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Showing papers in "IEEE Transactions on Dielectrics and Electrical Insulation in 2003"


Journal ArticleDOI
TL;DR: A description of commonly used chemical diagnostics techniques along with their interpretation schemes for transformer insulation condition assessment is presented.
Abstract: Cellulosic paper and oil insulation in a transformer degrade at higher operating temperatures. Degradation is accelerated in the presence of oxygen and moisture. Power transformers being expensive items need to be carefully monitored throughout their operation. Well established time-based maintenance and conservative replacement planning is not feasible in a current market driven electricity industry. Condition based maintenance and online monitoring are now gaining importance. Currently there are varieties of chemical and electrical diagnostic techniques available for insulation condition monitoring of power transformers. This paper presents a description of commonly used chemical diagnostics techniques along with their interpretation schemes. A number of new chemical techniques are also described in this paper. A number of electrical diagnostic techniques have gained exceptional importance to the utility professionals. Among these techniques polarisation/depolarisation current measurement, return voltage measurement and frequency domain dielectric spectroscopy at low frequencies are the most widely used. This paper describes analyses and interpretation of these techniques for transformer insulation condition assessment.

680 citations


Journal ArticleDOI
TL;DR: There is a rapid, nonlinear conduction increase through a rapidly evolving pore population, and this causes the fast membrane discharge previously termed "breakdown", and a stochastic pore hypothesis is consistent with features of electroporation in planar lipid membranes.
Abstract: Electroporation, widely used in research and applications, is briefly reviewed. Both cell and artificial planar bilayer membranes exhibit dramatic changes if the transmembrane voltage is raised to /spl sim/0.2 to 1 V by various electric field pulses. Ionic and molecular transport increases by orders of magnitude, with both reversible and irreversible outcomes. Initially the term breakdown was used, but ion pair generation of classic dielectric breakdown was ruled out. Instead, a stochastic pore hypothesis is consistent with features of electroporation in planar lipid membranes. There is a rapid, nonlinear conduction increase through a rapidly evolving pore population, and this causes the fast membrane discharge previously termed "breakdown". Phenomena due to primary aqueous pores and secondary processes such as heating and chemical exchange have been observed in planar bilayers, cell single systems encountered mainly in vitro, multicellular systems relevant to in vivo applications, and possibly subcellular structures such as mitochondria. For membrane systems that approach nanoscales, modified behavior should occur because of conformational constraints, and deterministic processes may become more important. Understanding electroporation is a subset of a general problem: obtaining a quantitative description of how electromagnetic field-altered changes in chemical species within a biological system govern observed effects.

276 citations


Journal ArticleDOI
TL;DR: A novel, semi-automatic, and empirical wavelet-based method is proposed to recover PD pulses buried in excessive noise/interference comprising of random, discrete spectral, pulsive, and any combination of these interferences occurring simultaneously and overlapping-in-time with the PD pulses.
Abstract: Achieving acceptable levels of sensitivity during online and/or onsite partial discharge (PD) measurements still continues to remain a very challenging task, primarily due to strong coupling of external (random, discrete spectral and stochastic pulsive) interferences. Many analog and digital approaches have been proposed for suppressing these interferences, and amongst these, rejection of the pulsive type of interferences is known to be very difficult, if not impossible. The time and frequency characteristics of the pulsive interference being very similar to that of the PD pulses is the main reason posing difficulty in their separation. In this paper, a novel, semi-automatic, and empirical wavelet-based method (using multi-resolution signal analysis) is proposed to recover PD pulses, buried in excessive noise/interference comprising of random, discrete spectral, pulsive, and any combination of these interferences occurring simultaneously and overlapping-in-time with the PD pulses. A critical assessment of the proposed method is carried out, by processing both simulated and practically acquired PD signals. The results obtained are also compared with those from the best digital filter (infinite impulse response, IIR and finite impulse response, FIR) method proposed in literature. From the results it emerges that, the wavelet approach is superior and further, has the unique capability of successfully rejecting all the three kinds of interferences, even when PD signals and one or all interferences occur simultaneously and overlap-in-time.

