar performance, methods based on linear prediction require longer filter orders when compared to cascaded IIR notch filters. The nonadaptive methods are found to be stable against impulsive disturbances, while adaptive methods are unstable. The method proposed gives the best performance, low distortion to a sequence of PD pulses, good stability, and fast filtering time. The performance at higher sampling rates, even with PD pulses of long widths, is also found to be superior. The method is implemented using fixed-point arithmetic leading to faster processing. Hence, the method is suitable for on-site PD measurements. >
TL;DR: The consequences of the inherent high variability of life data are described, and some objective methods to aid in the design and analysis of aging experiments are reviewed in this paper, where it is argued that before accelerated aging tests and proposed aging models can acquire credibility with high-voltage (HV) equipment designers, testing of many more specimens and improved analysis methods are needed.
Abstract: The consequences of the inherent high variability of life data are described, and some objective methods to aid in the design and analysis of aging experiments are reviewed. It is argued that before accelerated aging tests and proposed aging models can acquire credibility with high-voltage (HV) equipment designers, testing of many more specimens and improved analysis methods are needed. The recent availability of sophisticated computer programs will aid in the analysis of aging data. >
TL;DR: In this paper, the pulse height distribution (PHD) functions of partial discharges (PDs) generated by AC voltage in air are investigated and the results indicate that the multiple-source discharges are the superposition of the distribution functions of the discharges and the component sources acting alone.
Abstract: The pulse height distribution (PHD) functions of partial discharges (PDs) generated by AC voltage in air are investigated. The electrode systems used allow the investigation of single-source PDs and/or multiple-source discharges. Because voltage and the electrode configuration alter the PHD functions of even a single PD source, the overall effect of voltage an multiple-source discharges is rather complicated. The results indicate that the PHD functions of the multiple-source discharges are the superposition of the distribution functions of the discharges and the component sources acting alone. Knowledge of the PHD functions of the typical PD sources together with some kind of deconvolution technique could help in interpreting the results of PD measurements performed on more complex, real insulation systems and, perhaps, identify the main sources of PD in those systems. >
TL;DR: In this paper, the internal structure of water trees is examined in detail, particularly the nonuniformity of their internal structure, and the quantitative space distribution of bouquets and microcavities is given.
Abstract: The internal structure of water trees is examined in detail, particularly the nonuniformity of their internal structure. The quantitative space distribution of bouquets and microcavities is given. Based on the fact that the water tree is composed of a number of microcavities filled with liquid, the authors analyze the behavior of water trees, i.e., the dielectric properties of the zone of the water tree and its influence on the distribution of the dielectric field. An interpretation of the development of the water tree is proposed and a possible cause of water-tree-induced breakdown is suggested. >
TL;DR: The polaron concept is used to describe trapping of charge in a dielectric medium as mentioned in this paper, which is associated with defects identified as being due to a local decrease of the electronic polarizability.
Abstract: The polaron concept is used to describe trapping of charge in a dielectric medium It is shown that trapping is associated with defects identified as being due to a local decrease of the electronic polarizability The polarization energy around a charge is estimated, using a self-consistent calculation of the local field In nonpolar dielectrics this energy is 5 eV per charge, in the limit of validity of the Clausius-Mosotti relation In polar dielectrics it can be much higher A flashover process is proposed as resulting from the destabilization of the space charge by a variety of perturbations (electrical, mechanical, thermal), followed by the mechanical relaxation of the lattice, initially polarized by the charge >
TL;DR: In this paper, the physical processes occurring during recovery of a vacuum interrupter after high-current interruption are surveyed by the application of modern diagnostic techniques like laser shadow imaging, laser-induced fluorescence of atoms and of metal vapor ions, Mie scattering of droplets, and high-resolution recording of voltage and current on digital oscilloscopes.
Abstract: The physical processes occurring during recovery of a vacuum interrupter after high-current interruption are surveyed. New results have been obtained by the application of modern diagnostic techniques like laser shadow imaging, laser-induced fluorescence of atoms and of metal vapor ions, Mie scattering of droplets, and high-resolution recording of voltage and current on digital oscilloscopes. The density of metal vapor produced by the arc determines the kind of breakdown processes occurring after current zero. Liquid droplets and residual plasma play a minor role. The commonly used contact material, i.e., copper-chromium, is compared with pure copper, and its advantage is explained by the surface structure of the melt. >
TL;DR: A set of computer programs designed for research and educational objectives in the analysis of low frequency electric and magnetic field phenomena are described, capable of solving Poisson's equation for arbitrarily shaped axisymmetric and two-dimensional geometries.
Abstract: A set of computer programs designed for research and educational objectives in the analysis of low frequency electric and magnetic field phenomena is described. These programs are developed around a standard and easily extensible user interface, run on both PC-compatible and X window platforms, and offer the user a wide range of analysis tools. They are capable of solving Poisson's equation for arbitrarily shaped axisymmetric and two-dimensional geometries. >
TL;DR: In this paper, the significance of memory propagation in controlling the stochastic behavior of partial-discharge phenomena is demonstrated by determination of various conditional amplitude and phase-of-occurrence distributions for both measured and simulated discharge pulses.
Abstract: The significance of memory propagation in controlling the stochastic behavior of partial-discharge phenomena is demonstrated by determination of various conditional amplitude and phase-of-occurrence distributions for both measured and simulated discharge pulses. A system that can be used to measure directly a set of both conditional and unconditional pulse amplitude and phase distributions needed to reveal memory effects and quantify the phase-resolved stochastic properties of partial-discharge pulses, is briefly described. It is argued that not only is an unraveling of memory effects essential in any attempt to understand the physical basis for the observed stochastic behavior of partial-discharge phenomena, but also that the data on conditional distributions provide additional statistical information that may be needed to optimize the reliability of partial-discharge pattern recognition schemes now being considered for use in insulation testing. >
TL;DR: In this article, the boundary element method is used to calculate the electric field profiles at needle tips commonly used for electrical treeing tests, and field distributions are also obtained for polyethylene containing a space charge, at the needle tip, and compared with the values previously obtained by the finite difference method.
