1,720,955 research outputs found
Corrosive sulphur in large transformers: impact, quantification and detection
No full textSeveral power apparatus use some type of oil insulation system. Transmission level transformers, one of the most expensive components in power networks, use mineral oil as both electrical insulation and cooling. Due to the financial risk posed, if this equipment fails unexpectedly, several quality and condition monitoring techniques are used to test the insulation system. Nevertheless, in 1990 approximately 50 % of the mineral oils used in transformers was contaminated with corrosive sulphur species [1], which passed undetected by the standard corrosion tests at the time, resulting in transformers failures worldwide. CIGRE estimates that between 2000 and 2009 there were approximately 100 related failures, not considering small distribution transformers too small for any investigation to be carried out.The work presented investigates how CuxS faults develop, examines possible techniques to monitor the corrosion process and the failure scenarios caused by sulphur corrosion. A sample production method capable of generating 90 mm square Kraft paper samples with homogeneous CuxS deposition, with a less than 1 % variation, and a reproducibility of 3:5% is detailed. Empirical data demonstrate how the generation of CuxS deposits to DBDS concentration, temperature, ageing atmosphere, paper-copper interfaces and location of deposits. Based on the empirical data obtained, a copper sulphide deposition model using multiple parallel CuxS formation mechanisms was developed.The development of condition monitoring techniques and laboratory-scale validation experiments have been completed successfully, with the use of both field and laboratory samples. It has been shown that x-ray fluorescence (XRF) is technically capable of quantifying very accurately sulphur and copper in oil, with a limit of quantization at 4.05 and 1.95 ppm respectively. In addition, XRF measurements demonstrated that through historical sulphur trends, sulphur depletion rates can be calculated to extrapolate if there is an onset sulphur corrosion. Frequency dielectric spectroscopic analysis of CuxS contaminated Kraft paper demonstrated empirically that CuxS deposits have resonance frequency, at approximately 1 mHz, and that the magnitude of the resonance relates to the quantity of CuxS. Furthermore, laboratory samples accurately replicate field samples containing CuxS deposits and other impurities in terms of dielectric data analysis.The effect of sulphur corrosion and possible failure scenarios are investigated. The electrical breakdown experiments demonstrate that the CuxS deposits reduced the electrical breakdown strength of each Kraft paper layer by 79.5 %. By applying DP life expectancy models to empirical data it is demonstrated that the corrosion process reduces 25 % of the transformer life expectancy at normal working conditions. The excess dielectric loss, generated from a CuxS contaminated insulation paper system, has increased by a factor of approximately 27.5. The thermal conductivity also increased 75%. It is demonstrated the generation of a hotspot is very likely, which then generates a snowball effect of generating further CuxS deposits and further increasing the local temperature.<br/
X-ray fluorescence as a condition monitoring tool for copper and corrosive sulphur species in insulating oil
No full textCurrently there are no standard techniques to detect copper sulphide deposits in transformers to act as an early warning system. This paper develops and tests a procedure using X-Ray Fluorescence (XRF) spectroscopy to tackle this problem and to monitor dissolved copper in oil, which can have a major impact on the dielectric properties of insulating oil. Initially calibration curves for sulphur and copper demonstrate the XRF’s limits of quantitation. Subsequently, a laboratory scale sample preparation procedure is developed to demonstrate that corrosive sulphur depletion trends may indirectly monitor copper sulphide formation. To confirm depleting sulphur species are corroding copper samples are analysed with Energy Dispersive X-Ray spectroscopy. Finally XRF demonstrates that corrosive oil has a low impact on the long term concentration of copper in oil. An XRF condition monitoring technique feasibility study is conducted and recommendations are given in how to implement it in the field
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
SSIMS Molecular Selective Imaging: a new diagnostic tool to investigate metal passivators in scrapped transformers
Get PDFIn every high voltage grid, the replacement of assets is a slow but steady process that guarantees long-term reliability of the power distribution networks. The prioritisation of such interventions is based on complex rating criteria specifically designed to highlight potential issues of certain machines (or families of machines) in need of care. Given the tremendous costs of operations such as the replacement of a power transformer it is not surprising to observe constant efforts devoted to finding new and better monitoring and diagnostic tools. These are capable of delivering invaluable information about the conditions of a transformer, in service or after it is either failed or proactively scrapped, allowing a better comprehension of underlying chemical-physical phenomena occurring. Ideally, advanced monitoring and diagnostic tools should ultimately result in improved rating parameters to be applied in the evaluation of future interventions. This feasibility study evaluates the use of static secondary ion mass spectrometry (SSIMS) molecular selective imaging as a diagnostic tool for power transformer. SSIMS is herein demonstrated to be able to assess, without doubts, the presence and integrity of the passivation layer produced by Irgamet®39 on copper surfaces in laboratory tests. The technique has also been tested on real samples collected from one of the phases of a 400/275kV autotransformer proactively scrapped and proved to be applicable without significant sample preparation. The possibility of its use in the study of the distribution of Irgamet®39 across the windings is also demonstrated. Further development of SSIMS as a diagnostic tool would be significantly increasing the grade of detail at which scrapped/failed units could be inspected. A better understanding on how the operating conditions or the design of a transformer can affect the anticorrosion protection layer at the molecular level would open the way to significant ad hoc improvements of both operative guidelines and rating criteria for power transformers
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
- …
