Showing papers in "IEEE Transactions on Electrical Insulation in 1980"
TL;DR: In this paper, the breakdown process of polymers is discussed from the standpoint of the inherent properties such as chemical structure, structural irregularities, the presence of additives, molecular motion, and so on.
Abstract: Much experimental work has been done on the dielectric breakdown of solid dielectrics, and a number of breakdown theories have been proposed. Many problems, however, still remain on the breakdown process of polymers. Here, the breakdown process of polymers are discussed from the standpoint of the inherent properties of polymers such as chemical structure, structural irregularities, the presence of additives, molecular motion, and so on. Further, as for the long-time breakdown processes of polymer insulation systems, electrical degradations caused by (PD) and treeing breakdown have been mentioned as important factors. Using experimental results obtained in our laboratory together with those presented by others, our considerations for fundamental processes of electrical degradation are reported. Also, the behavior of dc trees caused by space charge accumulation are discussed with the nature of carrier injection and trapping in polymers, which are estimated by TSC and TL measurements.
383 citations
TL;DR: In this article, the effect of morphological structure on the electric strength and some physico-chemical properties of polymers with flexible chains (HDPE), LDPE, PP, and polymers had rigid chains (CA).
Abstract: This paper describes the effect of morphological structure on the electric strength and some physico-chemical properties of polymers with flexible chains (HDPE, LDPE, PP) and polymers with rigid chains (CA). It is shown that a polymer body has a discrete structure consisting of elements of different densities. The most regular structure with high density is characteristic of spherulites. Their size may be modified by different methods: heat treatment, plasticization, addition of nucleating agent, modification of molecular weight, etc. The inter-spherulitic boundary regions are shown to determine the electrical properties of the specimen as a whole. As the spherulite size decreases, the density of the polymer within the boundary regions increases, improving the electric strength.
129 citations
TL;DR: In this paper, a gaseous model of dielectric breakdown in solids is described in terms of four stages: Formative, Tree Initiation, Tree Growth and Return Streamer.
Abstract: The mechanism of dielectric breakdown in solids, according to recent experimental evidence, involves the creation of a gaseous channel through the dielectric. The high conductance of breakdown appears to be associated with this channel, not with conduction through the solid itself. The central problem in the theory of dielectric breakdown in solids is thus to explain the development, in a strong electric field, of a macroscopic gaseous channel through the dielectric before the large change of conductance characteristic of dielectric breakdown. Recent experimental results will be reviewed and a gaseous model of breakdown in solids will be described in terms of four stages: Formative, Tree Initiation, Tree Growth and Return Streamer. The model is still in the stage of phenomenological development.
120 citations
TL;DR: In this article, the growth of electrical trees in polyethylene by the simultaneous measurement of light intensity and partial discharges has been investigated, and a comparison of the results obtained for different types of trees has been made.
Abstract: This paper describes an investigation into the growth of electrical trees in polyethylene by the simultaneous measurement of light intensity and partial discharges. The emission of light has been studied using an image intensifier. A comparison of the results obtained for different types of trees has been made. The detection of discharges shows that each category of tree is characterized by a particular discharge rate.
117 citations
TL;DR: In this paper, the value of thirty-five electronegative gases as replacement gases for SF6 has been analyzed in terms of their useful pressure range at lower operating temperatures, and empirically correlated with molecular structures.
Abstract: Sparking potential measurements are reported on some thirty-five electronegative gases. Their value as replacement gases for SF6 has been analyzed in terms of their useful pressure range at lower operating temperatures, and has been empirically correlated with molecular structures. Figures of merit have been developed.
105 citations
TL;DR: In this paper, a method for calculating complex fields between lec electrods in conducting media is proposed, where dual relationships between complex fields due to an alternating current source in a conducting medium and an electrostatic field due to a charge in a dielectric medium are shown.
Abstract: A method for calculating complex fields between lec electrods in conducting media is proposed. It is shown that there exist dual relationships between a complex field due to an alternating current source in a conducting medium and an electrostatic field due to a charge in a dielectric medium. If a solution to the problem of an electrostatic field is known, then the solution to the corresponding problem of a complex field is easily bobtained on the basis of the above dual relationships. Numerical calculations and experiments were carried out to verify the proposed method.
