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1
Zandberg, Hermanus Andries Jakobus. "Wireless transformer condition monitoring system." Thesis, Cape Peninsula University of Technology, 2013. http://hdl.handle.net/20.500.11838/1186.
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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.
2
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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O'Sullivan, Francis M. (Francis Martin) 1980. "A model for the initiation and propagation of electrical streamers in transformer oil and transformer oil based nanofluids." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40504.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 305-309).
The widespread use of dielectric liquids for high voltage insulation and power apparatus cooling is due to their greater electrical breakdown strength and thermal conductivity than gaseous insulators, while their ability to conform to complex geometries and self-heal means that they are often of more practical use than solid insulators. Transformer oil is a particularly important dielectric liquid. The issues surrounding its electrical breakdown have been the subject of extensive research. Much of this work has focused on the formation of electrical streamers. These are low-density conductive structures that form in regions of oil that are over-stressed by electric fields on the order of 1 x 108 (V/m) or greater. Once a streamer forms it tends to elongate, growing from the point of initiation towards a grounding point. The extent of a streamer's development depends upon the nature of the electrical excitation which caused it. Sustained over-excitation can result in a streamer bridging the oil gap between its point of origin and ground. When this happens an arc will form and electrical breakdown will occur. Streamers can form due to both positive and negative excitations. Positive streamers are considered more dangerous as they form at lower electric field levels and propagate with higher velocities than negative streamers. Historically, the modeling of streamer development has proved to be a very difficult task. Much of this difficulty relates to the identification of the relevant electrodynamic processes involved. In the first section of this thesis a comprehensive analysis of the charge generation mechanisms that could play a role in streamer development is presented.
(cont.) The extent of the electrodynamics associated with Fowler-Nordheim charge injection, electric field dependent ionic dissociation (the Onsager Effect) and electric field dependent molecular ionization in electrically stressed transformer oil are assessed and it is shown that molecular ionization, which results in the development of an electric field wave, is the primary mechanism responsible for streamer development. A complete three carrier liquid-phase molecular ionization based streamer model is developed and solved for a positive needle electrode excitation using the COMSOL Multiphysics finite element simulation suite. The modification of the liquid-phase molecular ionization model to account for the two-phase nature of streamer development is described and the performance of both the liquid-phase and gas/liquid two-phase models are compared with experimental results reported in the literature. The second section of this thesis focuses on the insulating characteristics of transformer oil-based nanofluids. These nanofluids, which can be manufactured from a variety of materials, have been shown to possess some unique insulating characteristics. Earlier experimental work has shown that oil-based nanofluids manufactured using conductive nanoparticles have substantially higher positive voltage breakdown levels than that of pure oil. A comprehensive electrodynamic analysis of the processes which take place in electrically stressed transformer oil-based nanofluids is presented, which illustrates how conductive nanoparticles act as electron scavengers in electrically stressed transformer oil-based nanofluids. As part of this analysis, a completely general expression for the charging dynamics of a nanoparticle in transformer oil is developed.
(cont.) The solutions for the charging dynamics of a range of nanoparticle materials are presented and the implications these charging dynamics have on the development of streamers in oil-based nanofluid is explained. To confirm the validity of the electrodynamic analysis, the electric field dependent molecular ionization model for streamers in pure oil is modified for use with transformer oil-based nanofluids. This model is solved for nanofluids manufactured using conductive and insulating particles and the results that are presented confirm the paradoxical fact that nanofluids manufactured from conductive nanoparticles have superior positive electrical breakdown performance to that of pure oil. The thesis concludes by exploring the possibility of developing simplified streamer models for both transformer oil and transformer oil-based nanofluids, which are computationally efficient and can be solved quickly meaning that they can be used as practical design tools.
by Francis M. O'Sullivan.
Ph.D.
4
Cargol, Timothy L. (Timothy Lawrence) 1976. "A non-destructive transformer oil tester." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/81576.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.Includes bibliographical references (leaves 62-63).
A new non-destructive test of transformer oil dielectric strength is a promising technique to automate and make more reliable a diagnostic that presently involves intensive manual efforts. This thesis focuses some of the issues that must be understood to bring the test from the laboratory to the field. Emphasis is placed on reliability and safety by exploring any effect the test has on the transformer oil, the mechanical parameters necessary to give optimal reliability, and failsafe electronics.
by Timothy L. Cargol.
M.Eng.
5
Schlicker, Darrell Eugene. "Flow electrification in aged transformer oils." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/38844.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (p. 317-348).
by Darrell Eugene Schlicker.
M.S.
6
Cho, Sung Don. "Parameter estimation for transformer modeling /." Available online. Click here, 2002. http://sunshine.lib.mtu.edu/ETD/DISS/chosd/SungCho.pdf.
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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.
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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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Jagers, Janine Norma. "Comparing the reliability of older and newer transformer designs." Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/11059.
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This dissertation describes the findings of an investigation that was conducted to determine if the reliability of older designs was significantly different from newer designs, and whether the observed differences (if any) were the result of developments in design, manufacture and technology of transformers during different periods.
9
Archer, Dale S. "An adaptive thermal module for transformer monitoring." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/11992.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1988.Includes bibliographical references (leaves 132-133).
by Dale S. Archer.
M.S.
10
Mouayad, Lama. "Monitoring of transformer oil using microdielectric sensors." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/39497.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1985.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.
Includes bibliographical references.
by Lama Mouayad.
M.S.
11
Mahmud, Shekhar. "Influence of contamination on the electrical performance of power transformer oil." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/379273/.
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Transformer failure statistics from all over the world showed that almost 30% of them were due to insulation. Large amount of those failures were due to particles in transformer oil. Main focus of this research is to effects of contamination on electrical performance of transformer oil. A literature review of major causes of transformer failure, breakdown mechanisms of transformer oil has been conducted. The experimental setup and results from the pressboard-dust-contaminated transformer mineral oil test are also discussed. Several experiments have been carried out with cellulose particle contaminated transformer mineral oil. The experiments of bridge formation are conducted under the influence of DC, AC, and DC biased AC voltages. Samples with several levels of contaminant are tested under different voltage levels. The influence of different electrode systems is also tested i.e. bare electrode, covered electrode, bare electrodes with paper barrier, spherical and needle – plane electrodes. These experiments revealed that the bridges are always formed under the influence of DC voltages. The particles are attracted towards high electric field due to Dielectrophoretic (DEP) force and become charged once in contact with the electrode surface. Long fiber particles were attached to the electrodes and aligned parallel to electric field towards the other electrode. More particles attached to the initial fibers and the process continued until a full bridge formed between the electrodes. The conduction current increased with contamination levels as the bridge thickened with increment of contaminations. There is no complete bridge formed under AC electric field. The particles were attracted to the high electric field and attached to the electrodes but the particles are not been able to charge before the polarity of AC electric field alters with spherical electrodes. The current for AC remained unchanged with the increment of particle contamination levels as there is no bridge formed. However, when the DC biased AC signal is applied, the bridge is formed for all the three voltage levels tested. DC and AC breakdown tests were also conducted for several contamination levels. Experiments with kraft paper covered spherical electrodes confirmed that a tightly bonded cover does not stop the bridge; only a loose bonded cover stopped the bridging. Another test with a paper barrier between bare electrodes also did not stop the bridging. Partial discharge (PD) and breakdown test of the contaminated transformer oil is also measured but the results were not conclusive. An initial mathematical model of pressboard dust accumulation using Finite Element Analysis (FEA) software, COMSOL multiphysics has been conducted. The result of the simulation model for charging-discharging and bridging showed similar trend as experimental results. There are a number of changes that can result in improved simulations. There are several variables affecting the simulation i.e. the pressboard dust particle shape, size, conductivity of impregnated pressboard fiber etc.
