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In the era of Industry 4.0, digital transformation has spurred the swift advancement of technologies, including intelligent predictive maintenance scheduling, prognostics and health management. The accurate prediction of remaining useful life plays a crucial role in these technologies as it extends power equipment’s safe operational duration and decreases the maintenance costs associated with unforeseen shutdowns. Also, the increased accessibility of data for monitoring system conditions has paved the way for the more immense adoption of machine learning models in prognostics and health management for power transformers. At the moment, with the ever-increasing demand for electricity, there is a corresponding increase in the degradation processes of power transformers. Transformers insulation system and more importantly, the paper insulation happens to be the principal part where the degradation is prominent. Therefore, an accurate prediction of the insulating paper condition through its degree of polymerization is required to guarantee the reliability of power transformers. In this regard, the predictions, reliability, and health monitoring of this power equipment can be actualized by modeling the degradation of transformer insulation paper through several machine learning frameworks. In this view, this review paper has been drafted not only to serve as a guide for researchers interested in the fields of transformer insulation system fault prognosis but also to offer insights into potential research directions as existing literature in modeling and evaluating transformer paper insulation is presented.

Letters in literature intimately convey information to both the characters and the reader; letters in literature also represent captured moments that the characters can revisit over and over again to relive memories of themselves and the letter’s author from the vantage of temporal distance. When characters keep letters into their old age, the letter becomes a catalyst for reflection on who they have become in their society. In Henry James’s novella The Aspern Papers, the titular papers are in possession by a famous author’s former lover, now an old woman, and a young man is trying to purchase them for their literary value. The old woman uses the letters as leverage to claim power for herself and her niece. Edith Wharton’s novella The Touchstone similarly focuses on the letters of a famous dead author, but in this case, it is a man having to confront the passionate affair of his youth, when wanting to settle into the prescribed social views on marriage and career. Both of these works use the letter as a way to explore the tensions that come with having a record of cavalier youthful behaviors with the desire to maintain a position in society – the tension between dissention and conforming. These two novellas take two different positions on this tension with James favoring the former and Wharton the latter. Both illustrate the complicated cultural forces that shape perceptions of ageing

Abstract Focussing on the insulating material of power transformer—cellulose insulation paper, this paper first introduces the basic characteristics and engineering application background of insulation paper. Then, the research progress of improving the mechanical properties, thermal stability and electrical properties of insulation paper by nano modification in recent years is compared, and the promotion mechanism is analysed. In addition, in practical engineering application, the oil–paper composite insulation system composed of insulation paper and insulating oil is used for the internal insulation of oil immersed transformer. Therefore, the influence of modified insulation paper on the performance of oil–paper composite insulation system is analysed. Finally, the newly reported new insulation paper is introduced, and the future development trend of modification of traditional insulation paper is analysed.

Abstract The insulation paper is a crucial factor for evaluating the insulation status of transformers. The traditional evaluation methods for insulation paper are dissolved gas component content analysis (CO and CO2) and furfural (2‐FAL) content analysis in oil. The detection principle of the former leads to its low accuracy, while the field application effect of the latter is not ideal due to the easy oxidation of furfural and low content. Methanol, result of its good stability and high production compared with other marker products (CO, CO2, 2‐FAL) has been investigated as a novel marker for aging evaluation of transformer insulating paper in recent years. The results of the investigation indicated that there is a good correlation between the content of methanol in oil and the degree of polymerization under laboratory conditions, which reflected the insulation aging state of the transformer insulating paper more accurately. This paper summarizes the current research status of methanol formation mechanism, detection methods and aging evaluation in insulating oil, and points out the key problems to be solved and development prospects, hoping to provide relevant reference for aging evaluation of oil immersed power transformer.

