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1
Phillips, Lyndal, University of Western Sydney, of Science Technology and Environment College i of Science Food and Horticulture School. "Analysis of polychlorinated biphenyls in transformer oils". THESIS_CSTE_SFH_Phillips_L.xml, 2002. http://handle.uws.edu.au:8081/1959.7/766.
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Polychlorinated Biphenyls (PCBs) were seen as a significant engineering advance when first commercially produced in 1929. They were used as insulators and cooling fluids in electrical transformers and capacitors. There are 209 PCB congenors that are chemically and thermally stable with low inflammability and reactivity. However,they are also highly toxic, suspected carcinogens and bioaccumulate in the food chain. Due to these characteristics they are listed by the United Nations as one of the sixteen worlds persistent organic pollutants POPs). By international agreement, undertaken by the UN, the production of PCBs has been banned and gradually their use will be phased out. Several tests and procedures are discussed in some detail in this research.Master of Science (Hons)
2
Martin, Daniel. "Evaluation of the dielectric capabilities of ester based oils for power transformers". Thesis, University of Manchester, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.694702.
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Khan, Imad Ullah. "Assessment of the performance of ester based oils in transformers under the application of thermal and electrical stress". Thesis, University of Manchester, 2009. http://www.manchester.ac.uk/escholar/uk-ac-man-scw:189512.
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Soares, Valdeir Ribeiro. "Requisitos e restrições do uso do óleo vegetal de tungue como líquido isolante para transformadores elétricos de distribuição de média tensão". Universidade Tecnológica Federal do Paraná, 2015. http://repositorio.utfpr.edu.br/jspui/handle/1/3192.
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Devido à necessidade de se desenvolver um líquido isolante renovável em alternativa ao uso de óleo mineral em transformadores, a comunidade cientifica e empresas do segmento de energia buscam desenvolver óleos vegetais para essa aplicação. Sendo que, atualmente os óleos vegetais utilizados de forma comercial em transformadores possuem base vegetal que competem com a indústria alimentícia. Dessa forma o presente trabalho tem como objetivo verificar a possibilidade do óleo de tungue ser utilizado em transformadores de distribuição, face sua alta capacidade produtiva e o mesmo não competir com a alimentação humana. Para isso, foi utilizado como referência, as características físico-químicas da norma NBR 15422 – Óleo vegetal isolante para equipamentos elétricos, que é a norma responsável para uso também em transformadores. Visando reduzir a acidez do óleo de tungue para níveis normatizados, foi realizado processo de adsorção dos componentes polares através de Terra Fuller. O tratamento com Terra Fuller se mostrou ineficaz para o óleo de Tungue bruto, sendo assim, foi realizado um processo industrializado para refino do óleo para reduzir sua acidez. Para verificação das características do óleo de Tungue, foi construído um protótipo de transformador e realizado os ensaios dielétricos de rotina conforme norma NBR 5356, sendo que não foram detectadas falhas elétricas e ainda, foram obtidos níveis de resistência de isolamento próximos aos obtidos em transformadores que utilizam óleos isolantes mineral e vegetal comercializados para equipamentos elétricos.Due to the need to develop a renewable insulating liquid alternative to mineral oil used in transformers, the scientific community and energy sector companies look for to develop vegetable oils for this application. Whereas, now the vegetable oils used in transformers in a commercial way have vegetable based competing with human food. Thus, the present work aims to verify the possibility of tung oil be used in distribution transformers, given its high production capacity and it does not compete with human food. For this, was used as a reference, the physicochemical characteristics of the NBR 15422 - vegetable insulating oil for electrical equipment, which is the standard responsible for use also in transformers. Aiming to reduce the acidity of tung oil at standardized levels was performed adsorption process of polar components through Fuller Earth. Treatment with Fuller Earth was ineffective for raw tung oil, therefore, an industrial process for oil refining was carried out to reduce its acidity. For verification of tung oil characteristics, a transformer prototype has been built and performed routine dielectric tests according to NBR 5356, with electrical faults were not detected and also were obtained resistance of isolation levels close to those obtained in transformers use vegetable and mineral insulating oils marketed for electrical equipments.
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Khelifa, Hocine. "Propriétés diélectriques des nanofluides : tenue diélectrique, électrisation statique, décharges partielles et décharges surfaciques". Electronic Thesis or Diss., Ecully, Ecole centrale de Lyon, 2024. http://www.theses.fr/2024ECDL0048.
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Cette thèse explore le développement, la préparation et la caractérisation des nanofluides (NFs) pour améliorer la performance diélectrique des liquides d'isolation couramment utilisés dans les transformateurs de puissance, y compris les esters synthétiques, les esters naturels et les huiles minérales en incorporant différents types de nanoparticules (NPs). Ces dernières sont conductrices (Fe3O4, C60, et Gr), semiconductrices (ZnO et CuO) et isolantes (Al2O3, ZrO2, SiO2 et MgO). L'étude vise à améliorer les propriétés diélectriques, notamment la tension de claquage en courant alternatif, la résistance aux décharges partielles, la tendance à la charge électrostatique et les caractéristiques de décharge de surface. Une analyse complète couvrant l'évolution historique, les techniques de préparation (méthodes en une ou deux étapes) et les mécanismes de stabilisation essentiels pour obtenir des nanofluides stables avec des propriétés diélectriques optimales est présentée. Les protocoles de préparation des NP, ainsi que les différents montages expérimentaux et les méthodes utilisées pour les caractériser sur le plan diélectrique, sont ensuite décrits. L'impact des caractéristiques des NPs, telles que le type, la taille, la concentration et le traitement de surface, sur les performances diélectriques des liquides de base est systématiquement évalué. Les données expérimentales sont ensuite analysées à l'aide d'outils statistiques tels que le test d'adéquation d'Anderson-Darling et l'analyse de probabilité de Weibull, et les tensions correspondant à des niveaux de risque de 1 %, 10 % et 50 % ont été déterminées. Les mécanismes impliqués dans l'amélioration/la détérioration de la tension de claquage en courant alternatif sont discutés. Les résultats expérimentaux indiquent que les nanofluides (NFs) améliorent de manière significative les propriétés diélectriques en réduisant l'activité de décharge partielle, la tendance à la charge électrostatique et la longueur d'arrêt des décharges de surface. Cette amélioration est obtenue en influençant la mobilité des charges dans les liquides. Les nanoparticules (NPs) conductrices et isolantes, en particulier Fe3O4 et Al2O3, présentent des avantages substantiels qui peuvent contribuer à atténuer les événements de rupture et à prolonger la longévité des équipements. En outre, l'interaction des nanoparticules aux interfaces solide-liquide affecte les comportements de décharge de surface, ce qui renforce le rôle des nanofluides dans l'amélioration de la durabilité de l'isolationThis thesis explores developing, preparing, and characterizing nanofluids (NFs) to enhance the dielectric performance of insulation liquids commonly used in power transformers, including synthetic esters, natural esters, and mineral oils by incorporating different types of nanoparticles (NPs). These later being conducting (Fe3O4, C60, Gr), semi-conducting (ZnO and CuO), and insulating (Al2O3, ZrO2, SiO2, and MgO). The study aims to improve dielectric properties, including the AC breakdown voltage, partial discharge (PD) resistance, electrostatic charging tendency, and surface discharge characteristics. A comprehensive analysis covering the historical evolution, preparation techniques (one-step and two-step methods), and stabilization mechanisms essential for achieving stable nanofluids with optimal dielectric properties is presented. The preparation protocols of NFs, as well as the various experimental set-ups and methods used to characterize them dielectrically, are then described. The impact of NP characteristics, such as the type, size, concentration, and surface treatment, on the dielectric performance of base liquids is systematically assessed. The experimental data are then analyzed using statistical tools such as the Anderson-Darling goodness-of-fit test and Weibull probability analysis, and the voltages corresponding to 1%, 10%, and 50% risk levels were determined. The involved mechanisms in the improvement/deterioration of AC breakdown voltage are discussed. The experimental results indicate that nanofluids (NFs) significantly enhance the dielectric properties by reducing partial discharge activity, the electrostatic charging tendency, and the stopping length of surface discharges. This improvement is achieved by influencing charge mobility within the liquids. Both conducting and insulating nanoparticles (NPs), particularly Fe3O4 and Al2O3, demonstrate substantial benefits, which can help mitigate breakdown events and extend equipment longevity. Additionally, the interaction of nanoparticles at solid-liquid interfaces affects surface discharge behaviors, further supporting the role of nanofluids in enhancing insulation durability
6
Schlicker, Darrell Eugene. "Flow electrification in aged transformer oils". Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/38844.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (p. 317-348).
by Darrell Eugene Schlicker.
M.S.
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Wilson, Gordon. "Characterisation of mineral transformer oil". Thesis, University of Surrey, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392140.
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Cargol, Timothy L. (Timothy Lawrence) 1976. "A non-destructive transformer oil tester". Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/81576.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.Includes bibliographical references (leaves 62-63).
A new non-destructive test of transformer oil dielectric strength is a promising technique to automate and make more reliable a diagnostic that presently involves intensive manual efforts. This thesis focuses some of the issues that must be understood to bring the test from the laboratory to the field. Emphasis is placed on reliability and safety by exploring any effect the test has on the transformer oil, the mechanical parameters necessary to give optimal reliability, and failsafe electronics.
by Timothy L. Cargol.
M.Eng.
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O'Sullivan, Francis M. (Francis Martin) 1980. "A model for the initiation and propagation of electrical streamers in transformer oil and transformer oil based nanofluids". Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40504.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 305-309).
