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Dielectrics and Electrical Insulation, IEEE Transactions on

Issue 5 • Date October 2008

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Displaying Results 1 - 25 of 38
  • IEEE Transactions on Dielectrics and Electrical Insulation - Table of contents

    Page(s): c1
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    Freely Available from IEEE
  • Executive Committee

    Page(s): c2
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    Freely Available from IEEE
  • Aiming at a more rigorous understanding in electrical insulating materials research

    Page(s): 1201 - 1214
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1604 KB) |  | HTML iconHTML  

    Professors Inuishi, Ieda and Yahagi were pioneers of research in dielectrics in Japan. Their philosophy was that in order to understand a certain property of a material or to clarify the mechanism of a phenomenon, research must be done with scientific rigor and a scholarly approach. Here, the author wishes to illustrate their philosophy through a number of examples of his own research on both inorganic and organic materials and on topics ranging from vacuum discharge, through defect centers in inorganic glasses, to the water tree degradation phenomena in insulating polymers. Finally he will make some comments upon the way in which fundamental research can be useful in an engineering context. View full abstract»

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  • Photoluminescence in polyamide/mica and polyethylene/ MgO nanocomposites induced by ultraviolet photons

    Page(s): 1215 - 1223
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1006 KB) |  | HTML iconHTML  

    Nature of electronic states in the energy band is investigated by means of optical absorption and photoluminescence induced by vacuum ultraviolet photons for polyamide-6/mica and low-density polyethylene/MgO nanocomposites. The nanofiller loading does not affect the absorption spectra of polyamide samples. Contrary to this, two absorption bands are induced at around 5.0 and 6.2 eV by the nanofiller loading in polyethylene samples, but they are due to absorption by the fillers. A luminescence band is observed at around 3.0 eV in polyamide samples, whereas three luminescence bands are observed at around 4.3, 3.7, and 2.9 eV in polyethylene samples. However, for all the luminescence bands, neither emission nor excitation energies change by the addition of nanofillers. Decay profiles of all the luminescence bands are essentially unchanged by the nanofiller loading. Moreover, no new PL bands are induced in the observed wavelength range. These results indicate that localized states, at least as far as the ones that can emit luminescence photons with intensities more than the sensitivity of the present research, are not induced by the nanofiller loading. View full abstract»

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  • Thermal, mechanical and dielectric properties of nanostructured epoxy-polyhedral oligomeric silsesquioxane composites

    Page(s): 1224 - 1235
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1026 KB) |  | HTML iconHTML  

    This paper presents the results of the thermal, mechanical and dielectric measurements conducted on polymer nanocomposites consisting of epoxy and polyhedral oligomeric silsesquioxane (POSS). The material composites were analyzed with a scanning electron microscope (SEM), an atomic force microscope (AFM) and a transmission electron microscope (TEM). Glass transition temperatures of the composites were measured with differential scanning calorimeter (DSC). Stress, strain, modulus and impact strength of epoxy nanocomposites were tested. Ac and lightning impulse (LI) breakdown strength of the composites were measured. Relative permittivity, loss factor and volume resistivity measurements were also conducted on the material samples. Two types of POSS, glycidyl and octaglycidyldimethylsilyl, were used in different quantities. Statistical analysis was applied to the measurement results to determine the effects of the additive type and amount on the properties of epoxy. The paper discusses the possibilities and restrictions in order to achieve advantages in high voltage applications using polyhedral oligomeric silsesquioxanes. View full abstract»

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  • Effect of calcium doping on dielectric and pyroelectric properties of PLZT

    Page(s): 1236 - 1241
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4863 KB) |  | HTML iconHTML  

    Effect of calcium doping on structural, dielectric and pyroelectric properties of Pb0.92-xLa0.08Cax(Zr0.65Ti0.35)0.98O3 (PLCZT) composition derived by the solid state reaction method was studied. Rhombohedral perovskite phase was confirmed in all the PLCZT samples. Calcium doping did not show any structural change in PLCZT (8/65/35) up to 2.5 % doping, however grain size and crystallite size was found to increase up to 1%, but no systematic variation of transition temperature was found with Ca doping. P-E hysteresis loop parameters (Ec and Pr) and pyroelectric properties were found to decrease with Ca doping up to 1% and there after increased. View full abstract»

