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Thermally upgraded Kraft (TUK) "Insuldur®" papers prepared from the same batch process but with a different percentage of stabilizing additives (1.2, 2.6 and 4.4% of nitrogen) were studied under accelerated aging at 170 °C. The increment of stabilizing additives in paper with the consequent increment of nitrogen content slows down the rate of molecular chain scission of the cellulose and reduces the paper tensile strength loss rate. However, a progressive reduction in the enhancement of the paper life span by the increment of nitrogenous additives in paper was observed. The cellulose degradation methanol and ethanol markers were found to be reliable and accurate for tracking the aging of TUK papers even with the variation of nitrogen content in paper. A promising correlation between methanol concentration and the paper tensile index with different nitrogen content was determined. This correlation could be used as a basis for developing tools to assess power transformers residual life. FTIR-ATR analyses of dicyandiamide in aged papers showed a rapid reaction and decomposition of dicyandiamide in other compounds that slows down cellulose aging. The nitrogen content of aged paper, measured with the Dumas method, showed a slight variation during the study. This implies that the nitrogen compounds continue to be attached, presumably by polar forces to the paper. Thermogravimetric analysis (TGA) of new and aged Insuldur® paper samples showed that nitrogen additives improve the thermal stability of paper at high temperatures. [ABSTRACT FROM PUBLISHER]

Oil-paper insulation system is an extraordinarily essential system of converter transformer as well as HVDC bushing. This paper studies the interface charge accumulation and dissipation characteristics of oil-paper insulation system under DC voltage. In this paper, an induced electrification was used to charge the oil-paper samples. The amplitudes of the DC voltage varied from 1 to 4 kV and the paper was 0.13 mm in thickness. From the research of different voltage amplitudes and charging times of the paper, conclusions can be drawn that the decay is fast initially, and then becomes slower with the lapse of time. At last the dissipation trend tends to be flat. With the increase of the voltage amplitudes, the surface potential rises more rapidly, and higher voltage would also cause the charge to dissipate more quickly. Longer charging times would cause the charge to dissipate a bit more slowly. The decay rate of the negative voltage is a little smaller than that of the positive charge. Moreover, when it comes to the effect on the interface charge of the paper layers, the surface potential is more proportional to the increase of paper layers. When the amplitude of the voltage applied in the test is small or the charging time is short enough, the interface charge can be hardly accumulated on the bottom layer. In addition, the tdV/dt and the decay time curves under the positive voltage usually have two peak values, while there is only one peak value in most of the curves under the negative condition. [ABSTRACT FROM PUBLISHER]

The temperature distribution is vital to the lifetime and reliability of converter transformer bushings. However, the temperature distribution of epoxy impregnated paper converter bushings under a certain current has usually been calculated through the two dimensional model, without considering the heat convection and radiation effects. In this paper, using the computational fluid dynamics (CFD) and finite element method (FEM) analysis, a 3-D electromagnetic-fluid-thermal analysis method has been proposed. With the considering of heat conduction, heat convection and radiation, the temperature distribution of the converter transformer bushing has been simulated according to the actual operating environment. The temperature and velocity distribution of the converter transformer bushing has been obtained. Moreover, the simulation results have been compared with the experimental results to verify the accuracy of the simulation method. The simulation results, especially for the inner conductor, external conductor and the epoxy impregnated paper, are very close to the experimental results and the maximum temperature difference percentage is within 10 %, which indicates the accuracy and effectiveness of the electromagnetic-fluid-thermal analysis method proposed. [ABSTRACT FROM AUTHOR]

Results of a comparative analysis of two non-dimensional coefficients, calculated based on signals emitted by partial discharges (PD) are presented in the paper. The PD were generated using setups for modeling of three basic types of PD sources, which can occur in paper-oil insulation in power transformers. The following measuring methods were considered: electrical, ultra-high frequency, acoustic emission, and optical spectrophotometry. All measurements, for each of the PD-source configuration using the various methods, were conducted simultaneously in a laboratory under same measurement conditions. Based on the gathered results it was stated that it is possible to recognize the partial discharges form based on the non-dimensional coefficients, which differ in value for all of the considered methods except for the acoustic emission. The main contribution of the research performed lies in the simplicity of the applied signal processing procedure, which can be adopted to a device or system for diagnosis of partial discharges occurring in paper-oil insulation. [ABSTRACT FROM AUTHOR]

This paper presents a radio frequency plasma equipment designed to be used for the conservation procedures, such as decontamination, cleaning, and consolidation of cellulose-based materials. Decontamination and cleaning are carried out by the low-temperature nitrogen plasma generated between two electrodes, connected to a 1.5-MHz generator. The paper consolidation is performed by coating with compatible polymers in view of long term protection. Surface analyses (color analysis and electron microscopy) were undertaken to assess the uniform display of the polymer on the paper surface. The microbiological tests made on representative samples collected from historical books attested the complete inhibition of bacteria and fungi after, at most, 7-min treatment duration, depending on the initial infestation degree. [ABSTRACT FROM AUTHOR]