The widespread use of dielectric liquids for high voltage insulation and power apparatus cooling is due to their greater electrical breakdown strength and thermal conductivity than gaseous insulators, while their ability to conform to complex geometries and self-heal means that they are often of more practical use than solid insulators. Transformer oil is a particularly important dielectric liquid. The issues surrounding its electrical breakdown have been the subject of extensive research. Much of this work has focused on the formation of electrical streamers. These are low-density conductive structures that form in regions of oil that are over-stressed by electric fields on the order of 1 x 108 (V/m) or greater. Once a streamer forms it tends to elongate, growing from the point of initiation towards a grounding point. The extent of a streamer's development depends upon the nature of the electrical excitation which caused it. Sustained over-excitation can result in a streamer bridging the oil gap between its point of origin and ground. When this happens an arc will form and electrical breakdown will occur. Streamers can form due to both positive and negative excitations. Positive streamers are considered more dangerous as they form at lower electric field levels and propagate with higher velocities than negative streamers. Historically, the modeling of streamer development has proved to be a very difficult task. Much of this difficulty relates to the identification of the relevant electrodynamic processes involved. In the first section of this thesis a comprehensive analysis of the charge generation mechanisms that could play a role in streamer development is presented.
(cont.) The extent of the electrodynamics associated with Fowler-Nordheim charge injection, electric field dependent ionic dissociation (the Onsager Effect) and electric field dependent molecular ionization in electrically stressed transformer oil are assessed and it is shown that molecular ionization, which results in the development of an electric field wave, is the primary mechanism responsible for streamer development. A complete three carrier liquid-phase molecular ionization based streamer model is developed and solved for a positive needle electrode excitation using the COMSOL Multiphysics finite element simulation suite. The modification of the liquid-phase molecular ionization model to account for the two-phase nature of streamer development is described and the performance of both the liquid-phase and gas/liquid two-phase models are compared with experimental results reported in the literature. The second section of this thesis focuses on the insulating characteristics of transformer oil-based nanofluids. These nanofluids, which can be manufactured from a variety of materials, have been shown to possess some unique insulating characteristics. Earlier experimental work has shown that oil-based nanofluids manufactured using conductive nanoparticles have substantially higher positive voltage breakdown levels than that of pure oil. A comprehensive electrodynamic analysis of the processes which take place in electrically stressed transformer oil-based nanofluids is presented, which illustrates how conductive nanoparticles act as electron scavengers in electrically stressed transformer oil-based nanofluids. As part of this analysis, a completely general expression for the charging dynamics of a nanoparticle in transformer oil is developed.
(cont.) The solutions for the charging dynamics of a range of nanoparticle materials are presented and the implications these charging dynamics have on the development of streamers in oil-based nanofluid is explained. To confirm the validity of the electrodynamic analysis, the electric field dependent molecular ionization model for streamers in pure oil is modified for use with transformer oil-based nanofluids. This model is solved for nanofluids manufactured using conductive and insulating particles and the results that are presented confirm the paradoxical fact that nanofluids manufactured from conductive nanoparticles have superior positive electrical breakdown performance to that of pure oil. The thesis concludes by exploring the possibility of developing simplified streamer models for both transformer oil and transformer oil-based nanofluids, which are computationally efficient and can be solved quickly meaning that they can be used as practical design tools.
by Francis M. O'Sullivan.
Ph.D.
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TANTEH, DERICK NJOMBOG, SHAFIQ YOUSEF AL-LIDDAWI i DANIEL SSEKASIKO. "PROPERTIES OF TRANSFORMER OIL THAT AFFECT EFFICIENCY". Thesis, Blekinge Tekniska Högskola, Institutionen för tillämpad signalbehandling, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-2664.
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Abstract. Transformer explosions caused by dielectric failure account for over 50% of the disasters. The aim of this thesis is to examine, compare and outline the differences, in function, as dielectric insulators, vegetables oil has, with respect to the mineral oil used in high-power transformers. We will first consider the vegetable oil which has less dielectric capabilities than the mineral oil used in power transformers. Later in the experiments, we will focus mainly to examine the breakdown voltage property, as we try to alter some properties of the respective oils used. Considering the fact that vegetable oil has low viscosity, with its chemical compounds constituting less molecular masses compared to mineral oil, we endorse, from our experimental findings, that mineral oil is indeed worthy and reasonable to be used as a dielectric in high power transformers. In this write-up, we have considered eleven transformer oil properties. In the experiment proper, we considered only the acidity, whose concentration in the transformer oil increases with aging if the transformer, moisture, and a ‘suitable’ impurity like NaOH(aq). At first glance, one would be tempted to think, as we were, that since the increase in acid content of the oil deteriorates its dielectric performance, an increase in alkaline content of the transformer oil, would increase its dielectric ability; reversing the acid effect. But as we see in the results from our experiments, this is false. We think that the visible degradation of the insulating property of the oil, with the introduction of NaOH(aq), is because it acts as an impurity to suitable dielectric function. From the experiments, the heating procedures resulted in the production of toxic gases. This indicated the actual loss of chemical structure and significant breakage of chemical bonds. The resulting chemical composition of the oil does not produce the same dielectric properties as the initial oil sample. Also, here has been considerable inconsistency in the addition of NaOH(aq) or HCl(aq) to both oils. We only added HCl(aq), before every measurement, in two of the experiments. The other experiments were either with moisture, or a single addition of 2cm3 of either HCl(aq) or NaOH(aq) before heating; after which several measurements were taken, at specific intervals, as the mixture cools. We did so, in the latter, in which we had only one addition of a 2cm3 chemical, because in real life, given the short time frame of the experiment, the total amount of acid in the oil has a negligible change. So, in a functioning heated transformer, within a short time frame, there is actually deterioration in oil insulation properties
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Phillips, Lyndal. "Analysis of polychlorinated biphenyls in transformer oil /". View thesis, 2002. http://library.uws.edu.au/adt-NUWS/public/adt-NUWS20031222.095244/index.html.
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Thesis (M.Sc.) (Hons.) -- University of Western Sydney, 2002.A thesis submitted to the University of Western Sydney in fulfillment of the requirements for admission to the [degree of] Masters of Science (Honours). Bibliography : leaves 156-163.
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Mouayad, Lama. "Monitoring of transformer oil using microdielectric sensors". Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/39497.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1985.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.
Includes bibliographical references.
by Lama Mouayad.
M.S.
13
N'Cho, Janvier Sylvestre. "Développement de nouvelles méthodes de diagnostic et de régénération des huiles pour transformateurs de puissance". Thesis, Ecully, Ecole centrale de Lyon, 2011. http://www.theses.fr/2011ECDL0004/document.
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L’indisponibilité d’un transformateur de puissance a de fortes répercussions financières aussi bien pour les exploitants de réseaux d’énergie électriques que pour les clients qui y sont connectés. Afin de prévenir les pannes et d’optimiser la performance de ces équipements d’importance stratégique, de nombreuses techniques et outils de diagnostic ont été développés. L’huile contient environ 70 % des informations de diagnostic sur l’état des transformateurs. Le défi consiste à y accéder et à les utiliser efficacement. L’atteinte d’un tel objectif passe nécessairement par des techniques de diagnostic fiables. En plus des techniques traditionnellement utilisées, trois nouvelles techniques de diagnostic issues des normes ASTM sont utilisées : (1) le test de stabilité qui permet de simuler le comportement sous champ électrique d’une huile en fournissant des informations sur la qualité de celle-ci ; (2) la spectrophotométrie UV/Visible qui permet de mesurer la quantité relative de produits de décomposition dissous dans l’huile ; et (3) la turbidité qui mesure la pureté d’une huile neuve ou usagée. Une méthode quantitative permettant de déterminer les paramètres affectant la formation du soufre corrosif sur les conducteurs en cuivre dans les transformateurs de puissance est proposée. Il est montré entre autres que la tendance au gazage des esters naturels est plus faible que celle de tous les autres types d’huile (minérales, esters synthétiques, silicone). La turbidité et la spectrophotométrie UV/Visible permettent de quantifier efficacement les contaminants qui résultent de l’action d’une décharge électrique sur l’huile isolante. Un nombre important de cycles de régénération (au moins 15) est nécessaire pour qu’une huile vieillie en service retrouve les aptitudes d’une huile neuve. Une nouvelle technique de régénération est présentée pour réduire le nombre de cycles de régénération ; celle-ci consiste à utiliser la terre à foulon traitée avec de l’azote. Il est montré également que le temps constitue le paramètre le plus nuisible dans la formation de soufre corrosif. L’action combinée du temps et de l’agressivité de l’oxygène dissous l’accélère fortementA power transformer outage has a dramatic financial consequence not only for electric power systems utilities but also for interconnected customers. In order to prevent any failure and to optimize their maintenance, various diagnostic techniques and tools have been developed. Insulating oil contains about 70% of diagnostic information on the transformer condition. The challenge is to access and use them efficiently. To meet this objective reliable diagnostic techniques are required. In addition to traditional testing methods, three recently developed ASTM testing techniques were used: (1) oil stability testing that simulates the behaviour of oil under electrical stress by providing information on its quality; (2) the UV/Visspectrophotometry that measures the amount of the relative dissolved decay products in insulating oil; and (3) the turbidity that measures the purity of virgin and aged oil. A quantitative laboratory technique capable of determining the parameters affecting the formation of corrosive sulphur deposition on copper conductors in power transformer is proposed. It is shown among other that the gassing tendency of natural esters is lower than that of the other types of insulating fluids (mineral oil, synthetics esters and silicone oil). The turbidity and UV/Vis spectrophotometry allow quantifying effectively, the relative amount of contaminants resulting from electrical discharge in oils. A large number of reclamation cycles (around 15 passes) are required for in-service aged oil to regenerate to the level of new oil. Anew technique enabling reducing the number of reclamation cycles is proposed; this latter consists in the use of Fuller’s Earth previously treated with dry nitrogen. It is also shown that time is the most influential parameter in the formation of corrosive sulfur. The process is accelerated when time and aggressiveness of oxygen are partnered
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Lingamaneni, Veerendra. "Investigation of 'off-line‘ relaxation phenomena in oil filled transformers". Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/34424/1/Veerendra_Lingamaneni_Thesis.pdf.