266 citations


Journal ArticleDOI
TL;DR: In this article, the main principles of time domain dielectric spectroscopy, its application to conductive systems and possible methods of electrode polarization corrections in time domain are introduced.
Abstract: The main principles of time domain dielectric spectroscopy, its application to conductive systems and possible methods of electrode polarization corrections in time domain are introduced. A comprehensive theoretical and experimental study of static and dynamic dielectric properties of different biological systems including globular, and membrane proteins, hydrate water, human erythrocytes, and normal and malignant blood cells of different types is presented in the paper.

226 citations


Journal ArticleDOI
TL;DR: In this paper, a simple relationship is proposed for apparent trap-controlled mobility, which is affected by significant approximations, but can be applied successfully for material characterization and aging investigation, and the proposed methodology permits finding information on charge trapping/detrapping processes in polymeric materials, using a simple experimental procedure, as well as to extract quantities that seem very attractive as aging markers.
Abstract: Assuming that aging of polymeric insulation consists of irreversible chemical-physical and microstructural modifications, effective ageing markers could be achieved from measurements of properties, which should vary with material microstructure. Among these properties this paper focuses on the estimation of apparent trap-controlled mobility and trap distribution, based on the results of space charge measurements. The depolarization characteristic obtained recording space charge magnitude when, after poling, electric field is removed and electrodes are short-circuited and grounded, is the experimental reference for the application of the expressions for apparent trap-controlled mobility and trap depth calculation derived in this paper. A simple relationship is proposed for apparent mobility, which is affected by significant approximations, but can be applied successfully for material characterization and aging investigation. It is applied to experimental results coming from space charge measurements carried out by the pulsed electroacoustic (PEA) technique on cross-linked polyethylene (XLPE) specimens, unaged and aged, cut from high-voltage cables. The trap depth distribution is calculated for the same material, and the results are cross-correlated with mobility estimates, revealing good agreement. Both apparent trap-controlled mobility and trap depth distribution reveal noticeable modifications with aging. The proposed methodology permits finding information on charge trapping/detrapping processes in polymeric materials, using a simple experimental procedure, as well as to extract quantities that seem very attractive as aging markers.

213 citations


Journal ArticleDOI
TL;DR: In this article, a fuzzy classifier is used for noise suppression in measurements performed by ultra wide band digitizers, able to record a large quantity of partial discharge (PD) pulse waveforms.
Abstract: Noise rejection, defect identification and degradation diagnosis in on-field partial discharge measurements are sought by industry, but hardly achieved in practice. This paper presents tools for automatic noise suppression in measurements performed by ultra wide band digitizers, able to record a large quantity of partial discharge (PD) pulse waveforms. Noise and PD signals are split in different classes on the basis of their shape by means of a fuzzy classifier. Tools used for establishing whether a given class of recorded signals is due to external noise or not are proposed. As an example, two kinds of noise are considered: random noise and rectifier-generated noise. A companion paper will explain how the same classification tools can be employed for the purpose of defect identification.

199 citations


Journal ArticleDOI
TL;DR: In this paper, a simple conduction model based on the processes of dissociation of a neutral electrolytic species and recombination of the generated ions is presented, which is first applied to parallel plane electrode geometry to describe the build-up of the heterocharge.
Abstract: Mildly polar liquids generally exhibit an ohmic behavior when subjected to electric fields of limited values. The resulting conduction is then associated with heterocharge layers of finite thickness in the vicinity of the electrodes. In the absence of charge injection or induction, a simple conduction model based on the processes of dissociation of a neutral electrolytic species and recombination of the generated ions is presented. This model is first applied to parallel plane electrode geometry to describe the build-up of the heterocharge. Then, the case of point/plane configuration is considered where the effect of Coulomb force is different in the two layers next to the electrodes. A net motion toward the point electrode is predicted to occur. With a rough approximation for the harmonic field, an analysis is presented which leads to an expression for the axial component of the net force exerted on the liquid. A simple static pump is designed and built to experimentally investigate the pressure head generated through pure conduction. Two working fluids (refrigerant R-123 and n-hexane) and two different electrode designs are considered in this study. The experimental results are qualitatively compared to the theoretical predictions.