12
Al, lulu Sadi, Lezan Amen, Mohammad Aljichi, and Mats Isaksson Sandberg. "Wireless signal transmission for HV Transformer." Thesis, Uppsala universitet, Institutionen för elektroteknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-448131.
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Mitzel, Anne M. (Anne Marie) 1977. "Characterization and modeling of a 30 kilohertz transformer." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/86690.
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Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.Includes bibliographical references (p. 101-102).
by Anne M. Mitzel.
M.Eng.
14
McNeill, John Neville. "Current transformer circuits for power electronics applications." Thesis, Edinburgh Napier University, 2008. http://researchrepository.napier.ac.uk/Output/6196.
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This thesis investigates the operation of the current transfonner (CT) when sensing retum-to-zero current pulses in power electronic circuitry. The CT's output signal is nonnally rectified when sensing current pulses and the effects of the different rectification techniques on peak current and average current droop are evaluated. Initially, the various current sensing techniques and their application in power electronics circuits are reviewed. The CT and both diode and synchronous rectification are then reviewed in more detail. Operation of the CT with diode rectification (DR) and natural resetting is investigated. Three operating modes are identified. These are the discontinuous magnetizing current, continuous magnetizing current and discontinuous secondary current modes. The error (droop) in the average output signal obtained is found to be predominantly defined by CT core losses. Coefficients are given for correcting the error due to droop, provided that the discontinuous secondary current mode is avoided. Diode rectification with the dual CT arrangement is also investigated. Operation of the CT with synchronous rectification (SR) and natural resetting is then investigated. The SR topologies possible using a discrete MOSFET are categorized. During experimentation the arrangement used to drive the MOSFET's gate is found to be important if distortion is to be minimized. It also is found that the average current droop is dependent on the oscillatory behaviour of the resetting circuit and has an effectively random component. The magnitude of this component is defined by the voltage drop exhibited by the SR MOSFET's intrinsic anti-parallel diode. SR is then implemented using a commercially available analogue switch. The problems detailed with the use of a discrete MOSFET are largely alleviated. Another benefit is that the increased restriction on maximum duty factor imposed by introducing a discrete MOSFET is also eased. However, whichever SR technique is implemented, an operational amplifier is used and the transient response of this circuit element is important. A method of minimizing droop by indirect sensing of the CT's peak core flux excursion is then presented. A corresponding correcting voltage is applied in series with the CT's output terminals during a current pulse. The magnitude of this voltage is based on the magnitude of the resetting voltage sensed during previous switching cycles. A circuit is implemented and simulated. Experimental results are presented. A switched-mode circuit operating at a frequency higher than that of the main power circuit is then used to apply the correcting voltage with the objective of reducing the power drawn. Again, the circuit is implemented and simulated and experimental results are presented.
15
Moodley, Nadarajan. "Power transformer health assessment derived from low energy and dissolved parameters." Doctoral thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/5154.
Full textAbstract:
Includes abstract.Includes bibliographical references.
This dissertation studied the mechanisms of transformer health in terms of energy and dissolved parameters and establishes a novel method to identify a trigger for a change in transformer condition from normal to defective state. The study took the form of both analytic research to create a low energy degradation model and then empirical testing of the model on field data in the form of dissolved gas analysis as recorded from 201 GSU transformers that have either failed or are presently in service.
16
Zhang, Xingxing. "STRANDED CORE TRANSFORMER LOSS ANALYSIS." UKnowledge, 2008. http://uknowledge.uky.edu/gradschool_theses/533.
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We will present the approaches used to investigating the power loss for the stranded core transformers. One advantage of using stranded core is to reduce power loss or enhance transformer efficiency. One difficulty in the modeling of this type of transformer is that the core is not solid (there are small gaps between core wires due to circular cross section). A two dimensional finite element method with nodal basis function for magnetostatic field was developed to study the effects of the small gaps between core wires. The magnetic flux densities are compared for the uniform (solid) cores and the stranded cores for various permeability values. The effects of different air gap dimensions in stranded core to the magnitude of magnetic flux density were also discussed. The results of the two dimensional study were applied to modify the B-H curves in a 3D simulation with an equivalent simplified uniformed core transformer model via Ansoft Maxwell 3D. This is achieved by output the magnitude of magnetic flux density at fixed points of mesh center. The total core loss of a transformer was predicted by integration of the losses of all elements.
17
Chang, Woo Sok 1964. "An electromechanical valve drive incorporating a nonlinear mechanical transformer." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/38201.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (leaves 145-147).
In traditional internal combustion engines, a camshaft acts on the valve stems to open and close the valves. Valve timing is fixed relative to piston position. On the other hand, if a valve is flexibly controlled by a variable valve actuation (VVA) system, we can achieve significant improvements in fuel efficiency, engine performance, and emissions. One of the most advanced variable valve actuation systems is the VVA operated by an electromechanical actuator without a camshaft, the so-called bi-positional electromechanical valve drive (EMVD). Existing EMVDs characteristically use a spring to provide the required mechanical power for operating a valve. The use of a spring provides many benefits to the design of the system, but it also results in difficult design challenges. The large holding force against the spring at the ends of the stroke suggests the use of a normal-force electromagnetic actuator, which, from a servomechanical point of view, is considerably inferior to a shear-force actuator. Furthermore, the large holding force generates a large jerk at the beginning and the end of a stroke and makes it difficult to achieve soft valve landing. An innovative electromechanical valve drive (EMVD) design is proposed, which incorporates a nonlinear mechanical transformer and a shear-force actuator. This allows not only fast but also smooth valve motion, almost zero seating velocity, zero holding power, and improved control with acceptable electric power. This proposed concept is modeled, analyzed, simulated, designed, and implemented. Experimental results show the beneficial features of the promising proposed concept.
by Woo Sok Chang.
Ph.D.
18
Zaretsky, Mark Carmeron. "Parameter estimation using microdielectrometry with application to transformer monitoring." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14722.
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Boyd, Mary Jane. "Intelligent on-line transformer monitoring, diagnostics, and decision making." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9953.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1998.Includes bibliographical references (p. [231]-235).
by Mary Jane Boyd.
Ph.D.
20
Etumi, Adel. "Current signal processing-based techniques for transformer protection." Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/94716/.