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Power transformers are one of the most important and costly equipment in power generation, transmission and distribution systems. Current average age of transformers in Australia is around 25 years and there is a strong economical tendency to use them up to 50 years or more. As the transformers operate, they get degraded due to different loading and environmental operating stressed conditions. In today‘s competitive energy market with the penetration of distributed energy sources, the transformers are stressed more with minimum required maintenance. The modern asset management program tries to increase the usage life time of power transformers with prognostic techniques using condition indicators. In the case of oil filled transformers, condition monitoring methods based on dissolved gas analysis, polarization studies, partial discharge studies, frequency response analysis studies to check the mechanical integrity, IR heat monitoring and other vibration monitoring techniques are in use. In the current research program, studies have been initiated to identify the degradation of insulating materials by the electrical relaxation technique known as dielectrometry. Aging leads to main degradation products like moisture and other oxidized products due to fluctuating thermal and electrical loading. By applying repetitive low frequency high voltage sine wave perturbations in the range of 100 to 200 V peak across available terminals of power transformer, the conductive and polarization parameters of insulation aging are identified. An in-house novel digital instrument is developed to record the low leakage response of repetitive polarization currents in three terminals configuration. The technique is tested with known three transformers of rating 5 kVA or more. The effects of stressing polarization voltage level, polarizing wave shapes and various terminal configurations provide characteristic aging relaxation information. By using different analyses, sensitive parameters of aging are identified and it is presented in this thesis.
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Zhou, Yuan. "Electrical properties of mineral oil and oil/impregnated pressboard for HVDC converter transformers". Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/376538/.
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Modern power industry requires higher performance dielectric liquids. Mineral oil is one of those most important and widely used insulating materials. Recently, research on the dielectric properties of mineral oil insulation reveal that oil resistivity can greatly influence the field distribution within an oil-pressboard insulation system in a DC field environment, especially during polarity reversals. Basic test methods such as dielectric spectroscopy and polarization and depolarization measurement have already been used to test mineral oil and pressboard conductivity. However, the knowledge about the mechanism of electrical conduction ininsulating oil and pressboard is still limited. Therefore, the goal of this thesis is to gain a better understanding of the mechanism of electrical conduction in mineral oil and oil impregnated pressboard. Polarization and depolarization current method (PDC) has gained huge popularity for insulation diagnosis. This time-dependent measurement may provide sufficient information about the dielectric properties of mineral oil and its electrical performance. Here, the dielectric characteristics of three types of mineral oils with different ageing times have been studied using the PDC method. A new polarization theory involving two kinds of charge carriers have been proposed to explain the dielectric behaviour observed in our measurements. Dielectric spectroscopy is a powerful tool to study dipole relaxation, electrical conduction and structure of molecules. Electrode polarization, as a parasitic effect due to the blocking of charge carriers in the vicinity of an electrode, can make the frequency response at low frequency difficult to understand. Since charge carriers in mineral oil are not only generated from dissociation but also from injection at electrodes, the current induced by the motion of the injected charge carriers should also be taken into consideration. The polarization caused by the injection current has been studied in this thesis. When the electric field is not intense, the injection current is proportional to the field and only contributes to the imaginary part of the complex permittivity. A new computer based calculation method and a modified space charge polarization theory have been proposed with this injection current being involved. The frequency responses of three different kinds of mineral oils have been measured and the experimental results have been compared with the simulation using the modified model. It seems the density of the injected charge carriers increases with the aging period. This new model enables one to gain a better understanding of electrical conduction in mineral oil. The design and choice of an electrode system is important in DC conductivity measurement of insulating liquid. In this thesis, the electric field distribution of an electrode system which consists of two parallel circular metallic electrodes and a guard electrode has been studied using Comsol Multiphysics software. A new parameter which is not yet involved in current standards, the edge radius, has been investigated by means of field calculation. It has been found out that there are regions in the vicinity of the edges of the guard and measuring electrode at which the field is dramatically distorted. If the edges of these two electrodes are sharp, the maximum electric field in the test cell will be much higher than the average field between the measuring electrode and the high voltage electrode. An empirical equation has been proposed to calculate this maximum field. The classic correction expression of effective radius has been re-evaluated with the edge radius being taken into account. Experimental work has been performed to confirm this conclusion. Three kinds of mineral oils with different aging times have been tested under the DC field using a guarded electrode system and the electric strengths of these oils have been estimated. A recommendation has been made to current standards in insulating liquid measurement. The dielectric properties of the oil impregnated pressboard sample have been evaluated with the PDC measurement under different temperatures and electric fields. The classic R-C equivalent model has used to explain the dielectric behaviour of the oil/pressboard sample in our PDC measurement. As the electrode effect should be taken into consideration in a DC field, a modified R-C equivalent model has been proposed and used to fit the experimental results and good fitting has been obtained.
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Kuang, Ye Chow. "Recovery voltage in transformer oil-paper insulation diagnosis". Thesis, University of Southampton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416494.
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Wu, Wei. "CFD calibrated thermal network modelling for oil-cooled power transformers". Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/cfd-calibrated-thermal-network-modelling-for-oilcooled-power-transformers(9199cbcc-c6df-4f26-aa9b-dde055ef44ea).html.
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Power transformers are key components of electric system networks; their performance inevitably influences the reliability of electricity transmission and distribution systems. To comprehend the thermal ageing of transformers, hot-spot prediction becomes of significance. As the current method to estimate the hot-spot temperature is based on empirical hot-spot factor and is over-simplified, thermal network modelling has been developed due to its well balance between computation speed and approximation details. The application of Computational Fluid Dynamics (CFD) on transformer thermal analysis could investigate detailed and fundamental phenomena of cooling oil flow, and the principle of this PhD thesis is then to develop more accurate and reliable network modelling tools by utilising CFD.In this PhD thesis the empirical equations employed in network model for Nusselt number (Nu), friction coefficient and junction pressure losses (JPL) are calibrated for a wide range of winding dimensions used by power transformer designs from 22 kV to 500 kV, 20 MVA to 500 MVA, by conducting large sets of CFD simulations. The newly calibrated Nu equation predicts a winding temperature increase as the consequence of on average 15% lower Nu values along horizontal oil ducts. The new friction coefficient equation predicts a slightly more uniform oil flow rate distribution across the ducts, and also calculates a higher pressure drop over the entire winding. The new constant values for the JPL equations shows much better match to experimental results than the currently used 'off-the-shelf' constants and also reveals that more oil will tend to flow through the upper half of a pass if at a high inlet oil flow rate. Based on a test winding model in the laboratory, the CFD calibrated network model's calculation results are compared to both CFD and experimental results. It is concluded that the deviation between the oil pressure drop over the pass calculated by the network model and the CFD and the measured values is acceptably low. It proves that network modelling could deliver quick and reliable calculation results of the oil pressure drop over windings and thereby assist to choose capable oil pumps at the thermal design stage. However the flow distribution predicted by network model deviates from the one by CFD; this is particularly obvious for the cases with high flow rates probably due to the entry eddy circulation phenomena observed in CFD. As no experiment validation has been conducted, further investigation is necessary. The CFD calibrated network model is also applied to conduct a set of sensitivity studies on various thermal design parameters as well as loads. Because the studies are on a directed oil cooling winding case, an oil pump model is incorporated. From the studies recommendations are given for optimising thermal design, e.g. narrowed horizontal ducts will reduce average winding and hot-spot temperatures, and narrowed vertical ducts will however increase the temperatures. Doubled oil block washers are found to be able to significantly reduce the disc temperatures, although there is a slight reduction of the total oil flow rate, due to the increase of winding hydraulic impedance. The impact of different loadings, 50%~150% of rated load, upon the forced oil flow rate is limited, relative change below 5%. The correlations between the average winding and hot-spot temperatures versus the load factors follow parabolic trends.
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Fors, Jonathan. "Modeling and OpenFOAM simulation of streamers in transformer oil". Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-80932.
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Electric breakdown in power transformers is preceded by pre-breakdown events such as streamers. The understanding of these phenomena is important in order to optimize liquid insulation systems. Earlier works have derived a model that describes streamers in transformer oil and utilized a finite element method to produce numerical solutions. This research investigates the consequences of changing the numerical method to a finite volume-based solver implemented in OpenFOAM. Using a standardized needle-sphere geometry, a number of oil and voltage combinations were simulated, and the results are for the most part similar to those produced by the previous method. In cases with differing results the change is attributed to the more stable numerical performance of the OpenFOAM solver. A proof of concept for the extension of the simulation from a two-dimensional axial symmetry to three dimensions is also presented.Elektriska genomslag i högspänningstransformatorer föregås av bildandet av elektriskt ledande kanaler som kallas streamers. En god förståelse av detta fenomen är viktigt vid konstruktionen av oljebaserad elektrisk isolation. Tidigare forskning i ämnet har tagit fram en modell för fortplantningen av streamers. Denna modell har sedan lösts numeriskt av ett beräkningsverktyg baserat på finita elementmetoden. I denna uppsats undersöks konsekvenserna av att byta metod till finita volymsmetoden genom att implementera en lösare i OpenFOAM. En standardiserad nål-sfär-geometri har ställts upp och ett flertal kombinationer av oljor och spänningar har simulerats. De flesta resultaten visar god överensstämmande med tidigare forskning medan resultat som avviker har tillskrivits de goda numeriska egenskaperna hos OpenFOAM-lösaren. En ny typ av simulering har även genomförts där simulationen utökas från en tvådimensionell axisymmetrisk geometri til tre dimensioner.
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Yang-Peláez, Julie Anshun 1970. "Development of oil-filled microcellular foam for transformer insulation". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/37740.
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Kisch, Ryan John. "Using refractive index to monitor oil quality in high voltage transformers". Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/5636.