83 citations
TL;DR: In this article, the results of study in a laboratory on the measurement of ion mobility and on the breakdown process in dielectric liquids are presented when an electrode system such as razorblade emitter-grid-collector is used for measuring ion mobility by the time of flight method.
Abstract: On the optical studies of electrical conduction and breakdown in dielectric liquids, recent works which have been studied in Japan are briefly reviewed first. Next, the results of study in our laboratory on the measurement of ion mobility and on the breakdown process in liquids are presented. When an electrode system such as razorblade emitter-grid-collector is used for the measurement of ion mobility by the time of flight method, the field uniformity between grid-collector is calculated, and the space charge effect related to the current density is investigated. Through these researches suitable condition for ion mobility measurement are revealed. On the breakdown process, the schlieren method and high-speed photography are used under a pulse voltage applied to a needle-plane gap. Various aspects of the breakdown process from streamer initiation to main stroke, the polarity effect of streamer propagation, the relation between the mean velocity of positive streamer Vm and molecular structure of liquid, the relation between vm and pre-breakdown current, Vm of mixed liquid etc. are described.
80 citations
TL;DR: In this article, a method to calculate the uniform field breakdown gradients for SF6-N2, SF6 air and SF6 CO2 mixtures is discussed and compared with experimentally measured values using plane-plane electrode configuration and direct applied voltages.
Abstract: A method to calculate the uniform field breakdown gradients for SF6-N2, SF6-air and SF6-CO2 mixtures is discussed. Calculated values of the breakdown gradients in these mixtures are compared with experimentally measured values using plane-plane electrode configuration and direct applied voltages. The results show a reasonably good degree of agreement between the calculated and the measured values.
77 citations
TL;DR: A literature survey on the mechanisms of water-treeing electrical cables is presented in this article, which provides an introduction, some background, and examples of current research on water treeing mechanisms.
Abstract: A literature survey on the mechanisms of water-treeing electrical cables is presented The survey provides an introduction, some background, and examples of current research on water-treeing mechanisms The mechanisms of water-treeing have been broken into three categories: chemical, electrical, and mechanical Along with discussion on the types of mechanisms, methods are discussed for reducing tree growth by fillers, additives, or structural changes in polyethylene Some interesting new theories have been proposed which may help to explain the appearance and growth of water trees in electric cables
66 citations
TL;DR: In this paper, the deformation mode at the end of a water tree channel is described and the strain amplitude of the PE at the water interface can be calculated using a simple model.
Abstract: Water treeing is a well known fracture phenomenon in polyethylene (PE) and crosslinked polyethylene (XLPE) high voltage cable insulation. We studied two phenomena: (1) The insulation material is mechanically fatigued by electrostriction as is shown by measuring the relevant electrostriction constant, which moreover is compared with literature values on other polymers. The observed "electrostriction" is found to originate mainly from the Coulomb force. Using a simple model, the deformation mode at the end of a water tree channel can be described and the strain amplitude of the PE at the water interface can be calculated. (2) Under high voltage, the surface tension at the PE-water interface decreases strongly as we found experimentally. The observation that this decrease is proportional to the square of the applied field strength is explained. The joint effect of the Coulomb force and the reduced surface tension may cause a fracture phenomenon, well known in the field of polymers, called environmental fatigue failure (or thermal softening). The same assumption is made as in "common" environmental stress cracking of PE with aqueous detergents, viz. that the low surface tension plays an essential and not a coincidental role.
57 citations
TL;DR: In this paper, the TSC peak is enhanced by drawing and also the SCL current characteristics are modified by the increase of trap sites in polyethylene due to change of morphology in crystalline lamellae.
Abstract: Polyethylene consists of crystalline parts and amorphous parts. Trap sites for electrons or ions exist on a boundary between them. Mechanical drawing or isothermal crystallization of a bulk from its melt provides increased trap sites due to change of morphology in crystalline lamellae. The trap sites for electrons might be physical cavities, where the cavity probably is best pictured as an irregular space bounded by a particular local arrangement of molecular chains which would be changed by drawing or annealing. The TSC peak is enhanced by drawing, and also we observe particular SCL current characteristics modified by the increase of trap sites. 90% of the vinyl groups in polyethylene are reported to be located at the surface of the crystallite and are able to become trap sites. However, no increase of vinyl groups (910 cm-1 and 990 cm-1) in IR spectra could be detected in a film drawn twice. The morphology of crystalline lamellae is changed by drawing. Breakdown strength is controlled by the tilting of slip planes in crystalline lamellae due to an applied force. Crystalline blocks aligned along the tensile axis might be resistive for electrons attempting to accelerate across aligned chains. It is well known that homogeneous deformation of spherulites due to straining provides a direction for development of an electrical tree. In our experiment, the breakdown strength is higher in the case of a small difference in density between crystalline lamellae and amorphous parts.