Paper degradation products dissolved in the oil are used as chemical markers for predicting the power transformers lifespan in paper-oil systems. For a compound to be useful as a solid insulation marker, it must be derived exclusively from insulating paper, must be thermally and chemically stable over time, and must have known migration behavior and paper/oil partitioning at different temperatures. Methanol was considered to be potentially useful as marker. The stability of methanol in the presence of organic acids formed by degradation of insulating oil and paper was evaluated in detail, using FTIR and Gas Chromatography Mass Spectrography (GC/MS), in samples of fresh mineral insulating oil (MIO) and high-acidity MIO removed from a transformer in the field, to which formic and acetic acid and methanol were added. The samples were subjected to thermal aging and the results showed that the main problem in using methanol as a marker for paper degradation was its high volatility, apart some possible esterification with low molecular mass acids formed with of paper and /or oil degradation. [ABSTRACT FROM AUTHOR]

Our community publishes peer-reviewed journal, magazine, and conference papers and articles sharing a commitment to originality and to quality content and writing. These papers vary in their characteristics and style, depending on their objectives and their targeted readership. The IEEE Publication Services and Products Board (PSPB) Operations Manual (OM) also provides guidelines differentiating these paper types. There is confusion sometimes, however, concerning the features of magazine papers in particular. Some authors, especially early-career authors, do not fully appreciate certain differences between magazine papers and their journal, transaction, and letter counterparts. This can create a challenge for magazine editors and may result in delay, or rejection, of papers that could have been accepted if written with a better understanding of what magazines are about. We focus our attention here on this issue as it applies to IEEE Communications Magazine (ComMag) in particular. Our goal is to help our new and/or young authors who want to publish in ComMag to customize their writing to the nature of this magazine and enable them to author papers with higher chances of acceptance. [ABSTRACT FROM AUTHOR]

To investigate the characteristics of micro bridges and their interactions with partial discharge (PD) in oil-paper insulation under DC voltage, an experimental platform with two-copper-electrode models is established. Generation and growth of micro bridge impurities are observed. PDs in experimental process are detected and analyzed. The result shows that the generation and growth of micro bridges have three stages based on their quantity and shape. At first stage PD accelerates the generation of micro bridges. At second stage the grown bridges trigger stronger discharges. At the last stage a so-called "hazardous bridge" that triggers highly intensive PDs emerges, through which breakdown happens. Therefore, bridges and PDs promote each other to cause insulation failure. In addition, impurities at the second stage are observed to transform into pile-like, bridge-like or particle-like shapes. The transformation process is considered to relate with the change of composition force on fiber bundles. Besides, a "cluster discharging" phenomenon is observed at the second stage, which is associated with the generation and disappearance of micro bridge impurities. [ABSTRACT FROM AUTHOR]

Aging of transformer paper insulation is commonly investigated through indirect measurements conducted in the oil, e.g. furanic compounds. In addition to the conventional indicators, recent investigations showed that alcohols like methanol and ethanol in oil could be used as paper aging indicators. This paper focuses on the applicability of these new paper aging indicators in a novel, gas-to-liquid (GTL) technology based transformer oil through an accelerated laboratory aging experiment. The experiment was conducted at 120 °C for up to 280 days. A conventional mineral oil was also tested as a reference. Kraft paper aged in both oil types showed similar reductions in degree of polymerization (DP) and tensile strength (TS). Amount of methanol in oil is higher than that of 2-FAL in oil when DP is over 375, confirming the promise of using methanol as an early paper aging indicator. Both the new paper aging indicator, methanol and the conventional paper aging indicator, 2-FAL are applicable for the GTL oil without any modifications. In addition, oil only aging experiments showed that oil does produce methanol but it is negligible compared with oil paper aging experiment; however the amount of ethanol measured in the present oil paper aging experiment is believed to be originated from oil oxidation rather than from paper aging. [ABSTRACT FROM PUBLISHER]

Presents the best paper awards for 2019-2021 and includes the list of reviewers who contributed to this publication in 2021. [ABSTRACT FROM AUTHOR]

Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers. [ABSTRACT FROM AUTHOR]

The Second International Conference on Advances in Plasma Science and Technology (ICAPST-21) was held during May 27–29, in 2021, at the Sri Shakthi Institute of Engineering and Technology, Coimbatore, India. As Dr. K. Navaneetha Pandiyaraj, the Organizing Chair of the Conference, states in the Preface of the conference’s Book of Abstracts: [ABSTRACT FROM AUTHOR]

