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Current source converters for extraction of power from HVAC linesJanse van Rensburg, Johannes Frederik 11 1900 (has links)
Thesis (D. Tech. Engineering : Electrical ; Dept. Applied Electronics and Electronic Communications) -- Vaal University of Technology / Two methods to convert an AC current source to an AC voltage source are presented.
Both methods make use of a current transformer to provide energy extraction from
the main system while maintaining galvanic isolation between the main system and
the output system. Control is via a pulse width modulation scheme in both instances.
The ftrst method uses a storage element to provide a DC voltage, which feeds an
inverter that supplies the AC load with a voltage source. The second method does
not use a storage element but is a direct AC current source to AC voltage source
converter employing a current transformer. This has not been done before.
A possible application of this study is in the extraction of power from high voltage
transmission lines without the conventional substation and rural grid to supply small
users such as the telecommunication industry.
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Investigation into the correlation between paper insulation thermal ageing estimation using the arrhenius equation and other methods for generator transformersMetebe, Michael Tebogo January 2015 (has links)
A dissertation submitted to the Faculty of Engineering and the Built
Environment, University of the Witwatersrand, in fulfilment of the requirements
for the degree of Master of Science in Engineering
Date submitted: 28 August 2015 / Many generator transformers were installed many years ago during the initial
commissioning of Eskom’s power stations. Many of these transformers have started
showing signs of significant ageing of the paper insulation and hence require regular
monitoring. There are two methods that are currently being employed to assess the
degree of ageing of the paper insulation in a generator transformer, which are paper
sampling and furan level measurement.
This dissertation investigates an alternative method of predicting the degree of ageing of
the paper insulation instead of what is used currently. This method uses the Arrhenius
equation that relates time and temperature to determine the degree of degradation of
organic materials. The reliability of the Arrhenius estimation method is assessed by
comparing the predicted DP (Degree of polymerisation) values with the measured DP
values of the same transformer paper insulation.
The results obtained showed that there is reasonable correlation between the DP values
estimated from the Arrhenius equation and the DP values estimated from the measured
furan levels.
The accuracy of the prediction method is reduced when the oil temperature
greatly differs from the paper insulation temperature.
The application of the Arrhenius equation to estimate the ageing of paper insulation is a
great milestone in the quest to predict the remaining life of a transformer. It is the only
method available to do this prediction and using online temperature measurement on
transformers makes the method more reliable. / MT 2017
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Life assessment and life extension of high voltage equipment in transmission substations.Singh, Omchand. January 2004 (has links)
In order to sustain transmission grid availability and reliability it is imperative that the
condition of vital and costly high voltage equipment is ascertained on a continuous or
regular basis. It is necessary to establish the effective diagnostic tools or surveillance
devices that can be used to assess equipment condition.
Emphasis has been placed on refining well-established and more novel but
developing condition assessment techniques. It is important to note that condition
assessment of equipment also allows the opportunity to predict failure. Based on a
complete and systematic assessment, the failure of defective equipment may be
evident or predicted in time, thus preventing a forced outage and loss of valuable
'system minutes'. It has also become necessary to extend the life of existing
equipment since most of them are reaching the end of their useful life. Replacement
strategies have proven to be ineffective due to financial and resource constraints
experienced by utilities.
Life extension is the work required to keep equipment operating economically beyond
its anticipated life, with optimum availability, efficiency and safety. One of its principal
components is condition assessment, with the possibility of predicting remnant life.
As a result, refurbishment projects are then raised. Refurbishment by replacement,
uprating, modifications or change of design of certain key components to extend the
life usually requires a substantial amount of capital to be invested. These projects
must be economically justified.
This thesis focuses on establishing condition assessment techniques for major power
equipment such as power transformers. Assessment techniques for instrument
transformers and circuit breakers are included, since these are commonly replaced
or modified under refurbishment projects.