TL;DR: In this paper, the authors analyzed thermally stimulated analysis on trapped charges and mobile ions in dielectrics and showed that the electronic trap levels can be calculated from the initial rise of TSC and the space charge polarization due to mobile ions can be measured from the TSC charge.
Abstract: Thermally stimulated current (TSC), thermally stimulated surface potential (TSSP or thermally stimulated charge decay, TSCD) and thermoluminescence (TL) in dielectrics are due to dipoles, electronic trapped charges and mobile ions. Dipolar TSC has been well analyzed mathematically [1], but there is no complete thermally stimulated analysis on trapped charges and mobile ions because of the complexity of the phenomena. However, the electronic trap levels can be calculated from the initial rise of TSC [2] and the space charge polarization due to mobile ions can be measured from the TSC charge [3].
TL;DR: In this paper, a review of available activation energies, from which values can be selected for conservative extrapolations on an Arrhenius plot, is made, based on which a required long-term temperature target can be extrapolated on the same slope to a range of short-time exposure temperatures suitable for accelerated tests.
Abstract: Arrhenius plots are useful in predicting long-term use temperatures of organic materials and in choosing parameters for accelerated aging. For materials and components without established Arrhenius curves, a conservative value for the slope of the curve (which is also a measure of the activation energy of degradation) would allow longer-term predictions from a few short-term tests. Conversely, a required long-term temperature target can be extrapolated on the same slope to a range of short-time exposure temperatures suitable for accelerated tests. A review is made of available activation energies, from which values can be selected for conservative extrapolations on an Arrhenius plot.
TL;DR: In this paper, a quasimetallizing treatment of the surface of an alumina insulator with coatings incorporating varying amounts of Cr, Mn, and Ti can increase the vacuum voltage holdoff capability of the insulator significantly (up to 25%).
Abstract: Treatment of the surface of an alumina insulator with coatings incorporating varying amounts of Cr, Mn, and Ti can increase the vacuum voltage holdoff capability of the insulator significantly (up to 25%). During processing (quasimetallizing) the coating penetrates into the alumina, making it insensitive to mechanical damage. This quasimetallizing treatment is also compatible with subsequent metallizing and brazing of the alumina insulator. A 7/1 Mn/Ti mix performed very well, being found to be as effective on a 94% A12O3 alumina as on the previously investigated 95% A12O3, 1% Cr2O3 alumina. Mixes of 6/1/1 Mn/Ti/Cr and 6/3 Mn/Cr performed about as well as the 7/1 Mn/Ti mix, but no better. Quasimetallizing with pure Mn improved the voltage holdoff capability of alumina by about half as much as when using the 7/1 Mn/Ti mix. Mixes with relatively high titanium content (4/3 Mn/Ti and 3/3/2 Mn/Ti/Cr) significantly increased the voltage holdoff capability of the alumina, but unfortunately were much more prone than the 7/1 Mn/Ti mix (or plain alumina) to suffer severe and permanent damage when a breakdown did occur. Quasimetallizing with appropriate formulations. has been shown to change the surface characteristics of alumina in two ways: (1) it decreases the surface resistivity of the alumina, and (2) it decreases the secondary electron emission yield of the alumina. Each change improves the voltage holdoff characteristics of the alumina.
TL;DR: In this article, the rod-rod and rodplane electrode configurations in transformer oil were studied for extremely long gap lengths in the range of 150 to 1000 mm under conditions of lightning impulse, switching impulse, and alternating current voltages.
Abstract: Flashover characteristics of rod-rod and rod-plane electrode configurations in transformer oil are studied for extremely long gap lengths in the range of 150 to 1000 mm under conditions of lightning impulse, switching impulse, and alternating current voltages. The relation between flahsover voltage and gap length and the polarity reversal effect for switching impulse voltages are described in detail.