183 citations


Journal ArticleDOI
TL;DR: In this paper, a correlation has been found between the fundamental and low frequency harmonic components of leakage current and different forms of aging, where erosion could be associated with an increase in the level of both the low frequency and fundamental components.
Abstract: The paper presents the results of using the fundamental and the low frequency harmonic components of leakage current to study aging of silicone rubber in salt-fog. Experiments have been conducted on RTV and HTV coated rods at different fields (0.25-0.6 kV/cm) and conductivities (1000 to 2500 /spl mu/S/cm). The onset of dry-band arcing on samples could be determined by measuring the low frequency harmonic components. A correlation has been found between the fundamental and low harmonic components of leakage current and different forms of aging. Where erosion could be associated with an increase in the level of both the fundamental and low frequency harmonic components of leakage current. For example, surface damage for HTV rods occurred when the fundamental component of leakage current was greater than 2 mA. On the other hand, when the samples approached failure, the fundamental component of leakage current reached relatively high values ( > 6 mA for HTV rods and > 2 mA for RTV rods) and the low frequency harmonic components of the leakage current tended to decrease. The results suggest that both the fundamental and low frequency harmonics of leakage current can be used as a tool to determine both the beginning of aging and end of life of silicone rubber in salt-fog.

172 citations


Journal ArticleDOI
TL;DR: In this paper, a new inference method for the diagnosis of solid insulation systems, based on partial discharge (PD) measurements, is presented, which is based on fuzzy logic and enables the recognition of PD generated from different basic sources, such as internal, surface and corona discharges.
Abstract: Results of investigations performed to evaluate the effectiveness of a new inference method for the diagnosis of solid insulation systems, based on partial discharge (PD) measurements, are reported in this paper. Signal separation, noise recognition, and PD source identification are the main features of the proposed inference method. Techniques for signal separation and automatic noise rejection are reported in the 1st part of this paper, while the problem of the identification of PD phenomena, occurring in defects of insulation systems, is approached in this 2nd part. The identification is based on fuzzy logic and enables the recognition of PD generated from different basic sources, such as internal, surface and corona discharges. It is shown that the different source typologies can be identified by means of fuzzy rules applied to a selection of parameters derived from PD-pulse phase and amplitude distribution analysis, once PD phenomena have been clustered in homogeneous class through a fuzzy algorithm based on PD-pulse shape. The proposed identification procedure is finally applied to rotating machines and cables, affected by insulation defects, showing promising on-field applications.

140 citations


Journal ArticleDOI
TL;DR: Submicrosecond, intense pulsed electric fields applied to living cells achieve preferential effects on intracellular rather than surface membranes, potentially providing new approaches for selective/generalized cell or tissue ablation, growth stimulation and tissue remodeling.
Abstract: Development of technology to produce nanosecond duration pulsed electric fields has allowed examination of the effects of ultrashort duration, high intensity electric fields on living cells Theoretically, high intensity (MV/m) electric field applications with durations of less than one microsecond, when shortened toward nanoseconds, should increasingly affect intracellular rather than surface membranes of living cells Experimentally, square-wave, 60 ns duration, high energy (36-53 kV/cm) pulses applied in trains of 1-10 pulses result in progressive increases in the numbers of permeabilized intracellular granules in a human eosinophil cell model-without large surface membrane effects Electron micrographic examination of cells treated in this way demonstrates alteration of intracellular granule morphology consistent with permeabilization of granule membrane, ie, intracellular electromanipulation Continuous microscopic examination of individual living cells exposed to long or short duration pulsed electric field applications shows that permeabilization of surface membrane (median 5 minutes) with anodic preference (electroporation) and prompt cellular swelling follow a single, long duration (100 microsecond) pulse In contrast, after a single short duration (60 ns) pulse, onset of surface membrane permeability is delayed (median 17 minutes), the increased permeability shows no anodic preference, and cellular swelling is absent suggesting that these effects are due to intracellular electromanipulation rather than direct effects on the surface membrane Submicrosecond, intense pulsed electric fields applied to living cells achieve preferential effects on intracellular rather than surface membranes, potentially providing new approaches for selective/generalized cell or tissue ablation, growth stimulation and tissue remodeling