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Insuring reliable operation of high voltage electrical equipment, such as transformers and cables,
is of great importance to the power industry. This is done by monitoring the equipment. A large
portion of this monitoring includes analyzing the quality of the insulating oils and observing
various compounds formed in the oils during aging. Most often, transformer monitoring
includes routine oil sampling and analysis, which has proven to be very effective at diagnosing
faults and determining the insulation condition. Many techniques have been demonstrated for
the purpose of online monitoring, and various commercial products are available. However,
utility companies are still looking for more cost effective methods to monitor their equipment
between sampling intervals. The work presented here was performed in order to investigate the
use of refractive index for monitoring insulating oils. The refractive indices of various oil
samples obtained from the field were measured and differences were observed. Accelerated
aging experiments were conducted in a laboratory and increases in the refractive indices of these
artificially aged oils were observed. Experiments were conducted to determine what by-products
would contribute to this increased refractive index by investigating the effects of individual
groups on the refractive index change. These groups included aromatic compounds, polar
compounds, furans, acid, and fault gases. We observe that the formation of furans, acids, and
fault gases cannot be detected using refractive index for the concentrations typically found in the
field. We conclude that changes in the refractive index of an oil can be used as an indicator of
the oil’s aging and its break down and the formation of aromatic and polar compounds.
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Pillai, Ilona G. "Identification and carcinogenicity of polycyclic aromatic hydrocarbons in transformer oil". Thesis, Cranfield University, 2003. http://dspace.lib.cranfield.ac.uk/handle/1826/4239.
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Insulating oils are rich in polycyclic aromatic hydrocarbons (PAHs) which act as inhibitors of oil breakdown, but are believed to be the main source of oil mutagenicity when converted to their epoxide form by mammalian enzymes. The current industry- recognised measurement of oil risk, the IP 346 method, measures total aromatic content and therefore cannot be directly related to PAH risk. This thesis describes efforts made to establish the contribution of PAH species alone to total oil mutagenicity.
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Tee, Sheng Ji. "Ageing assessment of transformer insulation through oil test database analysis". Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/ageing-assessment-of-transformer-insulation-through-oil-test-database-analysis(9d99e3a3-8795-4b85-a484-48fae2f02d2e).html.
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Transformer ageing is inevitable and it is a challenge for utilities to manage a large fleet of ageing transformers. This means the need for monitoring transformer condition. One of the most widely used methods is oil sampling and testing. Databases of oil test records hence manifest as a great source of information for facilitating transformer ageing assessment and asset management. In this work, databases from three UK utilities including about 4,600 transformers and 65,000 oil test entries were processed, cleaned and analysed. The procedures used could help asset managers in how to approach databases, such as the need for addressing oil contamination, measurement procedure change and oil treatment discontinuities. An early degradation phenomenon was detected in multiple databases/utilities, which was investigated and found to be caused by the adoption of hydrotreatment oil refining technique in the late 1980s. Asset managers may need to monitor more frequently the affected units and restructure long term plans. The work subsequently focused on population analyses which indicated higher voltage transformers (275 kV and 400 kV) are tested more frequently and for more parameters compared with lower voltage units (33 kV and 132 kV). Acidity is the parameter that shows the highest correlation with transformer in-service age. In addition, the influence of the length of oil test records on population ageing trends was studied. It is found that it is possible to have a representative population ageing trend even with a short period (e.g. two years) of oil test results if the transformer age profile is representative of the whole transformer population. Leading from population analyses, seasonal influence on moisture was investigated which implies the importance of incorporating oil sampling temperature for better interpretation of moisture as well as indirectly breakdown voltage records. A condition mismatch between dielectric dissipation factor and resistivity was also discovered which could mean the need for revising the current IEC 60422 oil maintenance guide. Finally, insulation condition ranking was performed through principal component analysis (PCA) and analytic hierarchy process (AHP). These two techniques were demonstrated to be not just capable alternatives to traditional empirical formula but also allow fast, objective interpretation in PCA case, as well as flexible and comprehensive (objective and subjective incorporations) analysis in AHP case.
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Overby, Alan Bland. "Dissolved Gas Analysis of Insulating Transformer Oil Using Optical Fiber". Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/48598.
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The power industry relies on high voltage transformers as the backbone of power distribution
networks. High voltage transformers are designed to handle immense electrical loads in hostile
environments. Long term placement is desired, however by being under constant heavy load
transformers face mechanical, thermal, and electrical stresses which lead to failures of the
protection systems in place. The service life of a transformer is often limited by the life time of
its insulation system. Insulation failures most often develop from thermal faults, or hotspots, and
electrical faults, or partial discharges. Detecting hotspots and partial discharges to predict
transformer life times is imperative and much research is focused towards these topics. As these
protection systems fail they often generate gas or acoustic signals signifying a problem. Research
has already been performed discovering new ways integrate optical fiber sensors into high
voltage transformers. This thesis is a continuation of that research by attempting to improve
sensor sensitivity for hydrogen and acetylene gasses. Of note is the fabrication of new hydrogen
sensing fiber for operation around a larger absorption peak and also the improvement of the
acetylene sensor's light source stability. Also detailed is the manufacturing of a field testable
prototype and the non-sensitivity testing of several other gasses. The developed sensors are
capable but still could be improved with the use of more powerful and stable light sources.Master of Science
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Elzagzoug, Ezzaldeen. "Chromatic monitoring of transformer oil condition using CCD camera technology". Thesis, University of Liverpool, 2013. http://livrepository.liverpool.ac.uk/12233/.
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Power transformers are essential components within the power distribution system. Transformer failures having a high economic impact on the distribution operators and the industrial and domestic customers. Dielectric mineral oil is used in transformers for electrical insulation between live parts, cooling and protection of the insulation papers in the transformer. Oil contamination and changes in the chemical structure of the oil result in the decay of insulation paper and reduced insulation and cooling which can lead to a transformer failure. The general approach to oil monitoring has been for an operator to examine the colour index (ASTM) of the oil, electrical strength, acidity, water contents and dissolved gas analysis results and form an opinion as to the extent of oil degradation. Chromatic techniques enable data from di↵erent sources to be combined to give an overall evaluation about the condition of a system being monitored. One of the main goals for this work was to use chromatic techniques for integrating the oil data from the di↵erent sources and sensors. In addition the chromatic approach enables liquids to be monitored optically so a second aim was to apply chromatic optical oil monitoring using portable system by transmitting polychro- matic light through the oil sample, which is contained in a transparent cuvette and imaged using a mobile phone camera. A number of oil samples were optically analysed with portable chromatic sys- tem and the optical data was compared with the colour index and chromatically companied with the dissolved gas and other oil data to give overall evaluation of oil degradation. The chromatic optical result compared favourably with the colour index. It was also possible to classify the oil samples chromatically into categories of low, medium and high degradation. This enabled the chromatic data combination approach to be implemented as a prototype system in Matlab software that an operator could use to get a classification of an oil sample. Essential experiment was introduced to monitor di↵erent oil particles by obtaining the result of di↵erent filtered samples through the filter paper. Beside the ability to analyse data and distinguish between fresh and contam- inated oil samples the chromatic technique has the ability to track the history of di↵erent degraded oil samples which can give an indication about failure faults and it could give a prediction of any future faults. Therefore a commercially viable reliable system can be developed to extend the service life and extend the maintenance schedules. These monitoring systems could lead to extending the service life of the transformers, making the electricity supply more reliable and giving the consumer a better quality of life.
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Hao, Miao. "Space charge behaviour in thick oil pressboard insulation systems for converter transformers". Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/383685/.
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With increasing desire for renewable energy integration and international power trade, the development and utilization of the high voltage direct current (HVDC) technologies for the long distance and massive power transmission have been boosted in the recent years. The reliability of the converter transformer, which is one the most important components in HVDC transmission, has become a general concern, because of its complex structure and operating conditions. It is well known that the presence of space charge can distort the electric field distribution within the dielectrics, which can potentially influence the reliability of the converter transformer by accelerating the insulation ageing or failure. Therefore, investigation and evaluation of the space charge behaviours within the insulation system similar to those in converter transformers is paramount for delivery of a reliable HVDC transmission system. Unfortunately, the space charge behaviours in thick oil pressboard insulation systems used in converter transformers have rarely been studied due to its complex solid and liquid mixed insulation structure and severe attenuated signal that cannot be easily measured. Therefore, in this work a purpose built pulsed electroacoustic system (PEA) has been developed to allow the measurement of space charge in a thick oil-gap and pressboard combined insulation system with a total thickness of 2 mm. In order to have a better understanding of the space charge characteristics in converter transformers, three different sample configurations have been used and they are single layer pressboard, oil gap combined with single layer pressboard and oil gap sandwiched between two pressboard layers. Investigations of space charge dynamics in thick oil pressboard insulation systems under various DC stresses, polarity reversal voltages and AC/DC superimposed stresses have been successfully conducted. In addition, the impact of aged oil on the space charge behaviour has been analysed by extracting space charge features using numerical calculations to evaluate the insulation performance of the long time served converter transformer The results identified that the space charge dependent electric field distribution is significantly distorted in the pressboard bulk or at the oil/pressboard interface under the DC stress. The peak electric stress could be much more severe than the predicted by calculations based on Maxwell-Wagner theory, particularly in the aged oil samples. After polarity reversal, the electric field increase across the oil gap can be significant due to the residual space charge in the pressboard. A method to estimate the maximum electric field enhancement immediately after polarity reversal by using the DC space charge characteristics is proposed in this work, and its effectiveness and accuracy have been experimentally validated. The space charge behaviours under AC/DC superimposed stress, in oil-pressboard insulation system are investigated for the first time in this research. The results revealed the non-linear charge injection behaviour under the superimposed stress in the oil pressboard insulation, which has been evidenced experimentally by the accelerated space charge movement and the increased charge amount when compared with under AC or DC stress separately. This research demonstrates the severe electric field distortion caused by the space charge accumulation in the thick oil pressboard insulation system under real operating conditions of the converter transformer. This fundamental study paves the way for further improving the reliability of HVDC transmission system, leading to the realization of new rules of design, testing, operation, and maintenance are needed for converter transformers in the power industry.
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Robalino, Vanegas Diego M. "Loss of life of medium voltage oil-immersed current transformers under thermal accelerated ageing a dissertation presented to the faculty of the Graduate School, Tennessee Technological University /". Click to access online, 2009. http://proquest.umi.com/pqdweb?index=0&did=1934058311&SrchMode=1&sid=2&Fmt=6&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1264684717&clientId=28564.
