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Dielectrics and Electrical Insulation, IEEE Transactions on

Issue 2 • Date Apr 2001

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Displaying Results 1 - 23 of 23
  • Tracking and erosion of HTV silicone rubber and suppression mechanism of ATH

    Page(s): 203 - 211
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (828 KB) |  | HTML iconHTML  

    Tracking and erosion of high temperature vulcanizing (HTV)-silicone rubber (SIR) and the suppression mechanism of alumina trihydrate (ATH) filler were investigated in the present study. The tracking and erosion resistance of HTV-SIR filled with 0 to 60%wt ATH was evaluated by employing an IEC 587 inclined plane (IP) tracking and erosion test, during which leakage current pulses on HTV-SIR were counted. Surface temperature distributions and the occurrences of thermal spots >400°C also were observed by means of an infrared thermovision study. We employed thermogravimetry (TG)-differential thermal analysis (DTA)-mass spectrometer (MS) to observe the thermal degradation of unfilled and filled HTV-SIR in both air and argon. The test results indicate that 40%wt is a critical ATH level and whether tracking and erosion is allowed in the IP tracking and erosion test. Highly filling ATH (>40%wt) reduces the number of low unit silicone oligomer precursors which promote dry-band arcing as well as the presence of residual carbon which leads to carbonization. Chemical modifications of water vapor liberated from heated ATH to methyl groups, which occurs at the thermal decomposition temperature of silicone rubber, were found to result in the above process. The protection mechanisms of ATH for the tracking and erosion of HTV-SIR are formulated herein View full abstract»

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  • A study of partial discharges from water droplets on a silicone rubber insulating surface

    Page(s): 262 - 268
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB) |  | HTML iconHTML  

    This paper presents measurements of partial discharge (PD) from water droplets on a silicone rubber insulating surface in an ac field. Tests are done by placing droplets on the surface using a micro-pipette, and by condensing water in a controlled humidity chamber. The field enhancement factor due to droplets placed on the insulation surface is experimentally and numerically determined. Values in the range of 3.8 to 6.3 are obtained depending on the size and number of droplets. The time resolved analysis of PD from water condensation indicates a threshold field, between 3.0 and 3.5 kV/cm, above which the PD activity increases with time, and brings the insulation to a surface breakdown. The corresponding field enhancement factor obtained for the condensation experiments is between 5.8 and 6.8. The results therefore suggest that the PD activity on the hydrophobic surface can be used effectively to learn about the insulation surface conditions View full abstract»

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  • Effect of liquid impregnation on electrical tree initiation in XLPE

    Page(s): 239 - 243
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (444 KB) |  | HTML iconHTML  

    The tree initiation voltage of impregnated crosslinked polyethylene (XLPE) with a dielectric liquid is drastically improved compared to normal XLPE for both ac and impulse voltage application. It is considered that liquid fills the polymer free volume, and removes space for electrons to be accelerated to high energy. The experimental results support that collision impact of electrons accelerated in polymer free volume is the dominant cause of electrical tree initiation, and also show that liquid impregnation is a promising way to improve performance and prolong the life of polymeric insulating materials View full abstract»

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  • Integro-differential equation of absorptive capacitors

    Page(s): 244 - 247
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    Equations for the internal discharge and residual voltage in absorptive capacitors are given. The after-effect phenomena are described by an integro-differential equation whose solution is obtained with the assumption that dielectric relaxation functions obey the Curie-Schweidler formula View full abstract»

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  • Insulation optimization by electrode contour modification based on breakdown area/volume effects

    Page(s): 162 - 167
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (436 KB) |  | HTML iconHTML  

    This paper shows how to determine the electrode contour with the best insulation performance on the basis of an area effect and a volume effect in the breakdown field strength. Previous electric field optimization techniques have provided us only with an optimum electric field distribution, For the design of power apparatus insulation, we have to consider the dielectric breakdown characteristics rather than the electric field distribution. As a first step, we developed a new optimization technique which enables us to obtain an optimum electrode contour with the highest breakdown strength while taking into account the area and volume effects of breakdown strength of insulating media. From the results, we have confirmed that the proposed optimization method improved the breakdown voltage more than did the electric field optimization. This leads to an effective insulation design of electric power apparatus View full abstract»

