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1
Siebrits, F. B. (Francois Bart). "Field implementation of a transient voltage measurement facility using HV current transformers." Thesis, Stellenbosch : Stellenbosch University, 2003. http://hdl.handle.net/10019.1/53426.
Full textAbstract:
Thesis (MScEng)--University of Stellenbosch, 2003.ENGLISH ABSTRACT: The bandwidth of standard HV measurement devices such as capacitive voltage transformers is too limited in order to measure wideband phenomena. This thesis is concerned with the investigation into a non- intrusive HV transient voltage measurement facility using standard substation HV current transformers (CI's) configured in a transconductance topology. The sensing, summation and integration of the CT capacitive earth currents are investigated. This thesis also reports on the development of a optically isolated link using optical fibre for signal transfer and a computer based data acquisition system.
AFRIKAANSE OPSOMMING: Standaard hoogspannings (HS) meettoerusting soos kapasitiewe spannmgs transformators het beperkte bandwydte vir die meet van wyeband verskynsels. Hierdie tesis handel oor die implementering van 'n HS meetstelsel wat op meinbrekende wyse oorgangsverskynsels meet deur middel van HS stroomtransformators wat in 'n transkonduktansie topologie gekonfigureer is. Die meet, sommasie en integrasie van kapasitoewe grondstrome word ondersoek. Hierdie tesis doen ook verslag aangaande die ontwikkeling van 'n optiese geisoleerde koppelvlak wat gebruik word vir seinoordrag en 'n rekenaar gebasseerde data versamelaar.
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Barham, Oliver M. "Microfabricated Bulk Piezoelectric Transformers." Thesis, University of Maryland, College Park, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10615552.
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Piezoelectric voltage transformers (PTs) can be used to transform an input voltage into a different, required output voltage needed in electronic and electro- mechanical systems, among other varied uses. On the macro scale, they have been commercialized in electronics powering consumer laptop liquid crystal displays, and compete with an older, more prevalent technology, inductive electromagnetic volt- age transformers (EMTs). The present work investigates PTs on smaller size scales that are currently in the academic research sphere, with an eye towards applications including micro-robotics and other small-scale electronic and electromechanical sys- tems. PTs and EMTs are compared on the basis of power and energy density, with PTs trending towards higher values of power and energy density, comparatively, indicating their suitability for small-scale systems. Among PT topologies, bulk disc-type PTs, operating in their fundamental radial extension mode, and free-free beam PTs, operating in their fundamental length extensional mode, are good can- didates for microfabrication and are considered here. Analytical modeling based on the Extended Hamilton Method is used to predict device performance and integrate mechanical tethering as a boundary condition. This model differs from previous PT models in that the electric enthalpy is used to derive constituent equations of motion with Hamilton’s Method, and therefore this approach is also more generally applica- ble to other piezoelectric systems outside of the present work. Prototype devices are microfabricated using a two mask process consisting of traditional photolithography combined with micropowder blasting, and are tested with various output electri- cal loads. 4mm diameter tethered disc PTs on the order of .002cm
3 , two orders smaller than the bulk PT literature, had the followingperformance: a prototype with electrode area ratio (input area / output area) = 1 had peak gain of 2.3 (± 0.1), efficiency of 33 (± 0.1)% and output power density of 51.3 (± 4.0)W cm
-3 (for output power of80 (± 6)mW) at 1M? load, for an input voltage range of 3V-6V (± one standard deviation). The gain results are similar to those of several much larger bulk devices in the literature, but the efficiencies of the present devices are lower. Rectangular topology, free-free beam devices were also microfabricated across 3 or- ders of scale by volume, with the smallest device on the order of .00002cm
3 . These devices exhibited higher quality factorsand efficiencies, in some cases, compared to circular devices, but lower peak gain (by roughly 1/2 ). Limitations of the microfab- rication process are determined, and future work is proposed. Overall, the devices fabricated in the present work show promise for integration into small-scale engi- neered systems, but improvements can be made in efficiency, and potentially voltage gain, depending on the application
3
Lavalle, Juan Carlos. "Failure detection in transformers using vibrational analysis." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/106705.
Full textAbstract:
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING
Bibliography: leaves 191-194.
by Juan Carlos Lavalle.
M.S.
4
Carvajal, Angel J. "First principles design of coreless power transformers." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120875.
Full textAbstract:
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 117-118).
This thesis presents a theoretical foundation and methodology for designing novel 4-coil high frequency coreless power transformers from first principles via lumped equivalent circuit models. The procedure is applied to construct a design for 100W transformer with an S21 parameter value of .96. Using MATLAB and LTspice, simulation tools have been developed to produce accurate predictions of inductance, resistance, coupling coefficients, and S21 parameter values for an ensemble of coil models. These theoretical calculations have been employed for spiral and cylindrical coils and have been validated with numerous constructed experimental designs. The utility uses a first principles approach and derives these calculations directly from the physical parameters and relative positions of the coils. Simulation outputs greatly aid the engineering task of designing an efficient coreless power transformer.
by Angel J. Carvajal.
M. Eng.
5
Amuanyena, L. A. T. "Effects of geomagnetically induced currents on power transformers and reactors." Master's thesis, University of Cape Town, 2003. http://hdl.handle.net/11427/5235.
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Chuthi, Noel Nelson Stima. "Current transformers transient response modelling using electromagnetic transient program (EMTP)." Master's thesis, University of Cape Town, 1997. http://hdl.handle.net/11427/19564.
Full textAbstract:
The subject of this thesis is Current Transformer Transient response study using an electromagnetic Transient program (EMTP). Current transformers are considered eyes for power system protection. Behaviours of protection systems depend largely on information fed to them by instrument transformers. Ferromagnetic current transformers have for many years provided practical method of current measurement, however there are limitations associated with current transformer operation:- notably, difficult in maintaining accuracy over the full range of operating conditions, and most particularly current transformers tendency to suffer saturation of iron core during severe faults, with accompanying severe ratio or loss of output. These limitations might lead to mal operation of protective relays due to distorted inputs from current transformers particularly in transient periods. This thesis involved studying the behaviour of current transformers in both steady state and transient periods. An emphasis being put on transient periods which are very crucial in behaviour of current transformers because transformation errors are greatest in these periods. Errors in current transformer transformation might affect operation of entire protection schemes. Maloperation of current transformers in transient periods have very bad effect on relay co-ordination and worst condition might be failure of protection scheme operation altogether. Over the past decades engineers have been trying to develop a current transformer model that would represent a current transformer well in transient periods. It has proved to be rather difficult to come up with a single detailed model that would satisfy all possible conditions. This is due to non-linearity of magnetising curve and saturation effects of current transformer iron cores. The author has considered different current transformer models with their merits and demerits being highlighted. It has been shown that different current transformer models have to be used when considering different operating conditions of a current transformer in a power system. ATP-EMTP an Electromagnetic Transient Program was developed in the sixties for the study of electromagnetic transients in power systems. It has proved to be a very useful tool in this regard. The program development is still going on today to accommodate a wide application in power systems. Several components have been developed to represent different components in a power system. It is only recently that there has been a growing interest to include modelling of protective equipment. This has been accelerated by the inclusion of MODELS in the EMTP program. This thesis explores the effect of transients taking into account different conditions like transient fault currents, effects of high frequency waves and surges. Effects of different types of burdens on current transformers were explored as well. Due to limitations of EMTP, simulation results are only applicable to current transformers with ARMCO M4 oriented steel with ungapped cores. The author arrived at several conclusions. The most important conclusion is that mal operation of protective relays due to current transformer saturation can be avoided easily if proper current transformer selection is given priority in power protection design. EMTP package proved to be very useful and handy when studying transients though one has to be careful with numerical oscillations which might be present during simulations. Problems of numerical oscillations have been discussed under current transformer simulation tools.
7
Beckers, Peter C. "Design of a Self Regulated and Protected Electrification Transformer." Thesis, Link to the online version, 2007. http://hdl.handle.net/10019/335.
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Ovadya, Aviv. "Origami transformers : folding orthogonal structures from universal hinge patterns." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62667.
Full textAbstract:
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 57) and index.
We investigate a new approach to origami design using simple universal hinge patterns where the crease patterns for different shapes are just different subsets of a common hinge pattern. Several algorithms have previously been developed to design folded states for particular shapes, but they require a different crease pattern for each shape. Our motivations include the development of robotic "origami transformers," artistic tools, and theoretical insights. We show how to compose "cube gadgets" to fold any N-cube polycube from an O(N) x O(N) rectangle of paper, using only O(N 2 ) time to compute the parameters of the unambiguous folding sequence. We also describe extensions of our basic algorithm to larger classes of shapes with improved paper efficiency. Finally, we demonstrate that an implementation of this technique can actually be used to partially automate geometric paper folding.
by Aviv Ovadya.
M.Eng.
9
Mousavi, Takami Kourosh. "Process Control and Simulation of Ferromagnetic Strip in the Power Transformers and Electrical Machines Applications : Electric power systems." Doctoral thesis, Västerås : School of Sustainable Development of Sociaty and Technology, Mälardalen University, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-6648.
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Zandberg, Hermanus Andries Jakobus. "Wireless transformer condition monitoring system." Thesis, Cape Peninsula University of Technology, 2013. http://hdl.handle.net/20.500.11838/1186.