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McEwan, Michael. "The antifungal effects of plant essential oils and their production by transformed shoot culture". Thesis, University of Strathclyde, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246327.
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Marko, Robert Michael. "Thermal modelling of a natural-convection-cooled, oil-immersed distribution transformer". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/mq23407.pdf.
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Hwang, Jae-Won George 1980. "Elucidating the mechanisms behind pre-breakdown phenomena in transformer oil systems". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/60145.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 321-334).
The widespread use of dielectric liquids for high voltage insulation and power apparatus cooling is due to their greater electrical breakdown strength and thermal conductivity than gaseous insulators. In addition, their ability to conform to complex geometries and self-heal means that they are often of more practical use than solid insulators. Unfortunately, as with all insulation, the failure of the liquid insulation can cause catastrophic damage. This has led researchers to study the insulating properties of dielectric liquids in an attempt to understand the underlying mechanisms that precede electrical breakdown in order to prevent them. This thesis develops a set of mathematical models which contain the physics to elucidate the pre-breakdown phenomena in transformer oil and other oil-based systems. The models are solved numerically using the finite element software package COMSOL Multiphysics. For transformer oil, the results show that transformer oil stressed by a positively charged needle electrode results in the ionization of oil molecules into positive ions and electrons. The highly mobile electrons are swept back towards the positive electrode leaving a net positive space charge region that propagates towards the negative electrode causing the maximum electric field to move further into the oil bulk. It is the moving electric field and space charge waves that allow ionization to occur further into the oil. This leads to thermal dissipation and creates a low density streamer channel. In comparing the numerical results to experimental data found in the literature, the results indicate that positive streamer propagation velocity regimes or modes are dictated by the onset of different ionization mechanisms (i.e., field ionization, impact ionization, photoionization) that are dependent on the liquid molecular structure and the applied voltage stress. In particular, the field ionization of different families of molecules plays a major role in development of slow and fast mode streamers, especially in liquids that are comprised of many different types of molecules such as transformer oil. The key characteristics of the molecules that affect streamer propagation are their molecular structure (i.e., packing, density, and separation distance) and ionization potential. A direct outcome of this work has been the ability to show that by adding low ionization potential additives to pure dielectric liquids, the voltage at which streamers transition from slow to fast mode can be significantly increased, a result counter-intuitive to conventional wisdom and common practice. For transformer oil with nanoparticle suspensions (nanofluids), the effects of nanoparticle charging on streamer development have been thoroughly investigated. The charging dynamics of a nanoparticle in transformer oil show that electron trapping by conductive nanoparticles is the cause of a decrease in positive streamer velocity. resulting in higher electrical breakdown strength for transformer oil-based nanofluids. Further generalized analysis of the charging of a perfectly conducting sphere from a single charge carrier or two charge carriers of opposite polarity, with different values of volume charge density and mobility and including an ohmic lossy dielectric region surrounding a perfectly conducting sphere or cylinder are also examined. Streamer development in liquid-solid insulation systems, such as oil-pressboard systems, is also investigated. Great effort has been undertaken to model the solid insulation region and a method has been developed to model the oil-solid interface to account for surface charge build up, which is important for streamer dynamics. Various ohmic and migration conduction laws are used for oil and solid insulation to solve for the time and space development of surface charge distributions in closed form for one-dimensional parallel plane and numerically for two-dimensional geometries. The work on streamers in oil-pressboard systems has shown that streamers are attracted to the oil-pressboard interface, due to the larger permittivity of the pressboard. Moreover, the models have shown that the determination of how streamers propagate in the presence of solid insulation is strongly dependent on the extent to which the solid insulation alters the streamer shape and the electric field created by the streamer's space charge. These results obtained from the modeling of streamers in oil-pressboard systems are supported by and help to explain the experimental data in the literature.
by Jae-Won George Hwang.
Ph.D.
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Mahmud, Shekhar. "Influence of contamination on the electrical performance of power transformer oil". Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/379273/.
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Transformer failure statistics from all over the world showed that almost 30% of them were due to insulation. Large amount of those failures were due to particles in transformer oil. Main focus of this research is to effects of contamination on electrical performance of transformer oil. A literature review of major causes of transformer failure, breakdown mechanisms of transformer oil has been conducted. The experimental setup and results from the pressboard-dust-contaminated transformer mineral oil test are also discussed. Several experiments have been carried out with cellulose particle contaminated transformer mineral oil. The experiments of bridge formation are conducted under the influence of DC, AC, and DC biased AC voltages. Samples with several levels of contaminant are tested under different voltage levels. The influence of different electrode systems is also tested i.e. bare electrode, covered electrode, bare electrodes with paper barrier, spherical and needle – plane electrodes. These experiments revealed that the bridges are always formed under the influence of DC voltages. The particles are attracted towards high electric field due to Dielectrophoretic (DEP) force and become charged once in contact with the electrode surface. Long fiber particles were attached to the electrodes and aligned parallel to electric field towards the other electrode. More particles attached to the initial fibers and the process continued until a full bridge formed between the electrodes. The conduction current increased with contamination levels as the bridge thickened with increment of contaminations. There is no complete bridge formed under AC electric field. The particles were attracted to the high electric field and attached to the electrodes but the particles are not been able to charge before the polarity of AC electric field alters with spherical electrodes. The current for AC remained unchanged with the increment of particle contamination levels as there is no bridge formed. However, when the DC biased AC signal is applied, the bridge is formed for all the three voltage levels tested. DC and AC breakdown tests were also conducted for several contamination levels. Experiments with kraft paper covered spherical electrodes confirmed that a tightly bonded cover does not stop the bridge; only a loose bonded cover stopped the bridging. Another test with a paper barrier between bare electrodes also did not stop the bridging. Partial discharge (PD) and breakdown test of the contaminated transformer oil is also measured but the results were not conclusive. An initial mathematical model of pressboard dust accumulation using Finite Element Analysis (FEA) software, COMSOL multiphysics has been conducted. The result of the simulation model for charging-discharging and bridging showed similar trend as experimental results. There are a number of changes that can result in improved simulations. There are several variables affecting the simulation i.e. the pressboard dust particle shape, size, conductivity of impregnated pressboard fiber etc.
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Cleary, Gerard Patrick. "Interpretation of UHF signals produced by partial discharges in oil-filled power transformers". Thesis, University of Strathclyde, 2005. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21575.
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Oil-insulated power transformers are key components of the electrical transmission network. Knowing the state of their insulation is therefore of considerable interest to utilities. Failure in transformers often occurs as a result of electrical breakdown in the insulation materials. Such breakdowns may occur following insulation damage caused over a substantial period of time by the cumulative adverse effects of partial discharge (PD) activity. Recognition of PD in power transformers is important because early detection can allow utilities to take appropriate preventative measures in order that costly failures do not occur. In this work, a range of on-line partial discharge (PD) measurement techniques are reviewed. Ultra high frequency (UHF) and measurements based on the International Electro-technical Commission (IEC) standard 60270 are considered to be the most suitable. UBF measurements have the advantage that PD can be located using time flight measurements, while IEC 60270-based measurements can be quantified in terms pC. A test cell is designed, and PD current pulses are measured when the insulating oil at the tip of a sharp, conducting protrusion breaks down. Current pulses are recorded using two different measurement circuits, and different pulse shapes are observed. The experiments are of fundamental significance because UBF signals are only excited when discharges occur on timescales of around 1 ns or less. Results demonstrate that the durations of current pulses in oil can be sufficiently short to cause the excitation of UHF signals. Characteristics of PD generated in air, new transformer oil and used transformer oil are compared. PD current pulses are measured simultaneously with both EEC 60270-based and UHF measurements systems. Since EEC 60270-based and UBF measurement systems operate on very different principles their responses to PD current pulses of known magnitude provides a useful basis for comparing the performance of both systems. A range of insulation defects that would cause concern in an operational power transformer are then investigated. Radiated UHF signals are measured simultaneously using two broadband electric field sensors. The spectral content and energy of rating measured using each sensor during both half cycles are shown to be useful methods to assist with the understanding of discharge behaviour. UHF PD signals are also measured in a phase-resolved form, and these are analysed in ways that provide evidence of the physical differences between insulation defects. First tests are carried out on a 1000 MVA, 400 kV/ 275 kV power transformer, and results demonstrate that the UBF measurement technique is a very promising approach for PD monitoring. The research contributes to the knowledge base required for the development of continuous monitoring systems for partial discharge and arcing in oil-filled power transformers.
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Kim, In Soo. "A quantitative enzyme linked immunosorbent assay for polychlorinated biphenyls in transformer oil". Thesis, Cranfield University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323838.
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Ghaffarian, Niasar Mohamad. "Partial Discharge Signatures of Defects in Insulation Systems Consisting of Oil and Oil-impregnated Paper". Licentiate thesis, KTH, Elektroteknisk teori och konstruktion, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-105785.
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Partial discharge measurement is a common method for monitoring and diagnostics of power transformers, and can detect insulation malfunctions before they lead to failure. Different parameters extracted from the measured PD activity can be correlated to the PD source, and as a result it is possible to identify the PD source by analyzing the PD activity. In this thesis, possible defects that could cause harmful PDs in transformers were investigated. These defects include corona in oil, a void in pressboard, a metal object at floating potential, surface discharge in oil, a free bubble in oil and small free metallic particles in oil. The characteristics of disturbing discharge sources were analyzed, like corona in air, surface discharge in air, and discharge from an unearthed object near to the test setup. The PD activity was recorded both in the time domain and phase domain, and possible characteristics for each PD pattern and waveform were extracted in order to find the best characteristic for the purpose of classification. The results show that in the phase domain parameters such as phase of occurrence, repetition rate and shape of PD Pattern are most suitable for classification while magnitude of discharge can only be useful in specific cases. The results show that the PD waveforms correlated to different defects are similar; however the time domain data include all the information from the phase domain, and also has the power to identify the number of PD sources. The PD dependency on temperature was investigated on the four test objects including surface discharges in oil, corona in oil, bubble discharges in oil, and metal object at floating potential. The effect of humidity was investigated for corona in oil. The results show that at higher temperature the corona activity in oil and PD activity due to a metal object at floating potential in oil decrease. However, for a bubble in oil and for surface discharge in oil the PD activity increases with the increase of the oil temperature. It was shown that the amount of moisture in oil has a strong impact on number of corona pulses in oil. The last part focused on ageing of oil-impregnated paper due to PD activity. Investigation was made of the behavior of PD activity and its corresponding parameters such as PD repetition rate and magnitude, from inception until complete puncture breakdown. The results show that both the number and magnitude of PD increase over time until they reach to a peak value. After this point over time both curves decrease slowly, and eventually full breakdown occurs. The effect of thermal ageing of oil impregnated paper on time to breakdown and PD parameters was investigated. The results show that thermal aging of oil-impregnated paper increases the number and magnitude of PD. Dielectric spectroscopy was performed on the samples before and after PD ageing and the result was used in order to explain the behavior of PD over time.QC 20121129
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Hägerbrand, Jonathan. "Measurements of resistivity in transformer insulation liquids". Thesis, Uppsala universitet, Institutionen för elektroteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-413804.