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  • Surface field dynamics in dc film capacitors under an impulse voltage perturbation

    Page(s): 293 - 298
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (572 KB) |  | HTML iconHTML  

    For metalized polymer film capacitors, the dynamics of electric field on the electrode surface and its resulting energy dissipation influence the onset and scale of breakdown discharges within the capacitor unit, which in turn is indicative of the reliability and lifetime. To gain an understanding of the dependence of surface electric field on key system parameters, an equivalent circuit model is developed to simulate the temporal evolution of the, electric field distribution within a dc film capacitor subjected to an external impulse electric stress. A mosaic pattern of electrode segmentation is taken into account by means of an effective surface resistance and its effects on surface electric field and energy dissipation are computed numerically. Also considered are the effects of the number of electrode segments across a given length. In addition, electric energy dissipation is calculated to assess the level of possible temperature rise within the capacitor. By addressing these two issues, it is shown that the numerical code developed and its underlying methodology can serve as a complimentary tool to the present practice of capacitor designs and performance assessment View full abstract»

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  • Anomalous creeping flashover characteristics in N2/SF 6 mixed gas under single pulse voltage

    Page(s): 195 - 202
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB) |  | HTML iconHTML  

    Creeping flashover characteristics for the needle electrode-plane electrode filled with N2/SF6 gas mixtures have been investigated. In the case of the needle-plane configuration, the flashover voltage was enhanced by an admixture of SF6 into N 2. On the other hand, by the insertion of a solid dielectric barrier between the needle and the plane, only the negative creeping flashover voltage was reduced drastically by the admixture of SF6 gas into N2 gas, and a highly emissive region at the top of a creeping corona was found in N2/SF6 gas mixture. This behavior is strongly affected by the creeping corona extension process, depending on the creeping distance and the gas pressure View full abstract»

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  • PD characteristics in an air-filled void at room temperature under superimposed sinusoidal voltages

    Page(s): 269 - 275
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB) |  | HTML iconHTML  

    Partial discharge in an artificial air-filled void under superimposed sinusoidal voltages is investigated at room temperature in order to clarify the effect of voltage superposition. The applied voltage waveform is composed of a 60 Hz fundamental sinusoidal wave and a high frequency sinusoidal wave of 300 Hz to 1.2 kHz. It was found that PD started when the peak value of the superimposed voltage reached the PD inception voltage under 60 Hz sinusoidal voltage. Also, PD occurrence frequency increased remarkably when the peak value of the high frequency component exceeded a critical value, which is smaller than the PD inception voltage under 60 Hz sinusoidal voltage. PD characteristics under such conditions were discussed as the effect of the residual voltage, caused by the surface charge deposited in the void by the preceding PD. The obtained experimental results suggest that the superposition of high frequency component accelerates the degradation of the solid insulator containing void defects View full abstract»

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  • Study of normal and malignant white blood cells by time domain dielectric spectroscopy

    Page(s): 253 - 261
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (852 KB) |  | HTML iconHTML  

    The aim of this paper is to present a comprehensive theoretical and experimental study by means of time domain dielectric spectrometer (TDDS) of static and dynamic dielectric properties of normal and malignant blood cells. The successful use of the TDDS method as a tool of human cell study required a special protocol and algorithms for all stages of cell preparation, measurements and data treatment. The routine developed in this study was used in the experimental analysis of nine lines of malignant, transformed and normal lymphocytes. It was shown that dielectric permittivity, capacitance and conductivity values of the cell membrane are higher for normal lymphocytes in comparison with malignant ones View full abstract»

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  • A digital technique for the on-line measurement of dissipation factor and capacitance

    Page(s): 228 - 232
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB) |  | HTML iconHTML  