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Transformer is an expensive device and one of the most important parts in a power system. Internal faults can cause a transformer to fail and thus, it is necessary for it to be protected from these faults. Protection doesn’t mean that it prevents damage to the protected transformer but it is to minimize the damage to the transformer as much as possible, which consequently minimizes the subsequent outage time and repair cost. Therefore, fast and reliable protection system should be used for limiting damages to the transformer by rapidly disconnecting the faulty transformer from the network, which also leads to the elimination of the stresses on the system itself and preventing damage to adjacent equipment. The main aim of this thesis is to propose transformer protection technique that is fast and highly sensitive to internal faults that occur inside the transformer, to overcome the problems of current transformer saturation and inrush current, and to make it immune to the external faults (through faults) that occur outside of the transformer protection zone. The current transformer saturation and inrush current are significant problems since they cause malfunction of the protection system, which consequently will disconnect the transformer because they are considered faults. This improper disconnection of transformer is not desirable as it shortens its life time. So the proposed protection technique was designed to be fast and to avoid maloperation caused by saturation and inrush current. The proposed protection technique was based on current signal processing. Three methods, namely the application of correlation coefficients, current change ratio (CCR) and percentage area difference (PAD) were proposed based on practical and simulation tests. These techniques were successfully proved by carrying out tests on Simulink models using MATLAB/SIMULINK program and on a practical laboratory model. In transformer transient state, the response time for the methods that were used to address the problem of inrush condition, was 10 ms for CCR when transformer was on no-load and 5 ms for PAD when the transformer was on-load. This response time Current Signal Processing-Based Techniques for Transformer Protection v is faster than the most popular method relying on second harmonic, which needs at least one cycle (20ms in 50 Hz systems) to recognize the condition. In transformer steady state, it was proved that the proposed correlation method was capable of detecting the internal faults successfully within a very short time, ranging from 0.8 to 2.5 ms according to the type and severity of the fault and in addition was able to overcome the problem of current transformer (CT) saturation. The contribution of this research is the development of a transformer protection technique, which is simple in design, fast and reliable in fault detection and at the same time capable of overcoming the problems of current transformer saturation and inrush current.
21
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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Oyedokun, David Temitope. "Geomagnetically induced currents (GIC) in large power systems including transformer time response." Doctoral thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/16708.
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Includes bibliographical referencesGeomagnetically induced currents (GIC) are the result of changing geomagnetic fields which are a consequence of a geomagnetic disturbance (GMD). The flow of GIC through transmission lines and transformers across the power network could have severe consequences, if the magnitudes of the GIC are high enough. Problems that could arise from the flow of GIC in transmission networks include an increase in the amount of reactive power demand by GIC-laden transformers, half-wave saturation, excessive heating in transformers, incorrect operation of transmission line protection schemes and voltage collapse in affected sections of the network. In the past, GIC were calculated without taking the transformer's response time into account. The limitation of this approach is that the size and core type of the transformer is neglected. This may affect the assessment of GIC in the power network as the flux pattern and winding inductance distribution are not uniform across all transformer core structures. This thesis postulates that these characteristics could have far-reaching effects on the GIC that flows through a transformer as a function of time. Based on this assumption, a novel way of calculating GIC is introduced in this thesis. This method combines the uniform plane wave model and the network Nodal Admittance Matrix (NAM) method and incorporated for the first time, the transformer time response, which does not appear to have been considered in previous calculation methods. A general formula, which describes the transformer's time response to GIC was derived, followed by the derivation of the electric field induced in each transmission line. A key input to the prospective GIC with transformer time response calculation, is a set of piecewise linear equations derived from a laboratory test and PSCAD simulations. These suitably characterise the response of three transformer core structures, namely: bank of single phase (3(1P-3L)), three-phase three-limb (3P-3L) and three-phase five-limb transformers (3P-5L). Each of these core types were considered as a Generator Step-up Unit (GSU) and a Transmission Transformer (TT). The results of the laboratory experiment and simulations in PSCAD led to the conclusion that the transformer time response to GIC is irregular across the transformer cores that were tested. The 300 VA transformer core structure with the shortest response time is the 3P-3L, followed by the 3P-5L and the 3(1P-3L). For the 500 MVA transformers, the order was: 3P-3L; 3(1P-3L); and 3P-5L. The 3P-3L transformers permit the flow of GIC through the windings of the transformer over a shorter length of time. Therefore based on the order in response time, during GMDs leading to higher GIC, the prospective GIC with or without transformer time response flowing through 3P-3L transformers will be similar. Furthermore, the response time to GIC in 3P-3L, 3P-5L and 3(1P-3L) transformer core types are load-dependant. The 3(1P-3L) and 3P-5L transformers operating as TT's (modelled as transformers at 40 % load) have the longest response time to GIC, while 3P-3L transformers operating as a GSU (modelled as transformers at full load) have the longest response time to DC. The shortest response time to DC was with a GSU at light load (modelled as transformers at 80 % load), which was consistent across the three transformer core types. This correlates well with the notion that power networks could stand a better chance of surviving a high GMD when all generating units and loads are online. Three different core structures were modelled with a variation of DC current levels and load conditions, both in PSCAD and in the laboratory. These results are unique to the transformer models used, but are representative of major types of core configurations used on power networks. These results provide an indication that it is incorrect to lump the responses of all transformers and transformer time response should be taken into consideration, especially when sampling at intervals as low as 2 seconds.
23
Walton, Michael. "Development and prototyping of a Point Coupled Linear Transformer (PCLT) displacement sensor." Master's thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/5087.
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Includes bibliographical references (leaves 78-80).The main aims of this project were to develop and prototype a Point Coupled Linear Transformer (PCLT) displacement sensor, and to perform a general exploration of the PCLT technology. The PCLT is a recent invention that has planar PCB windings and a non-contacting movable core, and relies on variable induction to detect displacement. Different core materials and shapes are investigated. The transformer windings layout is optimized for symmetrical response and high primary to secondary voltage coupling.
24
Jansson, Vincent, David Bergman, and Niklas Hermansson. "High Frequency Transformer : Implementation of prototype." Thesis, Uppsala universitet, Elektricitetslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-387307.
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Since its invention in 1885 by Otto Bláthy, Miksa Déri and KárolyZipernowsky, transformers have become an important cornerstone of theelectrical infrastructure we have today. They are found mostprominently in any machinery or device that requires a differentlevel of voltage or current than a general grid can supply, such ascomputers, motors or even cars. In the case of this project, thetransformer was originally intended to be connected to a resonatingH-bridge which supplies the primary coil with high frequency voltagepulses to be converted into a higher voltage transferred to arectifier unit. Because of the level of frequency supplied, thetransformer was required to be constructed with a different type ofcore and cable for the winding. When it became clear that the cablecouldn't be supplied in time, the focus shifted towards constructinga prototype instead. The prototype was designed to generate a certainamount of leakage inductance while subjected to a short circuit test.After a couple of attempts, the group managed to construct atransformer whose leakage inductance was well within range of thespecifications. The finished transformer prototype was delivered andthe group had thus successfully constructed what is to be used as atemplate for further transformers of the same type.A special thanks to ScandiNova Systems AB for initiating this projectand giving us the opportunity to participate, and to Per Nilsson, PerBenkowski and Klas Elmqvist for mentoring us along the way.
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Fu, Le. "Voltage stability monitoring and enhancement in electrical power systems using transformer tap changers." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.506484.
