Uma série de equipamentos de eletrônica de potência é ligada à rede de corrente alternada através de transformadores, que exercem as funções de isolamento galvânico, elevação/abaixamento de tensão, etc. Estes transformadores podem sofrer saturação em condições transitórias (inrush) ou quando o conversor ligado a ele impõe valor médio não nulo de tensão. O problema é normalmente sanado nas malhas de controle do conversor, no entanto o ajuste destas malhas em ambiente de simulação computacional requer um modelo que represente adequadamente a característica de saturação do núcleo ferromagnético. Este trabalho apresenta um modelo de simulação computacional adequado para transformadores operando em saturação intensa, visando aplicações em projetos de equipamentos de eletrônica de potência com transformador monofásico alimentado por inversor. Além disso, é demonstrado um método experimental de obtenção da característica de saturação do núcleo, sem necessidade das suas características construtivas. Resultados de simulação obtidos são comparados com resultados experimentais para validação do modelo e método. / Several power electronics based equipments are connected to the alternating current network through transformers, which perform galvanic insulation, voltage increasing/lowering, etc. These transformers may experience saturation under transitory conditions (inrush), or when its converter imposes non-zero average voltage. Such problem is commonly treated in the converter\'s control loops, but the tuning of these loops in a computer simulation environment requires a transformer model that represents adequately the ferromagnetic core saturation effect. The current work proposes a computer simulation model that adequately describes the operation of the transformer at deep saturation, suitable for design of power electronics applications with single phase transformers connected to power inverter. Additionally, an experimental method for determining its core saturation characteristic is demonstrated. This method does not require previous knowledge of the core\'s constructive parameters. Simulation and experimental results are presented to confirm the validity of the model and the method.

The research concerns the design and implementation of mechatronic systems to assist in the operation and control of a sugar cane harvester. Two functions were chosen for attention, the primary separation system, and the ‘topper’ that discards the leafy crown. Although these operations are given low priority by the operator of the harvester, their optimisation is of particular significance to the industry. Optimum separation requires a fine balance between discarding ‘trash’ that would contaminate the quality of the cane billets and losing good sugar-bearing material through over cleaning. Poor control of the topper can create extra load for the separation system and cause it to operate at a low efficiency with high loss. Alternatively it can cause a length of sugar-bearing cane stalk to be lost before it even enters the harvester system at all. A variety of mechatronic techniques were explored, that addressed the problem of providing useful data directly from the harvester functions and the electronic instrumentation to allow the data to be collected in a useful form in real-time. Computer control issues were also investigated, to make best use of the data stream. Novel acoustic transducers were introduced to the sensory separation system to provide a signal that indicated material striking the fan blades. A rotary transformer was required to allow transmission of the signal, and a signal interface system was implemented to record the returned data. Many real-time time-series analyses were conducted, and from these a suitable algorithm to extract an impact signal was developed. This system was assessed under harvesting conditions with results that confirmed its ability to quantify the amount of cane lost from the harvest. An investigation was conducted to detect the optimum topping height on a sugar cane stalk. The techniques considered both the internal and external attributes of the stalk, and a method was selected to measure the sugar concentration with a chemical sensor. An important design parameter was that the sensor must operate on the harvester in real time. The novel refractometer worked well in laboratory conditions, yielding repeatable and accurate results. The field environment complicated the application of this system, however this was partly overcome with introduction of a custom sample-crushing mechanism. This device provided the necessary juice sample from a selection of the topped cane stalks. The complete sampling and measuring mechanism operated well on cane stalks, and returned encouraging results. Both sets of data returned useful information regarding the operation of the particular harvester operations. The control of either the separation system or the topper requires careful balancing, and novel control techniques that consider the ergonomics for the operator are discussed. These include visual indication devices through to automatic control algorithms. With the integration of mechatronic techniques into the functioning of the sugar cane harvester, the overall efficiency of many of its functions may be improved, and the operator’s task may be greatly simplified. The ultimate objective is to maximise the yield with an improved level of harvested and separated cane.