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  • Reliability evaluation with weibull distribution on AC withstand voltage test of substation equipment

    Page(s): 1242 - 1251
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    For the development of a ldquoshort-duration AC withstand voltage testrdquo, an insulation specification of substation equipment, there is a precise method of reliability evaluation using a Weibull distribution function. Regarding this method, there remains a subject of handling coexistence of multiple voltage levels. This paper first defines the two reliability evaluation methods, ldquoindependence methodrdquo; and ldquoaccumulation methodrdquo, applying to Weibull evaluation for coexistence of multiple voltage levels in relation to their physical meanings. Next, the influence of the Weibull parameter values are examined on the cumulative fault probabilities and test voltages calculated using these methods. When the time shape parameter a>1, the accumulation method gives higher values than the independence method; When a=1, the two methods give the same values; When a<1, the former gives lower values than the latter. Then, appropriate reliability evaluation methods are investigated for various insulation media and insulation structures of substation equipment from the viewpoint of inception and development mechanisms of dielectric breakdown and partial discharge. According to the result of engineering evaluation of the presently available data, the independence method may be appropriate for both gas insulated switchgear and oil-immersed transformers. View full abstract»

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  • Diagnosis of electric power apparatus using the decision tree method

    Page(s): 1252 - 1260
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1754 KB) |  | HTML iconHTML  

    To diagnose the electric power apparatus, the decision tree method can be a highly recommended classification tool because it provides the if-then-rule in visible, and thus we may have a possibility to connect the physical phenomena to the observed signals. The most important point in constructing the diagnosing system is to make clear the relations between the faults and the corresponding signals. Such a database system can be built up in the laboratory using a model electric power apparatus, and we have made it. The next important thing is the feature extraction. We used oslash - V - n patterns and POW patterns for feature variables, and feature extraction is made by the extended moments, usual moments, and the parameters in the underlying distributions such as the generalized normal distribution and the Weibull distribution. By simple arrangements, we will be able to classify the faults and noise with high accuracy such that the misclassification rate is lower than 5%. If we set appropriate pre-processing procedure carefully, we might have a possibility of classification accuracy of less than 2%. Therefore, the decision tree with adequate feature extraction is considered to be a promising method as one of the classification tools. View full abstract»

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  • Influence of voltage application history on insulation test with one-minute step-up method

    Page(s): 1261 - 1270
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1235 KB) |  | HTML iconHTML  

    For the development of test conditions for a short-duration power-frequency withstand voltage test, which is one of the insulation specifications of substation equipment, there is a precise method of evaluating reliability using a Weibull distribution function. For this method, "independence method" and "accumulation method" have been proposed in order to handle the coexistence of multiple voltage levels. In this paper, an insulation test based on the one-minute step-up method as condition for the coexistence of multiple voltage levels is used to calculate and evaluate the test results using these two methods. Consequently, the insulation characteristics obtained from the one-minute step-up test are found to have differences from the true values. If the independence method is adopted, there is a certain deviation regardless of the Weibull time shape parameter "a-value" and, the smaller the Weibull voltage shape parameter "m-value", the larger the deviation. If the accumulation method is adopted, on the other hand, the larger the "a-value" or the smaller the "m-value", the larger the deviation. The 50% breakdown voltage value, the standard deviation "sigma-value", and the "m-value" that can be obtained from the insulation test based on the one-minute step-up method were evaluated for their deviations from the true values. The results suggest that, when a test is conducted on an oil-filled transformer, the design may turn out to be on the dangerous side due to overestimation of the dielectric strength by around 8%. View full abstract»

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  • Design of insulation test with one-minute step-up method for substation equipment

    Page(s): 1271 - 1280
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1266 KB) |  | HTML iconHTML  