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Edwards, Laura E. (Laura Elaine). "Optimization of data storage for the adaptive transformer monitoring system." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/12770.
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Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1992.Includes bibliographical references (leaves 150-151).
by Laura E. Edwards.
B.S.
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Rhodes, Scott A. (Scott Adrian). "The effects of separable cores on high power transformer design." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/41419.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (p. 157-159).
by Scott A. Rhodes.
M.Eng.
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Grönström, Niclas. "Optimal Demagnetization of Transformer After Winding Resistance Measurements." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-291560.
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In this thesis, transformer demagnetization in connection to winding resistance tests is investigated. In transformer testing, winding resistance measurement (WRM) is an important test used to detect winding or connection faults. It is common practice to measure the resistance by injecting a DC current into the windings of a transformer. The method magnetizes the core, which leads to the transformer core remaining magnetized even after the test. A magnetized core can cause various problems, such as inrush currents that are several times higher than the rated current. Furthermore, residual magnetism may influence other AC diagnostic tests, such as the SFRA (Sweep Frequency Response Analysis) test and the excitation current test. Therefore, it is recommended to demagnetize transformers after WRM. The core-type and winding configuration may impact the demagnetization process. This makes the different demagnetization approaches of interest, so that the most efficient method can be used. This thesis presents demagnetization experiments on several power transformers with different core-types and winding configurations. The transformers were magnetized with WRM and then a TRAX (transformer and substation test system) was used to demagnetize the transformers with different approaches. Numerous measurements were performed on a three-limb and a five-limb power transformer. The effectiveness of the demagnetization methods was measured by using the excitation current in magnetized and demagnetized state as a comparative tool. It is shown that the demagnetization approach for the three-limb core had little impact on the magnetization result. The excitation currents at demagnetized state for the different combinations was roughly equal. The five-limb transformer was demagnetized on the middle limb, and then demagnetized on the outer limbs to see if the demagnetization gave better results. For the five-limb transformer, the measurements showed that the demagnetization approach impacted the results. Different Yy configurations were tested, and the result showed that the remanence was removed after one demagnetization with a phase to phase approach. However, if a Yy configuration was demagnetized with phase to neutral, then the transformer had to be demagnetized twice to remove the remanence. The result for the Yd configuration showed that it was not improved by a phase to phase approach. The phase that was magnetized did in general have a slightly larger excitation current than the other phases, even after demagnetization.I detta examensarbete undersöks avmagnetisering av transformatorer i samband med lindningsresistansprovning. Vid transformatorprovning är mätning av lindningsresistans ett viktigt test som används för att upptäcka lindningseller kopplingsfel. Vanligtvis mäts resistansen genom att en likström injiceras i transformatorns lindningar. Processen magnetiserar kärnan, vilket leder till att transformatorn förblir magnetiserad även efter testet. En magnetiserad transformator kan orsaka olika problem med diagnostiska tester och leda till inkopplingsströmmar som är flera gånger högre än märkströmmen. Vidare kan restmagnetism påverka AC-tester, såsom SFRA-testet (Sweep Frequency Response Analysis) och exciteringsströmstestet. Därför rekommenderas det att transformatorer avmagnetiseras efter lindningsresistanstest. Kärntyp och lindningskonfiguration kan ha påverkan på avmagnetiseringsprocessen. Det gör det intressant att undersöka olika avmagnetiseringsmetoder, så att den mest effektiva metoden kan användas. Detta arbete demonstrerar avmagnetiseringsexperiment på flera krafttransformatorer med olika kärntyper och lindningskonfigurationer. Transformatorerna magnetiserades genom lindningsresistansmätning och sedan användes en TRAX (transformer and substation test system) för att avmagnetisera transformatorerna med olika tillvägagångssätt. Flera mätningar utfördes på trebenta och fembenta krafttransformatorer. Avmagnetiseringsmetodernas effektivitet mättes genom att jämföra exciteringsströmmen i magnetiserat och avmagnetiserat tillstånd. Det visas att avmagnetiseringsmetoden för den trebenta kärnan hade liten inverkan på magnetiseringsresultatet. Exciteringsströmmarna vid avmagnetiserat tillstånd för de olika kombinationerna var ungefär lika. Den fembenta transformatorn avmagnetiserades först på mittbenet och sedan på de yttre benen för att se om resultaten förbättrades. För den fembenta transformatorn visade mätningarna att avmagnetiseringsmetoden påverkade resultaten. Olika Yy-konfigurationer testades och resultatet visade att remanensen avlägsnades efter den första avmagnetiseringen med fas till fas tillvägagångssättet. Men om Yy-konfigurationen avmagnetiserades med fas till neutral, då krävdes det att transformatorn avmagnetiseras två gånger för att få bort remanensen. Resultatet för Yd-konfigurationen visade ingen förbättring genom fas till fas tillvägagångssättet. Den fas som magnetiserades hade i allmänhet en något större exciteringsström än övriga faser, även efter avmagnetisering.
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Karlsson, Martin. "Improved Transformer Duality Model for Geomagnetically Induced Currents." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-234907.
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A lumped element transformer tank model has been developed for evaluating the power dis-sipation in the tank and flux distribution in the transformer when it is subjected to a DC current in the neutral. FEM simulations are performed to assist in developing a per-phase magnetically separated transformer tank model that takes into account currents induced in the tank. The tank is modeled with a reluctance network that is transformed to its electrical equiv- alent using the duality principle. The electrical equivalent lumped element transformer models are simulated using circuit simulation software. The models are subjected to a DC current in the neutral in the circuit simulation software. For the T-core transformer the tank is saturated at comparably low DC currents in the neutral. The power dissipation in the tank for DC currents in the neutral is found to be low compared to other loss components. However, the proposed per-phase models show a higher power dissipation in the tank compared to the zero-sequence tank model. Lumped element modeling provides an efficient alternative to FEM simulations for simu- lating the electromagnetic behavior of the power transformer when subjected to DC currentsin the neutral.En modell, baserad påeffektutveckling i transformatorlådan samt flödesdistribution i transformatorn när den utsätts för en DC-ström i nollan.FEM-simuleringar utförs för att assistera i utvecklandet av en per-fas magnetiskt separerad lådmodell som tar hänsyn till inducerade strömmar i lådan.Lådmodellen modelleras med ett reluktansnätverk som sedan, baserat på dualitetsprincipen, transformeras till en elektriskt ekvivalent modell.Transformatormodellernas elektriska ekvivalent, baserade på diskreta element, simuleras i ett kretssimuleringsprogram. Modellerna utsätts för en DC-ström i nollan i kretssimuleringsprogrammet. För en T-kärna mättas lådan vid relativt låga DC-strömmar i nollan. Effektutveckligen i transformatorlådan, vid DC-strömmar i nollan, visar sig vara förhållandevis låg jämfört med andra förlustkomponenter. De magnetiskt separerade modellerna visar dock en högre effektutveckling i lådan jämfört med den tidigare föreslagna nollföljdsmodellen.Modellering med diskreta element tillhandahåller ett effektivt alternativ till FEM-simuleringarför att studera transformatorns elektromagnetiska beteende vid DC-strömmar i nollan
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Lyon, David J. "Couette flow measurement of equilibrium and energization charging in transformer insulation." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/112666.