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This thesis focuses on measuring techniques and results of resistivity in four commercially available insulating transformer oils: mineral oil, ester oil and two isoparaffin oils. Two measuring techniques, the industrially used diagnostic system for electrical insulation IDA and the Labview implemented Triangular Method, are used for resistivity measurements and the techniques are compared, a correction algorithm to the triangular method is suggested. Dielectric properties of mineral & ester and isoparaffin A&B mixtures are investigated, it is experimentally shown that the transformer oils that show high resistivity also show low loss factor. The effect moisture has on resistivity in mineral and ester oil are shown both in terms of relative humidity and actual water content in parts per million. A previous measurement cell is redesigned, the cell is manufactured in copper and gold. It is found that the material choice of the cell significantly affects the resistivity measurements. The electrical double layer and contact resistance between the oil and cell are investigated as a way to explain the difference in measured resistivity. These experiments are limited to the mineral oil and isoparaffin oil A, it is found that contact resistance is a plausible explanation. The electrical double layer is fairly constant for both oils and the Debye length of the double layer is negligible compared to the total distance between the electrodes of the cell. Lastly, the field of insulating transformer oils and its future is discussed, from data obtained regarding the dielectric properties and environmental aspects of the four transformer oils used in this study. A positive trend which combines the high insulating properties with good biodegradability qualities is found. Suggesting a positive future in the field of insulating transformer oils. The results found in this thesis can be used as a basis for future theses regarding transformer oils used for HVDC applications.
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Mohamed, Ali Mohamed. "ANALYZING THE IMPACT OF PHOTOVOLTAIC AND BATTERIE SYSTEMS ON THE LIFE OF A DISTRIBUTION TRANSFORMER". Thesis, Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-54952.
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This degree project presents a study case in Eskilstuna-Sweden, regarding the effect of the photovoltaic (PV) systems with battery energy storage system (BESS) on a power distribution transformer, and how they could change the transformer lifespan. For that, an extensive literature review has been conducted, and two MATLAB models were used to simulate the system. One model simulates the PV generation profile, with the option of including battery in the system, and the other one simulates the transformer loss of life (LOL) based on the thermal characteristics. Simulations were using hourly time steps over a year with provided load profile based on utility data and typical meteorological year weather data from SMHI and STRÅNG. In this study, three different scenarios have been put into consideration to study the change of LOL. The first scenario applies various levels of PV penetrations without energy storage, while, the other scenarios include energy storage under different operating strategies, self-consumption, and peak shaving. Similarly, different battery capacities have been applied for the purpose of studying the LOL change. Thus, under different PV penetrations and battery capacities, results included the variation of LOL, grid power, battery energy status, and battery power. Moreover, results concluded that the PV system has the maximum impact on LOL variation, as it could decrease it by 33.4 %, and this percentage could increase by applying different battery capacities to the system. Finally, LOL corresponding to the battery under peak shaving strategy varies according to the battery discharge target. As different peak shaving targets were used to control the battery discharge, and hence, study the impact on the transformer and estimate its LOL.
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Xiang, Jing. "Pre-breakdown and breakdown study of transformer oil under DC and impulse voltages". Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/prebreakdown-and-breakdown-study-of-transformer-oil-under-dc-and-impulse-voltages(f6dd1d8c-8336-4015-baa5-40928e87330f).html.
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Streamer characteristics, breakdown strengths and gassing behaviour of insulating liquids under electric stresses are taken into account for a reliable design and safe operation of the transformer. Ester liquids which are biodegradable and have high fire point have been widely used in distribution transformers and some power transformers in recent years. It is also interesting to introduce ester liquids into High Voltage Direct Current (HVDC) converter transformers due to the fast development of HVDC transmission lines. Therefore, this thesis aims to investigate the pre-breakdown, breakdown characteristics and gassing behaviour of a synthetic ester liquid under DC and various impulse voltages where a mineral oil is tested as the benchmark. A comprehensive study of streamer characteristics and breakdown strength of the mineral oil and the synthetic ester liquid under both positive and negative DC voltages was carried out in the point-plane electric fields. Characteristics of streamer length, propagation velocity and shape were analysed based on shadowgraph images obtained at a gap distance of 10 mm, using a multi-channel ultra-high speed camera. Streamer inception voltages with the tip radii of 5 µm, 10 µm, 20 µm and 50 µm and breakdown voltages at various gaps of 2 mm, 5 mm, 10 mm, 20 mm and 30 mm were also investigated. The results indicate that there is no obvious streamer propagation (less than about 10% of the gap distance) under negative polarity even when the applied voltage approaches breakdown voltage. At the same applied voltage level, the streamer in the synthetic ester liquid propagates faster and further than that in the mineral oil. As a result, the breakdown voltages of the synthetic ester liquid are lower than those of the mineral oil at all the gap distances investigated under both polarities. Experimental and modelling studies of pre-breakdown and breakdown phenomena in the mineral oil and the synthetic ester liquid under impulse waveforms with different tail-time were carried out in the point-plane electric fields. A compact solid-state switch based impulse generator was used to provide different impulse waveforms from short tail-time to 'step-like' tail-time: 0.8/8 µs, 0.8/14 µs, 0.8/30 µs and 0.8/3200 µs. A point-plane electrode configuration with a small gap distance of 10 mm and a tip radius of 10 µm was used. The results indicate that the shorter tail-time impulse waveform results in a shorter stopping length and higher breakdown voltage; however it does not affect the instantaneous breakdown voltage and time to breakdown. A mathematical model is therefore described to predict the breakdown voltage under different impulse waveforms. In addition, with the similar stopping length, higher energy injected from the short tail-time impulse caused the streamers to have more branches than those under the long tail-time impulse. The characteristics of fault gas generation in the mineral oil and the synthetic ester liquid under various levels of electrical faults were studied. A test platform with functions of automatic spark fault control and data acquisition was developed. The effects of spark numbers (from 20 to 500), gap distance (5 mm and 10 mm) and voltage levels (Vb-99.9% and 1.5Vb-99.9%) on fault gas generation in liquids were studied. The key gases in the mineral oil are H2 and C2H2, while the key gases in the synthetic ester liquid are H2, C2H2 and CO. The amount of fault gas generation increases linearly with the number of sparks. However, the number of sparks does not have an obvious effect on fault gas pattern and gas generation per unit fault energy in µL/J. Spark at a larger gap distance or under a higher applied breakdown voltage generates more fault gases due to higher injected fault energy.
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Okubo, Hitoshi, i Katsumi Kato. "Charge Behavior and Field Measurement Techniques in Different Kinds of Insulating Oil for Power Transformers". IEEE, 2008. http://hdl.handle.net/2237/12076.
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Gallarotti, Maura. "CFD ANALYSIS ON THE COOLING OF NON GUIDED OIL NATURAL AIR NATURAL TYPES OF TRANSFORMERS". Thesis, KTH, Mekanik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-203970.
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ABB is moving towards more powerful and compact transformers and an efficient cooling is of paramount importance in order to avoid overheating.In this master thesis, transformers without guides for the oil flow have been analysed: they allow a faster and cheaper manufacturing process, but at the same time the absence of guides makes the cooling design more difficult.In order to be able to perform several parametric studies, a script with the Pointwise mesher has been developed for the automatic generation of the geometry and mesh of transformer windings. This has allowed to analyse transformer windings with a different shape, assessing the effect of a certain number of geometrical parameters on the cooling efficiency.The software ANSYS Fluent was used to perform 2D axisymmetric unsteady simulations on the company cluster and the simulation set up was validated thanks to comparison with experimental measurements in ABB in Vaasa (Finland), that showed an average relative error below 2%.A remarkable result of this study is the identification of a periodic pattern in the temperature of the windings from the inlet to the outlet of the transformer, with hot spot locations every 10-20 disc windings. This conclusion has also been confirmed by the experimental measurements performed in Vaasa on a test transformer. Furthermore, a periodic behaviour of the temperature of the windings and of the oil in time has also been identified.Finally, transformers with an additional cooling channel in the disc windings have been studied, revealing that an accurate design is needed when adding oil channels through the windings in order to avoid the formation of unexpected hot spots.
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Jiao, Yuhe. "CFD Study On The Thermal Performance of Transformer Disc Windings Without Oil Guides". Thesis, KTH, Kraft- och värmeteknologi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-102546.
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The hotspot temperature of disc windings has a close relation with the transformer age. In oil immersed transformers, oil guides are applied generally to enhance the cooling effects for disc windings. In some cases disc windings without oil guides are used. However, the lack of oil guides is expected to result in a more complicated thermal behavior of the windings, making it more difficult to predict the location and strength of the hotspot temperature (i.e. the hottest temperature in the winding). To get an improved understanding of the thermal behavior, a CFD study has been performed. This article describes the implementation of CFD simulation for 2D axisymmetry models without oil guides, and then analyzes the results of a series of parametric studies to see the sensitive factors influencing the cooling effects. These parameters include radial disc width, inlet mass flow rate, horizontal duct height, vertical duct width and the inlet/outlet configurations. Three main characteristics, the hotspot temperature, the location of the hotspot and the number of oil flow patterns are detected to describe the thermal performance.