An experimental investigation was carried out to determine the effectiveness of
integrating data of two diagnostic techniques i.e. dissolved gas analysis (on-line) and
acoustic detection of partial discharges. It was found that there is a correlation
between data obtained from an acoustic detection system and an on-line single gas
(Hydrogen) analyser. By integrating the data of both on-line monitoring systems, the
diagnostic process is further enhanced. In addition, the location of a fixed discharge
source was verified by using an acoustic detection system. Further, the sensitivity of
the acoustic technique to partial discharge inception voltage, relative to the
established electrical detection technique was determined for the experimental
arrangement used. The results obtained indicated that this is an effective technique
for the evaluation of activity within a transformer structure. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2004.
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Carregador de baterias bidirecional com tranformador planarRocha, Fabio Dalla Vecchia 27 August 2013 (has links)
CAPES / Este trabalho traz um estudo da aplicação do conversor Full-Bridge bidirecional como um carregador de banco de baterias em um barramento CC de fontes de energia renováveis. O problema principal destas fontes é que são sazonais e não oferecem uma continuidade de fornecimento de potência. Assim, o uso de banco de baterias, conectado a um barramento CC compartilhado com outras fontes renováveis traz contribuições na continuidade do fornecimento de energia. O conversor proposto neste trabalho visa conectar o banco de baterias ao barramento CC e ao mesmo tempo que faz a integração dos modos de carga e descarga em um único conversor. Adicionalmente, para reduzir volume, é utilizado um transformador planar que oferece alta eficiência (máximo de 99,5%) e uma reduzida relação volume/potência. O conversor foi desenvolvido para carregar um banco de baterias de 192V. No modo de descarga, ele é suado para alimentar um barramento CC de 400V com uma potência máxima de 1,34kW. Apesar do uso do conversor full-bridge não ser novidade nestes tipos de aplicação, dois fatores serviram de motivação para este trabalho: o uso do transformador planar e a tendência mundial de integração de fontes renováveis. / This work presents a study of the application of the Full-bridge bidirectional DC converter as a battery bank charger in a DC bus of renewable energy sources. The main problem is that these sources are seasonal and do not offer a continuously power supply. Thus, the use of a battery bank connected to a DC bus shared with other renewable sources brings contributions in the continuity of power supply. The converter proposed in this work aims to connect the battery bank to the DC bus at the same time it integrates the charging and discharging modes into a single converter. Additionally, to reduce the volume, it is used a planar transformer that provides high efficiency (up to 99.5%) and a reduced volume/power ratio. The converter is designed to charge a bank of batteries of 192V. At the discharge mode, it is designed to feed a 400V DC bus with maximum power of 1.34 kW. Despite the use of the full-bridge converter is not new in these types of application, two factors served as motivation for this work: the use of planar transformer and the global trend of integration of renewable sources.
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Carregador de baterias bidirecional com tranformador planarRocha, Fabio Dalla Vecchia 27 August 2013 (has links)
CAPES / Este trabalho traz um estudo da aplicação do conversor Full-Bridge bidirecional como um carregador de banco de baterias em um barramento CC de fontes de energia renováveis. O problema principal destas fontes é que são sazonais e não oferecem uma continuidade de fornecimento de potência. Assim, o uso de banco de baterias, conectado a um barramento CC compartilhado com outras fontes renováveis traz contribuições na continuidade do fornecimento de energia. O conversor proposto neste trabalho visa conectar o banco de baterias ao barramento CC e ao mesmo tempo que faz a integração dos modos de carga e descarga em um único conversor. Adicionalmente, para reduzir volume, é utilizado um transformador planar que oferece alta eficiência (máximo de 99,5%) e uma reduzida relação volume/potência. O conversor foi desenvolvido para carregar um banco de baterias de 192V. No modo de descarga, ele é suado para alimentar um barramento CC de 400V com uma potência máxima de 1,34kW. Apesar do uso do conversor full-bridge não ser novidade nestes tipos de aplicação, dois fatores serviram de motivação para este trabalho: o uso do transformador planar e a tendência mundial de integração de fontes renováveis. / This work presents a study of the application of the Full-bridge bidirectional DC converter as a battery bank charger in a DC bus of renewable energy sources. The main problem is that these sources are seasonal and do not offer a continuously power supply. Thus, the use of a battery bank connected to a DC bus shared with other renewable sources brings contributions in the continuity of power supply. The converter proposed in this work aims to connect the battery bank to the DC bus at the same time it integrates the charging and discharging modes into a single converter. Additionally, to reduce the volume, it is used a planar transformer that provides high efficiency (up to 99.5%) and a reduced volume/power ratio. The converter is designed to charge a bank of batteries of 192V. At the discharge mode, it is designed to feed a 400V DC bus with maximum power of 1.34 kW. Despite the use of the full-bridge converter is not new in these types of application, two factors served as motivation for this work: the use of planar transformer and the global trend of integration of renewable sources.