    This paper reports a computer-aided system for on-line monitoring of dielectric dissipation factor tan δ, and capacitance of HV apparatus. The method employs the discrete Fourier transform (DFT) which is performed on the scaled down analog voltage and current signals obtained using a digital storage oscilloscope (DSO) board. The results are displayed using the graphic user interface implemented with graphic (G) language, This technique uses optimal values of measurement parameters as indicated by software simulation and laboratory tests. Field tests were conducted at Manitoba Hydro's Dorsey station to evaluate the insulation of a 230 kV current transformer unit using the developed system View full abstract»

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  • The pollution flashover of ac energized post type insulators

    Page(s): 191 - 194
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB) |  | HTML iconHTML  

    This paper investigates the application of a theoretical model to predict the flashover of practical post type insulators. In particular, the model is applied to two 132 kV designs with different profiles and leakage path lengths. It is found that arc shortening due to inter-shed and inter-rib flashover and arc movement results in a significant deterioration of the pollution performance of the insulator. The theoretical results are confirmed by salt fog tests and field experience View full abstract»

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  • Space charge dynamics in LDPE films immediately before breakdown

    Page(s): 304 - 306
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    Space charge dynamics in low-density polyethylene (LDPE) films were observed by the pulsed electroacoustic (PEA) method during breakdown tests at various temperatures. In order to investigate the intrinsic electrical breakdown, the applied electric field was increased to 300 kV/mm in 150 ms, and kept constant until breakdown of the specimens, or 300 ms at the longest. Space charge profiles were measured at 1 ms intervals. A significant positive charge propagating into the sample was observed only immediately before the breakdown at 90°C. These measurements revealed that the positive charge behavior is strongly related to the breakdown phenomena View full abstract»

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  • Thickness dependent dielectric strength of a low-permittivity dielectric film

    Page(s): 248 - 252
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB) |  | HTML iconHTML  

    The dielectric strength of a promising interlevel low relative permittivity dielectric is investigated for various film thicknesses and temperatures by using I-V measurements with metal-insulator-semiconductor (MIS) structures. It is found that the dielectric breakdown mechanism also depends on thickness. For relatively thick films (thickness >500 nm), the dielectric breakdown is electromechanical in origin, i.e. the dielectric strength is proportional to the square root of Young's modulus of the films. By scanning electron microscopy (SEM) observation, a microcrack in thicker films may contribute to a lower value of Young's modulus, which may confirm that the electromechanical breakdown is the dominant mechanism for dielectric breakdown of thicker films. In addition, the thickness dependent dielectric strength can be described by the well-known inverse power-law relation by using different exponents to describe different thickness ranges, However for thinner films, i.e., <500 nm, the experimentally observed relationships among the dielectric strength, Young's modulus, and film thickness cannot be explained by the existing models View full abstract»

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  • Laser-triggered electrical breakdown in liquid dielectrics. Imaging of the process by the shadowing technique

    Page(s): 212 - 219
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (796 KB) |  | HTML iconHTML  

    Electric breakdown in transformer oil subjected to a quasi-uniform dc electric field has been triggered by a focused laser pulse and prebreakdown discharge phenomena were imaged by the shadowing technique. Extensive data were recorded of the prebreakdown phenomena, such as streamers and gas bubble growth, from the initiation of the laser plasma to the disruptive discharge. The data was used to qualitatively and semi-quantitatively describe these phenomena. The image material also was used to improve and modify the qualitative description of the laser-triggered breakdown process previously presented by Sunesson et al. [1994] View full abstract»

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  • Simplified digital acquisition of microdischarge pulses

    Page(s): 220 - 227
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (724 KB) |  | HTML iconHTML  