129 citations


Journal ArticleDOI
TL;DR: In this paper, the theoretical foundations of piezoelectric resonance, examines the experimental aspects, and reviews recent applications in the field of polymers. But the authors do not discuss the application of this technique in actuator applications.
Abstract: Piezoelectric polymers are widely used in sensor and actuator applications. Compared to ceramic materials, they have the advantage of mechanical flexibility and an acoustic impedance similar to those of water or air. Their electrical, electromechanical and mechanical properties can be investigated by analyzing piezoelectric resonances in their dielectric spectrum. Apart from its ability to reveal the high-frequency behavior of piezoelectric polymer films, this technique is appealing from a practical point of view because several important parameters can be measured with a single scan that only requires standard dielectric spectroscopy equipment commonly found in many laboratories. This article outlines the theoretical foundations of piezoelectric resonance, examines the experimental aspects, and reviews recent applications in the field of piezoelectric polymers.

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate that the information on the material contained in the response is identical regardless of the method used, and that the differences between methods stand only in the nature of the perturbation and its physical properties.
Abstract: For more than 25 years, various techniques have been introduced for the nondestructive measurement of the space charge distribution in solid dielectrics. All these techniques can be classified into a set of three methods: (i) the thermal method, (ii) the pressure-wave-propagation method and (iii) the electro-acoustic method. Despite their apparent differences they are based on the same physical idea: the perturbation of the equilibrium between electrostatic and elastic forces in the material induces a response, either electrical or mechanical, which can be analyzed. In this paper, we demonstrate that the information on the material contained in the response is identical whatever the method used. As a consequence the differences between methods stand only in the nature of the perturbation and its physical properties.

Journal ArticleDOI
TL;DR: This stage of the ARTEMIS programme is now complete and an analysis of the results will show how they may be correlated with the concepts proposed in aging theories.
Abstract: The aim of the European project "ARTEMIS" is to develop a diagnostic system for assessing aging in power cable insulation. Its first task was to make a thorough characterisation of the cable insulation before aging. This is intended to provide a background against which any changes introduced by thermo-electric aging can be identified. The aging markers derived from this initial characterisation will be considered both as diagnostic indicators in their own right, and also to develop an aging model for predictive purposes, if and when possible. This stage of the ARTEMIS programme is now complete and we will present an analysis of the results, and show how they may be correlated with the concepts proposed in aging theories.

Journal ArticleDOI
TL;DR: This work demonstrates rapid, non-destructive, field-dependent translocation of the plasma membrane inner leaflet phospholipid phosphatidylserine in Jurkat T lymphocytes, and shows that cells which exhibit a similar geometry in suspension, rat glioma C6 cells, are highly resistant to these pulses and respond differently even to much higher doses.
Abstract: Megavolt-per-meter electric pulses with durations shorter than charging time constants associated with external cell membrane dielectric properties can generate significant voltages on the membranes of intracellular structures. Nanosecond-duration, high-field (2-4 MV/m) pulses are not immediately lethal to cells and do not produce the conductive openings in the cytoplasmic membrane associated with long-pulse, low-field electroporation, but can induce profound physiological changes, including apoptosis (programmed cell death). We demonstrate rapid, non-destructive, field-dependent translocation of the plasma membrane inner leaflet phospholipid phosphatidylserine in Jurkat T lymphocytes, and we show that cells which exhibit a similar geometry in suspension, rat glioma C6 cells, are highly resistant to these pulses and respond differently even to much higher doses.