Aging sensitive information related to cellulosic insulation can be obtained from the monotonically decaying dielectric relaxation function ?(?). Several circuits comprising of energy storing and dissipating elements are reported for modeling the dielectric relaxation function. Maxwell's ladder structure is one of the most popular approaches for modeling the dielectric response. For better modeling of dielectric response, a modified Maxwell's ladder structure is also reported that considers the effect of the aging due to the presence of a radial temperature gradient. In this paper it is proposed that for more accurate modeling of the dielectric response, the axial temperature gradient present in an operating transformer must also be taken into consideration. A further improved Maxwell two parameter model has been proposed that incorporates the effect of such axial temperature distribution. In the proposed technique each series branch of the two parameter model has been further divided into a number of parallel branches representing the effect of aging due to axial temperature gradient. [ABSTRACT FROM PUBLISHER]

Dielectric response measurements in either time or frequency domain are being assessed in modern times for condition monitoring of transformer oil-paper insulation. Proper interpretation of the dielectric test results requires understanding of the physical processes taking place in the insulation structure during such tests. It is thus necessary to establish proper mathematical and analytical formulations of the insulation behavior. Dielectric response functions of various forms based on the classical ?single relaxation time? Debye model have been proposed by various researchers to model the experimental data. In complex dielectrics, it seems however, that the overall response be represented by a distribution of relaxation times (or frequencies), rather than a single ?average? response characteristic. The present contribution provides in brief, the mathematical background for estimating the dielectric response functions used so far for modeling dielectric response measurement data. Function representing distribution of relaxation frequencies has also been estimated. Experimental results on laboratory test samples and field transformers have been presented to study and understand the effects of insulation status and operating conditions on test data. [ABSTRACT FROM AUTHOR]

Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers. [ABSTRACT FROM AUTHOR]

Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers. [ABSTRACT FROM AUTHOR]

Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers. [ABSTRACT FROM AUTHOR]

Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers. [ABSTRACT FROM AUTHOR]

This paper presents a novel technique to determine the optimized slope of triangular excitation in frequency domain spectroscopy that can provide better information about condition of oil-paper insulation. In conventional frequency domain spectroscopy, estimation of frictional losses due to the interactions of oscillating dipoles helps in investigating insulation condition. But, different types of dipoles in insulation cannot have similar dielectric relaxation times. Therefore, excitation having multiple frequencies is necessary for the dipoles to undergo more synchronized oscillations. This synchronized oscillation of dipoles reduces the inter-dipolar interactions and provides better information regarding insulation condition. Hence, in this work, triangular excitation is used for frequency domain spectroscopy since its harmonic contents can be varied by changing the slope. The slope of the triangular excitation is optimized to obtain more accurate information about the insulation condition. The optimized triangular excitation for insulation is determined using the proposed equivalent circuit model. To experimentally determine the effectiveness of the model, three test samples having preset moisture content in paper have been prepared in the laboratory. The optimized triangular excitations are then applied to the test samples to estimate their insulation condition. Experimental results show that the use of optimized triangular excitation provides information regarding the condition of oil-paper insulation with greater accuracy. In order to investigate the applicability of the proposed equivalent circuit model, the experiment has also been performed on real-life transformers. [ABSTRACT FROM PUBLISHER]

Air-gap discharge in oil-paper insulation is one of the main types of partial discharge (PD) in power transformer. The discharge development stage for monitoring and diagnosis of transformer potential faults is a significant area of study. The method of wavelet packet energy entropy, which is based on different frequency bands energy distribution of PD signals at different insulation states, is provided to explore the variation characteristics of the whole PD process. In this paper, air-gap discharge model is built in the simulative transformer tank that collects PD signals based on constant voltage method. This model also utilizes wavelet packet decomposition method to partition PD signal bands obtaining signal energy distribution in each frequency band, as well as total signal energy tendency along with PD development process. Wavelet packet energy entropy, which is the new PD feature parameter describing the development process, represents the order degree of PD signals which corresponds to dielectric strength. Finally, because of the cyclic change of this method, the step points of wavelet packet entropy are taken as the way to effectively divide the PD development stage. [ABSTRACT FROM AUTHOR]

Thermal aging of insulation paper occurs during transformer operation, with the water produced during aging accelerating the thermal aging process. Insulation paper aging largely determines the operational life of a transformer pressboard; accordingly, research pertaining to insulation paper enhancement is significant with respect to the functional safety of transformers. Within molecular research, particularly that focusing on molecular simulation, appropriate force field selection is paramount in order to acquire accurate results, in addition to appropriately reflecting cellulose thermal stability and associated degradation mechanisms. In the current study, two diverse cellulose models (water only; water, dicyandiamide, melamine and polyacrylamide) are developed and analyzed. Numerous model variables, including the diffusion coefficient of water and cellulose chain distance, are collated, in order to examine the effects of amines on the thermal stability of cellulose. Additionally, a novel insulation paper is formulated by combining traditional insulation paper with three diverse amines; an accelerated aging experiment is thus undertaken, comparing traditional and modified insulation paper samples at 110 °C, together with periodic assessment of both microwater content and the degree of polymerization (DP). Results indicate that during transformer operation, a higher degree of elasticity is associated with the modified insulation paper, thus significantly increasing its toughness and extensibility, in parallel with decreasing it brittleness. Results also show that the DP associated with cellulose comprising the modified insulation paper decreases at a reduced rate, with measured water content significantly less than that of traditional insulation paper. Simulation results are consistent with experimental findings. Therefore, it may be concluded that the thermal aging properties of cellulose significantly improve upon addition of dicyandiamide, melamine, and polyacrylamide as thermal stabilizers. [ABSTRACT FROM AUTHOR]