Full textAbstract:
The Department of Electrical Engineering in fulfilment of the
requirements for the Magister Technologiae in Electrical
Engineering at the
Cape Peninsula University of Technology
November 2013Pole mounted transformers (PMT) in rural areas present an opportunity for local utilities to do current monitoring on these systems. These transformers are exposed to abnormal amounts of stress due to the vast power demand in these areas. The aim of this study is to develop a more cost-effective condition monitoring system. Transformer current monitoring can be a dangerous practice if not done by suitably trained utility electricians. Hence this study is partly aimed at the elimination of hazardous working environments associated with manual electrical measurements. An investigation to determine a safe and cost-effective way to obtain the electrical measurements required from PMTs is undertaken. Although current measurements can be done with a current clamp-on meter, these measurements still take place at the phases of the transformer and are unsafe. The possibility of implementing wireless data gathering on current clamp-on meters is therefore investigated. This is made possible by a wireless sensor node (WSN) which gathers information and transmits it wirelessly to a WSN base station. This wireless solution is battery powered, necessitating battery replacements, therefore leading to the investigation of magnetic fields, magnetic materials and magnetic induction. A current clamp able to generate a high voltage (HV) output with minimal magnetic field strength is developed. The magnetic fields produced by the transformer’s phase cables are used to generate an alternating voltage. With the help of a microcontroller and an energy harvesting circuit, this voltage is converted and used to charge supercapacitors. The magnetic fields are also used to determine the current flow in the transformer phase cables when the device is not in energy harvesting mode. The device will then undergo comprehensive laboratory testing to determine its accuracy and durability, and is then used to do ‘real life’ current measurements, the results of which are compared against an off-the-shelf current monitoring device.
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Malaquias, Paulo Eduardo 1969. "Avaliação da confiabilidade de transformadores de potência por meio de testes físico-químicos no óleo isolante e ensaios elétricos." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/259376.
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Orientador: José Pissolato FilhoDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
Made available in DSpace on 2018-08-24T01:29:05Z (GMT). No. of bitstreams: 1 Malaquias_PauloEduardo_M.pdf: 3237738 bytes, checksum: d302a1f85a6963a1f7102598ea519fa6 (MD5) Previous issue date: 2013
Resumo: Neste trabalho são descritos os mecanismos de envelhecimento do sistema isolante de transformadores papel-óleo mineral, com foco na degradação causada pela presença de umidade no interior dos transformadores. Com o propósito de verificar a degradação do sistema isolante foram executados ensaios em campo e em laboratório. Nos ensaios em laboratório foram retiradas amostras de óleo de treze transformadores de potência em operação e realizados ensaios de envelhecimento acelerado, com separação dos ácidos de baixa e alta massa molar. O objetivo foi correlacionar os ácidos de baixa massa molar com o envelhecimento do isolamento sólido. Os ensaios em campo foram feitos em dez transformadores e visaram verificar a relação da umidade no papel/ papelão isolante com a ocorrência de descargas parciais no interior desses transformadores. Os ensaios de envelhecimento acelerado mostraram a existência de correlação entre o envelhecimento do papel isolante e o teor dos ácidos de baixa massa molar presentes no óleo isolante. Já com os resultados dos ensaios em campo não foi possível comprovar a existência de relação entre umidade no isolamento sólido e descargas parciais no transformador
Abstract: This paper describes the aging mechanisms of the mineral oil-paper insulation system of transformers, focusing on the degradation caused by the presence of moisture inside the transformers. To verify the degradation of the insulation, tests were carried out in the field and in the laboratory. For the laboratory tests, oil samples were taken from thirteen power transformers in operation and accelerated aging tests were conducted. Low and high molecular weight acids were separated from these oil samples in order to correlate the low molecular weight acids with the solid insulation aging. Field tests were conducted in ten transformers and aimed to investigate the relationship between moisture in paper insulation and the occurrence of partial discharges inside the transformer. Accelerated aging tests have shown the correlation between the insulation paper's aging and the content of low molecular weight acids present in the oil. One having the results of the field trials, it was not possible to prove the existence of a relationship between moisture in the solid insulation and partial discharges in transformer
Mestrado
Energia Eletrica
Mestre em Engenharia Elétrica
12
Amaro, P. S. "Corrosive sulphur in large transformers : impact, quantification and detection." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/374902/.
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Several power apparatus use some type of oil insulation system. Transmission level transformers, one of the most expensive components in power networks, use mineral oil as both electrical insulation and cooling. Due to the financial risk posed, if this equipment fails unexpectedly, several quality and condition monitoring techniques are used to test the insulation system. Nevertheless, in 1990 approximately 50 % of the mineral oils used in transformers was contaminated with corrosive sulphur species [1], which passed undetected by the standard corrosion tests at the time, resulting in transformers failures worldwide. CIGRE estimates that between 2000 and 2009 there were approximately 100 related failures, not considering small distribution transformers too small for any investigation to be carried out. The work presented investigates how CuxS faults develop, examines possible techniques to monitor the corrosion process and the failure scenarios caused by sulphur corrosion. A sample production method capable of generating 90 mm square Kraft paper samples with homogeneous CuxS deposition, with a less than 1 % variation, and a reproducibility of 3:5% is detailed. Empirical data demonstrate how the generation of CuxS deposits to DBDS concentration, temperature, ageing atmosphere, paper-copper interfaces and location of deposits. Based on the empirical data obtained, a copper sulphide deposition model using multiple parallel CuxS formation mechanisms was developed. The development of condition monitoring techniques and laboratory-scale validation experiments have been completed successfully, with the use of both field and laboratory samples. It has been shown that x-ray fluorescence (XRF) is technically capable of quantifying very accurately sulphur and copper in oil, with a limit of quantization at 4.05 and 1.95 ppm respectively. In addition, XRF measurements demonstrated that through historical sulphur trends, sulphur depletion rates can be calculated to extrapolate if there is an onset sulphur corrosion. Frequency dielectric spectroscopic analysis of CuxS contaminated Kraft paper demonstrated empirically that CuxS deposits have resonance frequency, at approximately 1 mHz, and that the magnitude of the resonance relates to the quantity of CuxS. Furthermore, laboratory samples accurately replicate field samples containing CuxS deposits and other impurities in terms of dielectric data analysis. The effect of sulphur corrosion and possible failure scenarios are investigated. The electrical breakdown experiments demonstrate that the CuxS deposits reduced the electrical breakdown strength of each Kraft paper layer by 79.5 %. By applying DP life expectancy models to empirical data it is demonstrated that the corrosion process reduces 25 % of the transformer life expectancy at normal working conditions. The excess dielectric loss, generated from a CuxS contaminated insulation paper system, has increased by a factor of approximately 27.5. The thermal conductivity also increased 75%. It is demonstrated the generation of a hotspot is very likely, which then generates a snowball effect of generating further CuxS deposits and further increasing the local temperature.
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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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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.
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Crowley, Thomas Henry. "Automated diagnosis of large power transformers using adaptive model-based monitoring." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/13616.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1990.Includes bibliographical references (leaves 173-176).
by Thomas Henry Crowley.
M.S.
16
Mitchinson, Peter Mark. "Surface tracking in the inter-phase region of large transformers." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/64490/.
Full textAbstract:
Transmission and distribution operators throughout the world manage significant populations of ageing large transformers which use mineral oil and paper as the dielectric insulation. Many of these transformers are reaching the end of their projected service lives and subject to various end-of-life failures. One failure mode occurs in the inter-phase region which leaves evidence of surface tracking along the barrier boards. The failure mode is thought to occur in three stages but the propagation mechanism is unclear. This project focuses on this failure mode in particular and considers surface tracking on the oil-pressboard interface in general. Interaction between mechanisms forms the overall theme. The thesis reviews the current research into condition monitoring, ageing and internal electrical discharge in large liquid filled transformers and places the research in context with the industrial requirement for asset life extension. The project is experimentally based and resulted in the development of a unique test facility which formed a significant part of the work. The test facility permits high voltage from two independent sources to be applied to a model of the inter-phase barrier under controlled conditions of moisture and temperature. The development of the test facility and a new approach to the study of surface tracking on the oil-pressboard interface are described along with results from experiments conducted on new and service aged pressboard. The experiments have revealed the role of the interfacial layer in the transport of charge across the surface of the oil-pressboard interface. It is found that the interaction between the electric fields from adjacent voltage coils enhances the polarisation of the interfacial layer at the oil-pressboard interface and plays a role in the mechanism for creeping discharge. Finally, the interfacial layer is also the mechanism which decreases the bulk voltage withstand of the liquid dielectric medium across barrier surfaces.
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Borrill, Leslie David. "Duality derived topological model of single phase four limb transformers for GIC and DC bias studies." Doctoral thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/27429.
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Geomagnetic disturbances brought about by solar activity cause geo-electric fields in the Earth that drive geomagnetically induced currents through the earthed neutrals of transformers and through power transmission networks. The flow of these currents causes the magnetic cores of transformers to half-wave saturate. Saturated transformers pose problems for power system operators since they can cause harmonics, transformer heating, mal-operation of protection relays, generator heating and vibration, and consume a large reactive power that can cause voltage collapse. Network studies of slow transient phenomena such as transformer half-wave saturation require appropriate models with parameters that represent the transformer transient state aptly. In this thesis a novel duality derived reversible model is developed of a single phase four limb transformer. The test transformers' non-step lap butt type core joints are shown to be problematic and the model is developed further to include the core joints. Due to the irregular core stacking method joint parameter determination is at best an approximation and the model is reduced to a duality compliant equivalent pi model for accuracy reasons. The pi model parameters and saturation characteristics are determined through laboratory testing and a complete pi model is presented. An understanding of a single phase transformer's physical behavior to slow transients is undertaken through the use of appropriately developed test circuits. Search coils are used extensively to understand the transformer core's behaviour through flux mapping of the core and stray flux in the surrounding air space when the transformer saturates. Three phase testing is included using a three phase bank of test transformers. The electrical measurements of waveforms are analysed and fast Fourier transforms carried out to obtain the harmonic components. The effect on a motor load of the distortion caused by transformer half-wave saturation is determined. A novel method of determining the effective core joint area of the problematic non-step lap butt type core joints is developed and a joint utilization factor is proposed that can be used in the absence of transformer manufacturer design information about this joint type in other transformer models.
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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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Mui, Andrew K. "A 20 dBm 5-14 GHz power amplifier with integrated planar transformers in SiGe." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43071.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (leaves 73-74).