Journal ArticleDOI
Osamu Yamamoto1, Tadasu Takuma1, M. Fukuda1, Satoru Nagata1, T. Sonoda 
TL;DR: In this paper, a simple and reliable method of improving the surface insulation strength of a spacer used in vacuum is described, which is to roughen the spacer surface to an average roughness R/sub a/ higher than 1 or 2 /spl mu/m.
Abstract: This paper describes a simple and reliable method of improving the surface insulation strength of a spacer used in vacuum. The method is to roughen the spacer surface to an average roughness R/sub a/ higher than 1 or 2 /spl mu/m. The material of the spacer examined is SiO/sub 2/, PMMA, PTFE or Al/sub 2/O/sub 3/ and their shape is a right cylinder with 10 mm in height and 54 mm in diameter. The spacer is subjected to a ramped DC voltage and its surface charging is observed by using an electrostatic probe embedded in the cathode. It has been found that R/sub a/ decisively affects the charging, which decreases as R/sub a/ increases. Increasing R/sub a/ larger than about 2 /spl mu/m suppresses the charging until a higher applied voltage is reached, thus improving the insulation property.

Journal ArticleDOI
TL;DR: The uses and limitations of the electrostatic probe for the measurement of charge densities on insulating surfaces are discussed in this article, where two important limitations have together been overcome: (i) the effects on the probe signal of charges on all points of the surface have been taken into account by means of a matrix inversion procedure; and (ii) a robotic control system has been developed which enables the probe to follow and scan a wide range of axi-symmetric insulator profiles.
Abstract: The uses and limitations of the electrostatic probe for the measurement of charge densities on insulating surfaces are discussed. A development of the technique is described in which two important limitations have together been overcome: (i) The effects on the probe signal of charges on all points of the surface have been taken into account by means of a matrix inversion procedure; (ii) A robotic control system has been developed which enables the probe to follow and scan a wide range of axi-symmetric insulator profiles. The degree of resolution achieved enables the probe system to display and measure charge densities in individual streamer channels of a corona discharge on a polytetrafluoroethylene (PTFE) surface. An example is given and comparison made with a dust figure of the same event.

Journal ArticleDOI
TL;DR: In this article, the authors describe three pulse generators: a spark gap switched coaxial cable, a Spark gap switched Blumlein, and a solid state modulator, developed for applying ultrashort electrical pulses to biological materials in culture.
Abstract: This paper describes three pulse generators: a spark gap switched coaxial cable, a spark gap switched Blumlein, and a solid state modulator, developed for applying ultrashort electrical pulses to biological materials in culture. Research has shown that ultrashort pulsed electric fields can induce apoptosis in biological cells, and that pulses as short as 10 ns with field amplitude greater than 1 W/m cause membrane phospholipid rearrangement and activation of the effector enzymes of apoptosis. Pulses of very short duration use only tens of mJ per mL per pulse to induce apoptosis and other intracellular effects without causing thermal trauma. The pulse generators discussed here, each of a different topology, deliver ns pulsed electric fields (nsPEF) to cells in liquid suspension, and can be modified to drive electrodes for external, surgical, or endoscopic treatment of tissues in situ.

Journal ArticleDOI
TL;DR: In this article, the effects of an antioxidant additive on polymer morphology and space charge formation have been investigated, as a function of temperature, in melt-quenched films of low-density polyethylene.
Abstract: The effects of an antioxidant additive on polymer morphology and space charge formation have been investigated, as a function of temperature, in melt-quenched films of low-density polyethylene. On quenching, the additive-free polymer crystallizes to give extensive spherulitic structures; similar objects are not seen in the system containing the antioxidant. The pulsed electro-acoustic method was then used dynamically to follow both the formation of space charge at high voltage and its subsequent decay under short circuit conditions in both material systems. Data were obtained at room temperature, 50 and 70/spl deg/C. Comparing the additive free material with identical polymer containing a standard anti-oxidant package indicates that the addition of the antioxidant markedly changes both space charge formation and decay processes. At room temperature, both materials were found to behave similarly, suggesting that the changes in gross morphology described above are of secondary importance. At higher temperatures, the addition of the antioxidant enhances negative charge accumulation in the material, implying its association with relatively deep traps for the negative charges within the bulk.

