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Diagnosis of aging of the paper insulation in transformers has long been of interest to transformer manufacturers and utilities [1]-[3]. Such insulation is irreversibly aged during long-term operation, losing its mechanical strength and becoming brittle. The loss of mechanical strength is an important factor limiting the life expectancy of the transformer [4], [5]. Consequently diagnosis of aging and evaluation of residual life of paper insulation is important for the safe operation, condition-based maintenance, and replacement of power transformers [6]-[9]. [ABSTRACT FROM AUTHOR]

Furfural content in oil has been shown to be a powerful indicator of the deterioration of cellulose paper. The furfural content in oil may increase greatly when the moisture content increases in transformers. The increase of furfural content in oil can be attributed to various factors, such as aging of cellulose paper with the increase of moisture content and the difference in furfural production mechanism. In this research, thermal aging tests of oil-paper system with different moisture contents are conducted under laboratory conditions to determine the cause of such increase. Furfural content, both in insulation oil and in insulation paper, and the degree of polymerization values of insulation paper were regularly measured. Results show that the moisture content plays a significant role on the production of furfural, and the high initial moisture content in insulation paper leads to large amount of furfural produced when DP decreases to the same values. The difference in the moisture content apparently affects the distribution of furfural between oil and paper, and the increase in the moisture content in oil-paper system increases the diffusion of furfural from the insulation paper to the oil. [ABSTRACT FROM AUTHOR]

The paper presents the results of investigations on the thermal properties of cellulose and aramid paper impregnated with various liquid insulations. The liquid insulations investigated were mineral oil, synthetic ester, and natural ester. The heat transfer coefficient of the liquid was calculated on the basis of measurements of the thermal expansion, specific heat, density, thermal conductivity and kinematic viscosity of the liquid insulations. Temperatures in the paper and liquid insulations were calculated. The results allow to select the best paper and liquid insulations which provide the most effective cooling in transformers. [ABSTRACT FROM AUTHOR]

The converter transformer epoxy impregnated paper bushing is a multi-media electrical equipment, and the main materials include the internal conductor, the external conductor, transformer oil, SF6 gas, the air inside internal conductor, the main insulation material epoxy impregnated paper, sheath, and fittings. In actual operating, the converter transformer bushing is undertaken by the harmonic current with large number of high harmonics and the temperature distribution of the epoxy impregnated paper converter transformer bushings under actual current waveform needs to be researched. What's more, the temperature distribution of the epoxy impregnated paper converter transformer bushings is affected by several factors and to provide basis for the optimization of bushings it's necessary to research about the impact of these factors on the temperature distribution of the epoxy impregnated paper converter transformer bushings. In this paper, on the basis of our previous paper [8], the 3-D temperature distribution of the 400 kV epoxy impregnated paper converter transformer bushing under actual current waveform with large number of harmonics has been simulated by using the computational fluid dynamics (CFD) and finite element method (FEM) analysis. The temperature distribution regularity of the 400 kV converter transformer bushing under different influencing factors has been computed and analyzed. The dissipation structure of the bushing has been optimized and the DC steady-state electric field distribution of the 400 kV converter transformer bushing has been obtained considering the temperature gradient in epoxy impregnated paper. [ABSTRACT FROM PUBLISHER]

Cellulosic insulating paper is the essential component of the insulation in power transformers. Under the thermal stress inside the transformer, the cellulosic insulating paper degrades and generates formic acid. Meanwhile, the presence of formic acid further accelerates the aging process of cellulosic insulating paper. This study takes the cellulose molecule composed of D-glucose as the research object. The ReaxFF reactive force field is applied to simulate the high-temperature thermal aging process of cellulosic insulating paper. During pyrolysis process, the number of formic acid molecules presents short-term fluctuations and continuous increases. Though simulation, the main reaction pathways of cellulose pyrolysis to generate formic acid are obtained. In addition, an accelerated thermal aging experiment of oil-paper insulation is designed. The formic acid in the experimental samples is detected by the silanization derivatization method. Through the combination of simulation and experimental results, the feasibility of formic acid as an aging indicator for cellulosic insulating paper is further demonstrated. [ABSTRACT FROM AUTHOR]

Radio frequency identification (RFID) systems for the paper industry is an emerging research topic due to the need for an automated identification system for the paper industry which would carry on the identification codes of paper and board reels throughout their life cycle. This paper discusses the application of passive ultra-high frequency (UHF) RFID systems to the paper industry. Challenges, benefits, and the application environment of using passive UHF RFID systems in the paper industry are presented and discussed. The major challenges are development of globally operable tag antenna designs and integration of reader units and reader antennas to paper handling machinery. To confront and solve these challenges, this paper presents novel tag antenna designs for paper and board reel identification and proposes solutions for reader and reader antenna integration to paper handling machinery. In addition, the identification locations within the paper reel supply chain and the effects of RFID systems to supply chain visibility are presented and discussed. In addition, test results of using passive UHF RFID systems in the paper industry environment are presented. Note to Practitioners--An automated identification system, which would carry on the identification code of a specified paper or board reel throughout its life cycle, is needed in the paper industry. Nowadays when barcode identification systems are used the identity of the reels disappear when the wrapping of the reel and at the same time the barcode are removed. The RFID tag, however, would be attached to the paper reel core and thereby the identification code of the reel is restored throughout its life cycle. RFID systems would benefit the paper industry by enhancing the supply chain visibility and providing a more automated identification system than barcode identification. In the future, paper reels will be identified with clamp truck-integrated reader units which, on the other hand, enables adding more real-time information about the locations of the paper reels to information databases but also sets challenges for paper reel tag performance and integration of RFID reader units and reader antennas to paper handling machinery. This paper concentrates on passive UHF RFID systems and their application to the paper industry. Challenges and benefits of RFID systems in the specific application environment of the paper industry are presented and discussed. [ABSTRACT FROM AUTHOR]