Transformer oil, insulating paper, high voltage direct current (HVDC) bushings and on-load tap changer (OLTC) are essential parts of converter transformers. When the power flow of the HVDC system is reversed or a sudden outrage occurs, the charge field will deform the dielectric internal electric field, thus easily leading to the occurrence of discharge or insulation damage. In this case, it is necessary to carry out the characterization of the oil?paper interface to avoid these consequences. This paper analyses the interface charge accumulation and dissipation characteristics of an oil?paper insulation system under DC and polarity reversal voltages. In this paper, induced electrification was used to charge the composite oil?paper insulation. The amplitude of DC and polarity reversal voltages applied in this paper was 4 kV, and paper with thicknesses of 0.08 and 0.13 mm was used. This research offers a theoretical exploration to optimize the transformer oil? paper insulation structure and prevent damage to its insulation systems. From the research on different layers and thicknesses of paper, it can be concluded that the decay is fast in the initial period and then becomes slower with the lapse of time until finally the decay curve tends to become flat. With an increase in the number of the paper layers, the interface charge density decreases. So in real life multilayer paper is used to avoid failures owing to its structural weakness. Regarding the DC polarity reversal effect, increasing the thickness of the paper is equivalent to adding paper layers. The dissipation rate of the positive interface charge is quicker than that of the negative one. In the polarity reversal test, the dissipation rate becomes smaller as the reversal time gets longer. [ABSTRACT FROM AUTHOR]

The Last decade saw significant growth in the digital terrestrial television (DTT) subscribers. The High peak-to-average power ratio (PAPR) of the transmitted signal is implied by the large fluctuations in its amplitude, which is a serious issue in the contemporary and next generation DTT broadcasting systems. These large fluctuations prevent feeding the high power amplifier (HPA) at an operating point near its non-linear (NL) saturation region, thereby lowering its power efficiency. For a better future, energy-efficient green communications is the need of hour. This paper focuses on digital predistortion (DPD), which is among the widely used techniques for HPA linearization in order to minimize the NL effects. DPD technique requires a feedback signal. This paper proposes a novel adding signal-based digital predistortion, where the output of the HPA is gradually linearized by adding a signal at the input in an iterative manner. By Taylor series approximation, the DPD problem can be posed as a convex one. We prove that a tighter upper bound exists for the convergence factor and instead of directly solving the convex problem, we pick a convergence factor value within its bounds that offers a good trade-off between convergence speed and residual error value. The simulation results show that the proposed technique can quickly linearize the HPA with good convergence. [ABSTRACT FROM AUTHOR]

Frequency Domain Spectroscopy is a popular non-invasive method that is widely used for condition assessment of oil-paper insulation in real-life power transformers. Conventional Frequency Domain Spectroscopy is done using sinusoidal excitation over a wide frequency range. In this work, a different approach has been taken to investigate some more possibilities of Frequency Domain Spectroscopy using non-sinusoidal excitation for a better condition assessment of oil-paper insulation. For that, triangular waveshape was chosen as non-sinusoidal excitations whose slope can be changed to vary the harmonic content and amplitudes of constituent components. Samples with preset moisture contents that emulate the oil-paper insulation of real-life transformer have been prepared in the laboratory for the assessment of insulation condition. For a comparative study, both sinusoidal and triangular excitations having same peak as well as time period are applied to the prepared samples under controlled environmental condition and corresponding dielectric response currents are measured. From the applied voltages and corresponding dielectric response currents, dielectric dissipation factors are calculated and compared. It has been observed that use of nonsinusoidal excitation provides better results than sinusoidal excitation in the estimation of paper moisture content. It has also been observed that among the applied non-sinusoidal excitations, a particular waveform provides more accurate information about the paper moisture content. [ABSTRACT FROM AUTHOR]

This paper proposed a simulation method for the charge transport in single-layer oil-paper insulation. The method of transient upstream finite-element method (FEM) is derived in order to calculate the time variation of charge densities in medium. The numerical simulation of charge transport in the single-layer oil-paper insulation is realized by applying the transient upstream FEM to the transport equations of bipolar charges. With reasonable microparameter, the charge transport in an experimental object is simulated. The simulation results are consistent with the experimental data. A bent model of oil-paper insulation is analyzed to study the charge distribution under the actual condition. This paper provides an exploratory research to the simulation of charge phenomenon in oil-paper, and has guiding significance to the design of oil-paper insulation. [ABSTRACT FROM AUTHOR]