Natural and synthetic esters are increasingly being chosen instead of mineral oil for environmental and fire safety reasons. However, their use in power transformers is limited due to insufficiently well-understood ageing processes affecting their properties and the properties of cellulosic materials impregnated with them. The research results presented in many scientific papers prove that the use of esters slows the ageing process of cellulosic materials. This article presents the results of research aimed at answering the question of whether the effect of slowing the ageing process will also occur in the case of insulation with very low initial moisture. The answer to this question will allow us to better understand the role of water in the ageing process of the transformer’s insulation system. The thermal ageing process was carried out at a temperature of 150 °C in closed systems. The degree of cellulose polymerisation was taken as a measure of the degree of paper ageing. Great attention was paid to measuring the water content in both paper and electro-insulating liquids at various stages of their ageing. Furthermore, measurements of the properties of electro-insulating liquids were made, which are considered markers of ageing. The test results obtained indicate that in the case of a dry insulation system, corresponding to the initial moisture of the new units, the type of liquid used to impregnate the cellulosic material does not significantly affect its depolymerisation process. However, in the case of paper impregnated with natural esters, a lower dynamic of moisture increase in insulation was observed.

Insulation cellulose paper is a basic measure for a power transformer’s remaining useful life, and its advantageous low cost, electrical, and mechanical properties have made it an extensive insulation system when impregnated in a dielectric liquid. Cellulose paper deteriorates as a result of ageing due to some chemical reactions like pyrolysis (heat), hydrolysis (moisture), and oxidation (oxygen) that affects its degree of polymerization. The condition analysis of cellulose paper has been a major concern since the collection of paper samples from an operational power transformer is almost impossible. However, some chemicals generated during cellulose paper deterioration, which were dissolved in dielectric liquid, have been used alternatively for this purpose as they show a direct correlation with the paper’s degree of polymerization. Furthermore, online and non-destructive measurement of the degree of polymerization by optical sensors has been proposed recently but is yet to be available in the market and is yet generally acceptable. In mitigating the magnitude of paper deterioration, some ageing assessments have been proposed. Furthermore, researchers have successfully enhanced the insulating performance of oil-impregnated insulation paper by the addition of various types of nanoparticles. This study reviews the ageing assessment of oil-paper composite insulation and the effect of nanoparticles on tensile strength and electrical properties of oil-impregnated paper insulation. It includes not only significant tutorial elements but also some analyses, which open the door for further research on the topic.

The objective of this study was to characterise the anaerobic degradation of three paper mill waste water treatment residues in the shape of sludges and to correlate this anaerobic digestion to the physico-chemical characteristics of the paper sludges. After a deep characterisation of each paper sludge in their initial stage, several parameters were analysed on each paper sludge in mesophilic conditions for 40–50 days: pH, conductivity, chemical oxygen demand, total organic acids and organic fibres degradation. A special care was taken to identify and quantify the volatile fatty acids (VFAs) produced by the digestion using gas chromatography coupled with a mass spectrometer. The results showed that in paper sludges, cellulose mainly degrades over time while the degradation of the other fibres (hemicellulose and lignin) is limited. Consequently, the greater the cellulose content in a paper sludge, the greater the digestion and formation of VFAs. However, not all the cellulose degrades because of a shielding effect of lignin on cellulose, and a pH buffering effect of the calcium carbonate present in the paper sludges limits the hydrolysis-acidogenesis step of the anaerobic digestion. Finally, the gas chromatography–mass spectrometry (GC-MS) investigations showed that acetic acid is the main VFA produced by the anaerobic digestion of paper sludges. This work helps predicting paper mill sludge evolution in the purpose of using them in circular economy. [ABSTRACT FROM AUTHOR]

Natural and synthetic esters are increasingly being chosen instead of mineral oil for environmental and fire safety reasons. However, their use in power transformers is limited due to insufficiently well-understood ageing processes affecting their properties and the properties of cellulosic materials impregnated with them. The research results presented in many scientific papers prove that the use of esters slows the ageing process of cellulosic materials. This article presents the results of research aimed at answering the question of whether the effect of slowing the ageing process will also occur in the case of insulation with very low initial moisture. The answer to this question will allow us to better understand the role of water in the ageing process of the transformer's insulation system. The thermal ageing process was carried out at a temperature of 150 °C in closed systems. The degree of cellulose polymerisation was taken as a measure of the degree of paper ageing. Great attention was paid to measuring the water content in both paper and electro-insulating liquids at various stages of their ageing. Furthermore, measurements of the properties of electro-insulating liquids were made, which are considered markers of ageing. The test results obtained indicate that in the case of a dry insulation system, corresponding to the initial moisture of the new units, the type of liquid used to impregnate the cellulosic material does not significantly affect its depolymerisation process. However, in the case of paper impregnated with natural esters, a lower dynamic of moisture increase in insulation was observed. [ABSTRACT FROM AUTHOR]

