1,720,965 research outputs found
Oils with presence of corrosive sulphur: mitigation and collateral effects
No full textRecent years have witnessed a relatively large number of power transformers and shunt reactors failures, which were attributed to the presence of corrosive sulfur compounds in the insulating oils and their attending reactions with copper to form electrically conductive copper sulphides. The associated problems appeared to be initially resolved by the addition to the insulating oil small amounts of a metal deactivator, a derivative of 1, 2, 3 benzotriazole (BTA). However, over the past four years additional problems, arose that were principally associated with the evolution of gases from the electrical insulating oils. These observations, recorded in the field as well as reproduced in laboratories, are examined in this paper
Classification in iso-attention classes of hv transformer fleets
No full textThe largest electrical operators may have in service some hundreds of HV power transformers. It means that failures are to be expected along their operational times with possible heavy consequences in case of fire or explosion or other negative events. The traditional approach for preventing failures and their consequences is normally based on periodical evaluations of some physical, chemical and electrical parameters of the insulating oil and/or of the equipment but these data do not give any information on the overall state of health of the units when the observed properties are below the values assumed by the different existing Standards as acceptable limits. Also these data are not related to failure consequence. With this aim, a more complete risk evaluation may be an innovative powerful tool for preventing negative situation due to transformer failures and for classifying these electrical units in iso-attention classes. This risk is formed by three partial components, which are: 1) causes of the failure, 2) probability that a failure may provoke a damage and 3) type and entity of damages (magnitude). This approach may be a useful tool for supporting decisions and addressing periodical investments of electrical operators and utilities having in service transformer fleets. With this aim, approximately 700 different HV transformers of one of the biggest electrical operator have been examined, evaluating the single components forming their risks. This analysis has permitted to establish which transformers may be considered more critical with possibility to better address the successive maintenance strategies
Long Term Stability of Insultaing Mineral Oils following their Corrosive Sulfur Removal
No full textOver the last decade dibenzyl-disulphide (DBDS) was found to be present in many mineral insulating oils. This sulfur compound tends to react with the copper of the windings, forming harmful by-products (Cu2S). Different techniques to overcome the problem such as metal deactivation, oil change and chemical treatment, have been applied. The long term effectiveness of these techniques is examined and compared
Transformers Fleet Management Through the use of an Advanced Health Index
No full textPower transformers represent the highest value of the equipment installed in transmission substations, comprising up the 60% of the total investment. They are expected to operate for several decades without faults and possibly without relevant unscheduled maintenance practice. The new approach is developed for reducing time based maintenance and, increasing condition based maintenance and to introduce predictive maintenance as well. The aim of predictive maintenance is first to predict when transformer failure might occur, and secondly, to prevent occurrence of the failure by performing maintenance. Diagnostic information can be evaluated individually or better by a complex algorithm which merges all the single inputs and their Rate of Increase (RoI) creating a mono-dimensional figure called Health Index (HI). This concept represents a real 'shifting of paradigm', as it deeply affects the criteria for transformers grid management and selection of the electrical utilities and grid companies. © 2018 IEEE
Frequency dielectric spectroscopy and an innovative optical sensor to assess oil-paper degradation
No full textIn this paper, frequency dielectric spectroscopy (FDS) and an innovative optical sensor for the detection of 2-furaldehyde (2-FAL) are used to check the degree of ageing of differently processed oil-paper specimens when exposed to thermal stress. The analysis of the trend of moisture content and of 2-FAL concentrations confirms the influence of drying pre-Treatment of the specimens on their ageing conditions. FDS elucidated the nature of the drying process of the specimens and the optical sensor correctly assesses a lower 2-FAL production for the vapour phase dried specimens during thermal exposure
LCA and smoke test of dielectric fluids based on natural esters
No full textNatural esters for electrical applications are universally recognized as environmentally friendly and less impact on non-renewable resources consumption. In the framework of an Institutional Group promoted by the University of Roma 'La Sapienza', the National Firefighters Authority, the National Institute for Insurance against Accidents at Work (INAIL) and the Department for Geological Survey of Italy (ISPRA) there were performed several experimental comparative fire/smoke simulations of both mineral and natural ester liquids
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
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