The integration of radar systems has taken a long journey into the modern world. Advances in signal processing technology and integrated circuit technology have lead the way for smaller, more integrated radar systems. Specific to the hardware side of a radar, the RF generation and detection once done in one location in the radar is now being replaced by small sub-elements which combine RF generation and detection at the element level. This work describes a power amplifier that can be used at the element level. The design methodology for a single stage amplifier in a Silicon Germanium Bipolar process covering 5-14 GHz is discussed. Simulation results and measurement results closely match and show peak power outputs of 25 dBm and peak power-added efficiencies (PAE) of approximately 32 %.
by Andrew K. Mui.
S.M.
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Carriel, Lázaro Partamian 1950. "Carregamento e envelhecimento de transformadores elétricos de potência e aspectos prioritários para a manutenção baseada na condição : Loading and aging of electrical power transformers and main aspects to condition-based maintenance." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/259377.
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Orientador: José Pissolato FilhoDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
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Resumo: O transformador é o maior ativo, o mais importante e o mais caro do sistema elétrico de potência. Este estudo tem a finalidade de apresentar uma metodologia e um processo de análise do ciclo de vida útil de transformadores de potência baseada na condição, para evitar perda de vida adicional devido ao acréscimo de carga em condição de contingência no sistema. A abordagem foi feita em duas fases e abrangem tanto a metodologia da norma ABNT como a norma do IEEE. Na primeira fase é verificado o comportamento do modelo térmico devido a sobrecargas e, na segunda, a influência das condições do óleo isolante
Abstract: The transformer is the largest, most expensive, most important asset in the electric power system. This study will present a methodology to analyze the useful life of power transformers based on their condition, in order to avoid incremental loss of life caused by overload under contingent operating conditions. The approach has been performed in two phases, following both ABNT and IEEE standards. In the first phase, a thermal model evaluates the effect of overloads on transformers' useful life. In the second phase, the influence of the conditions of the insulating oil is verified
Mestrado
Energia Eletrica
Mestre em Engenharia Elétrica
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Czajtányi, Róbert. "Testování distribučních transformátorů." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2021. http://www.nusl.cz/ntk/nusl-442468.
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The aim of this thesis was to get acquainted with the electrical properties of distribution transformers, which are used in the area of high voltage technology. Further aim was to describe the existing diagnostic methods according to the standards and to introduce the measuring workstation. Finally, the diagnostic of transformer was performed, and the results were evaluated.
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Maziya, Mphumuzi Thembinkosi. "Investigation and analysis of the causes of 11/0.4 kV distribution transformers' high failure rate : case study - Swaziland Electricity Company." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20403.
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The distribution network of the Swaziland Electricity Company consists of a number of components like distribution lines, wooden poles, insulators, conductors, pole mounted transformers and metering, to mention but a few. The most expensive of these components per unit cost is the pole mounted transformer and it takes longer to install. The distribution network is the less reliable compared to the transmission network, and its components fail regularly, and the pole mounted transformers are among the components which have a significant contribution to the failures. Some interventions in the past have been tried, but the failure rate of transformers has not reduced to reasonable limits, thereby compromising the reliability of the distribution network. This research therefore tries to identify the causes of the high failure rate of transformers, the pattern of failure, areas where the failures are prevalent and what can be done to counter the root causes. Statistical data on the transformer failures was gathered over a period of four years, where on a daily basis, the number of failed transformers, weather conditions and time of day when the failures occurred were recorded. The weather conditions and time of day when the failures occurred made it easier to identify the possible causes of the failures. For instance, if there was a thunderstorm in a certain area and there were some failed units which were discovered immediately after the storm, then the failures of those units was attributed to lightning. Similarly, when there were no thunderstorms, but a transformer has failed windings, the likely cause of failure is overloading. After replacing that failed unit, its load was monitored to confirm overload and then take a corrective action. It is a standard practice that a failed transformer is replaced and the failed one taken for repairs and then later kept as a spare at the Swaziland Electricity Company. Basic tests on the failed transformers and visual inspections were carried out to determine the nature of damage on the failed unit, for instance, winding damage and bushing damage. Footing resistances were also recorded at the transformer structures and if there was a need, they were reduced to 10 Ω or less using the crowfoot earthing method or a combination of the crowfoot earthing method and conductive cement.
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Jadim, Ramsey. "On the estrablishment of effective condition monitoring parameters for copper corrosion problems in mineral oil-filled electrical transformers." Licentiate thesis, Linnéuniversitetet, Institutionen för maskinteknik (MT), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-99899.
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The power transformer is a critical equipment in which the protection process is essential for modern societies where continuous electric power supplies are required. Copper corrosion problems due to the formation of sulfur deposits on the copper windings of mineral oil-filled power transformers are considered a major issue that can lead to sudden failures, and in some cases, to costly fire and explosion accidents in the power plants. These kinds of problems are still being reported regardless of available condition monitoring (CM) parameters applied in power transformers' maintenance strategy. The currently applied CM parameters are based on three different types of technologies. The first is oil analysis focuses more on measurable variables such as measuring the concentration of the corrosive sulfur compounds in the insulating oil, evaluating the oil's capability to form sulfur deposits, and measuring an increase in the concentration of specific gases. The second is on-site electrical testing focuses on the variation of the transformer's electrical properties due to the sulfur deposits. The measurable variables used in the electrical testing are Frequency Domain Spectroscopy test and Polarization/Depolarization Current test. The last is online sensor technology using Corrosive Sulfur Sensor, where the sensor's outcome data provide information about the oil's capability to form sulfur deposits. The research problem addressed is how to establish more effective CM parameters for early detection of copper corrosion problems. The research problem is divided into three concretized research problems: What are the strengths and weaknesses of the currently applied condition monitoring parameters? Which measurable variables could be utilized to improve the currently applied condition monitoring parameters to be more effective for early detection of copper corrosion problems? And how to establish a procedure for the condition monitoring for detecting copper corrosion? Two research methodologies were applied to answer these questions, literature review and experimental work. The literature review showed significant gaps in the currently applied CM parameters for early detection of copper corrosion problems due to incomplete data of the corrosion reaction mechanism. Therefore, qualitative and quantitative investigations in the experimental work were carried out. The most important result was finding new relevant measurable variables, i.e. hydrogen sulfide gas and toluene compound, which are by-products of corrosion reaction. These measurable variables are utilized to establish more effective CM parameters for early detection of copper corrosion problems. The main conclusion of this thesis is the importance of detection corrosion problems in the initial stage by implementing more effective CM parameters to prevent catastrophic and costly failures, reduce the negative impacts on human life and the environment, and save the economic losses. Another conclusion is the importance of regularly following the measurable variables' uptrend during transformer useful life to avoid incorrect evaluation of corrosion conditions.
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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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Carrander, Claes. "Magnetizing Currents in Power Transformers : Measurements, Simulations, and Diagnostic Methods." Doctoral thesis, KTH, Elektroteknisk teori och konstruktion, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-208422.
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This thesis demonstrates a method for transformer core diagnostics. The method uses the no-load current of the transformer as an indicator, and gives different characteristic signatures for different types of faults or defects. Using the no-load current for the diagnostic gives high sensitivity. The method is therefore able to detect defects that are too small to have an impact on the losses. In addition to different types of fault, the method can in some cases also distinguish between faults in different locations within the core. Both single-phase and three-phase transformers can be diagnosed using this method, and the measurements can be easily performed at any facility capable of measuring the no-load loss. There are, however, some phenomena that occur in large transformers, and in transformers with high rated voltages. Examples include capacitive resonance and magnetic remanence. This thesis proposes and demonstrates techniques for compensating for these phenomena. With these compensating techniques, the repeatability of the measurements is high. It is shown that units with the same core steel tend to have very similar no-load behavior. The diagnostics can then be performed either by comparing the transformer to another unit, or to simulations. The thesis presents one possible simulation method, and demonstrates the agreement with measurements. This topological simulation method includes both the electric circuit and an accurate model of the magnetic hysteresis. It is therefore also suitable for other, related, studies in addition to core diagnostics. Possible subjects include ferroresonance, inrush, DC magnetization of transformers, and transformer core optimization. The thesis also demonstrates that, for three-phase transformers, it is possible to compare the phases to each other. This technique makes it possible to diagnose a transformer even without a previous measurement to compare to, and without the data required to make a simulation.QC 20170607
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Larsson, Jenny, and David Håkansson. "Evaluation of software using the finite element method by simulating transformers and inductors." Thesis, Linköpings universitet, Elektroniksystem, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-65759.
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In this bachelor thesis several software, capable of calculating andsimulating complex problems concerning the power losses in inductors andtransformers with the finite element method, have been evaluated and used tosolve test cases provided by the commissioner. The software have been evaluatedwith respect to several requirements stated by the commissioner.The aim is to be able to simulate power losses and inductance levels in complexdesigns of inductors and transformers. By reading the manuals to the software, aview of the methods and equations the different software use for their calculationshave been established. The enclosed tutorials have provided the knowledge forthe operations of the different software. By designing the test models providedby the commissioner, a deeper understanding of the work area has been reached.The test results provides an answer for the test models, the behaviour of themagnetic field has been analysed for the models and the calculated power lossesseem to correspond to the behaviour of the prototypes.The evaluation of the software has been done with regard to the commissionersrequirements. The recommendation will be to use either FEMM 4.2 or QuickField5.7, both software have a short training curve and an interface easy to maintain.For problems requiring a transient analysis the recommendation is QuickField, butthe material library maintainability is better in FEMM 4.2. Regarding COMSOLMultiphysics 3.5 and Ansys RAnsoft Maxwell Student Version 9, both softwareare highly qualified for the complex calculations needed for these kind of problems.The training curve for these software is however much longer than for the othertwo software and for the commissioner to be able to fully use all the possibilitiesin the software this will not be efficient.
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Ariza, Rocha Oscar David. "Dynamic transformers rating for expansion of expansion of existing wind farms." Thesis, KTH, Elektroteknisk teori och konstruktion, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-256531.