The Editorial Board of the IEEE Open Access Journal of Power and Energy (OAJPE) would like to recognize the following best papers published between October 2017 and September 2020 in OAJPE and its preceding journal, IEEE Power and Energy Technology Systems Journal (PETS-J). Also presents a list of reviewers who contributed to this publication in 2021.

A quantitative analysis supports the argument that very low acceptance rates of conference papers are more likely to impede publication of bold and innovative research results than to indicate the chosen papers' prestige and elite status. [ABSTRACT FROM AUTHOR]

This note clarifies an important approximation used to simulate the breakdown field in the SiO2 liner of a SiC Charge-Sheet Superjunction - a new power device structure - reported by Akshay and Karmalkar (2020). This electric field simulation sought to assure that the new device does not suffer from SiO2 reliability problems. The note answers two questions: (a) Why do we remove the SiO2 liner which is the very region of our interest during device simulation, when a simulator allows inclusion of such a region? (b) How can one solve for the field in a region (SiO2 in the present case) by neglecting that very region during device simulations? Our note reinforces the insight - “Modeling is the art of making approximations”.

To Keep up with the trend toward open access in science and technology publications, IEEE has created a number of open access journals including the IEEE Open Access Journal of Power and Energy (OAJPE). At present, due to the great number of emerging technologies in power and energy systems, our research and industrial communities are undergoing an unprecedented paradigm change.

This study investigates the effect of moisture content on space charge characteristics based on the dynamic space charge response and conductivity characteristics of oilpaper insulation under a DC electric field. Moisture contents ranging from 0.34–2.89% are considered under an electric field of up to 20 kV/mm. The results show that homocharge accumulates inside the oil-paper insulator near both electrodes, with the amount of charge gradually increasing as the moisture content rises. It may be related to the decreased charge injection barrier at the electrode-sample interface as the moisture level increases. The conductivity increases with the rise in moisture level. However, as the conductivity increases, the corresponding space charge accumulation during polarization does not decrease, but increases significantly. This indicates that space charge accumulation may be related to both charge injection and conductivity. The electric field distortion inside the oil-paper insulator increases as the moisture content rises, with the maximum electric field distortion rate going from 16.9 to 92.9% at 5 kV/mm and from 29.7 to 62.5% at 20 kV/mm. [ABSTRACT FROM AUTHOR]

Utilities need to understand the aging of paper insulation in order to prolong the life of transformers. If the paper becomes severely degraded, it loses its mechanical strength and thus its ability to insulate the windings. [ABSTRACT FROM PUBLISHER]

The effects of furfural generation and partitioning on the aging assessment of oil-paper insulation of power equipment were investigated. Oil-paper samples with various furfural contents were prepared using an accelerated thermal aging experiment. The mass of the furfural generated during the aging of insulation paper was calculated and used to establish the quantitative equation between the accumulated furfural and the degree of polymerization (DP) of the insulation paper. Results showed that the reciprocal of the DP value was linearly related to the amount of furfural generated by the insulation paper. Effects of temperature, moisture, and temperature on the furfural partitioning ratio between oil and paper were analyzed using a furfural partitioning experiment, and a furfural partitioning model was established. Results showed that the furfural partitioning ratio in oil was positively correlated with temperature and moisture but negatively correlated with the DP of the insulation paper. A method for assessing the age of an insulation paper by integrating the furfural generation and partitioning models was proposed and applied on a 500-kV reactor that was returned for factory maintenance. The application result indicated that the method could accurately assess the overall aging condition of the oil-paper insulation of the power equipment. [ABSTRACT FROM AUTHOR]

In this paper, seven groups of sheet insulation for use in liquid nitrogen immersed power transformers have been tested under three different standard electrodes from ASTM D149-97a. The seven groups consist of three different types of paper/film, nonadhesive Kapton 100 HN (Kapton), THERNOMID 14.20 paper (NMN), and Nomex 410 paper (Nomex). The porous paper, Nomex 410, is found to have ac dielectric strength of 62–68 kV/mm, which is likely to be independent from its thickness. The nonporous film, Kapton, shows the dielectric strength of 288 kV/mm, whereas NMN paper has a dielectric strength of 74–78 kV/mm, larger than Nomex with similar thickness. Liquid nitrogen gaps near the triple junction of electrodes as well as liquid nitrogen pockets between the fibers are the main sources of partial discharge (PD) for NMN and Nomex. For Kapton, PDs are more likely to occur in the cavities filled with liquid nitrogen, either on the surface of the electrode or around the impurities on the surface of the film. Electrodes with a small stressed volume are more appropriate for dielectric tests of thin paper/film insulation, such as Kapton, due to the lower influence of cavities on the electrode surface. In contrast, electrodes with a large stressed volume and uniform electric field distribution are suitable for the papers such as Nomex and NMN. [ABSTRACT FROM AUTHOR]