In this paper, we present a practical method to construct dirty paper coding (DPC) schemes using sum codes. Unlike the commonly used approach to DPC where the coding scheme involves concatenation of a channel code and a quantization code, the proposed method embodies a unified approach that emulates the binning method used in the proof of the DPC result. Auxiliary bits are used to create the desired number of code vectors in each bin. Sum codes are obtained when information sequences augmented with auxiliary bits are encoded using linear block codes. Sum-code-based DPC schemes can be implemented using any linear block code, and entail a relatively small increase in decoder complexity when compared to standard communication schemes. They can also lead to significant reduction in transmit power in comparison to standard schemes. [ABSTRACT FROM AUTHOR]

The relation between ageing and space charge is a hot area, but there is little direct evidence. In this paper, oil-paper samples were exposed to 20-kV/mm DC electrical field, 130°C temperature or both 20-kV/mm DC electrical field and 130°C temperature separately. Charge transport through them was analyzed at intervals by the pulsed electroacoustic (PEA) method. We find that the quantity of trapped charge increases with stressing durations, no matter what kind of stress oil-paper is exposed to. That indicates that energy release through space charge movement, such as charge trapping/detrapping and recombination, is another reason for traps generation besides deterioration caused by thermal ageing. However, because the difference in cellulose degradation mechanism among them, charge transport dynamics are thereby different under different stressing conditions. Space charge accumulates faster inner electrothermally stressed oil-paper than that inner another two kinds of oil-paper, and the sign of trapped charge is positive if oil-paper is electrically or electro-thermally stressed. The latter behavior is discussed in terms of electromagnetic dynamics due to cavity within oil-paper once there is external electric field. [ABSTRACT FROM PUBLISHER]

A new biodegradable dielectric fluid for transformers, palm fatty acid ester (PFAE), with better cooling performance and oxidation stability than conventional mineral oil (MO) was developed in 2008. The aging of thermally upgraded paper (TUP) in PFAE was evaluated, comparing to MO and natural ester (FR3). The electrical properties of aged dielectric fluids were compared. Sealed aging SUS tanks containing copper, silicon steel, TUP, and PFAE, MO and FR3 (partly) in a nitrogen environment were aged at 130 °C-170°C for 20-120 days, with low concentrations of oxygen and moisture strictly controlled. Paper degradation after aging was determined using the degree of polymerization measurements. The gas production characteristics during the aging process were also compared. The results show that the TUPs in PFAE age at slower rates than those in MO, while at faster rates than those in FR3. Under the possibly low initial concentration of oxygen and water in the fluids in the absence of other material which may produce water during aging process, the limit service temperature for TUP in MO and PFAE with expected 30-year lifetime (DP450) would possibly reach 109°C and 113°C, respectively. Life estimation results show that the lifetime of the TUP in PFAE aging at 110°C would be at least 1.6 times the lifetime of the TUP in MO, if DP450 was set as the end-of-life point of the TUP. Aged PFAE exhibits highest breakdown voltage among the three types of dielectric fluid. Much lower acid value of aged PFAE than FR3 reveals that PFAE has better hydrolytic stability, which could ensure the safe operation of transformers. The aging mechanism is proposed. [ABSTRACT FROM PUBLISHER]

Oil soluble chemical markers such as methanol, ethanol and 2-furaldehyde for assessing the condition of insulating paper still present many challenges for an accurate interpretation in real transformers. Indeed, many conceptual parameters such as design (shell vs. core) or type of cooling are needed for a more accurate interpretation of the data. Moreover, similarly to water, the measured marker concentrations in oil are temperature-dependent, i.e. an existing partition phenomenon between the oil and the solid insulation modify the solubility of the markers, thus changing their apparent concentrations in the oil. Consequently, to follow the real trend of these species during the transformer?s service life, it is crucial to correct their concentrations at a specific temperature, as is done for the water content. Knowing these facts and in order to calibrate a predictive model, Hydro-Qu?bec decided to access equipment when dismantled, which enables a large amount of paper to be sampled from different sections of the windings. This allows for a more accurate representation of the transformer paper conditions in relation to transformer design. The paper condition obtained by measuring the degree of polymerization in accordance with the presence of chemical markers is a valuable process. We believe that it is possible to better understand the behavior of the paper insulation and to assess markers concentration thresholds using the oil analysis. This article discusses the recent experience in this field with specific cases. [ABSTRACT FROM AUTHOR]