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Distribution system operators face the challenge to connect users rapidly to the grid and the opportunity to reduce costs for new connections. A method to enhance network operation and planning is dynamic transformer rating (DTR), which considers load and temperature variations to increase the rating of the transformer while maintaining in safe operation. This project investigates DTR application to an existing population of transformers connected to a wind park and proposes a method for adding new turbines to the grid using installed transformers. Five transformer locations and nine units belonging to E.ON AB are used to find the potential of DTR for network expansion. A weather analysis reveals that simultaneous high wind speeds and high temperatures seldom occur. An aging estimation based on the IEC 60076-7 standard shows that the transformers for wind power applications are underused. Considering the transformer thermal model, a sensitivity analysis shows that the parameters that mostly affect the aging rate are the moisture content, the hot spot factor, and the top-oil temperature rise. The maximum load to assure aging below 50 years is calculated for each transformer for different maximum hot-spot temperature levels showing that increasing the maximum allowed temperature reduces curtailment and increases aging. A single node analysis depicts the optimal expansion of wind power from a generator perspective, and a network analysis introduces further restrictions to the network. As a result, the optimal increase factor is around 30 to 50 % and is larger for higher hot-spot temperature limits. Accurate weather measurements and transformer parameters are necessary to make a proper estimation of transformer aging to unlock transformer potential. To use fiber optic temperature sensors in new transformers and on-site temperature measurements can increase the rating of the transformer. A maximum allowed temperature of 110◦C is conservative and limits the potential of the transformer for wind power applications. Finally, society benefits from DTR in wind power applications because there is a more efficient use of resources and additional renewable energy can be introduced to the network.Eldistributionsnätet står inför en utmaning att snabbt ansluta användare till nätet och en möjlighet att miska kostnaderna i nya ansultnigar. En metod för att förbättra nätverksdrift och planering är dynamisk lastbarhet hos transformatorer, eller dynamic transformer rating (DTR). Metoden beaktar belastings- och temperaturvariationer för att öka transformatorns lastbarhet samtidigt som den upprätthåller säker drift. Detta projekt undersöker tillämpningen av dynamisk lastbarhet till en befintling population av transformatorer kopplade till en vindkraftpark och föreslår en metod för att ansluta ytterligare turbiner till nätet med hjälp av befintliga transformatorer. Fem transformatorplatser och nio enheter som tillhör E.ON AB används för att undersöka potentialen för DTR inom tillämpningar för nätverksexpansion. En vänderanalysis avslöhar att både höga vindhastigheter och temperaturer sällan uppstår samtidigt. En uppskattning av åldrandet baserad på IEC 60076-7-standarden visar att transformatorer för vindkraftstillämpningar är underanvända. Med avseende på den termisk transformatormodellen visar en känslighetsanalys att parametrarna som påverkar minskning av livslängden mest är fuktinnehållet, hot spot-faktorn och ökning av top-olja-temperaturen. Den maximala belastningen för att säkerställa en åldring under 50 år beräknas för varje transformator, för olika värden på den maximala hotspottemperaturen. Detta visar att med ökning av den maximala tillåtna temperaturen minskar produktionsbortfall och ökar åldrandet. En-nods-analys visar den optimala expansionen av vindkraft från en producents perspektiv, och en nätverksanalys introducerar ytterligare begränsningar för nätverket. Detta resulterar i en optimal ökningsfaktor på cirka 30-50% och är större för högre värden på den maximala hotspottemperaturen. Noggranna vädermätningar och transformatorparametrar är nödvändiga för att göra en korrekt uppskattning av transformatorns åldrande. Att använda fiberoptiska temperatursensorer i nya transformatorer och platsspecifika temperaturmätningar kan öka transformatorns lastbarhet. En maximal tillåten temperatur på 110 ◦C är för konservativ och begränsar transformatorns potential för vindkraftstillämpningar. Samhället drar fördel av DTR i vindkraftstillämpningar eftersom det leder till en effektivare resursanvändning och att ytterligare förnybar energi kan introduceras i nätverket.
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Pham, Dinh Anh Khoi [Verfasser]. "A new method in determination of electrical parameters for failure diagnostic applicable to power transformers / Dinh Anh Khoi Pham." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2013. http://d-nb.info/1047413752/34.
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Van, Jaarsveld Barend Jacobus. "Wide-band modelling of an air-core power transformer winding." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/85823.
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Thesis (MScEng)-- Stellenbosch University, 2013.ENGLISH ABSTRACT: The objective of this project is to develop an electromagnetic model that can be used to accurately calculate the voltage distribution in a transformer winding structure when excited with standard impulse excitation waves. This voltage distribution is required during the design stage of a power transformer to ensure that the insulation is capable of withstanding the occurring electric field stresses during these tests. This study focuses on the modelling of a single disk-type power transformer winding without the presence of an iron-core. Methods of calculating self- and mutual-inductances of transformer windings are presented and validated by means of finite element method software simulations. The same is done for the calculation methods used for calculating the capacitances in and around the winding structure. The calculated and FEM-simulated results are compared to measured values as a final stage of validation. The methods used to calculate the various model parameters seem to produce results that agrees well with measured values. The non-linear frequency dependant dissipative nature of transformer windings is also investigated and a methodology to take this into account is proposed and implemented. The complete modelling methodology proposed in this thesis, which includes the calculation of the model parameters, model synthesis and solver algorithm, are applied to an actual case study. The case study is performed on an air-core reactor manufactured using a disk-type power transformer winding. The reactor is excited with standard lightning impulse waves and the voltages along the winding are measured. The calculated and measured voltage wave forms are compared in both the frequency and time-domain. From the comparison it is found that the model accurately represents the actual transient voltage response of the testunit for the frequency range of interest during standard factory acceptance tests.
AFRIKAANSE OPSOMMING: Die doel van hierdie projek is om 'n elektromagnetiese model te ontwikkel wat gebruik kan word om die spanningsverspreiding in 'n transformatorwindingstruktuur te bereken as standaard weerligimpulstoetse toegedien word. Hierdie spanningsverspreiding word vereis tydens die ontwerpstadium van ‘n kragtransformator om te verseker dat die isolasie in staat is om die elektriese veldsterkte tydens hierdie toetse te weerstaan. Hierdie studie fokus op die modelering van 'n enkele skyftipe-kragtransformatorwinding sonder die teenwoordigheid van 'n ysterkern. Metodes van berekening van self- n wedersydse-induktansie van transformatorwindings word aangebied en getoets deur middel van Eindige-Element-Metode (EEM) simulasies. Dieselfde word gedoen vir die metodes wat gebruik word vir die berekening van die kapasitansies in en rondom die windingstruktuur. Die berekende en EEM-gesimuleerde resultate word vergelyk met die gemeete waardes as 'n finale vlak van bekragtiging. Die metodes wat gebruik word om die verskillende modelparameters te bereken vergelyk goed met gemete waardes. Die nie-lineêre frekwensie-afhanklike verliese van transformatorwindings word ook ondersoek en 'n metode om hierdie in ag te neem is voorgestel en geïmplementeer. Die volledige voorgestelde modeleringsmetodiek in hierdie tesis, wat die berekening van die modelparameters, modelsintese en oplosingsalgoritme insluit word toegepas op 'n werklike gevallestudie. Die gevallestudie is uitgevoer op 'n lugkern-reaktor wat 'n skyftipe-kragtransformatorwinding. Die reaktor word onderwerp aan die standaard weerligimpuls golwe en die spanning al langs die winding word gemeet. Die berekende en gemete spanning golf vorms word met mekaar vergelyk in beide die frekwensie- en tyd-vlak. Uit die vergelyking blyk dit dat die model die werklike oorgangspanningsweergawe van die toetseenheid akkuraat verteenwoordig vir die frekwensie reeks van belang tydens standaard fabriekaanvaardingstoetse.
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Whitfield, Thomas Britain. "An analysis of copper transport in the insulation of high voltage transformers." Thesis, University of Surrey, 2001. http://epubs.surrey.ac.uk/843581/.
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Examination of the paper insulation and copper stress braiding during stripdown of a number of Current Transformers (FMK type 400kV) has revealed the presence of dark deposits. Copper foils are often interspersed within layers of paper insulation and mineral oil found in transformer windings. The dark deposits were often found in association with these foils, affecting several layers of paper in addition to the layer in contact with the copper foil. This thesis describes the research undertaken to identify these deposits and establish a mechanism for the transportation through the paper layers. Preliminary investigation using scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray analysis (EDX) has shown these dark deposits to be copper based. X-ray photoelectron spectroscopy was used to show that the transport of the copper deposit through the paper insulation was working under the influence of a diffusion controlled process, related to Fick's law. Laboratory studies in support of work designed to eliminate the problem have shown that corrosion of copper occurs in mineral oils containing a trace of oxygen. This corrosion is non protective in character and leads to migration of copper into adjacent layers of paper. It has been shown that the transport of copper through several layers of paper can be measured by XPS and that the concentration from one paper winding to the next declines in accord with Fick's law for non-steady state diffusion. Measurements of surface concentrations by XPS correlate well with measurements made with atomic absorption spectroscopy on solutions of extracts of the contaminated paper. The laboratory measurements have allowed determination of the diffusion coefficients and activation energy for the transport process and thus give a basis for interpretation of the diffusion profiles found in the transformer in terms of time and temperature of operation. The diffusion process is temperature dependant. The results have been used to produce long term prediction curves.
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Morozovska, Kateryna. "Dynamic Rating of Power Lines and Transformers for Wind Energy Integration." Licentiate thesis, KTH, Elektroteknisk teori och konstruktion, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-226564.