    Reliability evaluation method with Weibull distribution function is used for development of test conditions for short-duration power frequency withstand voltage test. Although the evaluations by ldquoindependent methodrdquo and ldquocumulative methodrdquo are proposed, the handling of multiple voltage application still remains as one of the subjects. Therefore, insulation test with one-minute step-up method is studied as an insulation test with coexistence of multiple voltage level. As a result, the insulation characteristics by one-minute step-up method deviated from their true values. In this paper, it was calculated and evaluated by two methods with parameters of test condition. For the one-minute step-up method, the deviations from the true values were found to be influenced by test conditions: the larger the test voltage step width, or the lower the test starting voltage, or the greater the number of voltage steps, the smaller the deviations from the true values. Furthermore, the approaches to designing appropriate conditions for the test were summarized in order to design test conditions for oil-filled transformer and gas insulated switchgear. As a result, the reasonable test conditions were evaluated as follows: for oil-filled transformers, the test starting voltage was 70% of the one-minute breakdown voltage value and the voltage step was 7% and, for gas insulated switchgear, the test starting voltage was 80% and the voltage step was 5%. This result is approximately the same as the test conditions used for the actual measurement data in the past. These examinations will help to establish appropriate test conditions in the one-minute step-up method and to evaluate insulation characteristics obtained from the test. View full abstract»

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  • Thermal aging micro-scale analysis of power transformer pressboard

    Page(s): 1281 - 1287
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1974 KB) |  | HTML iconHTML  

    In order to analyze the thermal aging mechanism of the insulation paper inside the power transformer, a series of accelerated thermal aging tests were performed on pressboard. Subsequently, the atomic force microscope (AFM) together with scanning electron microscope (SEM) and X-ray diffraction (X-RD) were utilized to observe the micro surface of the thermal-aged pressboard. The experiments and analysis indicate that either the links among the D-glucopyranose units or the hexagonal mesh structures of the D-glucopyranose units were broken under thermal stress; the number of D-glucopyranose units after 6 weeks of aging was 0.8-1 per nm2, only about one third of un-aged value. The wall of a cellulose cell was deteriorated and thinned by thermal stress. At the same time, the cracks expanded gradually on the surface of the cellulose, which shortened the average width of cellulose fiber from about 40 mu of un-aged sample to about 25 mu after 6 weeks of aging. Meanwhile, the relative crystallinity and the size of the crystallite in the pressboard decreased nonlinearly with the thermal aging time. View full abstract»

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  • Evaluation of breakdown characteristics of oil-immersed transformers under non-standard lightning impulse waveforms - method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms

    Page(s): 1288 - 1296
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (597 KB) |  | HTML iconHTML  

    To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of oil-immersed transformers and thus reduce equipment cost while maintaining high insulation reliability, it is required to identify the insulation characteristics under non-standard lightning impulse waveforms that are associated with actual surge waveforms in the field and quantitatively compare them with the characteristics under the standard lightning impulse waveform. In the previous research, field overvoltages in the lightning surge time region were analyzed, and four typical non-standard lightning impulse waveforms were defined. These four waveforms were used to measure the breakdown voltages and the partial discharge inception voltages on three models of the winding insulation elements of oil-immersed transformers. The average breakdown voltages were evaluated in terms of the overvoltage duration. This paper describes a method for converting of non-standard lightning impulse waveforms into standard lightning impulse waveforms with equivalent stress for the insulation. The constructed algorithm was applied to four examples representing two types of non-standard lightning waveforms. Due to the conversion into standard lightning impulse waveforms, the crest values were reduced by 14% to 26%. This seems to be a potential for reduction of lightning impulse insulation specifications of oil-immersed transformers. View full abstract»

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  • Rough-granular approach for impulse fault classification of transformers using cross-wavelet transform

    Page(s): 1297 - 1304
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    A novel approach based on information granulation using Rough sets for impulse fault identification of transformers has been proposed. It is found that the location and type of fault within a transformer winding can be classified efficiently by the features extracted from cross-wavelet spectra of current waveforms, obtained from impulse test. Results show that the proposed methodology can localize the fault within 5% of the winding length with a high degree of accuracy. The basic concepts of feature extraction using cross-wavelet transform and the method of classification of those features by rough-granular method are also explained. View full abstract»

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  • Temperature dependence of the resistance of modern epoxy mica insulation of HV rotating machines

    Page(s): 1305 - 1312
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (503 KB) |  | HTML iconHTML  

    This work presents the temperature dependence of the dielectric properties of two types of epoxy mica insulation systems. Polarization and depolarization currents, insulation resistance, capacitance and polarization index were measured over a temperature range of 20 to 100degC on whole rotating machine stator bars. An analytical relationship of the correction of the resistance as a function of temperature was derived from the experimental results. View full abstract»