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Signal Processing Tools To Enhance Interpretation Of Impulse Tests On Power TransformersPandey, Santosh Kumar 10 1900 (has links) (PDF)
No description available.
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Core loss characterization and design optimization of high-frequency power ferrite devices in power electronics applicationsGradzki, Pawel Miroslaw 06 June 2008 (has links)
An impedance-based core loss measurement technique for power ferrites, the modeling and analysis of mechanisms of high-frequency losses, and design methodology for optimization for high-frequency magnetics are presented.
The high-frequency losses of ferrite materials are characterized employing a large-signal impedance measurement technique. The impedance analyzer controlled through an IEEE-488 interface, measures the impedance of the inductor under test under large signal excitation via a power amplifier. The core loss is a form of a parallel resistance is derived from measured impedance characteristics. A wideband impedance probe, enables core loss characterization up to 100 MHz.
A comprehensive analysis of all major loss mechanisms in ferrites is presented. A new form of residual losses due to a magnetoelectric effect is postulated to account for losses at high frequencies. Two models of losses in ferrites are proposed, one with emphasis on analysis of loss mechanisms, and the other with an emphasis on the design of high-frequency magnetic components. Both models include the important effect of static bias field, which is the case in many power electronics applications. Magnetic losses due to magnetostriction are measured. Dependence of magnetoelastic resonances on the magnetic bias. core material, core shape and size is studied. The influence of diffusion after-effect on core loss under time-varying bias field is investigated.
Thermal stability of high-frequency magnetics is studied. A verification of one- and two- dimensional models of winding losses for solid and litz wire is performed. The optimum design method for high-frequency power transformers and inductors is proposed. / PhD
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Wide-band modelling of an air-core power transformer windingVan Jaarsveld, Barend Jacobus 12 1900 (has links)
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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Software para desenvolvimento de transformadores para equipamentos de eletrocirurgiaPaula, Jhonisson Ricardo de 20 September 2012 (has links)
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Este trabalho propõe e implementa um software que realiza o cálculo de vários modelos de transformadores de instrumentação e orienta o usuário em como efetuar medições e correções importantes nos mesmos. O software engloba transformadores de baixa e média potência, até 500 W, e com frequências de até alguns megahertz. O software cobre 3 modelos: o clássico quadripolo de baixa potência e baixa frequência; o quadripolo T com capacitor de saída para baixa potência e média frequência; e o modelo delta-estrela completo, para transformadores eletrônicos de alta frequência. O trabalho teve como objetivo criar uma ferramenta para o projeto de transformadores, especialmente transformadores de saída de instrumentação biomédica, como por exemplo, o transformador de saída do bisturi eletrônico. O software indica o modelo de acordo com os dados de entrada ou por escolha do usuário. O software foi criado para uso gratuito e foi desenvolvido em código Java, de modo que qualquer pessoa interessada possa usá-lo. Por suas características, o software pode trabalhar em todos os computadores, desktops ou celulares, e em quase todos os sistemas operacionais, basta que o usuário tenha a máquina virtual Java instalada em seu hardware. O usuário deve inserir os coeficientes necessários para realizar os cálculos, obtendo os resultados numéricos e gráficos do módulo da impedância versus frequência e de fase versus frequência na tela ou em um arquivo de dados no formato CSV (comma-separated values). O módulo de saída gráfica apresenta o módulo e a fase da impedância de entrada (Zin) em função da frequência. Isto permite ao usuário ver as ressonâncias e comportamentos característicos do transformador e tomar providências para executar um projeto conforme suas necessidades. / This work describes a software that performs calculation and gives some tips about building and measuring transformers parameters up to 500 W till a few megahertz. The software emulates 3 models: the classical T model for low power and low frequency; the T model with output capacitance; and the complete delta-star model, for high frequency electronic transformers. This work aimed to create a tool for design of transformers, especially biomedical instrumentation output transformers, like the output electrosurgical device transformer. Tips like, for example, how to wrap the secondary coil to minimize intrinsic capacitance are presented to the software user. The software indicates the model according to input data or by user choice. The software is for free use and is programmed in Java language, so that, any person interested can use it. It will be available on the internet for free download. This software can work on all computers, desktops or mobiles, and on almost all operating systems, as long as the user has the virtual machine in his hardware. The user must insert the coefficients required to perform the calculations. After this insertion he must click on the calculation button, so the results and the impedance (modulus and phase) versus frequency graphs are seen on the screen. The user can additionally export an XY CSV (comma-separated values) data file. The software graphical output modulus and phase parts shows behavior of the input impedance (Zin) versus frequency. This makes possible for the user see the resonances and characteristic behavior of the transformer.