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Dynamic Rating (DR) is usually associated with unlocking the capacity of power lines and transformers using available information on weather conditions. Our studies show that Dynamic Rating is a broad concept that requires further study and development. The capacity of the majority of power devices is highly dependent on the heat transfer properties of the materials which the devices are made of. To ensure correct power limits of the equipment, one must take into consideration not only the power load, but also ambient conditions, such as: temperature, wind speed, wind direction, solar irradiation, humidity, pressure, radiation into the atmosphere and magnetic losses. Dynamic rating is created as an alternative to standard constant rating that is designed with reference to extreme weather and load conditions. Some areas are more likely than others to experience extreme weather conditions, which have a chance of occurring only a few days per year for short periods of time. Such a distribution of weather parameters gives an opportunity to embed existing material properties of the power equipment and achieve a better utilization of the grid. The following thesis is divided into two simultaneous topics: Dynamic line rating and Dynamic transformer rating. The division is motivated by the importance of analysing the operation of the above-mentioned parts of the power network in greater detail. Power lines and transformers play a significant part in grid planning and have a potential to result in economic benefits when used with DR. The main focus of the doctoral project "Dynamic rating of power lines and transformers for wind energy integration" is on exploring potential ways to connect power generated from wind to the grid with the help of dynamic rating technologies. Therefore, great focus of the work lies on the analysis of DR connection of variable energy sources such as wind farms. The thesis presents the comparison of different line rating methods and proposes a new way of their classification. Evaluation of dynamic line rating application has shown the possibility to expand the power grid with additional capacity from wind power generation. Literature analysis and detailed evaluation of the conductor heat balance models have led to experimental evaluation of the convective cooling effect. The dynamic transformer rating application has shown a possibility to decrease the size of the power transformer without shortcoming in component availability.QC 20180423
Dynamic Rating for Wind Power
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Murthy, Bellur Dakshina S. "Hard-Switching and Soft-Switching Two-Switch Flyback PWM DC-DC Converters and Winding Loss due to Harmonics in High-Frequency Transformers." Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1278704361.
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Ambatipudi, Radhika. "Multilayered Coreless Printed Circuit Board (PCB) Step-down Transformers for High Frequency Switch Mode Power Supplies (SMPS)." Licentiate thesis, Mittuniversitetet, Institutionen för informationsteknologi och medier, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-13967.
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The Power Supply Unit (PSU) plays a vital role in almost all electronic equipment. The continuous efforts applied to the improvement of semiconductor devices such as MOSFETS, diodes, controllers and MOSFET drivers have led to the increased switching speeds of power supplies. By increasing the switching frequency of the converter, the size of passive elements such as inductors, transformers and capacitors can be reduced. Hence, the high frequency transformer has become the backbone in isolated AC/DC and DC/DC converters. The main features of transformers are to provide isolation for safety purpose, multiple outputs such as in telecom applications, to build step down/step up converters and so on. The core based transformers, when operated at higher frequencies, do have limitations such as core losses which are proportional to the operating frequency. Even though the core materials are available in a few MHz frequency regions, because of the copper losses in the windings of the transformers those which are commercially available were limited from a few hundred kHz to 1MHz. The skin and proximity effects because of induced eddy currents act as major drawbacks while operating these transformers at higher frequencies. Therefore, it is necessary to mitigate these core losses, skin and proximity effects while operating the transformers at very high frequencies. This can be achieved by eliminating the magnetic cores of transformers and by introducing a proper winding structure. A new multi-layered coreless printed circuit board (PCB) step down transformer for power transfer applications has been designed and this maintains the advantages offered by existing core based transformers such as, high voltage gain, high coupling coefficient, sufficient input impedance and high energy efficiency with the assistance of a resonant technique. In addition, different winding structures have been studied and analysed for higher step down ratios in order to reduce copper losses in the windings and to achieve a higher coupling coefficient. The advantage of increasing the layer for the given power transfer application in terms of the coupling coefficient, resistance and energy efficiency has been reported. The maximum energy efficiency of the designed three layered transformers was found to be within the range of 90%-97% for power transfer applications operated in a few MHz frequency regions. The designed multi-layered coreless PCB transformers for given power applications of 8, 15 and 30W show that the volume reduction of approximately 40-90% is possible when compared to its existing core based counterparts. The estimation of EMI emissions from the designed transformers proves that the amount of radiated EMI from a three layered transformer is less than that of the two layered transformer because of the decreased radius for the same amount of inductance. Multi-layered coreless PCB gate drive transformers were designed for signal transfer applications and have successfully driven the double ended topologies such as the half bridge, the two switch flyback converter and resonant converters with low gate drive power consumption of about half a watt. The performance characteristics of these transformers have also been evaluated using the high frequency magnetic material made up of NiZn and operated in the 2-4MHz frequency region. These multi-layered coreless PCB power and signal transformers together with the latest semiconductor switching devices such as SiC and GaN MOSFETs and the SiC schottky diode are an excellent choice for the next generation compact SMPS.
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Kaminskas, Almundas. "Elektros tinklų rekonstrukcija Skomantų kaime." Bachelor's thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2013~D_20130823_095922-30435.
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Elektros inžinerijos bakalauro baigiamojo darbo tema yra aktuali, nes elektros tinklai sumontuoti prieš 30–40 metų jau yra pasenę ir nebeatitinka šiuolaikinių poreikių. Vis daugiau elektros vartotojų keičia dujines virykles į elektrines, įsigija naujų elektros prietaisų, elektros suvartojimas auga, todėl būtina atnaujinti elektros tinklus, siekiant užtikrinti patikimą kokybiškos elektros energijos tiekimą. Šiuo projektu Skomantų kaime numatoma esamos oro linijos L-300 iš transformatorinės KT-V-305 rekonstravimas, ją pakeičiant apskaičiuoto skerspjūvio 0,4 kV elektros kabelių linijomis su reikiamu skaičiumi 0,4 kV skirstomųjų spintų (SS), įvadinių apskaitų skirstomųjų spintų (ĮASS) ir įvadinių apskaitų spintų (ĮAS). Numatoma trumpinti esamą oro liniją L-100 iš transformatorinės KT-V-305, pastatant dvi stulpines transformatorines su 25 kVA ir 40 kVA galios transformatoriais. Planuojamas oro linijos L-100 iš transformatorinės KT-V-305 ruožų nuo atramos Nr. 100/9 iki atramos Nr. 100/25 ir nuo atramos Nr. 101/18 iki atramos Nr. 101/25 demontavimas.His Bachelors’ degree electrical engineering thesis is relevant, because the electricity network built 30-40 years ago in Skomantai village is already old and no longer meets todays’ needs. More and more electricity consumers change gas stoves into electrical stoves, purchase new electrical devices. The usage of electricity is increasing. That’s why the renewal of electrical network is needed in order to maintain reliable supply of high quality electric power. The plan of this project in Skomantai village is the reconstruction of existing transmission line L-300 from the transformer KT-V-305 reconstructing it by changing with calculated cross-section 0,4 kV electricity cables’ lines with needed number 0,4 kV 0,4kV distribution boards (SS), electrical distribution and metering equipment boards (ĮASS) and lead-in metering boards (ĮAS). Shortening of the existing transmission lines L-100 from transformer KT-V-305 and building two pole transformers with 25 kVA and 40 kVA power transformers. Dismantling of transmission line L-100 from transformer KT-V-305 parts from pole No. 100/9 up to pole No. 100/25, and from pole No. 101/18 up to No. 101/25.
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Whitman, Daniel J. "The Effect of Winding Curvature and Core Permeability on the Power Losses and Leakage Inductance of High-Frequency Transformers." Wright State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=wright1624286375555269.
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Pradhan, Manoj Kumar. "Conformal Thermal Models for Optimal Loading and Elapsed Life Estimation of Power Transformers." Thesis, Indian Institute of Science, 2004. http://hdl.handle.net/2005/97.
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Power and Generator Transformers are important and expensive elements of a power system. Inadvertent failure of Power Transformers would cause long interruption in power supply with consequent loss of reliability and revenue to the supply utilities. The mineral oil impregnated paper, OIP, is an insulation of choice in large power transformers in view of its excellent dielectric and other properties, besides being relatively inexpensive.
During the normal working regime of the transformer, the insulation thereof is subjected to various stresses, the more important among them are, electrical, thermal, mechanical and chemical. Each of these stresses, appearing singly, or in combination, would lead to a time variant deterioration in the properties of insulation, called Ageing.
This normal and inevitable process of degradation in the several essential properties of the insulation is irreversible, is a non-Markov physico-chemical reaction kinetic process. The speed or the rapidity of insulation deterioration is a very strong function of the magnitude of the stresses and the duration over which they acted. This is further compounded, if the stresses are in synergy. During the processes of ageing, some, or all the vital properties undergo subtle changes, more often, not in step with the duration of time over which the damage has been accumulated. Often, these changes are non monotonic, thus presenting a random or a chaotic picture and understanding the processes leading to eventual failure becomes difficult. But, there is some order in this chaos, in that, the time average of the changes over short intervals of time, seems to indicate some degree of predictability.
The status of insulation at any given point in time is assessed by measuring such of those properties as are sensitive to the amount of ageing and comparing it with earlier measurements. This procedure, called the Diagnostic or nondestructive Testing, has been in vogue for some time now.
Of the many parameters used as sensitive indices of the dynamics of insulation degradation, temporal changes in temperatures at different locations in the body of the transformer, more precisely, the winding hot spots (HST) and top oil temperature (TOT) are believed to give a fairly accurate indication of the rate of degradation. Further, an accurate estimation of the temperatures would enable to determine the loading limit (loadability) of power transformer.
To estimate the temperature rise reasonably accurately, one has to resort to classical mathematical techniques involving formulation and solution of boundary value problem of heat conduction under carefully prescribed boundary conditions. Several complications are encountered in the development of the governing equations for the emergent heat transfer problems. The more important among them are, the inhomogeneous composition of the insulation structure and of the conductor, divergent flow patterns of the oil phase and inordinately varying thermal properties of conductor and insulation.
Validation and reconfirmation of the findings of the thermal models can be made using state of the art methods, such as, Artificial Intelligence (AI) techniques, Artificial Neural Network (ANN) and Genetic Algorithm (GA).
Over the years, different criteria have been prescribed for the prediction of terminal or end of life (EOL) of equipment from the standpoint of its insulation. But, thus far, no straightforward and unequivocal criterion is forth coming. Calculation of elapsed life in line with the existing methodology, given by IEEE, IEC, introduces unacceptable degrees of uncertainty. It is needless to say that, any conformal procedure proposed in the accurate prediction of EOL, has to be based on a technically feasible and economically viable consideration. A systematic study for understanding the dynamical nature of ageing in transformers in actual service is precluded for reasons very well known. Laboratory experiments on prototypes or pro-rated units fabricated based on similarity studies, are performed under controlled conditions and at accelerated stress levels to reduce experimental time. The results thereof can then be judiciously extrapolated to normal operating conditions and for full size equipment.