TL;DR: In this paper, the authors studied the intrinsic breakdown and electrical conduction in solid dielectrics with the insulator type band structure, where there exist no free electronic carriers (electron or hole) due to intrinsic or extrinsic mechanism such as injection from electrodes, or thermal dissociation of impurities.
Abstract: The nature of electrical conduction and breakdown in solid dielectrics has long been a target of intensive research all over the world, because of its vital technical importance for electrical insulating materials in power apparatuses, and also for the electronic application to electrostatic photography, semiconductor device isolation, etc. Since the required design stress of the insulation has been increasing due to the rise of transmission voltage, the nature of intrinsic breakdown and basic mechanism of electrical conduction in insulators also attract the attention of the practical engineer. In ideal dielectrics with the insulator type band structure, there exist no free electronic carriers (electron or hole). In actual case, however, a few free carriers exist in extended state (conduction band or valance band) due to intrinsic or extrinsic mechanism such as injection from electrodes, or thermal dissociation of impurities (donor or acceptor). The current density for these carrier density n at field E is given by
TL;DR: In this article, the breakdown strength and its polarity effect are determined by the combination of the energy input from electric field and energy loss which depend on electron mobility and internal vibrational mode respectively, therefore on molecular structure.
Abstract: High field carrier transport, electron multiplication and breakdown in liquids of various molecular structure are discussed. Breakdown characteristics depend on the molecular structure of liquids. Breakdown strength and its polarity effect are determined by the combination of the energy input from electric field and energy loss which depend on electron mobility and internal vibrational mode respectively, therefore on molecular structure. In rare gas liquids with high electron mobility like liquid Ar, Kr and Xe the electron avalanche is the mechanism of the breakdown. However, in liquid He, electron injection from cathode is the determining process for breakdown and the polarity effect of breakdown in liquid He is completely different from other liquids. In hydrocarbon liquids of ultra-high purity, which have high electron mobility in the case of spherical molecules, and also even in the case of linear molecules at high fields, the electron avalanche (or positive streamer) is also important in the short time range (nsec). However, thermal effects are significant in the long time range. Change of breakdown mechanism from bubble process to positive streamer process with decreasing pulse width and increasing pressure is indicated clearly in liquid N2 as an example. Effect of impurities on breakdown is also dependent on the molecular structure of liquids and solutes. Laser induced breakdown is strongly dependent on the molecular structuire and also can be explained in terms of electron avalanche by the high-frequency breakdown theory.
TL;DR: In this paper, the authors investigated the breakdown voltage of a rod to plate gap is largely affected by the insertion of an insulating paper in the gap and this is known as the barrier effect.
Abstract: The breakdown voltage of a rod to plate gap is largely affected by the insertion of an insulating paper in the gap and this is known as the barrier effect. The complicated characteristics of the breakdown were studied experimentally for dc, ac, lightning and switching impulse voltages. The explanation of these effects were attempted by considering the space charge distribution on the insulating paper. The trial to measure the space charge distribution was also made using an optical method.
TL;DR: In this paper, a review on the performance of outdoor HVDC insulators in a polluting environment is presented, where the effects of ambient weather conditions and the contamination process on the flashover characteristics of an insulator are discussed.
Abstract: A review is presented on the performance of outdoor HVDC insulators in a polluting environment. Results from several recent studies have been included. Physical conditions and processes that lead to electrical breakdown are delineated. Both field and laboratory test results are presented to demonstrate the effects of ambient weather conditions and the contamination process on the flashover characteristics of an insulator. In particular, recent field test data from the Pacific HVDC Intertie has been included. Particle deposition mechanisms under the influence of electric field are also summarized. Lastly, leading theories pertaining to this field are reviewed.
TL;DR: In this article, the authors consider the distance between the electrodes, the gap, which is selected according to arbitrary prejudices, and the available power supplies determine this selection, which makes it extremely difficult to use the published data to derive some valid and useful model of electrical breakdown.