As sugar is an important intermediate in the early stage in the degradation of cellulose, this paper proposes to use the concentration of total sugar as an indicator of the degree of aging of insulating paper in an oil-paper insulation system. The oil-paper insulation system was simulated at 90, 100 and 110°C, and total sugar concentration in insulating paper and in transformer oil was measured by spectroscopy. The spectrum of sugar reaction was obtained by spectrometer, and TQ Analyst software was used to process the data. Our experiments have shown that the total sugar concentration increases significantly in the early stage of aging, and there is a linear relationship between the logarithm of total sugar concentration and the degree of polymerization. We obtained the relationship between absorbance and total sugar concentration using the partial least square method and the regression goodness of fit is better than 0.91. [ABSTRACT FROM AUTHOR]

Interdisciplinary teams and studies need new approaches to design prototypes using tools indistinguishable from the ones they are used to. We utilize a digital pen and physical paper, as the everyday life tools, to build a smart interface for laser-cutters, giving non-technical experienced people the possibility to rapidly, seamlessly, and collaboratively fabricate creative prototypes. [ABSTRACT FROM AUTHOR]

Thermal aging of insulation paper has obvious effects on its moisture absorption property. The presented studies aim to investigating the effects of aging on moisture diffusion in oil-immersed insulation paper. Based on the experimental designs and preparation of experimental materials, the transient moisture contents of insulation paper with different aging status were obtained at different conditions. Then, the experimental results were discussed. Furthermore, the diffusion factors and equilibrium time constants were extracted based on the model of moisture diffusion in oil-immersed insulation paper, which are applicable to our studies. Finally, the effects of thermal aging on the diffusion factor and equilibrium time constant were analyzed. The results show that: 1) With the aging of insulation paper, the rate of moisture absorption increases, and the equilibrium moisture content of insulation paper decreases at the same temperature. Besides, the equilibrium time constant decreases with aging at the same temperature. 2) Considering the effects of aging, thickness of insulation paper and temperature, the empirical expression of diffusion factor was obtained and verified. [ABSTRACT FROM AUTHOR]

Pencil (graphite) on paper (PoP) electronics has gained significant attention due to its low cost and versatility in developing customizable disposable electronics. Despite the convenience of the PoP methodology in device fabrication its application in developing electronics is limited due to the absence of a bandgap in graphite. The present work is the first demonstration of the direct writing of 2D MoS2 trace on paper which was utilized as a pressure and strain sensor. Detailed characterization studies revealed the formation of rhombohedral and hexagonal phased MoS2 micro-flowers. XPS studies revealed the formation of mixed 1T (metallic) and 2H (semiconducting) phases of MoS2. With the increase in the number of traces of 2D MoS2 on paper, the resistance of the channel decreased owing to the increase in conducting channels. The as-fabricated pressure sensor displayed a sensitivity of 2.21 kPa−1 and strain sensor displayed a GF of 13. Also, the sensor displayed an excellent durability for 1600 cycles. The superior response of the sensor can be attributed to the synergistic properties of micro fibrous paper substrate and piezo-dependent electron transfer of 2D-MoS2. The presented technique enables “make it yourself” multifunctional device that have numerous potential applications in the field of consumer electronics and personal healthcare monitoring. [ABSTRACT FROM AUTHOR]

Due to the increasing size of integrated circuits (ICs), their design and optimization phases (i.e., computer-aided design, CAD) grow increasingly complex. At design time, a large design space needs to be explored to find an implementation that fulfills all specifications and then optimizes metrics like energy, area, delay, reliability, etc. At run time, a large configuration space needs to be searched to find the best set of parameters (e.g., voltage/frequency) to further optimize the system. Both spaces are infeasible for exhaustive search typically leading to heuristic optimization algorithms that find some tradeoff between design quality and computational overhead. Machine learning (ML) can build powerful models that have successfully been employed in related domains. In this survey, we categorize how ML may be used and is used for design-time and run-time optimization and exploration strategies of ICs. A metastudy of published techniques unveils areas in CAD that are well explored and underexplored with ML, as well as trends in the employed ML algorithms. We present a comprehensive categorization and summary of the state of the art on ML for CAD. Finally, we summarize the remaining challenges and promising open research directions. [ABSTRACT FROM AUTHOR]

This article is aimed at quantifying the health condition of the power transformer insulation system through its frequency-domain dielectric characteristic by using the concept of the resistor and fractional calculus. In this regard, the dielectric model of the fractional Poynting–Thomson (PT) is proposed, and a mathematical model for parameter identification of the proposed model is presented. The shuffled frog leaping algorithm (SFLA) is used to realize the parameter identification and the fractional PT model parameters of the oil-paper samples under different insulation health conditions. The influence of moisture and aging on the fractional PT dielectric model parameters is experimentally studied. Results show that, with the increase in the water content within the insulation system, the parameters of the fractional PT model gradually decrease, and there is a strong correlation between the relaxation time and the water content. This facilitates the employment of the fractional PT model parameters to quantify the aging and moisture content of the power transformer insulation system. [ABSTRACT FROM AUTHOR]