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Hwang, Jae-Won George 1980. "Elucidating the mechanisms behind pre-breakdown phenomena in transformer oil systems." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/60145.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 321-334).
The widespread use of dielectric liquids for high voltage insulation and power apparatus cooling is due to their greater electrical breakdown strength and thermal conductivity than gaseous insulators. In addition, their ability to conform to complex geometries and self-heal means that they are often of more practical use than solid insulators. Unfortunately, as with all insulation, the failure of the liquid insulation can cause catastrophic damage. This has led researchers to study the insulating properties of dielectric liquids in an attempt to understand the underlying mechanisms that precede electrical breakdown in order to prevent them. This thesis develops a set of mathematical models which contain the physics to elucidate the pre-breakdown phenomena in transformer oil and other oil-based systems. The models are solved numerically using the finite element software package COMSOL Multiphysics. For transformer oil, the results show that transformer oil stressed by a positively charged needle electrode results in the ionization of oil molecules into positive ions and electrons. The highly mobile electrons are swept back towards the positive electrode leaving a net positive space charge region that propagates towards the negative electrode causing the maximum electric field to move further into the oil bulk. It is the moving electric field and space charge waves that allow ionization to occur further into the oil. This leads to thermal dissipation and creates a low density streamer channel. In comparing the numerical results to experimental data found in the literature, the results indicate that positive streamer propagation velocity regimes or modes are dictated by the onset of different ionization mechanisms (i.e., field ionization, impact ionization, photoionization) that are dependent on the liquid molecular structure and the applied voltage stress. In particular, the field ionization of different families of molecules plays a major role in development of slow and fast mode streamers, especially in liquids that are comprised of many different types of molecules such as transformer oil. The key characteristics of the molecules that affect streamer propagation are their molecular structure (i.e., packing, density, and separation distance) and ionization potential. A direct outcome of this work has been the ability to show that by adding low ionization potential additives to pure dielectric liquids, the voltage at which streamers transition from slow to fast mode can be significantly increased, a result counter-intuitive to conventional wisdom and common practice. For transformer oil with nanoparticle suspensions (nanofluids), the effects of nanoparticle charging on streamer development have been thoroughly investigated. The charging dynamics of a nanoparticle in transformer oil show that electron trapping by conductive nanoparticles is the cause of a decrease in positive streamer velocity. resulting in higher electrical breakdown strength for transformer oil-based nanofluids. Further generalized analysis of the charging of a perfectly conducting sphere from a single charge carrier or two charge carriers of opposite polarity, with different values of volume charge density and mobility and including an ohmic lossy dielectric region surrounding a perfectly conducting sphere or cylinder are also examined. Streamer development in liquid-solid insulation systems, such as oil-pressboard systems, is also investigated. Great effort has been undertaken to model the solid insulation region and a method has been developed to model the oil-solid interface to account for surface charge build up, which is important for streamer dynamics. Various ohmic and migration conduction laws are used for oil and solid insulation to solve for the time and space development of surface charge distributions in closed form for one-dimensional parallel plane and numerically for two-dimensional geometries. The work on streamers in oil-pressboard systems has shown that streamers are attracted to the oil-pressboard interface, due to the larger permittivity of the pressboard. Moreover, the models have shown that the determination of how streamers propagate in the presence of solid insulation is strongly dependent on the extent to which the solid insulation alters the streamer shape and the electric field created by the streamer's space charge. These results obtained from the modeling of streamers in oil-pressboard systems are supported by and help to explain the experimental data in the literature.
by Jae-Won George Hwang.
Ph.D.
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Chisepo, Hilary Kudzai. "Measurements and finite element modelling of transformer flux with dc and power frequency current." Doctoral thesis, Faculty of Engineering and the Built Environment, 2019. http://hdl.handle.net/11427/31218.
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Geomagnetically induced currents (GIC’s) caused by solar storms or other sources of dc excitation in the presence of ac energization can disturb the normal operation of power transformers. If large enough, they cause half-cycle saturation of a power transformer’s core which could lead to overheating due to excessive stray flux. Finite element matrix (FEM) modelling software is of considerable use in transformer engineering as it is able to solve electromagnetic fields in transformers. For many problems, typically involving only specific parts of a transformer, fairly accurate solutions can be reached quickly. Modelling the effects of GIC or leakage currents from dc systems, however, is more complex because dc components are superimposed on ac in transformers with nonlinear electrical core steel parameters. At the beginning of the investigation, FEM models of different bench-scale laboratory transformers and a 40 MVA three-phase three limb power transformer were investigated, but the results did not sufficiently represent the measurement data due to the application of widely used modelling assumptions regarding the transformer joints. Following the preliminary analyses, practical measurements and FEM simulations were carried out using three industrially made model single-phase four limb transformers (1p4L) without tanks. These test transformers resemble a real power transformer because they have high-quality grain oriented electrical core steel and parallel winding assemblies. Practical laboratory measurements recorded during ac testing were used to calibrate 2D FEM models by adding “equivalent air gaps” at the joints. The implementation of this joint detail helped to overcome the shortcomings of the preliminary FEM simulation. Analyses of the electrical and magnetic responses of the FEM models using simultaneous ac and dc then followed. A refined 3D FEM simulation with more detailed modelling of the core joints of 1p4L model transformers agreed more closely with the practical measurements of ac only no-load conditions. Further, the depiction of stray flux leaving the transformer’s saturated core under simultaneous ac and dc excitation showed an improvement in the approach as measured in the physical model. Saturation inductance (Lsat) is an important parameter for input into mid- to low-frequency lumped parameter transformer models that are used in electromagnetic transients software such as PSCAD/EMTDC, but it is not easily measured and is seldom provided by manufacturers. Some Lsat measurements on the 1p4L test transformers are presented in this thesis, along with some 3D FEM analyses. The measurements and FEM analyses investigated “air core inductance” which represents a transformer without a core, and “terminal saturation inductance” which represents deep saturation due to dc excitation. An important finding in this thesis is that “terminal saturation inductance” is the more useful of the two for topological transformer models investigating realistic GIC excitation. Further to this, a new composite depiction of half-cycle saturation with a multi-parametric relationships supported by measurement and simulation is presented. The main contribution of this thesis is that it gives more accurately the electrical response and distribution of the leakage flux under conditions such as those caused by GIC or other sources of leakage dc excitation, as well as including of joint details in the FEM models through calibration with physical models. This calibration can aid transformer modelling and design in industry for mitigation of the effects of GICs, contributing to improved transformer survival during significant geomagnetic disturbances.
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Isumbingabo, Emma Francoise. "Evaluation and mitigation of the undesired effect of DC bias on inverter power transformer." Master's thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/5202.