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Sitorus, Henry Binsar Hamonangan. "The study of jatropha curcas oil-based biodegradable insulation materials for power transformer". Thesis, Ecully, Ecole centrale de Lyon, 2015. http://www.theses.fr/2015ECDL0022/document.
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Ce travail porte sur la caractérisation physico-chimique de l'huile de Jatropha Curcas et sa capacité à remplacer l'huile minérale dans les transformateurs de puissance. Ce produit présente plusieurs avantages sur les autres huiles végétales comme l'huile de palme ou l'huile de colza, qui recommandent sa production et son utilisation. En effet, la plante de Jatropha Curcas peut être cultivée sur des sols pauvres à faibles précipitations, évitant ainsi d'utiliser des sols plus fertiles pour sa culture permettant ainsi aux petits exploitants de réserver leurs terres aux cultures de base. Cette plante peut pousser facilement dans des zones où les niveaux de précipitations annuelles sont nettement inférieures à celles requises par d'autres espèces telles que le colza, le tournesol, le soja, le maïs, le palmier à huile et d'autres. Elle peut être cultivée sur tous les types de sol en Indonésie, même sur des terres arides, dans de nombreuses régions de l'Indonésie orientale, inexploitées en raison des difficultés à planter d'autres cultures. En outre, l'huile de Jatropha Curcas est un produit non alimentaire. En faisant subir à l’huile de Jatropha Curcas brute une estérification à base alcaline avec de l'hydroxyde de potassium (KOH), on obtient de l’huile de méthylester de Jatropha Curcas (JMEO) dont la viscosité et l’acidité sont acceptables pour les équipements à haute tension en particulier pour les transformateurs de puissance. Les propriétés physico-chimiques et électriques de JMEO ont été mesurées ainsi que celles de l'huile minérale (MO) pour la comparaison. Pour les propriétés physico-chimiques, il s’agit de la densité relative, la teneur en eau, la viscosité, l'acidité, l'indice d'iode, la corrosivité, le point d'éclair, le point d'écoulement, la couleur, l'examen visuel, et la teneur en ester méthylique. Quant aux propriétés électriques, elles concernent la rigidité diélectrique sous différentes formes de tension (alternative, continu et choc de foudre), les phénomènes de pré-claquage et de claquage sous choc de foudre, les décharges glissantes sur les surfaces de carton comprimé, immergé dans JMEO et MO. Les résultats obtenus montrent que les tensions de claquage moyennes en continu et en choc de foudre des huiles JMEO et MO sont très proches ; la tension de claquage moyenne de JMEO est même plus élevée que celle de l'huile minérale (de type naphténique). La mesure des tensions de claquage des mélanges d'huiles «80% JMEO + 20% MO» et «50% JMEO et 50% MO» montrent que la tension de claquage du mélange «80% JMEO + 20% MO» est toujours supérieure à celle de l'huile minérale sous tensions alternative et continue. Cela indique que le mélange d'huile minérale et de JMEO avec un rapport de 20:80 ne dégrade pas ses performances. Le mélange d'huiles peut se produire lors du remplacement de l'huile minérale par JMEO dans les transformateurs installés et en exploitation. L'analyse des caractéristiques des streamers (la forme, le temps d'arrêt, le courant associé et la charge électrique) se développant dans les huiles JMEO et MO sous tension impulsionnelle de foudre, montre une grande similitude. Aussi, la longueur finale (Lf) et la densité des branches des décharges surfaciques se propageant sur le carton comprimé immergé dans l'huile de Jatropha Curcas de méthylester (JMEO) et de l'huile minérale (MO), sous tensions de choc de foudre positif et négatif (1,2/50 μs), pour deux configurations d'électrodes divergentes (électrode pointe haute tension perpendiculaire et tangente au carton, respectivement), sont fortement influencées par l'épaisseur du carton comprimé. Pour une épaisseur donnée, Lf augmente avec la tension et décroît lorsque l'épaisseur augmente. Lf est plus long lorsque la pointe est positive que lorsque la pointe est négative. Pour une tension et une épaisseur du carton comprimé donnée, les valeurs de Lf dans l’huile minérale et l’huile JMEO sont très proches. [...]This work is aimed at the investigation of the physicochemical characterization of Jatropha Curcas seeds oil and its capacity to be an alternative option to replace mineral oil in power transformers. This product presents several advantages that recommend both its production and usage over those of other vegetable oils as crude palm oil and rapeseeds oil. Indeed, it may be grown on marginal or degraded soils avoiding thus the need to utilize those more fertile soils currently being used by smallholders to grow their staple crops; and it will readily grow in areas where annual rainfall levels are significantly lower than those required by other species such as palm oil, rape-seeds oil, sunflower oil, soybeans oil, corn oil and others. For instance, these plants can grow on all soil types in Indonesia, even on barren soil. The barren soil types can be found in many parts of eastern Indonesia that remain untapped because of the difficulty planted with other crops. Moreover, jatropha curcas oil is nonfood crops. Jatropha Curcas oil was processed by alkali base catalyzed esterification process using potassium hydroxide (KOH) to produce Jatropha Curcas methyl ester oil (JMEO) has a viscosity and a acidity that are acceptable for high voltage equipment especially in power transformer. The physicochemical and electrical properties of JMEO were measured as well as those of mineral oil (MO) for comparison. The physicochemical properties cover relative density, water content, viscosity, acidity, iodine number, corrosivity, flash point, pour point, color, visual examination, and methyl ester content. Meanwhile the electrical properties cover dielectric strength under AC, DC and lightning impulse voltages, pre-breakdown / streamers under lightning impulse voltage, creeping discharge over pressboard immersed in JMEO and MO. The obtained results show that the average DC and lightning impulse breakdown voltages of JMEO and MO are too close, even the average AC breakdown voltage of JMEO are higher than that of mineral oil (napthenic type). The measurement of breakdown voltages of two oil mixtures namely “80% JMEO + 20% MO” and “50% JMEO and 50% MO” shows that the breakdown voltage of the first mixture (i.e., “80%JMEO+20%MO”) is always higher than that of mineral oil under both AC and DC voltages. This indicates that mixing 20:80 mineral oil to JMEO ratio does not degrade its performance. The mixing of oils can occur when replacing mineral oil by JMEO in installed transformers. The analysis of the streamers characteristics (namely; shape, stopping length, associated current and electrical charge) developing in JMEO and MO under lightning impulse voltages, shows that these are too close (similar). It is also shown that the stopping (final) length Lf and the density of branches of creeping discharges propagating over pressboard immersed in Jatropha Curcas methyl ester oil (JMEO) and mineral oil (MO), under positive and negative lightning impulse voltages (1.2/50 μs), using two divergent electrode configurations (electrode point perpendicular and tangential to pressboard), are significantly influenced by the thickness of pressboard. For a given thickness, Lf increases with the voltage and decreases when the thickness increases. Lf is longer when the point is positive than with a negative point. For a given voltage and thickness of pressboard, the values of Lf in mineral oil and JMEO are very close. It appears from this work that JMEO could constitute a potential substitute for mineral oil for electrical insulation and especially in high voltage power transformers
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Hikita, M., M. Matsuoka, R. Shimizu, K. Kato, N. Hayakawa i H. Okubo. "Kerr electro-optic field mapping and charge dynamics in impurity-doped transformer oil". IEEE, 1996. http://hdl.handle.net/2237/6874.
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Jiao, Yuhe. "CFD Study On The Thermal Performance of Transformer Disc Windings Without Oil Guides". Thesis, KTH, Energiteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-102538.
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Huang, Bo. "Space charge behaviour of thick oil and pressboard in a HVDC converter transformer". Thesis, University of Southampton, 2018. https://eprints.soton.ac.uk/423615/.
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High Voltage Direct Current (HVDC) power transmission is essential for the development of long-distance power transmission. Within the HVDC conversion system, the most significant apparatus is a HVDC converter transformer. In converter transformers, on the one hand, the high operational electric field is desirable to decrease the dimension, weight, and material usage in converter transformers; on the other hand, the electric field must be lower compared to the dielectric strength to avoid the surface discharge or destructive breakdown of insulation materials. In addition the operation voltage, the electric field is also affected by space charge dynamics in insulation materials. For this reason, extensive efforts have been made to investigate space charge dynamics in the insulation material of converter transformers, such as the oil-impregnated paper. However, the space charge characteristics are not well understood for the thick oil and pressboard (PB) materials under a temperature gradient. Hence, a new purpose-built pulsed electroacoustic (PEA) system has been set up to measure the thick oil and PB space charge behaviour under a temperature gradient. This dissertation comprises the quantitative analysis of the space charge dynamics in thick oil and PB insulation materials under a temperature gradient through an experimental approach. With the purpose-built PEA system, the influential factor of temperature gradient on dynamics of space charge in thick oil and PB has been investigated. The space charge measured from the PEA system depends on the acoustic wave propagation in the insulation materials. The temperature can affect the acoustic velocity and thus space charge distribution. Therefore, for a one-layer sample, the space charge recovery method under a temperature gradient is important to ensure that the correct space charge pattern is acquired. Furthermore, in multilayer samples, an acoustic wave may experience different generation and transmission coefficients that lead to attenuation and dispersion after the propagation through the dispersive materials. Therefore, the space charge recovery method of multilayer samples under the temperature gradient is proposed. With the proposed space charge recovery method under a temperature gradient, the space charge influential factors, such as temperature gradient and multilayer oil and PB, are investigated. Furthermore, the polarity reversal (PR) effect on dynamics of space charge in multilayer oil and PB under a temperature gradient is presented using an experimental approach. The measured space charge is further interpolated into the COMOSOL model to quantitatively evaluate the electric field oil and PB after PR. The difference between the electric field after PR calculated by the Maxwell-Wagner theory and space charge density is compared. The thickness effect on the space charge is investigated on two-layer oil and PB materials. The simulation model is also expanded into four and six layers for the electric field calculation based on the estimated space charge results.