Floating feeder resonances are one of the new challenges being put forward by the renewable energy based distributed generation (DG) installations. Generally, the harmonic injection from DGs are within IEEE standard 519-1992 limits. Although the harmonics are within the IEEE limits, they are a potential threat to power equipment’s insulation system integrity due to floating feeder resonances. There is a reasonable probability that at some point in time the feeder resonant frequency may coincide with one of the injected harmonics. Such phenomenon amplifies the specific harmonic causing additional stress on the equipment’s insulation system. In this thesis a feeder resonance study is done on the IEEE 34 bus distribution feeder to show the resonance shift problem in a DG loaded distribution feeder. Electric field study is then carried out on transformer winding to assess the dependence of electric field on harmonic distortion. At first the acoustic emission (AE) technique is employed to identify the change in the electric field distribution inside the winding at higher frequency. The AE technique together with the acoustic waveguide is utilized to locate the partial discharges under power frequency and high frequency operation. The results show a change in partial discharge (PD) location, which implies that the electric field redistributes in the transformer winding at higher frequency In order to further understand the electric field distribution, a high voltage air core coil is modeled by R, L and C ladder network. The R, L and C parameters are solved by finite element method and finally the electric field is calculated by computing the node potentials in the ladder network at various frequencies. The electric field results show that at high frequency distortion the electric stress enhances between fourth and fifth layer of the winding which may give rise to a PD activity; hence degrading the insulation. An aging experiment is also performed to understand the impact of high frequency distortion on transformer paper insulation. Paper samples are taken from a field aged transformer. They are aged for 72 hours under power frequency and various distorted waveforms. Dissipation factor is used as a comparison tool for paper samples before and after aging. Results show that paper samples aged under distorted waveforms showed a double increase in dissipation factor compared to the samples aged under power frequency.

Instrument transformers are a crucial component of power system protection. They supply the protection system with scaled-down replicas of current and voltage signals present in a power network to the levels which are safe and practical to op- erate with. The conventional instrument transformers are based on electromagnetic coupling between the power network on the primary side and protective devices on the secondary. Due to such a design, instrument transformers insert distortions in the mentioned signal replicas. Protective devices may be sensitive to these distortions. The inuence of distortions may lead to disastrous misoperations of protective devices. To overcome this problem, a new instrument transformer design has been devised: optical sensing of currents and voltages. In the theory, novel instrument transform- ers promise a distortion-free replication of the primary signals. Since the mentioned novel design has not been widely used in practice so far, its superior performance needs to be evaluated. This poses a question: how can the new technology (design) be evaluated, and compared to the existing instrument transformer technology? The importance of this question lies in its consequence: is there a necessity to upgrade the protection system, i.e. to replace the conventional instrument transformers with the novel ones, which would be quite expensive and time-consuming? The posed question can be answered by comparing inuences of both the novel and the conventional instrument transformers on the protection system. At present, there is no systematic approach to this evaluation. Since the evaluation could lead to an improvement of the overall protection system, this thesis proposes a comprehensive and systematic methodology for the evaluation. The thesis also proposes a complete solution for the evaluation, in the form of a simulation environment. Finally, the thesis presents results of evaluation, along with their interpretation.

This thesis is mainly composed of two parts. The first part is to introduce the planar transformer-based circuits and their applications. The mixed-mode S parameters and the grounding effects for planar transformers are discussed. A physical model has been developed for modeling the planar transformers. In the second part, a new coil winding technique for planar transformers has been presented to realize a high-efficiency planar transformer with arbitrary turn ratio for power-split/combine and phase-shift applications. Especially, the power-split/combine architecture based on a planar transformer of cellular shape is first presented in this thesis, enabling various kinds of passive components to be widely realized using the integrated passive device processes. As an example, this thesis proposes a design procedure for high-efficiency balun component. Firstly, design a high Q transformer that considers the load impedance effects. Secondly, design the ground reference for un-balanced signal on the virtual ground symmetry axis for balanced signals. Thirdly, design impedance matching networks for minimizing un-balanced and balanced port return losses. Then, a high performance planar transformer-based balun design can be done.

Power transformers play an important role in electric networks. Copper windings wrapped in kraft paper and immersed in a tank of mineral oil are their main composition. Oil-impregnated paper is a very common insulator in power transforms, due to its durability and endurance. Kraft paper, a wood-based fiber from cellulose, can gradually degrade due to the ambient effects such as high-voltage electric field, temperature, and moisture in the normal working condition of transformers. Aged paper is more prone to experience electric breakdown which finally results in transformer failures. It is essential to monitor paper insulation condition. Conventional methods for evaluating kraft paper are mainly based on chemical analyses which require sampling of the surrounding oil and are usually time-consuming and expensive. Investigation on and classification of aged kraft paper with four different levels of thermal ageing using a potentially fast, simple, and inexpensive optical setup based on optical speckle is the main subject of this thesis. Speckle interference patterns from a laser diode source have been captured by a CCD camera. Classification based on textural features shows very good discrimination between ageing classes making this technique promising for industrial applications.