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  • A novel method to diagnose PWM-fed induction motors

    Page(s): 1313 - 1321
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (755 KB) |  | HTML iconHTML  

    A novel method for measurement and interpretation of PD phenomena in inverter-fed motors is discussed in this paper. The interpretation of PD measurements is carried out resorting to the direct-quadrature (dq) transform of the three voltages at motor terminals at the instant a PD event occurs. New tools (the dq loci, dq Hq and dq Hn patterns) are proposed to infer PD activity in a statistical way, similar to that used under AC supply. The method has been validated through tests on motorettes. In addition, measurements on low-voltage inverter-fed motors subjected to repetitive surges till breakdown are reported to support the capability of the method to infer onsetting faults. Measurements are performed through a reliable and lightweight (thus suitable for, e.g., automotive or avionics applications) antenna coupler characterized by excellent signal-to-nose ratio. View full abstract»

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  • Recent advances in high-k nanocomposite materials for embedded capacitor applications

    Page(s): 1322 - 1328
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (753 KB) |  | HTML iconHTML  

    In this paper, a wide variety of high dielectric constant (k) composite materials which have been developed and evaluated for embedded capacitor application are reviewed. Current research efforts toward achieving high dielectric performance including high-k and low dielectric loss for polymer composites are presented. New insights into the effect of unique properties of the nanoparticle filler, filler modification and the dispersion between filler and polymer matrix on the dielectric properties of the nanocomposites are discussed in details. View full abstract»

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  • Partial discharge diagnosis method using electromagnetic wave mode transformation in actual GIS structure

    Page(s): 1329 - 1339
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1788 KB) |  | HTML iconHTML  

    The diagnosis algorithm using ultra high frequency (UHF) method with the higher-order electromagnetic wave (EM-wave) was examined as the advanced partial discharge (PD) diagnosis method in a gas insulated switchgear (GIS) in the former paper. Previous studies evaluated the characteristics of EM-waves propagated in a simple coaxial cylindrical pipe, or through an L-shaped or a T-shaped pipe formed by combining these. In the present study, components (a hand hole, a post-type spacer, etc.) present in an actual GIS structure were identified, and an evaluation done mainly through an analysis on what effects their presence has on the mode transformation of EM-waves propagated inside a GIS tank. The direction in which a GIS tank is bent is horizontal (0deg) in the L-shape structure. If there is either a post-type spacer or a shield ring inside, and the signal source is in the 0deg direction, the distribution of the EM-wave strength varied according to through the L-shape structure. Also in the case of a T-shaped structure, the distribution of the output after signals are transmitted through the T-shaped junction varied depending on each component. Based on these characteristics, the diagnosis algorithm for PD with higher-order mode EM-waves was improved taking into account the effects of various components existing in an actual GIS, and a PD diagnosis method more suitable for an actual structure was established. View full abstract»

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  • Switching impulse flashover performance of different types of insulators at high altitude sites of above 2800 m

    Page(s): 1340 - 1345
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (605 KB) |  | HTML iconHTML  

    This paper explores the influence of air pressure, temperature and humidity on the switching impulse (SI) flashover performance of different types of clean and dry insulators at different high altitude sites of 2820 m to 5050 m along the Qinghai-Tibet Railway, the highest elevation railway in the world. Seven types of insulators are used in the flashover tests: one is a composite insulator, two are glass insulators and four are porcelain insulators. At the test sites, the ambient temperature varies between 6.7 degC to 28.5 degC and the absolute humidity is between 4.11 g/m3 to 9.69 g/m3. The test results show that the 50% switching impulse flashover voltage of different types of insulators at high altitude sites is independent of the materials and sheds of insulators but has a multi-factor non-linear relation with the shortest arc distance, the dry air pressure, the absolute humidity and the ambient temperature. The relative flashover voltage decreased with the ambient temperature is dependent on the voltage polarity, with 0.152% to 0.165% /degC for negative SI and 0.099% to 0.108% /degC for positive SI at the ambient temperature of from 6.7 degC to 28.5 degC. The relative flashover voltage increased with the absolute humidity and is dependent on the air pressure. The higher the altitude is, the more the influence is of the absolute humidity on the flashover voltage of insulators. View full abstract»