Abstract: The events leading to electrical breakdown of dielectric liquids have been the subject of many studies [1]. In recent years it has become evident that optical rather than electrical techniques should be used in this study since these events occur very rapidly [2-5]. In the investigation of these phenomena, the selection of the experimental conditions is important. Some investigators believe that their experimental equipment should simulate actual conditions occurring in industry. They select point-plane configurations [3-5] which produce highly divergent fields. Others select the simpler case of nearly uniform field conditions [2]. The next consideration is the distance between the electrodes, the gap, which is selected according to arbitrary prejudices. Often the available power supplies determine this selection. Therefore, the data coming from these investigations cover a variety of gap sizes, pulse forms, temperatures, and materials. This situation makes it extremely difficult to use the published data to derive some valid and useful model of electrical breakdown. For example, observations and conclusions based on point-plane and parallel plate electrode systems exhibit considerable disagreement even though both experiments use identical pulse shapes, liquids, gap spacing and ambient temperature [6]. Obviously, the nature of the electrical field has an influence on the process. The problem is further compounded by the use of different optical detection systems. Not every system offers the same resolution. Also, the time scales used for these observations differ greatly, ranging from nanoseconds to microseconds.
TL;DR: In this paper, a sample of ice without silica was found to have a breakdown strength of 0.3 MV/cm for ac voltages, and 0.6 MV/ cm for impulse voltages.
Abstract: An ice or ice-silica compound system is attractive for electrical insulation at cryogenic temperatures. A sample of ice without silica was found to have a breakdown strength of 0.3 MV/cm for ac voltages, and 0.6 MV/cm for impulse voltages. The breakdown strength of an ceicesilica compound system was 0.7 MV/cm for ac voltages. There were no visible macroscopic cracks in the sample, but microscopic cracks and voids may exist, since partial discharges were observed at about half the value of the ac breakdown voltage. The relationship between partial discharges and microscopic voids, and the voltage-time characteristics of this insulation system were studied.
TL;DR: In this article, the authors studied the effects of glass particles within vacuum interrupters and concluded that the presence of glass particle within the interrupter strongly alters the emission properties of highly stressed internal surfaces and significantly degrades dielectric capability.
Abstract: Pre-breakdown electron emission and breakdown voltages have been studied for three experimental vacuum interrupters, two of which contained numerous glass particles the largest of which were typically 50 ?m in their longest dimension. The contaminated interrupter differed from the uncontaminated interrupter in the following ways. 1) Continuously recorded Fowler-Nordheim plots had lower slopes and showed several stepwise changes in emission as the applied high voltage was varied. 2) 60 Hz breakdown voltages were lower and occurred randomly for sustained ac voltage at constant peak amplitude. 3) Electron emission current with dc high voltage applied was markedly sensitive to mechanical shock. Changes in emission occurred at statistically varying time intervals which may be several tens of milliseconds from the imposed shock. We conclude that the presence of glass particles within the interrupter strongly alters the emission properties of highly stressed internal surfaces and significantly degrades dielectric capability.
TL;DR: Water trees have been found in polymeric insulating materials even under the influence of dc stress as mentioned in this paper, and the status of research for water trees performed so far in Japan will be presented first, and then future work will be suggested.
Abstract: Experimental and theoretical investigations for water treeing have been performed on polymeric insulating materials subjected to ac and dc stresses. It was experimentally and theoretically presumed that no water trees are initiated in polymeric insulating materials when applying dc voltage. However, water trees have been found in polymeric insulating materials even under the influence of dc stress. To determine the effects of water trees upon a cable's life in service is now a serious problem in the world. The status of research for water trees performed so far in Japan will be presented first, and then future work will be suggested.
TL;DR: In this paper, the transient electric current is obtained by applying a step voltage of 167 V on Kapton(R) type H-films of 25 and 76 pm thickness, which consists of two components: one decays fast originating from a dielectric relaxation having approximately a single relaxation time, and the other is almost flat due to electric conduction.
Abstract: The transient electric current is obtained by applying a step voltage of 167 V on Kapton(R) type H-films of 25 and 76 pm thickness The current consists of two components: one decays fast originating from a dielectric relaxation having approximately a single relaxation time ?; and the other is almost flat due to electric conduction We find a correlation between the conductivity ? and the relaxation parameters which is close to ?=?0???/?, where ?? is the permittivity of free space and ??? is the change in relative permittivity, suggesting that the present dielectric relaxation is closely associated with the conduction process The change in ? with heat treatment time is also discussed
TL;DR: In this article, the microvoids in steam-cured XLPE cable insulation by heat treatment were investigated using a scanning electron microscope, which showed that the voids are filled with low molecular weight material composed of crystalline and amorphous polyethylene which exuded from the surrounding bulk polymer.