Journal ArticleDOI
TL;DR: In this paper, the authors provide an overview of the historical development, the experimental implementation of different thermal wave techniques, the theoretical foundation, methods for the data analysis and a comparison of thermal and acoustic techniques.
Abstract: Thermal techniques for probing space charge and electric field distributions in dielectric materials became available approximately 30 years ago. The techniques have reached maturity and they have been employed not only for the primary purpose of electric field or polarization profiling, but also in a wide range of problems posed by materials research. The present survey provides an overview of the historical development, the experimental implementation of the different techniques, the theoretical foundation, methods for the data analysis and a comparison of thermal and acoustic techniques. The thermal wave technique LIMM is used as an example among the thermal techniques, for a discussion of data analysis techniques and for the spatial resolution that can be achieved with thermal wave techniques. A tour d'horizon is provided through recent applications of thermal techniques, in order to demonstrate their capabilities for dielectric material characterisation.

Journal ArticleDOI
TL;DR: The relation of space charge derived quantities with aging stresses and time is discussed in this article, which indicates that such quantities can be considered as aging markers useful for the diagnosis of bulk degradation in insulation systems aged under electrical field, dc or ac, and temperature.
Abstract: The relation of space charge-derived quantities with aging stresses and time is discussed in this paper. Polyethylene-based materials, aged for different times under electrical and/or thermal stress, are subjected to space charge measurements. Quantities are derived, that is, the threshold for space charge accumulation and the apparent, trap-controlled mobility, obtained by the threshold and the depolarisation characteristics, respectively, which show time variations depending on the level of applied stress and aging time, i.e. on the extent of degradation. This indicates that such quantities can be considered as aging markers useful for the diagnosis of bulk degradation in insulation systems aged under electrical field, dc or ac, and temperature.

Journal ArticleDOI
TL;DR: In this article, two sources of corona have been investigated: corona from a metal electrode, and Corona from water droplets, and the results show that corona induced degradation is dominantly due to a combination of electro-chemical reactions rather than thermal effects.
Abstract: A majority of nonceramic insulator (NCI) application is under relatively clean conditions where leakage current may be nonexistent. Occurrence of corona for long periods of time on NCI operating under relatively clean conditions is possible due to localized high electric field (E-field) brought about by design and manufacturing deficiencies. Therefore, resistance to corona-induced degradation of NCI housing materials is an important factor that impacts NCI long-term reliability, and is the focal point of this paper. Two sources of corona have been investigated: corona from a metal electrode, and corona from water droplets. Field inspections were performed on 230 and 500 kV insulators to demonstrate the existence of corona even under relatively clean and dry conditions. Three commonly used NCI housing materials, namely high temperature vulcanized (HTV) silicone rubber (SIR), ethylene propylene diene monomer (EPDM) and a blend of EPDM and silicone polymer were evaluated in the laboratory. In addition, housing materials from several insulators removed from the field were analyzed. Data gathered from electrical and physicochemical analyses show that corona induced degradation is dominantly due to a combination of electro-chemical reactions rather than thermal effects.

Journal ArticleDOI
TL;DR: In this article, the nonlinear electrical behavior of zinc oxide, used to practical advantage in surge arresters on distribution power systems, has been replicated in epoxy resin, which has been filled with an appropriate volume fraction of this intrinsically semiconducting material.
Abstract: The non-linear electrical behavior of zinc oxide, used to practical advantage in surge arresters on distribution power systems, has been replicated in epoxy resin, which has been filled with an appropriate volume fraction of this intrinsically semi-conducting material. Comparison has been made with epoxy resin containing a similar volume fraction of aluminum oxide in order to establish that the non-linearity observed in zinc oxide filled resin is a function of the zinc oxide itself and not simply an artifact resulting from the presence of any filler and the interfacial phenomena thereby arising. Previous work in this field, in both thermo-setting and thermo-plastic insulation has concentrated on dc voltage application. This work, in addition to extending the range of host materials to include epoxy resin using dc, has also explored the ac behavior. The results demonstrate that the inclusion of zinc oxide in epoxy resin is capable of producing non-linear conductivity when the filler volume fraction exceeds the percolation threshold ( /spl sim/ 15%).