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  • Computation of AC wet flashover voltage of ceramic and composite insulators

    Page(s): 1346 - 1352
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (377 KB) |  | HTML iconHTML  

    This paper presents a theoretical method for calculating the flashover voltage of ceramic and composite insulators under wet conditions. The insulator surface is assumed to be clean. A 3-dimensional computer package (Coulomb) was used to calculate the electric field of wet surfaces. The surface wettability has been varied from hydrophobic to hydrophilic using the Swedish transmission research institute (STRI) method of classification. The calculated results are in good agreement with published data. View full abstract»

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  • Characterizing the internal strain in composite insulation under dry and wet conditions

    Page(s): 1353 - 1359
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (620 KB) |  | HTML iconHTML  

    This paper investigates the internal mechanical strain, developed within composite and polyester resin dielectrics, under dry and wet conditions. The paper characterizes this strain by a set of colored images, caused by relative retardation orthogonal components of the polarized white light used to illuminate the specimens in the microscope. An image-editing tool is used to analyze the structure of the strain-generated colors by assigning an intensity value to each pixel of the Red, Green and Blue components of the image. Each point in the image is identified by a set of three numbers ranging from 0 to 255. The Microsoft Excel is employed to process the results and to provide a simple comparison among various cases of the analyzed data. The change in the color map between dry and wet conditions for each examined specimen is used as an indicator of strain pattern variation, and consequently, as a tool to characterize the impact of water absorption on composites. This approach offers a quantitative data from strain images without a need for a complex mathematical procedure. On the other hand, the paper focuses on the resin as an absorber and transmitter of moisture, and tries to verify this hypothesis by subjecting the specimens of polyester resin, cast in different ways, to the same tests as that for the composite ones. Despite the dependence of the obtained results on the materials used and conditions applied, there is a clear effect of the moisture as an aging element on reducing the mechanical stress developed within the dielectric material. View full abstract»

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  • Properties of interfaces between silicone rubber and epoxy

    Page(s): 1360 - 1367
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1281 KB) |  | HTML iconHTML  

    An experimental set-up was designed for testing the impact of adhesion defects at interfaces between silicone rubber and epoxy in composite insulators. Test samples were aged in this set-up by discharges appearing under a presence of tangential electric field at the interfaces exposed to humid conditions. This combination of stresses simulated realistic conditions, in which ageing at the interface could possibly accelerate further deterioration of the adhesion between silicone rubber and epoxy. The test samples were prepared by joining both the materials with and without application of primer. Without the primer, bonding between epoxy and silicone rubber was reduced. The interfacial strength after the ageing was investigated by means of a modified peel test, whereas the changes of the dielectric properties were assessed by dielectric response measurements. Furthermore, the resulting degradation was analysed with infrared spectroscopy and optical microscopy. The analyses showed that the combined stresses affected to some extend both the epoxy and the silicone rubber. However, the interfacial mechanical strength was not reduced significantly, which is an indicator for possibility to tolerate existence of small interfacial defects in real composite insulators. View full abstract»

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  • Effects of saline water and temperature on surface properties of HTV silicone rubber

    Page(s): 1368 - 1378
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB) |  | HTML iconHTML  

    A study of the loss of hydrophobicity of high temperature vulcanized (HTV) silicone rubber (SIR) after immersion in saline solutions as a function of time (0 to 3000 h) at different temperatures is reported. The hydrophobicity is determined by measuring the static contact thetas between the tangent to the droplet of distilled water and the horizontal surface of the HTV SIR. The conductivity of the saline solution was varied from 0.005 to 100 mS/cm and the temperature from 0 to 98 degC. The contact angle which gives a measure of the hydrophobicity of the surface decreased sharply during immersion. The contact angle decreased from the original value of 100plusmn4.6deg to low value of 15deg after 3000 h of immersion at 98 degC in a solution of 0.005 mS/cm. The lower the conductivity, the larger was the decrease in the contact angle. The changes in the weight of the HTV SIR due to the uptake of water and the average surface roughness (ASR) are determined during the immersion. The increase/decrease in the weight and surface roughness of the HTV SIR are correlated with the contact angle and hence with the loss of hydrophobicity. The surface free energies gammasd, gammash and gammas, the interfacial energy of HTV SIR and water gammasl, and the energy of adhesion Wsi of water on HTV SIR are determined as a function of time during the immersion and related to the loss of hydrophobicity. View full abstract»