    A new concept of the measurement of the height of microdischarge pulses is proposed and implemented on a special hardware assembly. The concept utilizes the highly asymmetric shape of microdischarge pulses, i.e. the sharp rise edge and slowly decaying tail that forms an almost `horizontal' plateau. The maximum height of a pulse can be determined by imposing a certain time delay in saving sample points. The time delay must be equal to or longer than the time necessary for the full rise of the front edge of the pulse. The new concept completely removes time-consuming procedures seeking for signal local maxima used in current digitizers with logic circuits. This makes the system very fast and brings it to the very limit of the underlying natural process itself which represents the main advantage compared with other existing methods. A certain disadvantage of the new concept is in its restriction to asymmetric pulses only, but, however, this class of pulses comprises the broad spectrum of pulsating phenomena appearing in various branches of science and technology. This gives the proposed concept good applicability not only in the field of electric microdischarges but also in many other experimental domains View full abstract»

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  • Field solution in polluted insulators with non-symmetric boundary conditions

    Page(s): 168 - 172
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB) |  | HTML iconHTML  

    A finite difference (FD) method to calculate the electric field in polluted insulators with asymmetric boundary conditions is proposed. The method is based on neglecting the displacement currents that circulate through the porcelain and through the air, in comparison with the conduction currents that circulate over the semiconductive pollution layer covering the insulator. This assumption reduces the 3D problem to a 2D one over the insulator surface. The FD method is applied by superposing a grid composed of parallels and meridians over the insulator surface, setting up an FD equation for each mode, and solving the resultant set of simultaneous equations View full abstract»

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  • FRP rods for brittle fracture resistant composite insulators

    Page(s): 182 - 190
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (876 KB) |  | HTML iconHTML  

    Brittle fracture of fibreglass reinforced polymer (FRP) rods can lead to mechanical failures of composite insulators even at low mechanical loads during operational service. Although this fact has been known for 20 years, it may still be a problem in some designs of composite insulators at the present time. In order to find countermeasures against brittle fracture, a study was carried out in the early eighties. It turned out that brittle fracture is a problem of FRP material and that material compositions exist, resistant to brittle fracture. A brittle fracture resistant FRP rod introduced in 1983 in one particular design of composite insulators resulted in a 15 year excellent service performance. This study deals with details of brittle fracture of FRP rods. Test setups were established to induce brittle fracture artificially. It was realized that brittle fracture is some kind of stress corrosion related to the composition of the FRP material. A broad variety of FRP materials was evaluated, showing the influence of the components of FRP material on the brittle fracture behavior of FRP rods as well as the effects of different manufacturing processes. The compositions of brittle fracture resistant FRP rods are disclosed. The results from artificial testing are compared with brittle fracture of FRP rods that occurred in composite insulators in operational service. Although no quantitative correlation could be established, the trend concerning the material behavior of FRP rods is similar View full abstract»

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  • Insulator contour optimization by a neural network

    Page(s): 157 - 161
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (396 KB) |  | HTML iconHTML  

    Contour optimization of axi-symmetric insulators in multi-dielectric arrangements by a neural network (NN) has been carried out to obtain not only a uniform but also a complex electric stress distribution along the insulator surface. Three case studies have been reported In detail. Multilayer feed-forward networks with error backpropagation and also with resilient propagation learning algorithms have been employed. The training and test data have been prepared by means of electric field calculations. The results show that optimized insulator contours have been obtained with an acceptable degree of accuracy with the help of a trained NN View full abstract»

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  • On multistress aging of epoxy resins: PD and temperature

    Page(s): 299 - 303
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB) |  | HTML iconHTML  

    The results of partial discharge (PD) aging at different temperatures performed by means of PD electrical detection on specimens with a flat cavity are reported. First, polymethylmethacrylate (PMMA) resin was used to set up a suitable test methodology under multistress conditions, e.g. in a divergent electrical field and at a temperature higher than the ambient. Next, an epoxy resin of electrical and industrial interest was tested. To analyze the aging phenomena during the life tests and to identify the PD statistical features, physical and statistical off-line analysis of the acquired data were carried out. Temperature strongly changes PD activity in pulse number and amplitude, affecting the material lifetime as well. At the examined test conditions, the skewness parameter applied to the PD phase distribution was found to be useful in the dielectric aging progression analysis, as was found earlier by other authors. The reported results are considered useful for the PD performance study of electrical systems under working conditions View full abstract»