Floating feeder resonances are one of the new challenges being put forward by the renewable energy based distributed generation (DG) installations. Generally, the harmonic injection from DGs are within IEEE standard 519-1992 limits. Although the harmonics are within the IEEE limits, they are a potential threat to power equipment’s insulation system integrity due to floating feeder resonances. There is a reasonable probability that at some point in time the feeder resonant frequency may coincide with one of the injected harmonics. Such phenomenon amplifies the specific harmonic causing additional stress on the equipment’s insulation system. In this thesis a feeder resonance study is done on the IEEE 34 bus distribution feeder to show the resonance shift problem in a DG loaded distribution feeder. Electric field study is then carried out on transformer winding to assess the dependence of electric field on harmonic distortion. At first the acoustic emission (AE) technique is employed to identify the change in the electric field distribution inside the winding at higher frequency. The AE technique together with the acoustic waveguide is utilized to locate the partial discharges under power frequency and high frequency operation. The results show a change in partial discharge (PD) location, which implies that the electric field redistributes in the transformer winding at higher frequency In order to further understand the electric field distribution, a high voltage air core coil is modeled by R, L and C ladder network. The R, L and C parameters are solved by finite element method and finally the electric field is calculated by computing the node potentials in the ladder network at various frequencies. The electric field results show that at high frequency distortion the electric stress enhances between fourth and fifth layer of the winding which may give rise to a PD activity; hence degrading the insulation. An aging experiment is also performed to understand the impact of high frequency distortion on transformer paper insulation. Paper samples are taken from a field aged transformer. They are aged for 72 hours under power frequency and various distorted waveforms. Dissipation factor is used as a comparison tool for paper samples before and after aging. Results show that paper samples aged under distorted waveforms showed a double increase in dissipation factor compared to the samples aged under power frequency.

A Tesla-Blumlein PFL-Bipolar pulsed power generator, has been successfully designed, manufactured and demonstrated. The compact Tesla transformer that it employs has successfully charged capacitive loads to peak voltages up to 0.6 MV with an overall energy efficiency in excess of 90%. The Tesla driven Blumlein PFL generator is capable of producing a voltage impulse approaching 0.6 MV with a rise time close to 2 ns, generating a peak electrical power of up to 10 GW for 5 ns when connected to a 30 Ω resistive load. Potentially for medical application, a bipolar former has been designed and successfully implemented as an extension to the system and to enable the generation of a sinusoid-like voltage impulse with a peak-to-peak value reaching 650 kV and having a frequency bandwidth beyond 1 GHz. This thesis describes the application of various numerical techniques used to design a successful generator, such as filamentary modelling, electrostatic and transient (PSpice) circuit analysis, and Computer Simulation Technology (CST) simulation. All the major parameters of both the Tesla transformer, the Blumlein pulse forming line and the bipolar former were determined, enabling accurate modelling of the overall unit to be performed. The wide bandwidth and ultrafast embedded sensors used to monitor the dynamic characteristics of the overall system are also presented. Experimental results obtained during this major experimental programme are compared with theoretical predictions and the way ahead towards connecting to an antenna for medical application is considered.

abstract: t temperature (HST) and top-oil temperature (TOT) are reliable indicators of the insulation temperature. The objective of this project is to use thermal models to estimate the transformer's maximum dynamic loading capacity without violating the HST and TOT thermal limits set by the operator. In order to ensure the optimal loading, the temperature predictions of the thermal models need to be accurate. A number of transformer thermal models are available in the literature. In present practice, the IEEE Clause 7 model is used by the industry to make these predictions. However, a linear regression based thermal model has been observed to be more accurate than the IEEE model. These two models have been studied in this work. This document presents the research conducted to discriminate between reliable and unreliable models with the help of certain metrics. This was done by first eyeballing the prediction performance and then evaluating a number of mathematical metrics. Efforts were made to recognize the cause behind an unreliable model. Also research was conducted to improve the accuracy of the performance of the existing models. A new application, described in this document, has been developed to automate the process of building thermal models for multiple transformers. These thermal models can then be used for transformer dynamic loading. / Dissertation/Thesis / Masters Thesis Engineering 2014

Estudos de transitórios eletromagnéticos são importantes fontes de informação para que os transformadores sejam dimensionados de maneira correta. No entanto, para que tais estudos sejam bem sucedidos, os modelos utilizados devem refletir com fidelidade o comportamento do equipamento. Este trabalho mostra como os elementos do modelo de um transformador são influenciados pelas dimensões geométricas de sua parte ativa. Também introduz uma formulação alternativa, para o transformador saturável (STC) do ATP, desenvolvida dentro do programa MATLAB. Os ramos RL foram representados usando o Método de Integração Trapezoidal e a magnetização foi equacionada pelo Método da Compensação. Uma das contribuições que esta dissertação oferece é a possibilidade de identificar erros numéricos que ocorrem em simulações do ATP, bem como permitir a interpretação de resultados que apresentem oscilações numéricas. / Electromagnetic transient studies are an important source of information to develop transformer dimensioning. But, for the success of that purpose, it is important the models which are being used reflect with fidelity the behavior of the machine. This lecture presents how the transformer model elements are influenced by the active part geometrical dimensions. It also introduces an alternative formulation for the ATP saturable transformer (STC), written inside the MATLAB program. The RL branches are represented using the Trapezoidal Rule and the magnetization by the Compensation Method. One of the contributions of this dissertation is the possibility to identify numerical errors that occur in ATP simulations, and also permit numerical oscillatory results interpretation.