The terms of reference of the present work are as follows;
1. Computation of TOT and HST
Theoretical model based on Boundary Value Problem of Heat Conduction
Application of AI Techniques
2. Experimental Investigation for estimating the Elapsed Life of transformers
Based on the experimental investigation a semi-empirical expression has been developed to estimate the loss of life of power and station transformer by analyzing gas content and furfural dissolved in oil without performing off-line and destructive tests.
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Goynuk, Yilmaz. "Development Of An Electrical Machines Analysis And Optimum Design Software Package." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609788/index.pdf.
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In this study, three different programs are developed for the analysis of the
three-phase induction motor, single-phase capacitor type induction motor
and switched reluctance motor. The programs are developed by using Pascal
and C++ programming languages. In the performance calculations of motors,
analytical methods are used and these methods are tested for accuracy.
These programs have also capabilities to design an optimum motor, which
meets a set of performance, material and manufacturing constraints while
minimizing the weight or any other defined objective function.
In addition, in this study, an optimization tool is used to obtain an appropriate
optimization method for the design of different types of motors.
The software is tested over different commercial motors. The results illustrates
that the performance calculations and optimization approach of the
programs lead to good results.
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Souza, Kleymilson do Nascimento. "Optimization in calculation of active part three phase distribution transformer with use genetic algorithms aiming better efficiency and less cost." Universidade Federal do CearÃ, 2012. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=8364.
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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorThe present work is a study of a methodology that seeks to be more economical and efficient compared to traditional methods, the design of three phase distribution transformers. To this end, we use a tool of Computational Intelligence, based on previous calculations made in the traditional way by manufacturing industries and books that address this matter. It is evident here, another way to design the active part of the transformer, the dimension of the core and coil, for this, used Genetic Algorithms (GA) which will assist in the calculation and selection of parameters, providing the best choice of design of the transformer, minimizing, on average, 5% in the cost and losses in 2.5% as input parameters the following standard. With changes in the fitness function of GA, one can simply adapt to new requirements and standards. As a result of using the genetic algorithm can find a design solution that is more efficient than that used by the manufacturers. The losses calculated values meet established by NBR-5440.
O presente trabalho faz um estudo de uma metodologia que busca ser mais econÃmica e eficiente, em comparaÃÃo com mÃtodos tradicionais, no projeto de transformadores de distribuiÃÃo trifÃsico. Para tal, utiliza-se uma ferramenta de InteligÃncia Computacional, tendo como base cÃlculos anteriores feitos de forma tradicional por indÃstrias fabricantes e livros que tratam desse assunto. Evidencia-se, aqui, mais uma maneira de projetar a parte ativa do transformador, ou seja, o dimensionamento do nÃcleo e bobinas; para isso, utiliza-se Algoritmos GenÃticos (GA), que irÃo auxiliar no cÃlculo e escolha dos parÃmetros, proporcionando a melhor escolha do projeto do transformador, minimizando, em mÃdia, o custo em 5 % e as perdas em 2,5 %, conforme parÃmetros de entrada seguindo a norma. Com modificaÃÃes na funÃÃo de fitness do GA, pode-se adequar de maneira simples a novas exigÃncias e normas. Como consequÃncia da utilizaÃÃo do Algoritmo GenÃtico pode-se encontrar uma soluÃÃo de projeto que à mais eficiente do que a utilizada pelos fabricantes. As perdas calculadas atendem valores estabelecidos pela norma NBR-5440.
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Stefanou, Christos. "Investigation of the effect of moisture in transformers on the aging of the solid insulation for dynamic rating applications." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-235267.
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In the present thesis an investigation is performed for the effect of moisture contenton the aging of the solid insulation for transformers that are dynamically loaded. Theinvestigation is based on a theoretical analysis and a model.First, a literature review is conducted on the basics of transformer operation, transformerinsulation and moisture in oil-paper systems. Furthermore, a model is developedbased on moisture equilibrium curves created by Oommen and MIT, moisture diffusionprocesses in oil-paper insulation systems and calculations for the aging of cellulose insulationfrom IEC 60076-7. The model represents an experimental system which is loadedon different load patterns that simulate dynamic loading. The aim of the model is toconclude whether the load patterns will cause the paper to age differently dependingon the frequency that the moisture migration phenomenon between paper and oil occurs.The result of the modeling part is that the aging process is affected by the load pattern,and that the higher the frequency the moisture migration phenomenon occurs within aloading cycle, the larger the impact on insulation degradation. This difference, though,is too small to be measured experimentally in terms of DP and it is suggested thatdifferent load patterns are used in the experiment than those used in the model, whichwill amplify the effect of moisture migration even further.Finally, experimental work is conducted in the thesis, which focuses on implementingthe LabVIEW design from previous work into hardware, debugging the system andpreparing the experimental set-up on practical matters that occurred in the lab. Somefinal work is required before the experiment is able to run, such as preparation of theexperimental units.I detta examensarbete undersöks effekten av fuktinnehåll på åldring av fast isolationsmateriali transformatorer med dynamisk last. Arbetet är baserat på en teoretisk analysoch en modell.Först genomförs en litteraturstudie på grundläggande transformatorfunktion, transformatorisolationoch fukt i oljeimpregnerade papperssystem. Vidare utvecklas en modellbaserad på jämviktskurvor for fukt skapade av Oommen och MIT, fuktdifussionsprocesseri isolationssystem baserade på oljeimpregnerat papper och beräkning av åldringav cellulosaisolation från IEC 60076-7. Modellen representerar ett experimentellt systemsom lastas för att simulera dynamisk last. Målet med modellen är att avgörahuruvida lastprofilen påverkar åldrandet av pappret beroende på frekvensen av fuktmigrationenmellan papper och olja.Resultatet av modelleringen är att åldrandet påverkas av lastprofilen och desto oftarefuktmigrationen sker inom en lastcykel, desto större är effekten på isolationsdegraderingen.Skillnaden är dock för liten att mäta experimentellt med avseende på DP och andralastprofiler föreslås i framtida experiment, för att förstärka effekten av fuktmigration.Slutligen utförs experimentellt arbete som fokuserar på implementation av LabVIEWdesignenfrån tidigare arbete i hårdvara, felsökning av systemet samt förberedelse av denexperimentella installationen för praktiska bekymmer som uppstått i laboratoriemiljön.En liten mängd arbete återstår före experimentet kan utföras, såsom förberedelse av deexperimentella enheterna.
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Kotte, Hari Babu. "High Speed (MHz) Switch Mode Power Supplies (SMPS) using Coreless PCB Transformer Technology." Licentiate thesis, Mittuniversitetet, Institutionen för informationsteknologi och medier, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-13964.
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The most essential unit required for all the electronic devices is the Power Supply Unit (PSU). The main objective of power supply designers is to reduce the size, cost and weight, and to increase the power density of the converter. There is also a requirement to have a lower loss in the circuit and hence in the improvement of energy efficiency of the converter circuit. Operating the converter circuits at higher switching frequencies reduces the size of the passive components such as transformers, inductors, and capacitors, which results in a compact size, weight, and increased power density of the converter. At present the switching frequency of the converter circuit is limited due to the increased switching losses in the existing semiconductor devices and in the magnetic area, because of increased hysteresis and eddy current loss in the core based transformer. Based on continuous efforts to improve the new semi conductor materials such as GaN/SiC and with recently developed high frequency multi-layered coreless PCB step down power transformers, it is now feasible to design ultra-low profile, high power density isolated DC/DC and AC/DC power converters. This thesis is focussed on the design, analysis and evaluation of the converters operating in the MHz frequency region with the latest semi conductor devices and multi-layered coreless PCB step-down power and signal transformers. An isolated flyback DC-DC converter operated in the MHz frequency with multi-layered coreless PCB step down 2:1 power transformer has been designed and evaluated. Soft switching techniques have been incorporated in order to reduce the switching loss of the circuit. The flyback converter has been successfully tested up to a power level of 10W, in the switching frequency range of 2.7-4 MHz. The energy efficiency of the quasi resonant flyback converter was found to be in the range of 72-84% under zero voltage switching conditions (ZVS). The output voltage of the converter was regulated by implementing the constant off-time frequency modulation technique. Because of the theoretical limitations of the Si material MOSFETs, new materials such as GaN and SiC are being introduced into the market and these are showing promising results in the converter circuits as described in this thesis. Comparative parameters of the semi conductor materials such as the vi energy band gap, field strengths and figure of merit have been discussed. In this case, the comparison of an existing Si MOSFET with that of a GaN MOSFET has been evaluated using a multi-layered coreless PCB step-down power transformer for the given input/output specifications of the flyback converter circuit. It has been determined that the energy efficiency of the 45 to 15V regulated converter using GaN was improved by 8-10% compared to the converter using the Si MOSFET due to the gate drive power consumption, lower conduction losses and improved rise/fall times of the switch. For some of the AC/DC and DC/DC applications such as laptop adapters, set-top-box, and telecom applications, high voltage power MOSFETs used in converter circuits possess higher gate charges as compared to that of the low voltage rating MOSFETs. In addition, by operating them at higher switching frequencies, the gate drive power consumption, which is a function of frequency, increases. The switching speeds are also reduced due to the increased capacitance. In order to minimize this gate drive power consumption and to increase the frequency of the converter, a cascode flyback converter was built up using a multi-layered coreless PCB transformer and this was then evaluated. Both simulation and experimental results have shown that with the assistance of the cascode flyback converter the switching speeds of the converter were increased including the significant improvement in the energy efficiency compared to that of the single switch flyback converter. In order to further maximize the utilization of the transformer, to reduce the voltage stress on MOSFETs and to obtain the maximum power density from the power converter, double ended topologies were chosen. For this purpose, a gate drive circuitry utilising the multi-layered coreless PCB gate drive transformer was designed and evaluated in both a Half-bridge and a Series resonant converter. It was found that the gate drive power consumption using this transformer was less than 0.8W for the frequency range of 1.5-3.5MHz. In addition, by using this gate drive circuitry, the maximum energy efficiency of the series resonant converter was found to be 86.5% with an output power of 36.5W.