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  • Morphology and the growth of electrical trees in a propylene/ethylene copolymer

    Page(s): 284 - 292
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (916 KB) |  | HTML iconHTML  

    Growth of electrical trees under 50 Hz high electric stress has been studied in a clarified propylene/ethylene copolymer, to explore the effects of the applied field and the material microstructure. Crystallization of the copolymer at low temperatures (<128°C) produces a continuous lamellar texture and the material consequently is optically transparent. At higher crystallization temperatures (134°C), more sporadic nucleation occurs and, as a result of the larger scale structural features that develop, the material becomes optically scattering. Nevertheless, CCD images of evolving tree structures could be obtained in both systems. Electrical treeing was found to occur reproducibly, but in a markedly different manner in the two morphologically different but chemically identical materials. In the low temperature crystallized copolymer, electrically conducting tree structures were found to develop with a growth rate that increased monotonically with increasing applied voltage. Conversely non-conducting tree structures formed in the 134°C crystallized copolymer that mimic the well documented decreasing tree growth rate with increasing applied voltage behavior of both low density polyethylene and a flexible epoxy resin View full abstract»

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  • Electrorheological properties of anisotropically filled elastomers

    Page(s): 173 - 181
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB) |  | HTML iconHTML  

    We report the results of numerical simulations for the change of both mechanical and electrical properties of elastomers with anisotropically filled polarizable particles under capacitively graded electric and mechanical fields. Such composites have potential applications in electromechanical control. We have used numerical techniques to study the effect of particle shape, permittivity/conductivity ratio, and spatial arrangement on the shear modulus as a function of the electric field. We also investigated the influence of the high field and nonlinear conductivity in the polymer matrix. The results indicate that electrostatic energy and changes therein, which result in electro-rheological effects, are concentrated between particles, and that the electrostatic interaction between the particles is concentrated in a very narrow regime at the tip of the particles, The interaction increases with the electric field intensity until the field between the particles is high enough to cause nonlinear electrical conduction in the polymer, resulting in a redistribution of the electric field and electrostatic energy View full abstract»

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  • Characteristics of elastic waves caused by corona discharges in an oil-immersed pole transformer

    Page(s): 276 - 283
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (660 KB) |  | HTML iconHTML  

    Measurements of elastic waves brought by a pulse of simulated corona discharge in an oil immersed pole transformer and a model tank filled with oil were performed in order to identify the location of insulation deterioration, using an acoustic emission (AE) technique. The detected AE signals were analyzed by means of a fast Fourier transform (FFT), and properties of elastic waves influenced by the existence of insulated windings and magnetic core for power transformation in the transformer were investigated. The result shows that almost all the initial AE signals detected on the-wall of the transformer tank were Lamb waves caused by the oscillation waves passing through the insulating paper and oil with repeating transmission, reflection and refraction. Also, it was possible to recognize whether the measured elastic wave was influenced by windings and their insulating papers or not, by FFT analysis. This suggests that the location accuracy of the corona discharge in the transformers would be improved View full abstract»

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  • Light emission in XLPE subjected to HV in high vacuum and pressurized gas

    Page(s): 233 - 238
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (580 KB) |  | HTML iconHTML  

    The spectral and spatial resolution of electroluminescence, the light emitted from polymeric insulation subjected to high electric field, is studied in a test cell pressurized to 215 kPa with ultra high purity nitrogen gas. The paper also describes light emission from crosslinked polyethylene (XLPE) subjected to HV in an ultra high vacuum test cell. It is shown that the characteristics of light emitted from XLPE in the evacuated test cell are quite different from the light emitted when the test cell is pressurized. The mechanisms responsible for light emission under high vacuum condition are described and it is suggested that care should be taken when interpreting the light detected from polymeric insulation subjected to high electric fields View full abstract»

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Aims & Scope

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

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Reuben Hackam