Insulation cellulose paper is a basic measure for a power transformer's remaining useful life, and its advantageous low cost, electrical, and mechanical properties have made it an extensive insulation system when impregnated in a dielectric liquid. Cellulose paper deteriorates as a result of ageing due to some chemical reactions like pyrolysis (heat), hydrolysis (moisture), and oxidation (oxygen) that affects its degree of polymerization. The condition analysis of cellulose paper has been a major concern since the collection of paper samples from an operational power transformer is almost impossible. However, some chemicals generated during cellulose paper deterioration, which were dissolved in dielectric liquid, have been used alternatively for this purpose as they show a direct correlation with the paper's degree of polymerization. Furthermore, online and non-destructive measurement of the degree of polymerization by optical sensors has been proposed recently but is yet to be available in the market and is yet generally acceptable. In mitigating the magnitude of paper deterioration, some ageing assessments have been proposed. Furthermore, researchers have successfully enhanced the insulating performance of oil-impregnated insulation paper by the addition of various types of nanoparticles. This study reviews the ageing assessment of oil-paper composite insulation and the effect of nanoparticles on tensile strength and electrical properties of oil-impregnated paper insulation. It includes not only significant tutorial elements but also some analyses, which open the door for further research on the topic. [ABSTRACT FROM AUTHOR]

The insulation paper is a crucial factor for evaluating the insulation status of transformers. The traditional evaluation methods for insulation paper are dissolved gas component content analysis (CO and CO2) and furfural (2‐FAL) content analysis in oil. The detection principle of the former leads to its low accuracy, while the field application effect of the latter is not ideal due to the easy oxidation of furfural and low content. Methanol, result of its good stability and high production compared with other marker products (CO, CO2, 2‐FAL) has been investigated as a novel marker for aging evaluation of transformer insulating paper in recent years. The results of the investigation indicated that there is a good correlation between the content of methanol in oil and the degree of polymerization under laboratory conditions, which reflected the insulation aging state of the transformer insulating paper more accurately. This paper summarizes the current research status of methanol formation mechanism, detection methods and aging evaluation in insulating oil, and points out the key problems to be solved and development prospects, hoping to provide relevant reference for aging evaluation of oil immersed power transformer. [ABSTRACT FROM AUTHOR]

This study proposed a proof-of-concept methodology for the investigation of paper samples by utilizing ATR-FTIR spectroscopy supported by chemometric methods. An attempt on the analysis of aged writing papers due to the degradation of their chemical constituents with time has been made. The degradation of its constituents with time is directly linked to the age of the paper since its production. This further links the questioned document with the fraudster, and sometimes it becomes crucial information in the court of law to reach to conclusion. The present study offers a method to discriminate, and estimate the age of unknown writing paper. The statistical models like Curve Estimation (CE), multiple linear regressions (MLR), and partial least squares regression (PLSR), are built to predict the age of the papers. The maximum dating errors are in the CE model whereas, MLR and PLSR models show excellent age estimation of unknown paper with minimum error of ±5 days and ±3 days in actual and estimated date of artificial ageing respectively. The present methodology is expected to provide valuable insight for answering the queries related to the date/age of the suspected document documents/paper artefacts. [ABSTRACT FROM AUTHOR]

Smart, environmentally friendly alternatives, i.e., frankincense and rice starch, are recommended for usage in modern paper conservation processes during the re-sizing process treatments. Different concentrations of frankincense and rice starch were applied to paper samples before and after ageing. Multiple analysis methods were performed to ensure the effectiveness of these materials. Promising results were found, but at varying degrees according to the type and concentration of the materials. Scanning electron microscopy illustrated that the frankincense particles were completely absorbed into the cell walls after ageing. Results indicated that there was no considerable change in pH before and after treatment or ageing; the best results for decreasing the acidity utilized a treatment with a mixture of frankincense and rice starch in a 2 to 1 ratio (F2S1). Fourier transform infrared spectroscopy illustrated an increased CH2 region and decreased OH stretching as a result of the bonds formed from the starch and crystals formed by frankincense, which agreed with the increased coating and strength of the paper fibers. The total color change values of all the treated samples after ageing were less than 4.5. Frankincense was found to provide strength in supporting wood fibers. [ABSTRACT FROM AUTHOR]