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Inverters have traditionally been used mostly in standalone systems (non-grid connected), Uninterruptible Power Supplies (UPS) and, more recently, in distributed generated systems (DGs). DG systems are based on grid connected inverters and are increasingly being connected to utility grids to convert renewable energy sources to the utility grids. Such sources are likely to have a significant impact in the future in meeting the electricity demands of industry and domestic consumption. Common DGs utilize DC power sources such as fuel cells, batteries, photovoltaic (solar) power, and wind power. Most of power supplies in domestic and industries are AC power consumers and, for this reason, the DC power has to be converted to meet the requirement. Two main causes of DC current in inverter power transformer are: 1) Non-linearity and asymmetry in its switching mechanism which may result in undesired DC current at its input. This DC current introduced into an inverter transformer results in the transformer's magnetic flux distortion and in some cases magnetic saturation. This, in turn, results in asymmetrical primary currents in the transformer (inverter side). This is due to the non linear characteristics of the transformer magnetic flux. 2) The same effects can be produced by the connection of asymmetrical loads (e.g. asymmetrical rectifier) to the inverter output. The result in both cases is an asymmetrical magnetic flux in the transformer. This is manifested as even and odd current harmonics as well as an increase in the reactive power requirement from the inverter. vi To remedy this situation, it is, therefore, necessary to incorporate into the inverter's control system a mechanism of cancelling the DC magnetic motive force (mmf) that causes the magnetic flux distortion. This Thesis presents a method of introducing a DC voltage component in the inverter's voltage output so as to inject the necessary DC current into the primary side of the inverter's transformer so as to cancel the total DC mmf that the transformer is subjected to ( supply and load side). This project consists of three main parts namely: Modeling, Simulation and Laboratory Experiment. Activities undertaken under Modeling and Simulation were as follows: Determining the effects of DC current on a power transformer. Investigating the likely occurrence of saturation of the power transformer incorporated in inverter systems. Mitigating the effects that can be caused by the presence of a DC component in the windings of a power transformer. After understanding the literature on the subject of interest, MATLAB SIMULINK and MATLAB m-files were used to simulate the behavior of the power transformer under three situations : The transformer under linear load. The transformer subjected to asymmetrical loading. The inverter system that has a power transformer on its output were designed in MATLAB and used to simulate the situation for each case. To validate the theory and simulation results, experimental work was carried out as follows: vii Investigation of the effects that DC (current) injection can have on a 6 kVA power transformer. Investigation of the performance of a 6 kVA power transformer under linear loading. Investigation of the performance of a 6 kVA power transformer under non-linear loads. Investigation of the likely occurrence of DC offset in inverter system. Mitigation of the effect of DC bias on power transformer using extra windings. Mitigation of the effects of DC offset in power inverter transformer by using the second harmonic content of the primary current as a feedback signal. Results obtained showed a successful implementation of the proposed method. However limitations of the controller performances were experienced and will require future work. It was concluded that a total removal of the undesired effects of DC bias is achievable and that total removal of DC offset in power inverter transformer is possible if the limitations of the controller are overcome.
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Tuan, Abdullah Tuan Ab Rashid Bin. "Optimal management of failures, spare parts and transformer reconnections in an electrical distribution network." Thesis, University of Strathclyde, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501838.
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Tang, Qi. "Investigation of magnetic properties of electrical steel and transformer core at high flux densities." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/investigation-of-magnetic-properties-of-electrical-steel-and-transformer-core-at-high-flux-densities(d80aad50-e554-4cf0-86b5-07aa50c2f973).html.
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In a power transformer, the electrical steel core serves as a low reluctance path for the main magnetic flux linking primary and secondary windings. It is also one of the most costly components, whose properties are vital to design an efficient and reliable transformer. Normally, power transformers are predominantly operated within the linear portion of the core steel’s magnetisation curve with the maximum flux density limited at a certain value in the knee area. Nowadays, more technical challenges from the core saturation are raised, which are caused by the geomagnetically induced currents or the normal operation of Quadrature Boosters. The substantial power losses generated at such high flux densities can lead to the core overheating and consequential thermal degradation of the surrounding insulation, and even transformer failure. The characteristics of transformer core in deep saturation, however, are not readily available from measurements, and neither are the current IEC standards applicable above 1.8 Tesla for the measurement of magnetic properties of electrical steels owing to measurement difficulties, such as magnetic flux waveform stabilization. The simulation studies often need to extrapolate the steel’s magnetisation curve to high flux densities, which brings uncertainties to the results. In addition, the industry has often adopted a conservative transformer core design due to the insufficient knowledge of core loss and temperature rise under the extreme scenario. In order to fill the knowledge gap of electrical steels and transformer cores at high flux densities, this thesis uses an improved single strip test bench developed at Wolfson Centre for Magnetics to measure the magnetic properties of modern grain- oriented electrical steels up to 2.0 T under AC magnetisation up to 400 Hz. Based on the latest measurement results, a new single explicit expression is proposed to approximate and predict the AC magnetisation curve accurately over a wide range up to 2.0 T. A simple and accurate power loss separation algorithm is also proposed to identify the percentages of hysteresis loss, eddy current loss and anomalous loss, and predict the power loss at high flux densities. The finite element computational method based on Maxwell’s equations together with the measured magnetic properties of electrical steels up to 2.0 T leads to a more accurate predication for the distribution of magnetic flux and core losses in the power transformer core at high flux densities. The effects of core joint types, overlapping techniques, air gaps on the magnetic flux distribution are investigated in both 2D and 3D core corner joints. The distributions of the main flux, the leakage flux and the power loss in the core and the clamping structures are also obtained.
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Elzagzoug, Ezzaldeen. "Chromatic monitoring of transformer oil condition using CCD camera technology." Thesis, University of Liverpool, 2013. http://livrepository.liverpool.ac.uk/12233/.
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Power transformers are essential components within the power distribution system. Transformer failures having a high economic impact on the distribution operators and the industrial and domestic customers. Dielectric mineral oil is used in transformers for electrical insulation between live parts, cooling and protection of the insulation papers in the transformer. Oil contamination and changes in the chemical structure of the oil result in the decay of insulation paper and reduced insulation and cooling which can lead to a transformer failure. The general approach to oil monitoring has been for an operator to examine the colour index (ASTM) of the oil, electrical strength, acidity, water contents and dissolved gas analysis results and form an opinion as to the extent of oil degradation. Chromatic techniques enable data from di↵erent sources to be combined to give an overall evaluation about the condition of a system being monitored. One of the main goals for this work was to use chromatic techniques for integrating the oil data from the di↵erent sources and sensors. In addition the chromatic approach enables liquids to be monitored optically so a second aim was to apply chromatic optical oil monitoring using portable system by transmitting polychro- matic light through the oil sample, which is contained in a transparent cuvette and imaged using a mobile phone camera. A number of oil samples were optically analysed with portable chromatic sys- tem and the optical data was compared with the colour index and chromatically companied with the dissolved gas and other oil data to give overall evaluation of oil degradation. The chromatic optical result compared favourably with the colour index. It was also possible to classify the oil samples chromatically into categories of low, medium and high degradation. This enabled the chromatic data combination approach to be implemented as a prototype system in Matlab software that an operator could use to get a classification of an oil sample. Essential experiment was introduced to monitor di↵erent oil particles by obtaining the result of di↵erent filtered samples through the filter paper. Beside the ability to analyse data and distinguish between fresh and contam- inated oil samples the chromatic technique has the ability to track the history of di↵erent degraded oil samples which can give an indication about failure faults and it could give a prediction of any future faults. Therefore a commercially viable reliable system can be developed to extend the service life and extend the maintenance schedules. These monitoring systems could lead to extending the service life of the transformers, making the electricity supply more reliable and giving the consumer a better quality of life.