In this paper, to effectively distinguish between the aging and moisture of oil-immersed paper (OIP), and to enhance the accuracy of the nondestructive diagnosis of the insulating state for oil-paper insulation, we perform an in-depth study of the frequencydomain dielectric response theory. First, we present a theoretical explanation for frequency-domain spectroscopy (FDS) based on investigations into the mechanism and characteristics of conductivity loss and polarization loss. Secondly, we explore the classical loss characteristics by performing a systematic analysis of the relationship between the complex dielectric permittivity and the frequency based on the measured FDS curves. Finally, we study the influences of the aging condition and moisture content on FDS. We extract some of the characteristic parameters that are related to the insulation condition. The results obtained indicate that at low frequencies, the FDS characteristic was mainly influenced by the conductivity loss, which may be explained by the Dyre model. At high frequencies, the characteristic was mainly influenced by the polarization loss, which may be explained by the H-N model. In addition, the characteristic at mid-range frequencies was due to both the conductivity and polarization loss. The moisture content significantly affects only the conductance process. Therefore, the characteristic parameter, namely the DC conductivity σ 0, which is closely related to the conductance process, can be used to quantitatively describe the moisture content of OIP. Meanwhile, the characteristic parameters α, β, and τ, which are associated with the polarization process, can be used to quantitatively describe the aging status of OIP. [ABSTRACT FROM AUTHOR]

The paper presents new diagnostic method applied to assess aging degree for paper-oil insulation used in professional electrical power device, primarily including medium and high power transformers. The described method is based on modified diagnostics using the recovery voltage effect occurring in dielectrics (RVM ? Recovery Voltage Methods). Modification of the RVM method applied so far, which is now used only to assess moistening degree for paper-oil insulation in power transformers, consists in a new parametric analysis of recovery voltage time characteristics. Simulation and experimental tests carried out in laboratory conditions for adequately prepared insulation samples have proven that the time-constant of recovery voltage decay (?R_MIN) is the most susceptible parameter as regards quantitative change in the function of aging of the examined insulation. This conclusion is also confirmed by statistical studies, in which a multi-parameter variance analysis method has been applied. An original equivalent circuit diagram of the insulation has been used to simulate aging degree of paper-oil insulation samples in numerical tests. The diagram is based on the Cole-Cole type dielectric response model. [ABSTRACT FROM AUTHOR]

The compatibility of a newly developed ester fluid (PKOAE) with cellulose insulation paper is evaluated by performing thermal ageing of Kraft paper in the new ester fluid. Thermally accelerated ageing was performed in sealed mild steel pressure vessel containing ageing catalysts, thermally upgraded insulation paper, and dielectric fluid (mineral oil and palm kernel oil alkyl ester) at 150°C for 28, 56, and 84 days. Under the same illumination, the color level of ester aged paper samples decreased by 33% after 84 days of ageing as compared with the color level of aged mineral oil impregnated paper samples which decreased by 73% within the same time. Whilst the samples of PKOAE impregnated paper exhibited approximately 5% reduction in tensile strength after 28 days of ageing, the kraft paper samples closer to copper strips were found to have a significant faster degradation rate. The tensile strength of paper samples closer to copper plates dropped to about 35% of the tensile strength of the unaged sample after ageing for 28 days, and the paper layers farther away from the copper plates decreased by about 10%. The mechanisms that could be responsible for the slower ageing rate of kraft paper in PKOAE fluid are discussed. The characteristic breakdown strength of PKOAE impregnated paper is on the average, 42% better than mineral oil impregnated paper. The high breakdown strength of PKOAE fluid may be responsible for the higher breakdown field of ester-paper system since the applied electrical stress is shared by the oil-paper combination. [ABSTRACT FROM AUTHOR]

This paper studies the second-order coding rates for memoryless channels with a state sequence known non-causally at the encoder. In the case of finite alphabets, an achievability result is obtained using constant-composition random coding, and by using a small fraction of the block to transmit the empirical distribution of the state sequence. For error probabilities less than 0.5, it is shown that the second-order rate improves on an existing one based on independent and identically distributed random coding. In the Gaussian case (dirty paper coding) with an almost-sure power constraint, an achievability result is obtained using random coding over the surface of a sphere, and using a small fraction of the block to transmit a quantized description of the state power. It is shown that the second-order asymptotics are identical to the single-user Gaussian channel of the same input power without a state. [ABSTRACT FROM AUTHOR]

This paper presents a study of the impact of two important parameters, moisture and aging of the oil/paper dielectric used as insulation in power transformers.The way in which these two parameters influence different parameters of the Frequency Domain Spectroscopy (FDS) measurements, is emphasized.Different FDS parameters were measured by varying the moisturecontent and the aging degree of the oil impregnated paper.The use of two types of neural networks for analysis of the results was necessary in order to help discriminating the impact of moisture and aging on the FDS measurements and, in some cases, to estimate the aging duration of the paper impregnated with oil. [ABSTRACT FROM PUBLISHER]