To date, older adults have received little attention in the newly emerging technological narratives of transnational religion. This is surprising, given the strong association of later life with spiritual and religious engagement, but it likely reflects the ongoing assumption that older adults are technophobic or technologically incompetent. Drawing on ethnographic interviews with older Sinhalese Buddhist migrants from Sri Lanka, living in Melbourne, this paper explores the digital articulations of transnational religion that arise from older migrants' uses of digital media. We focus on how engagements with digital media enable older Sinhalese to respond to an urgent need to accumulate merit in later life, facilitating their temporal strategies for ageing as migrants. We argue that these digital articulations transform both the religious imaginary and the religious practices that validate and legitimize a life well‐lived. [ABSTRACT FROM AUTHOR]

This editorial summarizes the papers in issue 17(4) (2022). The first paper combines input–output modelling with priority weighting to analyse supply-chain impacts of disasters. The second paper examines skill-based functional specialization of value chains in Brazil using interregional and international value-added measures. The third paper questions the common belief that agglomeration economies are the driving force behind cluster formation using an agent-based model. The fourth paper applies modern instrumental variables techniques to measure the impact of forced migration flows from Venezuela to Colombia on house prices. The fifth paper explores the impact of an ageing population on per capita labour income, consumption and wealth at the regional level using a multivariate spatial econometric model. The sixth paper examines the impact of neighbouring countries on migrants' aggregate decisions to remit based on an advanced spatial econometric origin–destination model. [ABSTRACT FROM AUTHOR]

Tactile sensitivity is known to decline with age. Braille provides a vital method of reading and writing for working-age and older adults with acquired visual impairment. The proliferation of low-cost braille displays raises new possibilities for adult braille learners, with dots of greater height than standard paper braille, potentially benefitting older adults with reduced tactile sensitivity. This study explored the influence of reading medium (paper vs braille display) on the accuracy and speed of six working-age and older adult braille learners and examined differences when transitioning from one reading medium to another. Findings indicate that (1) learning letters on a braille display resulted in better speed and accuracy (time: M = 44.2, SD = 37.3, accuracy: M = 83%, SD = 24.8%) than on paper (time: M = 54.3, SD = 40.4, accuracy: M = 80.6%, SD = 28.1%); (2) transitioning from one medium to another generally resulted in the same or better performance (reading times decreased by 11.2% and accuracy improved by 2.4%); and (3) the advantage of the braille display appears to be greatest when reading letters in combination (reading times decreased by 26.8% and accuracy improved by 6.5% for letter-pairs vs a 1.9% reduction in speed and a 2% improvement in accuracy for single letters). The benefit of the braille display condition was most pronounced for participants with reduced tactile sensitivity. Although preliminary, these findings suggest that the use of braille displays in early braille instruction may decrease frustration for those with reduced tactile sensitivity and should not adversely affect the ability for learners to transition to standard paper braille, assuming that both formats are introduced and reinforced throughout training. [ABSTRACT FROM AUTHOR]

Most power transformers are oil-immersed transformers for which its insulation system consists of oil and cellulosic solid. The insulation liquid impregnates the solid-covering air spaces, which improves the efficiency of the insulation system. Not only does the oil ensure electrical insulation but it also works as coolants transferring the heat generated during transformer operation to the exterior of the transformer. Throughout normal operation conditions, transformers experience multiple stresses that degrade their insulation. Since the lifetime of oil-immersed transformers is defined mainly by the state of the insulation paper, it is critical to understand the behavior and degradation mechanisms of new insulation systems that try to overcome the drawbacks of mineral oil as well as to improve power transformer performances. The current increased prevalence of the nonlinear loads additionally stresses power transformers, which generates their premature ageing or even failure. Consequently, new materials and assessment methods are required to guarantee the suitable management of power transformer populations. In this Special Issue “Experimental and Numerical Analysis of Thermal Ageing in Power Transformers”, four papers have been published. The guest editor also describes briefly some challenges involved beyond the coverage of this Special Issue.