Selective detection and quantification of biomarkers related to human diseases are essential for preventive healthcare. Surface-enhanced Raman scattering (SERS) spectroscopy is a powerful analytical tool offering high sensitivity. However, the success of this promising analytical tool relies on the ability to effectively fabricate SERS substrate. Herein we have demonstrated a plasmonic paper-based flexible substrate (PPFS) for SERS sensing. In situ growth of silver nanostructures (AgNS) on the paper-based substrate was achieved by using a simple one-step silver mirror reaction (SMR). FESEM and TEM results depicts that the increasing silver ion content influences the morphology (growth of multifacets), as well as size of AgNS. Further, the PPFS substrate was tested with Rhodamine-6G (Rh-6G) dye and an attomole sensitivity with a LOD of 4.54 $\times \,\,10^{-{18}}$ M was achieved. Further, two biomarkers, lactic acid (LA) and uric acid (UA) were detected on the PPFS substrate, with ${\mu }\text{M}$ and pM sensitivity, having LOD values of 0.6 $\times \,\,10^{-{6}}$ and 0.3 $\times \,\,10^{-{12}}$ M respectively. Above detection levels for UA on PPFS is two orders better than reported values, whereas for LA it is comparable with reported substrates. Finally, UA, LA and their mixtures were tested on PPFS and results compared with commercial substrate. The performance of PPFS were found better in all cases, thus, multifaceted AgNS paper based PPFS offers the potential to be used as a biosensor for detection of various biomarkers from body fluids, responsible for the detection of the critical disease for preventive health care. [ABSTRACT FROM AUTHOR]

This work investigates which acid can mainly lead to the reduction of alcohols contents in insulating oil during transformer oil-paper insulation aging. In terms of the activation free energy barrier theory, the microscopic mechanisms for the preferential reactions of methanol and ethanol with formic, acetic, naphthenic and stearic acids are analyzed. It is revealed that the decrease in alcohols concentrations in the middle and late stages of transformer oil-paper insulation aging is mainly caused by the reaction between alcohols and naphthenic acid. The results are cross-validated by utilizing the frontier molecular orbital theory and accelerated thermal aging experiments. Additionally, it is observed that methanol is more susceptible to the effect of acids than ethanol in the middle and late stages of aging. The obtained conclusions, in this paper, could provide a theoretical basis for using alcohols in oil as aging indicators to characterize the full-stage aging status of transformer paper insulation. [ABSTRACT FROM AUTHOR]

Raman spectroscopy is an effective method for diagnosing the aging state of transformer oil-paper insulation. Aiming at overcoming the drawback of previous methods that require a large number of training samples, this research proposes a method for aging diagnosis of oil-paper insulation that can be used for few-shot learning. In this study, different Raman spectroscopy samples of aging insulating oil are obtained by accelerated thermal aging experiments. This paper uses identity matrix as node feature, calculates the connection weights between them by Gaussian kernel function, and constructs the graph structure of Raman spectroscopy library. Using graph convolutional neural network (GCN) based on the graph structure, a diagnosis model is established. The diagnostic accuracy rate is as high as 95.5%. This method provides a theoretical basis for establishing a new structured Raman spectroscopy library and assessing the aging state of transformer oil-paper insulation with a small number of training samples. [ABSTRACT FROM AUTHOR]

The low cost, simplicity, and ease of use of paper microfluidic devices have made them valuable medical diagnostics for applications from pregnancy testing to COVID-19 screening. Meanwhile, the increasing complexity of paper-based microfluidic devices is driving the need to produce new tools and methodologies that enable more robust biological diagnostics and potential therapeutic applications. A new design framework is being used to facilitate both research and fabrication of paper-based microfluidic biological devices to accelerate the investigative process and reduce material utilization and manpower. In this work we present a methodology for this framework to dynamically place and route microfluidic components in a nondiscrete design space where fluid volume usage, surface area utilization, and the timing required to perform specified biological assays are accounted for and optimized while also accelerating the development of potentially lifesaving new devices. [ABSTRACT FROM AUTHOR]

Sensitivity is an essential consideration for microfluidic paper-based analytical devices (μPADs) when these devices are used for low concentration sample detection. Very recently, ion concentration polarization (ICP)-based μPADs are emerging as novel tools for bio-sample preconcentration. In this study, we develop an enclosed paper-based microfluidic platform as a preconcentrator based on the ICP effect. This paper chip is fabricated by a Parafilm embedding technique and holds many advantages over traditional open-channel μPADs, which usually suffer from sample contamination and evaporation problems. The enclosed structure minimizes sample evaporation, reduces contamination risk, and increases the mechanical strength of the paper channel. The experiment results show that more than 100-fold concentration enhancement can be achieved in the enclosed paper device, which is comparable with most reported paper-based ICP devices. Additionally, other improved ICP performance has been observed on the enclosed device, including better concentration plug profile, increased concentration durability. [ABSTRACT FROM PUBLISHER]