Journal ArticleDOI
TL;DR: In this article, the authors used a fractal approach to describe the effects of tortuosity and branching of the lightning channel and used the model to make predictions of the probability of lightning strikes to practical structures.
Abstract: Recently fractal theory has been used to model the observed paths of lightning discharges. This paper extends previous work by using a fractal approach to describe the effects of tortuosity and branching of the lightning channel. In particular, we use the model to make predictions of the probability of lightning strikes to practical structures. Some of the specific estimates include the probability of strikes as a function of interception angle, predictions of the strike points on structures, and the probability of "side strikes" to tall structures. Significant polarity and geometric effects are shown. The shielding effects of nearby taller structures, shielding failure or "breakthrough" probabilities of so-called protected objects, and the effects of ground topography are also examined. The results are discussed in terms of the implications for the protection of structures against lightning.

Journal ArticleDOI
TL;DR: In this paper, an additive-free low-density polyethylene sheet was soaked in various liquid chemicals including the crosslinking byproducts and space charge distribution inside the sheet was measured under DC voltage application.
Abstract: It is known that space charge is formed in cables insulated with crosslinked polyethylene. It is probable that the crosslinking byproduct or the crosslinked polymer morphology is responsible for the space charge. In order to examine the former possibility, an additive-free low-density polyethylene sheet was soaked in various liquid chemicals including the crosslinking byproducts and space charge distribution inside the sheet was measured under DC voltage application. As a result, space charge appears in the vicinity of the injecting electrode only in the case that the sheet was soaked in the liquids with at least one hydroxyl group in their structures. Therefore, it is concluded that cumyl alcohol, which is the only byproduct with a hydroxyl group in its structure, is responsible for the formation of space charge in polyethylene on the assumptions that chemical functions of a given molecule act separately from each other and that other contributions such as the crosslinked polymer morphology are negligible.

Journal ArticleDOI
T.J. Lewis1
TL;DR: In this paper, two hitherto neglected mechanisms, which occur at the interface between insulating liquids and metal electrodes under high electrical fields, are considered and shown to be significant for the initiation of breakdown.
Abstract: Two hitherto neglected mechanisms, which occur at the interface between insulating liquids and metal electrodes under high electrical fields, are considered and shown to be significant for the initiation of breakdown. One involves the Lippmann effect in which the electrical fields of the double layers at the electrodes reduce the interfacial tension and lead to the generation of low-density microcavities on the electrode surfaces. The other is the Auger effect in which non-radiative recombination of electrons and positive holes across the large energy gap between these states leads to secondary electrons of high energy. The coupling between these two mechanisms is expected to be highly conducive to streamer initiation at the electrodes.

Journal ArticleDOI
TL;DR: In this paper, the electric field behavior in HVDC SF/sub 6/ gas insulated systems is investigated and the boundary value problem describing capacitive-resistive time-varying electric field is formulated.
Abstract: This paper reports on the electric field behavior in HVDC SF/sub 6/ gas insulated systems. In the field model definitions, the SF/sub 6//epoxy interfaces are assumed as thin slightly conducting layers with non-zero thickness. The boundary conditions involving surface-reduced parameters of these layers are adopted. This allows avoidance of problems of calculation regarding the proximity of interfaces between subdomains. The boundary-value problem describing capacitive-resistive time-varying electric field is formulated. On this basis, the transient HVDC electric field model and time domain-calculating algorithm are constructed. The model accounts simultaneously for both the surface layer properties and bulk conduction parameters of the bounding dielectrics, while surface conductivity may be specified as a non-linear or an arbitrary function. The method employs direct integration of a continuity equation in the time domain with the calculation of an electrostatic field approximation at each integration step. The basic features and applicability of the method are discussed. The model has been applied for analysis of HVDC electric field formation mechanism in SF/sub 6//epoxy insulation. It is demonstrated that charge accumulation phenomena cannot be described by a single time-stable mechanism. Some directions regarding further development of the field model and calculating algorithm are suggested.