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Software para desenvolvimento de transformadores para equipamentos de eletrocirurgiaPaula, Jhonisson Ricardo de 20 September 2012 (has links)
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Este trabalho propõe e implementa um software que realiza o cálculo de vários modelos de transformadores de instrumentação e orienta o usuário em como efetuar medições e correções importantes nos mesmos. O software engloba transformadores de baixa e média potência, até 500 W, e com frequências de até alguns megahertz. O software cobre 3 modelos: o clássico quadripolo de baixa potência e baixa frequência; o quadripolo T com capacitor de saída para baixa potência e média frequência; e o modelo delta-estrela completo, para transformadores eletrônicos de alta frequência. O trabalho teve como objetivo criar uma ferramenta para o projeto de transformadores, especialmente transformadores de saída de instrumentação biomédica, como por exemplo, o transformador de saída do bisturi eletrônico. O software indica o modelo de acordo com os dados de entrada ou por escolha do usuário. O software foi criado para uso gratuito e foi desenvolvido em código Java, de modo que qualquer pessoa interessada possa usá-lo. Por suas características, o software pode trabalhar em todos os computadores, desktops ou celulares, e em quase todos os sistemas operacionais, basta que o usuário tenha a máquina virtual Java instalada em seu hardware. O usuário deve inserir os coeficientes necessários para realizar os cálculos, obtendo os resultados numéricos e gráficos do módulo da impedância versus frequência e de fase versus frequência na tela ou em um arquivo de dados no formato CSV (comma-separated values). O módulo de saída gráfica apresenta o módulo e a fase da impedância de entrada (Zin) em função da frequência. Isto permite ao usuário ver as ressonâncias e comportamentos característicos do transformador e tomar providências para executar um projeto conforme suas necessidades. / This work describes a software that performs calculation and gives some tips about building and measuring transformers parameters up to 500 W till a few megahertz. The software emulates 3 models: the classical T model for low power and low frequency; the T model with output capacitance; and the complete delta-star model, for high frequency electronic transformers. This work aimed to create a tool for design of transformers, especially biomedical instrumentation output transformers, like the output electrosurgical device transformer. Tips like, for example, how to wrap the secondary coil to minimize intrinsic capacitance are presented to the software user. The software indicates the model according to input data or by user choice. The software is for free use and is programmed in Java language, so that, any person interested can use it. It will be available on the internet for free download. This software can work on all computers, desktops or mobiles, and on almost all operating systems, as long as the user has the virtual machine in his hardware. The user must insert the coefficients required to perform the calculations. After this insertion he must click on the calculation button, so the results and the impedance (modulus and phase) versus frequency graphs are seen on the screen. The user can additionally export an XY CSV (comma-separated values) data file. The software graphical output modulus and phase parts shows behavior of the input impedance (Zin) versus frequency. This makes possible for the user see the resonances and characteristic behavior of the transformer.
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