The recipients of the 2021 NSREC Outstanding Conference Paper Award are Daisuke Kobayashi, Kazuyuki Hirose, Keita Sakamoto, Yuta Tsuchiya, Shogo Okamoto, Shunsuke Baba, Hiroyuki Shindou, Osamu Kawasaki, Takahiro Makino, and Takeshi Ohshima for their paper titled “An SRAM SEU Cross Section Curve Physics Model.” [ABSTRACT FROM AUTHOR]

Flexible electronics based on the paper have attracted significant attention. A paper-based triboelectric nanogenerator (TENG) consisting of commercial and low-cost materials, e.g., printer paper, polytetrafluoroethylene tape, and conductive ink, was proposed in this study. This TENG unit can directly illuminate 24 blue commercial LEDs. Furthermore, compound paper-based TENGs were developed and a considerable enhancement of the electrical output performance was thereby realized. These compound TENGs can also serve as a height sensor. [ABSTRACT FROM AUTHOR]

Oil-paper insulation of higher voltage winding and traction winding in on-board traction transformers frequently withstand large AC fluctuation voltages mainly combined with AC and inter-harmonic components. This paper presents the characteristics of partial discharge (PD) of oil-paper insulation under superimposed inter-harmonic AC voltages. The experimental results show that the addition of the inter-harmonic to the fundamental sinusoidal component results in variation of peak voltage and dv/dt along the phase. This superimposed inter-harmonic AC voltages has a significant impact on PD including partial discharge inception voltage (PDIV), breakdown voltage, PD repetition rate, and phase resolved partial discharge (PRPD). In addition, a dynamic characterization method of PD statistical parameters is proposed to determine the developing trend. The critical values and inflection points of PD are obtained. Besides, the theoretical mechanism is expounded to better interpret and understand the influence of inter-harmonic component on PD properties. These methods will provide the dynamic datasets and more information for insulation condition assessment of on-board traction transformer. [ABSTRACT FROM AUTHOR]

The present study sets out to devise a universal function model to explain the characteristic curve obtained in the frequency domain spectroscopy (FDS) test on oil-paper insulation, based on its microscopic conduction and relaxation processes, and thus to enhance the accuracy and applicability of the test. First, from the analysis of the relationship between the real and imaginary parts of the dielectric's complex permittivity, it is demonstrated that a relaxation peak co-exists with the conduction process in the low-frequency band of an FDS curve obtained for oil-impregnated paper sample. Second, values for polarization barrier heights, essential to the determination of the microscopic polarization mechanisms, are presented as results of FDS and thermally stimulated depolarization current experiments carried out on oil-impregnated paper samples. The polarization peaks obtained in the imaginary permittivity frequency spectrum are determined as, respectively, space charge polarization and interface polarization. Finally, a function model in good agreement with experiment data is proposed, which quantitatively describes the FDS curve in oil-impregnated sample, including two relaxation processes and one conduction process. [ABSTRACT FROM AUTHOR]

Being an offline measurement technique, Polarization Depolarization Current (PDC) data is conventionally measured after the oil-paper insulation of the equipment reaches thermal equilibrium. Depending on the condition of the insulation, PDC data measurement time typically ranges from several minutes to few hours. It is understood that atmospheric conditions controls the value of ambient temperature. During field measurement, these conditions may not remain constant throughout the PDC recording process. Variation in ambient temperature disturbs the thermal equilibrium that the equipment may have attained at the start of the measurement procedure. Such a condition invariably affects the recorded dielectric response data. However, methods that are available for analyzing relaxation current assume that temperature equilibrium is maintained throughout the measurement period. Results presented in this paper show that dielectric response data is indeed affected if the ambient temperature increases/decreases monotonically. A method is also proposed in this paper using which the effect of such temperature variation on the recorded relaxation current data can be eliminated. This also ensures correct interpretation of PDC data for condition assessment. Analysis presented shows that the value of the equilibrium temperature does not affect the performance of the proposed technique. The applicability of the proposed methodology is first tested on laboratory samples. Thereafter, it is applied to data collected from a real life power transformer. [ABSTRACT FROM AUTHOR]

Furfural content in oil is a valuable indicator of cellulose paper degradation and is widely utilized in aging assessment for power transformers. However, with the same aging degree of insulation paper, the actual furfural content in oil is influenced by temperature because furfural partitioning behavior in the oil-paper insulation system of power transformers changes with temperature. Thus, correction of the temperature effect on furfural partitioning is crucial for accurate assessment of the aging of power transformers. In this research, oil-paper samples with different furfural contents were prepared through an accelerated thermal aging test. A furfural equilibrium experiment was conducted at different temperatures to construct a furfural partitioning diagram. The mass fraction of furfural in oil and paper was calculated. Results showed that the mass fraction of furfural in oil increases with temperature rising and aging deepening, which means that furfural tends to migrate from paper to oil at high temperatures and deep aging conditions. The change in furfural partitioning between oil and paper at different temperatures causes a deviation in paper aging assessment. To correct the temperature effect on furfural partitioning, a furfural correction factor was developed to normalize furfural contents in oil at different temperatures to a reference temperature. The furfural correction factor was verified by experimental data and then introduced into the relation between degree of polymerization of paper and furfural content of oil. Verification results showed that the corrected equation can enhance the accuracy of paper aging estimation at different temperatures. The findings of this work indicated temperature effect on furfural partitioning should be considered when determining the furfural thresholds and evaluating the aging condition of power transformers. [ABSTRACT FROM PUBLISHER]