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  • Effects of low pressure on tracking failure of printed circuit boards

    Page(s): 1379 - 1384
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (499 KB) |  | HTML iconHTML  

    In general, printed circuit boards (PCBs) used in power devices and system operation in low pressure environments are more susceptible to damage from surface discharges. Additionally, repetitive operation of power systems is an important factor leading to tracking failure. Whether the tracking phenomenon at low pressures is different from that at atmospheric pressure needs better understanding to ensure reliable applications. In this paper, studies of tracking failure of PCBs in a low-pressure chamber, are reported for an electrode configuration comprising a pointed end of track close to the side of a track. Test samples were made by printing these tracks onto a glass-cloth epoxy-resin laminate. Experiments were carried out using repetitive unipolar pulses to simulate voltage surges. The ambient pressure was reduced from atmospheric pressure to a very low pressure (0.6 kPa). The time to failure and the cumulative charge passing before failure were recorded as function of the pressure, temperature, pulse interval and insulation distance. The results obtained indicate that the low pressure enhances the breakdown endurance of PCBs and the breakdown phenomena at low pressure are different from those at atmospheric pressure. With the decrease of the pressure, the cumulative charge is increased but the tracking failure is delayed. At low pressures, increasing temperature has little effect on the cumulative charge, but has significant influence on the time to tracking failure. View full abstract»

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  • Application of fractional-moments statistics to data for two-phase dielectric mixtures

    Page(s): 1385 - 1392
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (669 KB) |  | HTML iconHTML  

    A new method for quantitative "reading" of dielectric data of two-phase dielectric mixtures is suggested. This method is based on ideas related to the application of the generalized mean value (GMV) function to random data series (statistics of fractional moments). The GMV function allows transformation of arbitrary random data series to smooth curves that in turn can be fitted by an analytical function with a limited number of parameters. These fitting parameters are sensitive to the influence of an external factor, so the dependence of these parameters on the external factor can be used as calibration curves. In this instance we analyzed dielectric data measured for ground hard red winter wheat with 12.5%, 17.9% and 21.2% moisture contents in the temperature range from 2degC to 76degC. This system is a complex system from the viewpoint of the complexity of the dielectric data interpretation. The common treatment of these dielectric spectra does not provide a monotonic calibration curve. We treated these spectra as random data series by the use of the GMV function. As a result of this treatment, we obtained the monotonic temperature dependence of several fitting parameters for the given moisture contents, and these relationships can be fitted by an analytical function for calibration use. We hope that this new method will find application for analysis of other complex systems. View full abstract»

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  • Chemical, physical and electrical properties of aged dodecylbenzene 2: thermal ageing of single isomers in air

    Page(s): 1393 - 1405
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (957 KB) |  | HTML iconHTML  

    The linear isomer of dodecylbenzene (DDB), 1-phenyldodecane, was aged at temperatures of 105 and 135 degC in air and the resultant products were analyzed using a range of analytical techniques. On ageing, the 1-phenyldodecane darkened, the acid number, dielectric loss and water content increased and significant oxidation peaks were detected in the infrared spectrum. When aged in the presence of copper, a characteristic peak at 680 nm was also detected by UV/visible spectroscopy but, compared with previous studies of a cable-grade DDB, the strength of this peak was much increased and no appreciable precipitate formation occurred. At the same time, very high values of dielectric loss were recorded. On ageing in the absence of copper, an unusually strong infrared carbonyl band was seen, which correlates well with the detection of dodecanophenone by gas chromatography/mass spectrometry and nuclear magnetic resonance spectroscopy. It was therefore concluded that the ageing process proceeds via the initial production of aromatic ketones, which may then be further oxidized to carboxylic acids. In the presence of copper, these oxidation products are present in lower quantities, most of these oxidation products being combined with the copper present in the oil to give copper carboxylates. The behavior is described in terms of a complex autoxidation mechanism, in which copper acts as both an oxidizing and a reducing agent, depending on its oxidation state and, in particular, promotes elimination via the oxidation of intermediate alkyl radical species to carbocations. 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.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Reuben Hackam