The diversity of video material, where a video is shot and produced using a single aspect ratio, and the variety of devices that can play video with screens in different aspect ratios make video retargeting a relevant topic. The process of fitting a video filmed in one aspect ratio to a screen in another aspect ratio is called video retargeting, and the retargeted video should ideally preserve the important content and structure of the original video as well as be free of visual artifacts. Important content and important structure are vague and subjective definitions, which makes this problem more difficult to solve. The video retargeting problem has been a challenge for researchers from the computer vision, computer graphics and human-computer interaction areas, and successful retargeting can improve the viewing experience and the content’s aesthetic value. Video retargeting is done by four tools: cropping, scaling, seam carving and seam adding. Previous research showed that one of the keys to successful retargeting is to use a suitable combination of operators. This study makes use of a vision transformer, a deep learning model which is trained to discriminate between original and retargeted videos. Solving an optimization problem using beam search, the transformer assists in choosing a combination of operators that will result in the best possible retargeted video. The retargeted videos were examined in a user A/B-test, where users had to choose their preferred variant of a video shot: the transformer’s output using beam search, or a singular version where the video underwent a single retargeting operation. The model and user preferences were compared to check if the model indeed can make retargeting decisions that are appealing for humans to watch. A significance test showed that no conclusion can be made, probably due to lack of enough test data. However, the study revealed patterns in the preferences of the users and the model that could be further fine-tuned or combined with other computer vision mechanisms in order to output better retargeted videos. / Variation av videomaterial, där olika videor är inspelade och producerade i olika bildförhållande, samt variation i apparater och skärmar som spelar upp videor i olika bildförhållanden gör ändring av videobildförhållande till en relevant fråga. Processen där en videos bildförhållande ändras heter video retargeting. När video retargeting används bör den nya videon helst bevara strukturen och viktigt innehåll från originalvideon samt vara artefaktfri. Struktur och viktigt innehåll är subjektiva definitioner vilket gör frågan svårlöst, och frågan har varit en utmaning för forskare inom datorseende, datorgrafik och människa-datorinteraktion. Lyckad ändring av en videos bildförhållande kan förbättra tittarupplevelsen och innehållets estetiska värde. Video retargeting kan göras med hjälp av fyra funktioner: klippning, skalning, seam carving och seam adding. Tidigare studier visar att en av nycklarna till lyckad retargeting är att hitta en lämplig kombination av funktionerna. I denna studie används Vision Transformer, en djupinlärningsmodell som tränas för att skilja mellan original och omvandlade videor. Genom att lösa ett optimeringsproblem med strålsökning hjälper modellen välja den kombination av funktionerna som resulterar i den bästa möjliga omvandlade videon. De omvandlade videorna testades genom ett användartest där användare valde vilket videoklipp de tyckte bättre om: modellens output som skapades med hjälp av strålsökning, eller en version där klippet genomgick en enklare retargeting med hjälp av endast en av funktionerna. Modellens och användarnas preferenser jämfördes för att se om modellen kan fatta beslut som användare upplever som bra. Ett signifikanstest visar att ingen slutsats kan dras, förmodligen på grund av det begränsade antalet videoklipp och data som användes i studien. Däremot visar studien mönster i användarnas och modellens preferenser som kan användas för att vidareutveckla problemlösningen inom området.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / Electrification of rural areas is one of the biggest challenges faced by ESKOM and methods are required to extend medium voltage distribution lines to these often remote areas. As loads increase due to line-extension, in-fills and energy theft, maintenance cost and life expectancy of distribution and power transformers becomes more critical. The thesis addresses these two aspects with the development of a self regulated and protected electrification transformer that makes use of current, voltage and ambient temperature measurements to regulate voltage and protect hardware from overloading. The design of the hardware that allows the system to run at 200% load without decreasing the lifetime of the transformer is examined. Temperature estimation techniques are used to estimate the temperatures in the 16 kVA, 22 kV to 230 V, distribution transformer to run above nameplate ratings without causing damage. The control of the system is implemented on TMS320F2812 digital signal processor from TI that is DSP/BIOS compatible. The control software is implemented using DSP/BIOS, which allows real-time scheduling and monitoring of procedures. Furthermore a distribution transformer was fitted with temperature sensors and heat run tests were performed. The results of the temperature tests were used to verify the estimation techniques and to determine constants used for temperature estimation.