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Lai, Sin Pin. "Furan measurement in transformer oil by UV-Vis spectroscopy using fuzzy logic approach". Thesis, Curtin University, 2009. http://hdl.handle.net/20.500.11937/2342.
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An Ultraviolet to Visible (UV-Vis) spectroscopic analysis based on fuzzy logic approach has been developed for furan content measurement in transformer oil. Following the successful identification and quantification of furan derivatives in transformer oil by ASTM D5837 standard, the new approach is able to approximate the furan content more conveniently and economically. As furan concentration level would determine the absorption intensity in UV-Vis spectral range, the fuzzy logic software model developed would exploit this characteristic to aggregate the furans content level in transformer oil. The UV-Vis spectral response at other ambient temperature is also studied. The proposed technique provides a convenient alternative to conventional method of furan measurement by High Performance Liquid Chromatography (HPLC) or Gas Chromatography Mass Spectrometry (GC/MS) in ASTM D5837 Standard.
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Lai, Sin Pin. "Furan measurement in transformer oil by UV-Vis spectroscopy using fuzzy logic approach". Curtin University of Technology, Department of Electrical and Computer Engineering, 2009. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=128452.
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An Ultraviolet to Visible (UV-Vis) spectroscopic analysis based on fuzzy logic approach has been developed for furan content measurement in transformer oil. Following the successful identification and quantification of furan derivatives in transformer oil by ASTM D5837 standard, the new approach is able to approximate the furan content more conveniently and economically. As furan concentration level would determine the absorption intensity in UV-Vis spectral range, the fuzzy logic software model developed would exploit this characteristic to aggregate the furans content level in transformer oil. The UV-Vis spectral response at other ambient temperature is also studied. The proposed technique provides a convenient alternative to conventional method of furan measurement by High Performance Liquid Chromatography (HPLC) or Gas Chromatography Mass Spectrometry (GC/MS) in ASTM D5837 Standard.
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Sonehag, Christian. "Modeling of Ion Injection in Oil-Pressboard Insulation Systems". Thesis, Uppsala universitet, Fasta tillståndets elektronik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-177600.
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To make a High Voltage Direct Current (HVDC) transmission more energy efficient, the voltage of the system has to be increased. To allow for that the components of the system must be constructed to handle the increases AC and DC stresses that this leads to. One key component in such a transmission is the HVDC converter transformer. The insulation system of the transformer usually consists of oil and oil-impregnated pressboard. Modeling of the electric DC field in the insulation system is currently done with the ion drift diffusion model, which takes into account the transport and generation of charges in the oil and the pressboard. The model is however lacking a description of how charges are being injected from the electrodes and the oil-pressboard interfaces. The task of this thesis work was to develop and implement a model for this which improves the result of the ion drift diffusion model. A theoretical study of ion injection was first carried out and proceeding from this, a model for the ion injection was formulated. By using experimental data from 5 different test geometries, the injection model could be validated and appropriate parameter values of the model could be determined. By using COMSOL Multiphysics®, the ion drift diffusion model with the injection model could be simulated for the different test geometries. The ion injection gave a substantial improvement of the ion drift diffusion model. The positive injection from electrodes into oil was found to be in the range 0.3-0.6 while the negative injection was 0.3 lower. Determination of the parameters for the injection from oil-pressboard interfaces proved to be difficult, but setting the parameters in the range 0.01-1 allowed for a good agreement with the experimental data. Here, a fit could be obtained for multiple assumptions about the set of active injection parameters. Finally it is recommended that the investigation of the ion injection continues in order to further improve the model and more accurately determine the parameters of it. Suggestions on how this work could be carried out are given in the end.
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Gharib, Ali Jalal Ibrahim, i Ali Abdulbasit Abdulaziz. "The Sustainability related opportunities and challenges with various transformer insulation fluids and business case on re-refining". Thesis, KTH, Skolan för kemivetenskap (CHE), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-222015.
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Transformers are electrical devices used in practice to increase or decrease voltages. Transformers are of various sizes and used mainly in power distribution. To provide cooling and insulation, transformer oils are used together with cellulose that acts as a solid insulation. The most common type of transformer oil is mineral oil and is a product derived from the refining of crude oil. Its low cost and good compatibility with cellulose are two factors that have led to its predominant position as the common transformer oil. There are also synthetic ester based transformer oils, and following an increased interest in environmentally friendly products, transformer oils made from natural esters such as sunflower, soybean and rapeseed. Mineral oil is not biodegradable and is deemed as hazardous waste. The ester based oils are biodegradable and promoted as a more environmentally friendly alternative to mineral oil. In this thesis, the possibility of re-refining used mineral transformer oil is assessed from a financial perspective in the form of a business case and an LCA study has been done to compare the environmental impacts between ester based transformer oils and mineral based transformer oil. The results from the LCA study showed that from a cradle-to-gate perspective, mineral oil has a lower environmental impact than ester-based transformer oils. The re-refining of used mineral transformer oil further reduces the environmental impact. The results from the business case showed that a small scale re-refining facility is financially feasible but highly dependent on the supply and demand of used transformer oil. It is recommended to pursue further studies before making any decision. There is lack of data regarding the re-refining market in Eastern Europe and the accuracy of the LCA study can be further improved by having emissions data from re-refining used mineral transformer oil.Transformatorer är elektriska komponenter som tillämpas vid spänningsregleringar. Dessa transformatorer har olika storlekar och används i eldistribution. Transformatorolja tillsammans med cellulosa används som elektrisk isolering och kylning av transformatorer. Den vanligaste typen av transformatorolja är mineralolja och är en produkt som erhålls vid raffinering av råolja. Dess låga kostnad och goda kompatibilitet med cellulosa är två faktorer som har lett till dess dominerande ställning. Det finns också syntetisk esterbaserad transformatorolja och efter ett ökat intresse för miljövänliga produkter så tillverkas även transformatoroljor av naturliga estrar så som solros, soja och raps. Mineralolja är inte nedbrytbar och anses vara farligt avfall. De esterbaserade oljorna är nedbrytbara och anses vara ett mer miljövänligt alternativ till mineralolja. I denna rapport utvärderades möjligheten till att återraffinera använd mineralolja ur ett ekonomiskt perspektiv i form av en affärsplan och en LCA-studie där esterbaserad olja och mineralolja har jämförts ur ett miljöperspektiv. Resultaten från LCA-studien visade att mineralolja från ett ”cradle-to-gate” perspektiv har en lägre miljöpåverkan än esterbaserade transformatoroljor. Återraffinering av använd mineralolja minskar dess miljöpåverkan ytterligare. Resultatet från affärsplanen visade att en småskalig återraffineringsanläggning är ekonomiskt hållbar men samtidigt väldigt beroende av utbud respektive efterfrågan på använd mineralolja. Det rekommenderas att göra en djupare analys innan man fattar ett beslut. Det finns brist på information med avseende på återraffineringsmarknaden i Östeuropa. Noggrannheten på LCA-studien kan förbättras ytterligare genom att emissionsdata från en återraffineringsanläggning är tillgänglig.
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Lee-Davey, Jon. "Application of machine olfaction principles for the detection of high voltage transformer oil degradation". Thesis, Cranfield University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405216.
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Dai, Jie. "Studies on failure mechanisms of transformer cellulose insulation with consideration of ester oil application". Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505484.
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Liu, Qiang. "Electrical performance of ester liquids under impulse voltage for application in power transformers". Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/electrical-performance-of-ester-liquids-under-impulse-voltage-for-application-in-power-transformers(3702b3a2-ec5f-4674-ab11-1032906e8c0c).html.
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Ester liquids including both natural ester and synthetic ester are being considered as potential alternatives to mineral oil, due to their better environmental performance and for some liquids their higher fire point. Although these liquids have been widely used in distribution and traction transformers, it is still a significant step to adopt ester liquids in high-voltage power transformers because the high cost and severe consequence of a factory test failure and the high level of safety and reliability required in service for these units, tend to lead to a cautious approach to any step change in technology. Lightning impulse strength as basic insulation level is of importance for insulation design of power transformers and lightning impulse test is commonly required in the factory routine tests for high-voltage power transformers, so this thesis is aimed to investigate the electrical performances including pre-breakdown and breakdown of natural ester and synthetic ester under impulse voltage. Two types of field geometry were considered in the study, one is sphere-sphere configuration which represents the quasi-uniform fields inside a transformer and another is strongly non-uniform point-plane configuration which represents the situation of a defect or a source of discharge. In quasi-uniform field study, standard breakdown tests were carried out under negative lightning and switching impulse voltages. Influence of various testing methods on the measured lightning breakdown voltage was studied and the 1% lightning withstand voltage was obtained based on Weibull distribution fitting on the cumulative probability plot built up using the approximately 1000 impulse shots. As for strongly non-uniform field study, streamer propagation and breakdown event in ester liquids either with or without pressboard interface were investigated at various gap distances under both positive and negative lightning impulse voltages. A relationship between the results under lightning impulse and previously published results under step voltage was built up to predict the lightning breakdown voltage of ester liquids at very large gaps. The results indicated that impulse strengths of ester liquids for both breakdown and withstand in a quasi-uniform field, are comparable to those of mineral oil. In a strongly non-uniform field, streamers in ester liquids propagate faster and further, than in mineral oil at the same voltage level. Thus breakdown voltages of ester liquids are generally lower than those of mineral oil, which could be as low as 40% at a large gap distance of approximately 1000 mm. Introduction of parallel pressboard interface has no influence on the streamer propagation and thus does not weaken the breakdown voltage, but it tends to reduce the acceleration voltage particularly for mineral oil under positive polarity. Last but not least, a unique phenomenon of secondary reverse streamer (SRS) was observed in ester liquids, which occurs subsequently and well after the extinction of the primary streamer (PS) propagation within a single shot of impulse voltage and has the reverse polarity to the PS. The formation mechanism of SRS is explained mainly due to the reverse electric field induced by the residual space charges left by the PS.