Abstract: The boundary element method is used to calculate the electric field profiles at needle tips commonly used for electrical treeing tests. Field distributions are also obtained for polyethylene containing a space charge, at the needle tip, and are compared with the values previously obtained by the finite difference method. >
TL;DR: In this article, the physical structure of water trees grown in power cables and in laboratory specimens made of crosslinked polyethylene is studied and compared by fluorescence microscopy, which provides images with good contrast and high resolution.
Abstract: The physical structure of water trees grown in power cables and in laboratory specimens made of crosslinked polyethylene are studied and compared. Detailed observations are made by fluorescence microscopy. This technique, used for the first time in this type of research provides images with good contrast and high resolution. It is completed by 3-D views acquired by confocal laser scanning microscopy. In both cases the tree structure is a network of continuous submicroscopic branched and zigzag tracks. The previous published observations are critically examined. Moreover, the self-luminescence of water trees and its neighborhood is studied, and is shown to be localized in the tree tracks. >
TL;DR: In this article, a theoretical model is proposed and used to analyze the movement of a small conducting sphere stressed with alternating voltage in transformer oil, and the model is verified by comparing it with the experimental observations of a metal particle of radius 0.5 mm in an electrode gap of 8 mm.
Abstract: A theoretical model is proposed and used to analyze the movement of a small conducting sphere stressed with alternating voltage in transformer oil. The model is verified by comparing it with the experimental observations of a metal particle of radius 0.5 mm in an electrode gap of 8 mm stressed with AC voltage. The model suggests that for practically existing micrometer-sized particles ( approximately=50 mu m diameter), the opposing viscous force is the most significant component. The viscous force is dissipated in the medium as fluid drag both along and perpendicular to the direction of movement. A theoretical analysis of the contribution of multiple particles to viscous drag is presented, and is shown to provide a possible explanation for the experimentally observed particle cloud formation at lower AC stresses and dispersion at higher AC stresses. >
TL;DR: A variety of definitions related to partial discharge (PD) phenomena are discussed and an attempt is made to elucidate some aspects of the PD definitions.
Abstract: A variety of definitions related to partial discharge (PD) phenomena are discussed. There is no general agreement at this time of writing as to the definitions of the various regimes of PD. A certain confusion exists which may be due to the multitude of PD manifestations. An attempt is made to elucidate some aspects of the PD definitions. Related problems needing more work are noted. >
TL;DR: In this article, the durability of several dielectric materials used for RF windows is discussed in terms of secondary electron emission (SEE), cathodoluminescence, and Dielectric loss.
Abstract: The breakdown of RF windows used in high-power klystrons is one of the most serious problems in the development of klystrons. The durability of several dielectric materials used for RF windows is discussed in terms of secondary electron emission (SEE), cathodoluminescence, and dielectric loss. High-power tests of these materials with TiN coatings, thus having low SEE, were also carried out using a traveling wave resonant ring. The results show that alumina ceramics are superior to sapphire and aluminum nitride. The origin of breakdown is investigated, and the requirements for RF window materials are presented. >
TL;DR: In this paper, the capacitive-resistive field distribution around a post-type insulator for different severities of surface pollution is calculated by a charge simulation method and the field calculations are carried out for power frequency voltage and also for lightning and switching impulse voltages.
Abstract: HV outdoor insulators are always subjected to pollution of different nature and severity and the performance of a HV insulator under polluted conditions is quite different from that under pollution-free conditions. The present paper is concerned with the field distribution around a post-type insulator for different severities of surface pollution. The capacitive-resistive field distribution around the polluted insulator is calculated by a charge simulation method. The field calculations are carried out for power frequency voltage and also for lightning and switching impulse voltages. The effects of uniform or partial surface pollution and the presence of dry bands on the field distribution around a polluted post insulator are presented and discussed in detail. >
TL;DR: In this article, a review of the development of electrical insulation for modern electric power systems is presented, including cross-linked polyethylene cables, gas-insulated switchgear, composite insulators and oil-immersed transformers.
Abstract: Recent progress in the research and development of electrical insulation for modern electric power systems is reviewed. Cross-linked polyethylene cables, gas-insulated switchgear, composite insulators and oil-immersed transformers are covered. A number of aging processes are presented and analyzed. Typical aging processes are considered to be due to tree formation, partial discharge, electrochemical processes and thermochemical processes. Almost all causes of aging have been itemized and have been phenomenologically verified. Several other theoretical aspects that need to be clarified are identified. >
TL;DR: In this article, the authors used a resonant ring to investigate the breakdown of alumina RF windows for S-band high-power use, and found that the flashover threshold depends on the dielectric materials; a sapphire with F-center defects shows a lower threshold.
Abstract: Breakdown phenomena on alumina RF windows for S-band high-power use were investigated using a resonant ring. Occasional flashovers were observed on TiN-coated surfaces, though the multipactor effect is suppressed by the coating. The flashovers show luminescence with a treelike pattern, resulting in a limitation of the transmittable power through the window. This flashover threshold depends on the dielectric materials; a sapphire with F-center defects shows a lower threshold. For further investigations of the flashover mechanism under a RF field, in situ measurements of the charges built up on the surface both before and after flashover and high-speed photography observations of the flashover avalanches were made. The results indicate an electron communication; its relaxation leaves positive charges on the surface. The relaxation time is found to be 10/sup 6/ m/s. >