Journal ArticleDOI
TL;DR: In this article, a dynamic model for predicting DC arc behavior and critical flashover voltage of ice-covered insulating surfaces is presented, taking into consideration insulating geometry, pre-contamination level, and characteristics of ice layers.
Abstract: A dynamic model for predicting DC arc behavior and critical flashover voltage of ice-covered insulating surfaces is presented. The model takes into consideration insulating geometry, pre-contamination level, and characteristics of ice layers. Assuming arc behavior as a time dependant impedance, it is possible to determine various arc characteristics such as time histories of leakage currents, potential gradient, channel radius, trajectory, propagation velocity and the energy injected into the zones free of ice (also called air gaps). The simulated results provided by the model are in agreement with those obtained experimentally using a simplified ice-covered cylinder as well as a short string of five IEEE standard porcelain suspension units covered with artificial ice.

Journal ArticleDOI
TL;DR: In this paper, the feasibility of using a very high frequency capacitive coupler technique to detect and locate partial discharge (PD) activity within HV cables and in particular cable joints has been investigated.
Abstract: In order to detect and locate partial discharge (PD) activity within HV cables and in particular cable joints, the feasibility of using a very high frequency WHO capacitive coupler technique has been investigated. In addition, an alternative PD offline test method for cable joints or cable sections within long cable systems has been developed. By energising the joint or a short section of the cable screen only this method has the advantage of reducing the power supply requirement of the test source. The application of capacitive couplers for this PD offline test method has been investigated. In order to use this approach there must be an insulation gap between the coupler and the outer sheath of the test cable. The effect of this gap on measured sensitivity has been investigated experimentally and through the use of a simulation model. Obtained results are in good agreement. Cross-correlation techniques have been implemented to automatically estimate the signal time of flight from different-coupler outputs. Methods of calibrating the coupler applied to the alternative PD offline test method have also been investigated.

Journal ArticleDOI
T.J. Lewis1
TL;DR: Reconsideration of the effect of an electrical field applied across a phospholipid bilayer membrane shows that, in addition to a compressive stress normal to the membrane plane, transverse traction stresses are generated in the lateral plane of the membrane.
Abstract: Reconsideration of the effect of an electrical field applied across a phospholipid bilayer membrane shows that, in addition to a compressive stress normal to the membrane plane, transverse traction stresses are generated in the lateral plane of the membrane. In the fields usually employed for electroporation these transverse stresses are likely to be sufficient to reduce the membrane tension considerably, causing electroporation and rupture. This mode of field-induced change in the membrane provides a natural model for the various forms of electroporation.

Journal ArticleDOI
TL;DR: In this article, the breaking capability of a series design consisting of two 24-kV vacuum circuit breakers with grading capacitors was investigated under worst-case conditions with regard to the rate of rise of the transient recovery voltage (TRV) exceeding the values given in the relevant IEC standard.
Abstract: This paper deals with the breaking capability of a series design consisting of two 24-kV vacuum circuit breakers (VCB) with grading capacitors. The investigations were done under worst-case conditions with regard to the rate of rise of the transient recovery voltage (TRV) exceeding the values given in the relevant IEC standard. In previous publications it was shown that the breaking capability of the series arrangement is higher than doubling the voltage of a single tube. In addition to these results it is shown that in some cases grading capacitors can increase the breaking capacity even more. Tests with simultaneous opening of the contacts of both tubes are presented with the application of different grading capacitors as well as the choice of different arcing times. In the case of reignition of one of the tubes the current circulating between the two tubes is shown. As a result of the tests the breaking capability of the arrangement depending on the arcing time and the value of the grading capacitors can be classified into three zones: area of reignition of the arrangement, scatter area and area of successful arc quenching.