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Elias, Junior Antonio 1980. "Uma contribuição ao estudo de limitadores de corrente elétrica supercondutores usando transformador e fita supercondutora de alta temperatura crítica." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/259008.
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Orientadores: Ernesto Ruppert Filho, Carlos Alberto BaldanDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
Made available in DSpace on 2018-08-19T21:08:53Z (GMT). No. of bitstreams: 1 EliasJunior_Antonio_M.pdf: 3083167 bytes, checksum: f6bea29b3a45a17156c136bda7644b30 (MD5) Previous issue date: 2011
Resumo: Esta dissertação apresenta um estudo sobre limitadores de corrente elétrica supercondutores que funcionam com um transformador e com material supercondutor de alta temperatura crítica (HTS) em forma de fita. Neste caso utilizou-se a fita supercondutora do composto de YBCO. Neste trabalho é apresentado um resumo da evolução da supercondutividade desde a origem dos materiais supercondutores de baixa temperatura crítica (LTS) até os de alta temperatura crítica (HTS), as fitas supercondutoras de segunda geração (2G), seus processos de produção, suas composições e suas propriedades. Também faz parte desta dissertação um estudo sobre diferentes equipamentos utilizados para limitar a corrente elétrica em sistemas de energia elétrica aprofundando o estudo sobre limitadores de corrente elétrica supercondutores que funcionam usando transformador. Por fim, simulou-se a operação do limitador de corrente elétrica em questão acoplado ao sistema elétrico usando o pacote MATLAB/Simulink/SimPowerSystems. A simulação foi baseada em características reais dos elementos do sistema, como transformador de distribuição e no comportamento resistivo do material supercondutor de alta temperatura crítica de YBCO
Abstract: This work presents a study about transformer type superconductive fault current limiter using high critical temperature (HTS) tape. In this case the YBCO superconductive tape was used. The history of superconductivity since the beginning of low temperature (LTS) superconductive materials until the high critical temperature superconductive second generation (2G) tapes is presented, also their production process and their compositions are studied. It is part of this work a study about different equipments used to limit the electrical current in electrical power systems going deeply in the transformer type superconductive fault current limiter. Finally, the operation of superconductive electrical current limiter coupled to the electrical power system using MATLAB/Simulink/ SimPowerSystems was simulated. The simulation was based on the real characteristics of power system elements, as distribution transformer and on the resistive behavior of high critical temperature superconductive material of YBCO type
Mestrado
Energia Eletrica
Mestre em Engenharia Elétrica
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Kavimandan, Mandar Dilip. "Integrated Inductors." Wright State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=wright1229637343.
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Bell, Simon Colin. "High-voltage partial-core resonant transformers." Thesis, University of Canterbury. Electrical and Computer Engineering, 2008. http://hdl.handle.net/10092/2161.
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This thesis first describes the reverse method of transformer design. An existing magnetic model for full-core shell-type transformers, based on circuit theory, is summarised. A magneto-static finite element model is introduced and two sample transformers are analysed. The magnetic model based on finite element analysis is shown to be more accurate than the model based on circuit theory.
Partial-core resonant transformers are then introduced and their characteristics are explained using an equivalent circuit model. A method of measuring the winding inductances under resonant operation is developed and used to investigate the characteristics of two different tuning methods. A finite element model of the partial-core resonant transformer is developed by adopting the model for full-core shell-type transformers.
The model results accurately match the measured inductance variation characteristics of three sample transformers and predict the onset of core saturation in both axial-offset and centre-gap arrangements. A new design of partial-core resonant transformer is arrived at, having an alternative core and winding layout, as well as multiple winding taps. The finite element model is extended to accommodate the new design and a framework of analysis tools is developed. A general design methodology for partial-core resonant transformers with fixed inductance is developed. A multiple design method is applied to obtain an optimal design for a given set of specifications and restrictions. The design methodology is then extended to devices with variable inductance.
Three design examples of partial-core resonant transformers with variable inductance are presented. In the first two design examples, existing devices are replaced. The new transformer designs are significantly lighter and the saturation effects are removed. The third design example is a kitset for high-voltage testing, with the capability to test any hydro-generator stator in New Zealand. The kitset is built and tested in the laboratory, demonstrating design capability. Other significant test results, for which no models have yet been developed, are also presented. Heating effects in the core are reduced by adopting an alternative core construction method, where the laminations are stacked radially, rather than in the usual parallel direction. The new kitset is yet to be used in the field.
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Lindell, Erik, and Magnus Svensson. "Teknisk-ekonomisk utvärdering av lokalkraftslösningar." Thesis, Högskolan Väst, Avd för automationssystem, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-8183.
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Transformatorstationer i det svenska elnätet innehar en vital funktion för att försörjningen av elenergi från producent till konsument skall fungera. Stationerna finns på olika spännings-nivåer – men de har alla en sak gemensamt: Behov av att lokalkraftsförsörjningen skall fungera enligt angivna krav. Försörjningen av en stations lokalkraftanläggning kan ske på flera olika sätt. I rapporten belyses alternativen stationstransformator, externt abonnemang, ok-lindning och ABB:s SSVT (Station Service Voltage Transformer). De olika lösningarna karaktäriseras av olika tekniska och ekonomiska aspekter och tillhörande för- respektive nackdelar. Studien utvärderar de fyra olika lokalkraftslösningarna ur ett helhetsperspektiv. Först redogörs för den bakomliggande grundläggande teorin kring lokalkraft och elkraftsekonomi. Därefter jämförs de tekniska och ekonomiska skiljaktigheterna gentemot varandra för respektive given transformatorstationstyp; fördelnings-, region- och stamstation. Vattenfall eftersöker de teknisk-ekonomiskt bästa lokalkraftsalternativen för deras transformatorstationer och rapporten skall fungera som underlag. Ur rapporten kan följande resultat och slutsatser erhållas: • Fördelningsstation: Stationstransformator och ok-lindning rekommenderas då de erbjuder teknisk funktionalitet till ett ekonomiskt försvarbart och likvärdigt pris. • Regionstation: Primärt rekommenderas alternativet ok-lindning. • Stamstation: Likväl som på de andra stationerna rekommenderas ok-lindning för försörjning av lokalkraft. Sammanfattningsvis erbjuder alla fyra alternativ de tekniska krav som finns för lokalkraftsförsörjning, men att en avvägning av vilken lösning som lämpar sig bäst för respektive transformatorstation bör utföras från fall till fall.Substations in the Swedish electric power network have a vital function regarding the supply of electric energy from producer to consumer. The substations are represented on different voltage levels in the network – but they all have one thing in common: The need for auxiliary power to function as intended. There are different options for the supply of substations auxiliary feed. In the thesis the following alternatives are described holistic: local transformer, external power subscription, auxiliary winding on ordinary transformer, and a new (for the Swedish market) alternative from ABB called SSVT (Station Service Voltage Transformer). The distinct solutions are characterized with different technical and economic aspects and associated pros and cons. The study evaluates the four different auxiliary power solutions from a holistic view. First, the underlying essential theory about auxiliary power and electrical power economy is explained. Afterwards, the technical and economical differences are visualized for each of the solutions, and in comparison to each other for each defined substation type; distribution, region and national substation. The company Vattenfall strives for the best technical-economical alternatives for their different types of substations and the report intends to act as a supportive document. From the report, the following results and conclusions can be obtained: • Distribution substation: Local transformer and auxiliary winding is recommended due the technical functionality relative to its equivalent economic aspects. • Region substation: Primarily, the auxiliary winding alternative is recommended, mostly because of the cost-effectiveness. There are fewer alternatives in this type of substation. • National substation: The auxiliary winding is recommended as local power solution. To sum up, all of the four alternatives fill the technical requirements, but consideration for which solution for which substation type must be done on a case to case basis.
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Bosi, Marco. "Development of a distributed measurement system for detection of high impedance faults in medium voltage power lines." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Find full textAbstract:
The aim of this thesis is to propose a new method to detect High impedance Faults, which relies on measuring the phase currents on electrical transmission and distribution grids using a common time source for synchronization. The goal is to measure the residual currents both at the transformer side and at the load side of the network. The time synchronization allows synchronized real-time measurements of the two residual currents at the two ends of the grid. In normal operating conditions and in all load conditions (balanced or unbalanced), the residual currents will result almost equal at the two ends. When a High Impedance Fault occurs, the residual currents at the two ends will differ. The difference in magnitude of the residual currents are monitored in real time and used as a pick-up criteria.
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Soares, Alexandre Batista de Jesus. "Estudo de paralelismo de alimentadores radiais de distribuição de energia elétrica." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/260747.
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Orientadores: Ernesto Ruppert Filho, Fujio SatoTese (outorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
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Resumo: Este trabalho apresenta uma ferramenta computacional denominada Gerenciador de Paralelismo de Alimentadores Radiais de Distribuição (GPARD), que foi desenvolvida para o estudo de manobras de paralelismo entre alimentadores radiais de distribuição de energia elétrica, localizados na mesma subestação ou em subestações diferentes, derivados do mesmo transformador ou de transformadores diferentes. O GPARD e uma ferramenta computacional que contribui para a operacao de sistemas de distribuição auxiliando os operadores do sistema na tomada de decisão para a realização de manobras de paralelismo durante a operacao ou em estudos prévios, fundamentada na analisem gráfica de resultados de simulação e de medidas remotas, resultando em flexibilidade operacional para o sistema e segurança para os consumidores. Tal ferramenta computacional poderá ser bastante utilizada em um ambiente de rede inteligente onde ações rápidas envolvendo medições, transmissão de dados e controle é necessária durante a operacao do sistema elétrico
Abstract: This work presents a computational tool named Management of Parallel Distribution Radial Feeders (GPARD), dedicated to the study of radial distribution feeders parallelism maneuvers, located in the same substation or in different substations, supplied by the same transformer or by different transformers. The GPARD is a computational tool that helps the operation of distribution systems helping system operators in making decisions for the maneuvers of parallelism during the operation or in previous studies, based on graphical analysis of simulation results and remote measurements resulting in operational flexibility to the system and safety to consumers. This computational tool can be utilized in a smart grid environment where fast actions involving measurements, data transmission and control are necessary for the operation of the electric system
Tese (outorado) - Universidade
Energia Eletrica
Doutor em Engenharia Elétrica
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Makowski, Nathanael Jared. "Proposal and Analysis of Demagnetization Methods of High Voltage Power System Transformers and Design of an Instrument to Automate the Demagnetization Process." PDXScholar, 2011. https://pdxscholar.library.pdx.edu/open_access_etds/431.