A piece of paper has many useful characteristics; it is affordable, lightweight, thin, strong, and highly absorbent. These features allow inexpensive and flexible devices to be fabricated easily and rapidly. We have proposed a new field, “paper mechatronics,” which merges printed robotics and paper electronics, and to realize electronic and mechanical systems by printing. Herein, we develop a method to print an actuator and a structure on a sheet of paper. A trilayer electrothermal actuator is printed to activate a printed robot. The paper self-folds along the printed pattern to form the three-dimensional (3-D) structure of the robot body. We also investigate important factors necessary to develop a printed robot. Experiments, including finite element analysis (FEA), confirm our bimetal modeling assumption for the printed actuator and improve the locomotive ability. The key factors in self-folding are paper thickness and humidity. Our findings can improve the reliability of printed robot designs. A self-folding A7-sized paper robot demonstrates locomotion at 10 mm per step. [ABSTRACT FROM PUBLISHER]

Sandwich-structured nanocomposites have the potential to improve the mechanical and electrical properties of materials simultaneously. Nanofibrillated cellulose (NFC) modified paper sheet (denominated as N) and softwood paper sheet (denominated as P) are used to prepare insulating paper. Different kinds of insulating paper with the structures of PPP, NNN, NPN and PNP are prepared. Tensile strength, DC conductivity, dielectric response, space charge and breakdown strength are measured. The activation energies of prepared materials are calculated through DC conductivity at 30, 50, 70, and 90 °C. The mechanism for sandwich structure regulating the mechanical and breakdown properties of insulating paper is discussed. Oil impregnated N/P/N paper has a remarkable improvement on tensile strength, conductivity, and DC breakdown strength, which provides a promising scheme to obtain the insulating paper with outstanding tensile and breakdown strength. [ABSTRACT FROM AUTHOR]

PMIA (Poly-m-phenylene isophthalamide) is an ideal substitute for traditional cellulose paper in oil-immersed paper insulating scenarios. This paper studies the partial discharge characteristics of oil-immersed laminated PMIA. According to the q−φ scatter diagram, discharge quantity and discharge phenomenon, the partial discharge process of PMIA is divided into 3 stages: creeping discharge, co-existence discharge and pre-breakdown. The micro-structure and chemical components of damaged PMIA are presented. The carbon trace, functional groups, carrier trap characteristics and residual insulation strength in different stages of partial discharge are studied. This paper provides a theoretical basis for the application of PMIA in electrical insulation. [ABSTRACT FROM AUTHOR]

Frequency Domain Spectroscopy (FDS) is a powerful tool to study the dielectric properties of oil-paper insulation, which is widely used under high electric field strength. The motion of charge carriers under high electric field strength will cause new dielectric characteristics in FDS curves, from which more information could be extracted for insulation state assessment. In this paper, FD spectra are measured under high electric field strength. The electric field dependence of the loss peak in middle frequency and the characteristics of dielectric loss in low frequency are studied. With the influence of trapping on the motion of charge carriers under electric field being considered, charge carriers hopping polarization model and charge carriers motion dependent conductance model are proposed. The trap energy level of oil-paper insulation decreases when the moisture content increases, thus, the motion characteristics of charge carriers change, leading to decreasing loss peak in middle frequency and inverse dielectric loss characteristics in low frequency. These two models introduce the influence of traps on carrier motion into the dielectric response and enable one to gain a better understanding of the dielectric properties of oil-paper insulation under high electric field strength. [ABSTRACT FROM AUTHOR]

Detecting insulation performance through testing the Raman spectroscopy of transformer oil is noninvasive and shows great promise in on-site diagnosis. The information, stored in spectra, that may reflect aging states of insulation aims to be effectively unfolded and provides decision support as well. In this article, a transformation method based on intrinsic product arithmetic is used to transform the 1-D Raman spectral data into 2-D image data. With the help of CNN based on the dimensionality expanding method, diagnosis of oil–paper insulation with different aging states based on the Raman spectroscopy was realized. The network-based oil–paper insulation aging diagnosis model has an accuracy of 95% in ten aging categories of 60 test samples and 100% in four aging categories. The result shows the trained CNN was able to identify the differences of transformer oil samples at each aging stage through visualized Raman spectral image. This method provides a more accurate determination method for diagnosing oil-immersed transformers’ aging conditions; it also develops an available method for a more detailed evaluation of insulation aging levels. [ABSTRACT FROM AUTHOR]