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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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Ogunnika, Olumuyiwa Temitope 1978. "A simple transformer-based resonator architecture for low phase noise LC oscillators." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/28338.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2004.Includes bibliographical references (leaves 86-87).
This thesis investigates the use of a simple transformer-coupled resonator to increase the loaded Q of a LC resonant tank. The windings of the integrated transformer replace the simple inductors as the inductive elements of the resonator. The resonator topology considered in this project is a simpler alternative to another proposed by Straayer et al [5] because it just requires a single varactor. A prime objective of this project is to prove that a transformer-coupled resonator which is simpler than that proposed by Straayer in [5] produces the same reduction in phase noise. The use of this type of resonator topology is a valuable technique which can be employed by RF engineers to reduce the phase noise generated by oscillators in high speed RF systems. Such techniques which increase the loaded Q of the resonator are very useful in practice because of the inverse squared relationship between resonator Q and the phase noise in the output signals of LC oscillators. The important aspect of this technique is that magnetic coupling between the windings of an integrated transformer increases their effective inductance while leaving their series resistance relatively unchanged. As a result, the Q of these inductive elements is increased and the phase noise generated by the oscillator is reduced. SpectreRF simulations of an LC oscillator with a center frequency of 5GHz were used to verify the performance of the proposed transformer-coupled resonator.
by Olumuyiwa Temitope Ogunnika.
S.M.
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Du, Yanqing 1971. "Moisture and temperature effects on the dielectric spectrum of transformer insualtion materials." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/39634.
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Thesis (S.M. and Elec.E.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (p. 139-143).
The presence of moisture in a transformer deteriorates the transformer insulation by decreasing its electrical, mechanical, and thermal strength. Therefore it is of great importance to monitor the moisture condition in both liquid and solid insulation to assure transformer performance. There are commercially available sensors to measure the moisture in oil. When the transformer system is in equilibrium, existing moisture partitioning curves for oil-paper system can be used to find the moisture in paper from the oil measurement. A comprehensive study of the moisture equilibrium curves are given for an overview of the classic curves and their history, and providing useful information on the relationships among them and their validity. Solubility tests for differently conditioned oil are performed. Results show the solubility of moisture in oil increases significantly only in severely aged transformer oil. When the system is not in equilibrium, the moisture curves are not applicable and the three-wavelength interdigital dielectrometry sensor developed at the MIT Laboratory for Electromagnetic and Electronic Systems is a unique way to measure the spatial profile of the moisture distribution in transformer pressboard. Preliminary measurements of oil and oil-impregnated pressboard are given in this thesis. A joint research group effort led to development of an improved design of the three-wavelength sensor which reduces the problems associated with the previous design and simplifies the inversion algorithm to convert the electrical signal to dielectric properties. The thesis focuses on the design and implementation of experimental studies based on interdigital dielectrometry using the new three-wavelength sensor. As a first step to relate measurable dielectric properties to absorbed moisture, the moisture and temperature effects on the dielectric spectrum of oil-free pressboard are measured using a parallel-plate geometry sensor for nine moisture levels and five temperature levels. A dielectric model for biological tissue is adopted here for cellulose structured pressboard. A universal curve is found relating dielectric properties to moisture concentration and temperature by fitting the data to the model. Preliminary measurements of oil-impregnated pressboard show similar characteristics. The moisture diffusion process of oil-free transformer pressboard is monitored using the new interdigital dielectrometry three-wavelength sensor in a specially constructed bench-top apparatus. Experiments are performed for five different temperatures at various moisture levels. The time evolution of the moisture spatial profile in transformer pressboard is estimated non-destructively. Experimental results have a good agreement with theoretical analysis on the effects of pressboard thickness and temperature on the diffusion process. The diffusion coefficient for oil-free pressboard as a function of temperature and moisture concentration is estimated and compared with literature values. Numerical methods of solving the diffusion equation are developed.
by Yanqing Du.
S.M.and Elec.E.
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Iuravin, Egor. "Transformer Design For Dual Active Bridge Converter." Miami University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=miami1532601248778308.
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Davoodi, Samirmi Farhad. "Multi-agent and knowledge-based system for power transformer fault diagnosis." Thesis, University of Liverpool, 2013. http://livrepository.liverpool.ac.uk/14455/.
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Transformer reliability and stability are the key concerns. In order to increase their efficiency, an automatic monitoring and fault diagnosing of the power transformers are required. Dissolved Gas Analysis (DGA) is one of the most important tools to diagnose the condition of oil-immersed transformer. Agents technology as a new, robust and helpful technique, successfully applied for various applications. Integration of the Multi-Agent System (MAS) with knowledge base provides a robust system for various applications, such as fault diagnosis and automated actions performing, etc. For this purpose, the present study was conducted in the field of MAS based on Gaia methodology and knowledge base. The developed MAS followed by Gaia methodology represents a generic framework that is capable to manage agents executions and message delivery. Real-time data is sampled from a power transformer and saved into a database, and it is also available to the user on request. Three types of knowledge-based systems, namely the rule-based reasoning, ontology and fuzzy ontology, were applied for the MAS. Therefore, the developed MAS is shown to be successfully applied for condition monitoring of power transformer using the real-time data. The Roger’s method was used with all of the knowledge-based systems named above, and the accuracy of the results was compared and discussed. Of the knowledge-based systems studied, fuzzy ontology is found to be the best performing one in terms of results accuracy, compared to the rule-based reasoning and ontology. The application of the developed fuzzy ontology allowed to improve the accuracy by over 22%. Unlike the previous works in this field, that were not capable of dealing with the uncertainty situations, the present work based on fuzzy ontology has a clear advantage of successfully solving the problem with some degree of uncertainty. This is especially important, as the most of the real-world situations involve some uncertainty. Overall, the work contributes the use of the knowledge base and the multi-agent system for the fault diagnosis of the power transformer, including the novel application of fuzzy ontology for dealing with the uncertain situations. The advantages of the proposed method are the ease of the upgrade, flexibility, efficient fault diagnosis and reliability. The application of the proposed technique would benefit the power system reliability, as it would result in reduction of the number of engineering experts required, lower maintenance expenses and extended lifetime of power transformer.
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Gong, Qiuming. "PEV Charging Control Considering the Distribution Transformer Life." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1354550558.
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Endo, Fumihiro, Shinpei Yamamoto, Takayuki Sadakane, Akira Yamagishi, Katsunori Miyagi, and Hitoshi Okubo. "Analysis of Gasses Generated by Electrical Discharges in Low Viscosity Silicone Oil." IEEE, 2008. http://hdl.handle.net/2237/11797.
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Hägerbrand, Jonathan. "Measurements of resistivity in transformer insulation liquids." Thesis, Uppsala universitet, Institutionen för elektroteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-413804.