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Present demagnetization methods for large power system transformers are time consuming and can be dangerous to persons performing demagnetization. The work of this thesis was to develop improved demagnetization methods and to construct an automated instrument that would implement the methods developed. One previously developed method was analyzed for effectiveness. Then, two new methods for demagnetization were developed and also analyzed for effectiveness. An automated test instrument prototype was redesigned to be able to accommodate these methods and to improve the safety of the user. The previously developed method attempts demagnetization based on current flow behavior characteristics. The first new method is a magnetic flux estimation based on saturation time. The second new method is also based on measuring saturation time, modified to account for the variable voltage loss due to wire resistance. The second of the two new methods developed proved to be the most effective for demagnetization and was able to demagnetize a transformer within an error margin of 2%. The instrument designed to perform the demagnetization with this new routine is now in early production stages for an expanded field trial with transformer maintenance teams.
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Strömberg, Fredrik. "Magnetfält alstrade kring nätstationer i samband med lokaldistribution av elkraft : Magnetic fields generated by electrical substations during distribution of electric power." Thesis, Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-20548.
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Abstract: This report covers primarily the work of documenting electromagnetic fields generated by one of the later parts in the electrical power distribution chain: The electrical substation, wherein 10 kV is transformed to 400 V for use by private consumers. Thus it is one of the most widespread and frequently occurring parts in the Swedish power grid and of particular interest, as electrical substations are found everywhere in populated areas, often in close vicinity to people and animals. The report deals with a number of formulated questions and/or hypothesis’ stated at the onset of the work undertaken, theory that is relevant for the topics the report covers, the details of the field work undertaken and the following analysis of the readings, which in term provide answers for the questions stated in the beginning. It also covers what is the currently known short term and long term risks associated with electromagnetic fields in the power frequent spectrum and of varying intensity in the vicinity of humans. The analysis also provides recommendations and identifies several points to carefully consider when planning for new installations or replacements of some parts of existing installations. For enhanced reading comprehension there is, aside from sections with pictures and attached explanatory texts and templates, several graphs, one-line diagram and maps of the power grid among the appendixes to the rapport.
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García, Ríos Sara. "Análisis de desequilibrios en transformadores y máquinas de inducción trifásicos." Doctoral thesis, Universitat Rovira i Virgili, 2019. http://hdl.handle.net/10803/668353.
Full textAbstract:
Aquesta tesi analitza l'efecte dels desequilibris del sistema de tensió trifàsic en màquines d'inducció i en transformadors trifàsics, mitjançant factors de desequilibri. Primer, s’ha caracteritzat un desequilibri de tensió mitjançant quatre paràmetres: tipus de desequilibri (q), component directa de la tensió (V1), VUF i angle del factor complex de desequilibri de tensió. Per analitzar els efectes de desequilibris en motors d'inducció, s’han realitzat simulacions en dos motors, i assajos de laboratori i simulacions en un tercer motor. S’ha observat que els paràmetres de desequilibri de tensió i angle del CVUF no tenen influència en el CUF i el TRF. També s’ha observat que hi ha una tendència lineal entre el CUF i el TRF respecte al VUF (per a valors constants de V1) i que hi ha una tendència lineal entre el CUF i el TRF respecte a V1 (per a valors constants de VUF). Petits desequilibris de tensió poden generar grans desequilibris de corrent i un fort arrissat de parell. En els assaigs de laboratori es s’han obtingut resultats molt propers als obtinguts mitjançant la simulació del motor 3. Aquests resultats han estat qualitativament iguals als obtinguts per als motors 1 i 2. S’han observat desequilibris en un transformador trifàsic. S’ha observat que els desequilibris de tensió en el debanat primari provoquen desequilibris en les tensions del secundari i en els corrents del primari i del secundari. També s’han observat tendències lineals entre els mateixos factors que els analitzats amb motors. Finalment, s’ha desenvolupat un nou mètode d'estimació de paràmetres del transformador monofàsic a partir d'assajos en càrrega mitjançant un algoritme que minimitzava l'error de pèrdues elèctriques de potència i de caiguda de tensió del debanat secundari. S’ha aconseguit estimar paràmetres més precisos del circuit equivalent Gamma del transformador monofàsic que els obtinguts amb els assajos de buit i curtcircuit.Esta tesis analiza el efecto de los desequilibrios del sistema de tensión trifásico en máquinas de inducción y en transformadores trifásicos, mediante factores de desequilibrio. Primero, Se caracterizó un desequilibrio de tensión mediante cuatro parámetros: tipo de desequilibrio (q), componente directa de la tensión (V1), VUF y ángulo del factor complejo de desequilibrio de tensión. Para analizar los efectos de desequilibrios en motores de inducción, se realizaron simulaciones en dos motores, y ensayos de laboratorio y simulaciones en un tercer motor. Se observó que los parámetros de desequilibrio de tensión y ángulo del CVUF no tienen influencia en el CUF y el TRF. También se observó que existe una tendencia lineal entre el CUF y el TRF respecto al VUF (para valores constantes de V1) y que existe una tendencia lineal entre el CUF y el TRF respecto a V1 (para valores constantes de VUF). Pequeños desequilibrios de tensión pueden generar grandes desequilibrios de corriente y un fuerte rizado de par. En los ensayos de laboratorio se obtuvieron resultados muy cercanos a los obtenidos mediante la simulación del motor 3. Dichos resultados fueron cualitativamente iguales a los obtenidos para los motores 1 y 2. Se simularon desequilibrios en un transformador trifásico. Se observó que los desequilibrios de tensión en el devanado primario provocan desequilibrios en las tensiones del secundario y en las corrientes del primario y del secundario. También se observaron tendencias lineales entre los mismos factores que los analizados con motores. Por último, se desarrolló un nuevo método de estimación de parámetros del transformador monofásico a partir de ensayos en carga mediante un algoritmo que minimizaba el error de pérdidas eléctricas de potencia y de caída de tensión del devanado secundario. Se consiguieron estimar parámetros más precisos del circuito equivalente Gamma del transformador monofásico que los obtenidos con los ensayos de vacío y cortocircuito.
This thesis analyses the effect of the unbalance of the three-phase voltage system in induction machines and in three-phase transformers, by means of unbalance factors. First, a voltage unbalance was characterized by four parameters: type of unbalance (q), positive-sequence voltage (V1), VUF and angle of the complex factor of voltage unbalance. To analyse the effects of unbalances in induction motors, simulations were carried out in two motors, and laboratory tests and simulations in a third motor. It was observed that the unbalance voltage and angle parameters of the CVUF have no influence on the CUF and the TRF. It was also observed that there is a linear trend between the CUF and the TRF versus VUF (for constant values of V1) and that there is a linear tendency between the CUF and the TRF versus V1 (for constant values of VUF). Small voltage unbalances can generate large current unbalances and strong torque ripple. In the laboratory tests, results very close to those obtained by the simulation of motor 3 were obtained. These results were qualitatively equal to those obtained for motors 1 and 2. Unbalances were simulated in a three-phase transformer. It was observed that the voltage unbalance in the primary winding causes unbalance in the secondary voltages and in the primary and secondary currents. Linear trends were also observed among the same factors as those analysed with motors. Finally, a new method for estimating the parameters of the single-phase transformer was developed from load tests using an algorithm that minimized the error of electrical power losses and voltage drop of the secondary winding. More precise parameters of the equivalent Gamma circuit of the single-phase transformer were estimated than those obtained with the open-circuit and short-circuit tests.
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Shih, Chun-Hao, and 施俊豪. "Natural convection in electrical transformers." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/26442324175423825180.
Full textAbstract:
碩士國立中央大學
機械工程研究所
89
Knowledge of the temperature and position of the hot spot is very important for the design and operation of power transformers. The rate of deterioration of the winding insulation increases with the conductor temperature. Thus it is necessary to know the hottest conductor temperature in order to ensure a reasonable life of the insulation. Pumping working fluid through a set of ducts generally cools the windings of large modern transformers. However, compared with forced convection cooling, natural convection cooling offers minimal safety requirements to avoid burnout. In the present study, the natural convection heat transfer in a disc-type pole-top transformer is investigated. The study depicts flow pattern of cooling fluid inside the windings of a transformer and provides an estimate of the position of the hot spot. The geometrical model consists of two arrays of rectangular heat-dissipating blocks arranged in line in a transformer tank. A two-dimensional, steady and turbulent flow is simulated. The set of transport equations is solved numerically using the finite volume technique. Solutions are presented for the temperature distribution in the disc coils and cooling horizontal ducts of a transformer. The attention is focused on the parameters, such as the Prandtl number, aspect ratio of the tank, heat dissipation rate, thermophysical properties, configuration, number and block ratio of the heated coils. The results show that the flow behavior has a primary clockwise circulating cell in the top region caused by buoyancy effects originating from the heat source. The bottom zone is almost stagnant and thermally stratified. The parametric study indicates that the block ratio, BR, and the aspect ratio, AR, have a significant influence. Increasing BR from 2 to 5, the maximum temperature drops by 20 percent. When aspect ratio increases from 0.257 to 0.4, the maximum temperature is lowered by 33 percent. The effects of other parameters are studied to arrive at qualitative suggestions that may improve the cooling design of the power transformers