Oil-paper insulation, as a major insulation mode used in power transformers, is continuously and unavoidably subjected to repeated lightning impulses, which may bring potential risk to the insulation system. Therefore, in this work, accumulative effect of repeated lightning impulses and its damage mechanism in oil-impregnated paper (OIP) are investigated. Firstly a repetitive impulse accumulating test platform was set up, and tests were performed to confirm the existence of accumulative effect of repeated lightning impulses. Then atomic force microscope observation and frequency domain spectroscopy were carried out on OIP samples with different times of lightning impulses, based on which the influence of lightning impulses accumulative effect on surface morphology and dielectric properties of OIP was investigated. The results indicate that repeated lightning impulses produce accumulative damage to the OIP and hence lead to the morphology change and generation of translucent gelatinous substance on the sample surface. Both the surface roughness and dielectric parameters increase with the accumulating of repeated lightning impulses, which can be attributed to the effects of polar products, fiber deformation and the translucent gelatinous substance together. At last, the possible mechanism of the accumulative effect was discussed and relevant tests were carried out to verify the speculation. [ABSTRACT FROM PUBLISHER]

Recognizing actions from still images has been popularly studied recently. In this paper, we model an action class as a flexible number of spatial configurations of body parts by proposing a new spatial sum–product network (SPN). First, we discover a set of parts in image collections via unsupervised learning. Then, our new spatial SPN is applied to model the spatial relationship and also the high-order correlations of parts. To learn robust networks, we further develop a hierarchical spatial SPN method, which models pairwise spatial relationship between parts inside subimages and models the correlation of subimages via extra layers of SPN. Our method is shown to be effective on two benchmark data sets. [ABSTRACT FROM PUBLISHER]

Describes the above-named upcoming special issue or section. May include topics to be covered or calls for papers. [ABSTRACT FROM AUTHOR]

A low profile dual-band frequency selective surface (FSS) for shielding the GSM applications is presented in this paper. The proposed FSS contains the unit cell made of modified double square loop elements with paper as its substrate. The overall thickness of the proposed FSS measures only 0.55 mm. The FSS offers band stop response at 930 and 1720 MHz with 18 dB shielding effectiveness for a bandwidth of 100 and 173 MHz, respectively, thus shielding the GSM signals. Additionally, the modified double square loop element-based FSS is symmetrical providing the advantage of polarization independency. It also exhibits angular stability up to 60° for both the horizontal polarized electric field (TE mode) and vertically polarized electric field (TM mode). A prototype of the proposed dual-band low profile FSS is fabricated. The simulation results are compared with the experimental results and are found to be in congruence with each other. [ABSTRACT FROM PUBLISHER]

The life expectancy of a transformer is closely related to the condition of its oil-paper insulation. In the present study, oil impregnated pressboard samples with different aging states and water contents were prepared under controlled laboratory conditions to analyze the oil-paper insulation condition of the power transformer by the dielectric response method. Dielectric response measurements, i.e., polarization and depolarization currents (PDC) and frequency domain spectroscopy (FDS), were conducted on the pressboard samples at different temperatures. Results show that the dielectric responses of oil impregnated pressboards are highly sensitive to aging, water, and temperature, but the influence of the temperature on FDS can be effectively eliminated by using the master curve technique. Meanwhile, dielectric characteristic parameters, which are sensitive to aging state and water content, were extracted to form a fingerprint database to indicate the various states of the oil impregnated pressboard. A grey correlation diagnosis model was first introduced to assess the aging state and water content of oil-paper insulation. Finally, FDS measurements were performed on a field transformer to verify the effectiveness of the new evaluation technique proposed in this paper for the condition assessment of the transformer oil-paper insulation. [ABSTRACT FROM AUTHOR]

This work investigates the effect of alternating current partial discharge (AC PD) byproducts on the dielectric frequency response (DFR) of oil-paper insulation comprising of a small cavity, in the frequency range of 1.0 mHz to 1.0 kHz. The investigations were done by utilizing experimental results in combination with a Finite Element Method (FEM) model. The results presented in this paper show that ageing by-products in the cavity (PD stressed volume) alone will not result into the change in DFR of oil-paper insulation. According to simulation results, the significant change in the DFR results is mainly caused by PD by-products (positive and negative charges, and electrons) which tend to conduct or diffuse into the bulk of oil-paper insulation. The change in a dissipation factor curve due to PD by-products was observed to occur mainly in the middle and low frequency regions. The results indicate that the dissipation factor curves in the middle and low frequency regions depend on the level of PD by-products in oil and paper, respectively. [ABSTRACT FROM AUTHOR]