Paper surfaces under the microscopic view are observed to be formed by intertwisted wood fibers. Such structures of paper surfaces are unique from one location to another and are almost impossible to duplicate. Previous work used microscopic surface normals to characterize such intrinsic structures as a “fingerprint” of paper for security and forensic applications. In this work, we examine several key research questions of feature extraction in both scientific and engineering aspects to facilitate the deployment of paper surface-based authentication when flatbed scanners are used as the acquisition device. We analytically show that, under the unique optical setup of flatbed scanners, the specular reflection does not play a role in norm map estimation. We verify, using a larger dataset than prior work, that the scanner-acquired norm maps, although blurred, are consistent with those measured by confocal microscopes. We confirm that, when choosing an authentication feature, high spatial-frequency subbands of the heightmap are more powerful than the norm map. Finally, we show that it is possible to empirically calculate the physical dimensions of the paper patch needed to achieve a certain authentication performance in equal error rate (EER). We analytically show that log(EER) is decreasing linearly in the edge length of a paper patch. [ABSTRACT FROM AUTHOR]

We consider the problem of communicating over a channel that randomly “tears” the message block into small pieces of different sizes and shuffles them. For the binary torn-paper channel with block length $n$ and pieces of length ${\mathrm{ Geometric}}(p_{n})$ , we characterize the capacity as $C = e^{-\alpha }$ , where $\alpha = \lim _{n\to \infty } p_{n} \log n$. Our results show that the case of ${\mathrm{ Geometric}}(p_{n})$ -length fragments and the case of deterministic length- $(1/p_{n})$ fragments are qualitatively different and, surprisingly, the capacity of the former is larger. Intuitively, this is due to the fact that, in the random fragments case, large fragments are sometimes observed, which boosts the capacity. [ABSTRACT FROM AUTHOR]

Traction transformers are one of the most important equipment in the traction power supply system. Thermal aging of transformer insulation system determines its reliable life. To achieve an estimation of the insulation life of traction power transformers operated under real load condition, the effects of traction loads on the thermal aging of oil-paper insulation in traction transformers were investigated. First, the design principles for the accelerated thermal aging experiment were studied and proposed by considering magnitude (i.e., load rate) and frequency (i.e. spare time and lasting time) of the traction load. Then, an experimental system was established in the laboratory to conduct extensive accelerated thermal aging experiments, in which the traction loads were mimicked by using positive temperature coefficient (PTC) heating plates and a programmable logic controller (PLC). Finally, the experimental results were analyzed and discussed to reveal the effects of traction load on the thermal aging of oil-paper insulation in traction transformers. [ABSTRACT FROM AUTHOR]

Methanol concentration as an aging indicator can assess cellulose aging and estimate cellulose degree of polymerization (DP). Despite the advantages of methanol (MeOH), its major disadvantage is that its concentration in the oil decreases after some time. This point is called the MeOH peak in this article. Therefore, using this indicator when MeOH concentration is reduced leads to incorrect results. When using methanol, the main problem is that whenever the methanol concentration in a transformer is measured, it cannot be identified that the measured concentration belongs to the left or right side of the MeOH peak. If the measured concentration belongs to the right side of the MeOH peak, the estimated DP is incorrect. In this article, an empirical equation is established to estimate the DP value as a function of methanol concentration when methanol concentration belongs to the left side of the MeOH peak. Then, a new index called methanol peak detector index (MPDI) composed of a 2-furfural/MeOH ratio and normalized DP is presented to ensure the validity of the calculated DP value. If it is found that the measured concentration belongs to the left side of the MeOH peak, then the estimated DP by the presented equation is valid. Finally, the application of this method is verified by applying it to measurement data samples indicating the validity of the method. [ABSTRACT FROM AUTHOR]

The traditional method for transformer moisture diagnosis is to establish empirical equations between feature parameters extracted from frequency domain spectroscopy (FDS) and the transformer’s moisture content. However, the established empirical equation may not be applicable to a novel testing environment, resulting in an unreliable evaluation result. In this regard, it is acknowledged that FDS combined with machine learning is more suitable for estimating moisture content in a variety of test environments. Nonetheless, the accuracy of the estimation results obtained using the existing method is limited by the algorithm’s inability to generalize. To address this issue, we propose an AdaBoost algorithm-enhanced back-propagation neural network (BP_AdaBoost). This study creates a database by extracting feature parameters from the FDS that characterize the insulation states of the prepared samples. Then, using the BP_AdaBoost algorithm and the newly constructed database, the moisture estimation models are trained. Finally, the results of the estimation are discussed in terms of laboratory and field transformers. By comparing the proposed BP_AdaBoost algorithm to other intelligence algorithms, it is demonstrated that it not only performs better in generalization, but also maintains a high level of accuracy. [ABSTRACT FROM AUTHOR]

Welcome to Volume 4 of IEEE Journal of Microwaves! In this issue, we bring you 11 quality papers: two invited and nine regular submissions. We also celebrate six of our Outstanding Reviewers of 2023 and announce our IEEE Journal of Microwaves 2022 Best Paper prize. Our author and reader pools continue to expand and our usage counts per article published now exceed 1530. All of our 232 published articles from 2021 to 2023 now appear on Clarivate's Web of Science and we are looking forward to possibly receiving an impact factor this July. Remember to take a look at our solicitation for papers that can fit into our Microwaves in Climate Change special issue, which we intend to release before the end of 2024.