Abstract: Morphological changes of microvoids in steam-cured XLPE cable insulation by heat treatment were investigated using a scanning electron microscope. The observations showed that the voids are filled with low molecular weight material composed of crystalline and amorphous polyethylene which exuded from the surrounding bulk polymer. The filling rate and the properties of the LMWPE are dependent on the temperature and the heat treatment. Void filling, especially partial filling, tended to accelerate bow-tie tree generation. On the other hand, the microvoids in steam-cured XLPE insulation, which contained some special additives, did not change by heat treatment even at temperatures higher than the bulk polyethylene melting point, and furthermore, few bow-tie trees were observed in this cable insulation.
TL;DR: In this paper, water absorption by polyethylene (PE) is discussed in relation to water treeing and two steps have been considered: the first is water diffusion into undamaged PE, the second is water migration into growing water-tree channels.
Abstract: Water absorption by polyethylene (PE) is discussed in relation to water treeing. Two steps have been considered: the first is water diffusion into undamaged PE, the second is water migration into growing water-tree channels. A critical discussion of published data is presented. Diffusion of water and Na+ ions into a low density PE film is studied by a radiotracer method in the absence of water-treeing. Na+ permeation is found to be very low (P < 4x10-15 cm2/s). A water permeability of 4.5x1O-10 cm2/s has been measured and is not affected by an applied uniform dc or ac electric field.
TL;DR: In this paper, the high-field conduction characteristics of a simple dielectric model were investigated and the results showed that significant collision ionization probably occurs in random bursts rather than in a steady, continuous manner.
Abstract: Calculations are presented for the high-field conduction characteristics of a simple dielectric model. The cathode is assumed to emit electrons following a Fowler-Nordheim law, and the anode blocks the emission of holes. The electrons are assumed to have a much greater mobility than the holes, and to be capable of causing collision ionization. The basic equations then permit computation of the steady state conduction characteristics. For sufficiently large current, the results show a region of negative resistance that depends significantly on the electrode geometry. Identification of the current-controlled instability with dielectric breakdown is beset with several severe difficulties. In the first place, significant collision ionization probably occurs in random bursts rather than in a steady, continuous manner. Secondly, the space charge associated with deep traps must contribute significantly to the field strength variation. A discussion is given of the way in which these complexities affect the problem in hand.
TL;DR: In this article, steady state solutions of the electric field and space charge density distributions using a drift dominated unipolar conduction model between coaxial cylindrical electrodes are reviewed and compared to experimental results obtained using the Kerr electro-optic ptic effect.
Abstract: Steady state solutions of the electric field and space charge density distributions using a drift dominated unipolar conduction model between coaxial cylindrical electrodes are reviewed and compared to experimental results obtained using the Kerr electro-optic ptic effect. With coaxial cylindrical electrodes, Kerr measurements generally showed weak positive charge injection when the outer cylinder was positive and strong positive charge injection when the inner cylinder was positive. For one case study, positive charge injection at the inner cylindrical electrode was so strong that the space charge shielding caused the electric field at the inner cylinder to be a minimum, with the field increasing to the outer cylindrical electrode in complete contrast to the usual space charge free 1/r field dependence. This polarity effect is observed also for a sinusoidal ac high voltage with an essentially space charge free field when the inner cylindrical electrode was instantaneously negative, and a space charge distorted uniform field when the inner cylinder was instantaneously positive.
TL;DR: In this paper, the effect of temperature on the probability of breakdown of mineral oil usinig power-frequency voltages has been investigated, and the breakdown probability is plotted on a Weibull distribuion and fit well in two straight lines intersecting at a certain transition point.
Abstract: The effect of temperature on the probability of breakdown of mineral oil usinig power-frequency voltages has been investigated. Results of the breakdown probability are plotted on a Weibull distribuion and fit well in two straight lines intersecting at a certain transition point. This transition corresponds to a breakdown probability and a breakdown voltage which are temperat ure dependent. Results suggest that different breakdown initiating mechanisms may be simultaneously active, and the dominance of one of them on the other is responsible for the observed transition in the breakdown probability characteristics.