The service life of a transformer is determined by the condition of its oil?paper insulation. A modified Cole?Cole model was introduced to describe the frequency domain spectroscopy (FDS) curves based on the classic Debye relaxation model and thereby accurately determined the ageing state of the insulation of a power transformer using FDS. Oil?paper insulation samples with different ageing states are prepared under laboratory conditions, and a characteristic parameter is extracted to quantify their ageing states after a detailed investigation of the frequency domain dielectric properties of the samples. Results reveal that the modified Cole?Cole model, including the ? relaxation components, dc and hopping conductivity components, can be employed to effectively model the frequency dielectric characteristics of oil?paper insulation. Furthermore, the extracted characteristic parameter from this model, ??, can be utilized in the quantitative evaluation of the ageing states of transformer insulation. A case example is discussed to demonstrate the applicability of the proposed technique in the condition assessment of field power transformers. [ABSTRACT FROM AUTHOR]

The non-standard lightning impulse waveforms (N-SLIWs) including oscillating lightning impulses, very fast transient voltages (VFTOs) and steep waveforms in the power system gravely endanger the inner insulation of power transformer. To prevent insulation failure and provide guidance for robust transformer design, in this paper, two typical insulation models of oil-immersed transformer were established and their breakdown characteristics under N-SLIWs were investigated. The research mainly focused on the influence of front time and oscillation frequency of N-SLIWs on the breakdown characteristics. The experimental results showed that the breakdown voltage increased with the decrease of front time. For low frequency-oscillating lightning impulse waveforms (LF-OLIWs), breakdown voltage increased with the increase of oscillation frequency and was up to 30% higher than that under standard lightning impulse waveform (SLIW). For VFTOs, with the increase of frequency, breakdown voltages presented a law of inverted "U" type. Insulation model could withstand the highest value of VFTO when the oscillation frequency was around 2.4 MHz. But when the frequency was as high as 9 MHz, breakdown voltage was close to that under SLIW. A very high frequency oscillation was the main reason for the reduction of breakdown voltage as its steepness dV/dt assisted the effective transmission of the sphere?s potential to the head of the streamer channel. [ABSTRACT FROM AUTHOR]

Repeated impulses have long been considered to affect the insulation properties of electrical equipment. This interesting but rarely studied phenomenon may pose great risks to the reliable operation of power equipment. Therefore, in this work, we focus on the accumulative effect of repeated lightning impulses on the oil-impregnated paper (OIP) used in power transformers. Specifically, we study the effect of space charge on the accumulative characteristics of OIP. A repetitive impulse accumulating test platform was set up, and the tests were conducted to obtain the accumulative characteristics of OIP under repeated lightning impulses. The accumulative characteristics of OIP with various interval time were experimentally identified to study the influence of interval time on the accumulative effect. Then, space charge in OIP samples were investigated using the pulsed electro-acoustic technique. Charge behavior in OIP was analyzed under different conditions, i.e., changing the applied times, amplitude and interval time of the applied lightning impulses. Charge injection and transport occurred during lightning impulse accumulation. The increased application of lightning impulses, high applied voltage, and short interval time contributed to the accumulation and transport of space charges. At last, the possible mechanisms of the accumulative effect are discussed in this article based on the experimental results. [ABSTRACT FROM AUTHOR]

Deposition of transparent oxide films at atmosphere pressure onto polymeric substrates at room temperature is a technique gaining rapid acceptance. These films can be used for numerous applications such as antiscratch and water permeation barrier coatings. In this paper, a \sim 1.4 - \mu \text{m} SiOx layer has been deposited on polypropylene-coated paper at atmosphere pressure with a filamentary dielectric barrier discharge (DBD). The DBD linear discharge was driven by a 30-kHz power supply. Scanning electron microscope, X-ray photoelectron spectroscopy, and attenuated total reflection-Fourier transform infrared spectroscopy were used to characterize the deposited film. The deposited thin film decreased water permeation through the paper by \sim 15$ %. [ABSTRACT FROM PUBLISHER]

A method of predicting the residual breakdown electrical field strength of an epoxy-mica paper insulation system is described. This method was developed by using data on service?aged stator bars from generators as well as accelerated aging model bars. Thermal aging, mechanical aging, and combined thermal and mechanical aging were done individually as accelerated aging. The partial discharge characteristics, dissipation factor, and breakdown voltage were measured on the model bars and service?aged bars from generators. From these results, the residual breakdown electrical field strength was predicted based on the partial discharge characteristics and dissipation factor. First, the dominant type of deterioration (thermal or mechanical aging) on a bar?s insulation was determined by the pattern of voltage?partial discharge magnitude characteristics. Then the residual breakdown electrical field strength was predicted by using a predicting equation for both thermal and mechanical aging. Each predicting equation uses dissipation factor tip-up (i.e. difference in dissipation factor values between 2 kV and rated voltage) and partial discharge inception electrical field strength. The accuracy of this method was confirmed using data measured on 112 service-aged stator bars from generators and 10 accelerated aged model bars. The 95% confidence interval level included 94% of the measured residual breakdown electrical field strength values. This result shows that the method enables precise predictions of the residual breakdown electrical field strength of an epoxy-mica paper insulation system. [ABSTRACT FROM AUTHOR]