Special Feature that lists the names of people involved in the review of technical papers for the IEEE Transactions on Industry Applications and Industry Applications Magazine. [ABSTRACT FROM AUTHOR]

This study investigated the influence of the main metal materials of transformers on the oil-paper insulation performance. Ten types of insulating specimens were subjected to accelerated thermal aging at 120°C. Some aging parameters, including oil acid number, furfural content and degree of polymerization (DP) of insulating paper, were measured and compared. At the same time, we conducted frequency domain spectroscopy, X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry on the insulating paper. The following conclusions were drawn: silicon lamination slightly deteriorates the insulating oil, copper increases the acidity and accelerates the production of furfural, metal materials can decrease DP of insulating paper and the effect of copper is greater than that of silicon lamination. During thermal aging, the dielectric dissipation factor of insulating paper increases and the carbon content of insulating paper increases. Metal materials can significantly increase the dielectric dissipation factor and carbon content of insulating paper and the effect of copper is greater than that of silicon lamination. [ABSTRACT FROM AUTHOR]

Epoxy resin-impregnated crepe paper (RIP) composites have been used as the inner insulation of dry condenser bushing in the ultra-high voltage direct current (UHVDC) power transmission system. In order to study the dielectric properties of pure epoxy resin and RIP composites, four kinds of samples (pure epoxy resin, RIP composites with 1, 2, 3 layers of crepe paper respectively) were prepared via the vacuum casting process. The Fourier transform infrared spectroscopy (FTIR) as well as three typical dielectric properties, i.e. complex permittivity, dc conductivity, thermally stimulated depolarization current (TSDC) have been investigated. It shows that the addition of crepe paper nearly brings about larger values of relative permittivity as well as dielectric loss factor than the pure epoxy resin. Samples containing crepe paper also have larger dc conductivities and TSDC currents. These differences are related to the abundant hydroxyl groups in the cellulose paper. The hydroxyl groups are polar groups and easy to absorb water or other impurities which resulting in larger permittivity and dc conductivity. Moreover, the crosslinking degree of the epoxy resin matrix decreases with the introduction of crepe paper. Then, the polarized dipole moments are easier to relax, which is responsible for the decrease of the trap depth corresponding to the process of glass transition. [ABSTRACT FROM AUTHOR]

Measurement of transformer remaining useful life has long been a goal for responsible asset management. Most testing laboratories offer furan concentration testing as a suitable method. The interpretive method of choice is usually the Chendong equation, expressed in practical terms as degree of polymerization of the paper with new paper at about 1000 and end of life at around 300. Typical mill transformers have thermal insulation ratings expressed as 55 °C rise for plain kraft or 65 °C, which corresponds to thermally upgraded kraft paper (TUP). It has been determined that TUP does not produce furans and, thus, provides a false indicator of the cellulose breakdown. There are several recent papers that have demonstrated that a measurement of methanol (MeOH) may be a better method to determine ageing of the TUP insulation and also better for transformers with plain kraft paper insulation. The objective of this paper is to provide an overview of the reasons why furans should not be used as the basis for measuring aging of thermally upgraded paper, why MeOH should be so used, and to compare actual furans and MeOH test data for service aged transformers in a process industry application [ABSTRACT FROM AUTHOR]

The article discusses a study which examines the sulfur content, bacterial content and level of sulfur and nitrogen leaching for commercial insulating papers. It explores the experimental method used such as sulfur analysis, bacteria analysis and leaching analysis. The study uses insulating electrical papers from well-known manufacturers and evaluates their Kraft and thermally upgraded qualities. It is concluded that different insulating papers contain significant amounts of sulfur which showed little migration. The increase of nitrogen content in oil exposed to thermally upgraded paper is said to suggest that migration from a transformer paper contributes to the amount of nitrogen-containing substances found in transformer oil.

In this paper, charge distributions in three-layered epoxy resin and epoxy resin impregnated paper samples under AC and AC-DC superimposed electric fields are measured by the improved high-speed pulsed electro-acoustic system. To exclude the interferences caused by the discontinuity of relative permittivity, a method to distinguish between net dipolar charges and free charges is proposed. Through analysis, the influences of frequency, AC component and DC component on the charge transport and trapping characteristics in multi-layered epoxy composites are obtained, which could provide important reference to the structural design and optimization of converter transformer bushings. [ABSTRACT FROM AUTHOR]

Moisture accumulates with the growing aging progress of oil-paper insulation and further shortens the remaining life of the transformer. The frequency-domain spectroscopy (FDS) technique can be used to realize the moisture estimation. However, the moisture estimation results would be unreliable once the aging effect on FDS was ignored. Given this issue, an alternative model including the aging effect is thus proposed using FDS and intelligent algorithm. In this work, the feature parameters of FDS data are used to build the databases for characterizing the aging degree and moisture. Then, the moisture estimation models are developed using the weighted K-nearest neighbor (K-NN) algorithm. The accuracy and applicability of the proposed models are finally discussed in laboratory and field conditions. In that respect, the findings reveal that the reported model is available for moisture estimation of transformer oil-paper insulation under various aging degrees and test temperatures. [ABSTRACT FROM AUTHOR]