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This thesis focuses on measuring techniques and results of resistivity in four commercially available insulating transformer oils: mineral oil, ester oil and two isoparaffin oils. Two measuring techniques, the industrially used diagnostic system for electrical insulation IDA and the Labview implemented Triangular Method, are used for resistivity measurements and the techniques are compared, a correction algorithm to the triangular method is suggested. Dielectric properties of mineral & ester and isoparaffin A&B mixtures are investigated, it is experimentally shown that the transformer oils that show high resistivity also show low loss factor. The effect moisture has on resistivity in mineral and ester oil are shown both in terms of relative humidity and actual water content in parts per million. A previous measurement cell is redesigned, the cell is manufactured in copper and gold. It is found that the material choice of the cell significantly affects the resistivity measurements. The electrical double layer and contact resistance between the oil and cell are investigated as a way to explain the difference in measured resistivity. These experiments are limited to the mineral oil and isoparaffin oil A, it is found that contact resistance is a plausible explanation. The electrical double layer is fairly constant for both oils and the Debye length of the double layer is negligible compared to the total distance between the electrodes of the cell. Lastly, the field of insulating transformer oils and its future is discussed, from data obtained regarding the dielectric properties and environmental aspects of the four transformer oils used in this study. A positive trend which combines the high insulating properties with good biodegradability qualities is found. Suggesting a positive future in the field of insulating transformer oils. The results found in this thesis can be used as a basis for future theses regarding transformer oils used for HVDC applications.
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Von, Guggenberg Philip A. (Philip Antony). "Applications of interdigital dielectrometry to moisture and double layer measurements in transformer insulation." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12735.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1993.Includes bibliographical references (p. 339-348).
by Philip A. von Guggenberg.
Ph.D.
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Li, Patrick. "Low frequency, millimeter wavelength, interdigital dielectrometry of insulating media in a transformer environment." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14818.
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Balehosur, Manjunath. "Prediction of no-load losses of stacked 3-phase, 3-limb transformer cores." Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/51925/.
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The work presented in this thesis can be utilised by electrical steel manufacturers and transformer designers to design energy efficient transformer cores possessing lower life cycle costs, thereby increasing financial gains. A novel computer based algorithm to predict losses of 3-phase, 3-limb transformer cores built with high permeability grain oriented steel (HGO) and conventional grain oriented steel (CGO) is presented. The algorithm utilises parameters like transformer geometry, global flux distribution, localised loss data and material properties thus enhancing the accuracy of the predicted results which were 1% of the measured values. This algorithm has contributed to new knowledge in the no-load loss prediction approach. Six, geometrically identical, 350 kVA stacked five packet 3-phase, 3-limb transformer cores assembled with HGO, CGO and four mixed combinations of HGO and CGO laminations in multi step lap (MSL) joint configuration were tested for the global flux density distribution and no-load loss. The investigation results are novel and suggest that the bolt hole diameter (slot width) and lamination width ratio affects the packet to packet variation of . This is a new contribution to the flux distribution regime in transformer cores. The no-load loss experimental results are novel and suggest that the variation of no-load losses with CGO content in mixed cores was non-linear because of the packet to packet variation of . This is a new contribution of knowledge in the field of mixed core loss behaviour. Novel data sets of localised specific loss increase and localised relative permeability decrease around different sizes of holes and slots for HGO and CGO were processed from data obtained by two dimensional finite element (FE) analysis. The data sets are a new contribution in the field of predicting localised magnetic properties around holes and slots.
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Du, Yanqing 1971. "Measurements and modeling of moisture diffusion processes in transformer insulation using interdigital dielectrometry sensors." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/16725.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Vita.
Includes bibliographical references (p. 307-316).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
The presence of moisture in a transformer deteriorates the transformer insulation by decreasing its electrical, mechanical, and thermal strength. Therefore, it is important to monitor the moisture condition in both liquid and solid insulation to assure transformer performance. There are commercially available sensors to measure the moisture in oil. When the transformer system is in equilibrium, moisture partitioning curves for the oil-paper system can be used to find the moisture in paper from the oil measurement. A comprehensive study of the classic moisture equilibrium curves is given, historical mistakes are corrected, and all relevant concepts are clarified. This research serves as a useful tool to utilities and manufacturers. A new set of moisture equilibrium curves is constructed for moisture in oil up to the saturation moisture content. A measurement technique exploiting the linearity between the relative humidity of the oil and the moisture content of the oil to indirectly measure the oil solubility is developed. Solubility tests are performed for differently conditioned oils: Fresh Shell Diala AX oil, lab-aged Shell Diala A oil, used oil from Ramapo Substation, and used oil from Texas Utilities. Results show that aging under normal operation at service temperature is not very likely to significantly change the water solubility. When the system is not in equilibrium, the equilibrium moisture curves are not applicable and the three-wavelength interdigital dielectrometry sensor developed at the MIT Laboratory for Electromagnetic and Electronic Systems provides a unique way to measure the spatial profile of the moisture distribution in transformer pressboard.
(cont.) reduces the problems associated with the previous design and simplifies the inversion algorithm to convert the sensor signal to dielectric properties. The thesis focuses on the design and implementation of experimental studies based on interdigital dielectrometry using the new three-wavelength sensor. As a first step to relate measurable dielectric properties to absorbed moisture, the moisture and temperature effects on the dielectric spectrum of oil-free pressboard are measured using a parallel-plate electrode sensor for nine moisture levels and five temperature levels. A dielectric model for biological tissue is adopted here for cellulose structured pressboard. A universal curve is found relating dielectric properties to moisture concentration and temperature by fitting the data to the model. Preliminary measurements of oil-impregnated pressboard show similar characteristics. The moisture diffusion process in oil-free transformer pressboard is monitored using the new interdigital dielectrometry three-wavelength sensor in a specially constructed bench-top apparatus. Experiments are performed for five different temperatures at various moisture levels. The time evolution of the moisture spatial profile in transformer pressboard is non-destructively estimated.
Experimental results show good agreement with theoretical analysis of the moisture diffusion equation on the effects of moisture level, pressboard thickness, and temperature on the diffusion process. The diffusion coefficient for oil-free pressboard as a function of temperature and moisture concentration is estimated. Numerical algorithms for solving the non-linear diffusion equation arederived. Literature results of the diffusion coefficient for cellulose insulation are compared and analyzed. The interdigital sensor setup is also combined in a transformer oil Couette Facility that simulates the transformer environment for studying temperatureand moisture transients in pressboard. The understanding of moisture-related processes in power transformers can be enhancedwith this methodology. Finally, a newly promoted in-situ time-domain measurement technique is implemented using the Tettex Recovery Voltage Meter. Time domain measurements are performed for oil-impregnated pressboard in both parallel-plate andcoaxial cylinder electrode geometries (the Couette Facility). The results for temperature and aging effects show good agreementwith theory.
by Yanqing Du.
Ph.D.
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Kurupakorn, C., H. Kojima, N. Hayakawa, F. Endo, N. Kashima, S. Nagaya, M. Noe, and H. Okubo. "Simulation of electrical and thermal behavior of high temperature superconducting fault current limiting transformer (HTc-SFCLT)." Institute of Physics, 2006. http://hdl.handle.net/2237/9147.
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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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