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M. Tech. (Power Engineering Department, Faculty of Engineering and Technology) -- Vaal University of Technology / This dissertation is devoted to the study of partial discharge evaluation of a high voltage transformer. The 400 V/300 000 V (300 kV) high voltage transformer in the high voltage laboratory was manufactured in 1967. Given the old age of the transformer and the crucial importance of insulation systems, it is vital to assess the condition of its insulation to ensure the effectiveness and the reliability of the transformer as well as the safety of the personnel using it. In order to achieve that, it is important to evaluate the partial discharge in the insulation system as this is the main cause of destruction of insulation. The phase-resolved partial discharge method was the main method used to perform the partial discharge measurements in this research. Partial discharge measurements were performed on a faulty 11 kV voltage transformer. Defects were also created in samples of solid insulation at predetermined locations with different shapes and sizes. The measurements taken on the 11 kV voltage transformer and samples of solid insulation formed a basis to prove the validity of the assessment methods on the 300 kV transformer. Using the method mentioned above, partial discharges were recorded with respect to the phase of the applied voltage with the aid of a commercial instrument which complies with IEC 60270, (ICM monitor - partial discharge detector from Power Diagnostix Systems GmbH). The observations from this study have furthered the understanding of partial discharge processes. The patterns recorded were analysed in order to conclude about the condition of the transformer. From the partial discharge pattern, the type and location of partial discharges were concluded. The patterns obtained from the transformer reveal that the device is healthy and can be operated up to 200 kV.

With the rapid development of the modern technology, radio frequency and microwave systems are playing more and more important roles. Since the time the first microwave device was invented, they have been leading not only the military but also our daily life to a new era. In order to make the devices have more practical applications, more and more strict requirements have been imposed. For example, good adaptability, reduced cost and shrank size are highly required. In this thesis, three devices are designed based on this requirement. At first, a symmetric four-port microwave varactor based 90-degree directional coupler with tunable coupling ratios and reconfigurable responses is presented. The proposed coupler is designed based on the modified structure of a crossover, where varactors are loaded. Then, a novel reconfigurable 3-dB directional coupler is presented. Varactors and inductors are loaded to the device to realize the reconfigurable performance. By adjusting the voltage applied to the varactors, the proposed coupler can be reconfigured from a branch-line coupler (90-degree coupler) to a rat-race coupler (180 degree coupler) and vice versa. At last, two types (Type-I and Type-II) of microwave baluns with generalized structures are presented. Different from the conventional transmission-line-based baluns where λ/2 transmission lines or λ/4 coupled lines are used, the proposed baluns are constructed by transmission lines with arbitrary electrical lengths.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfilment of the requirements of the degree of Master of Science in Electrical Engineering June 2016 / Through the Renewable Energy Independent Power Producer Procurement Program (REIPPPP) the South African government has awarded opportunities for growth of renewable energy through bidding rounds. Round 1 saw a total capacity of 397 MW being awarded to independent power producers (IPP). Subsequently Rounds 2, 3 and 4 each had a total capacity of 333 MW auctioned. The advent of renewables on the market has brought upon its own associated problems with regards to power quality issues and failure of HV equipment. This thesis will address transformer failures that occurred at an onshore wind farm. The nature of the transformer failures suggest transient overvoltages are mainly to blame. A comparison between transformer failures in South African and Brazil suggest a common failure mechanism. The failure starts with an inter-turn insulation failure which propagates to an inter-layer insulation. In worst cases the failure mode results in a puncture through the LV-HV barrier and punctures through the LV winding. An extensive literature review was performed to find appropriate methods to predict and explain the failure mode in wind turbine LV-MV step-up transformers. Of the different models which were reviewed the most notable was the Multi-conductor Transmission Line (MTL) model which was chosen as the preferred model due to its ability to predict the inter-turn/inter-layer voltage stresses. Verification of the developed MTL model by the author was then compared to published results of an MTL model of a disc winding transformer. The results of the comparison revealed a relatively good agreement between the developed model and the published model. The application of the MTL model to represent the voltage stresses in transformer windings was then extended to two specially constructed wind turbine step-up transformer prototypes. The prototypes differed in the winding arrangement of the MV coil. The other used two separate MV coils separated by an oil gap whereas the other had a single MV coil. To validate the model accuracy, a comparison of measured results versus those obtained analytically was done for the two prototypes. The analytical and measured results also had a relatively good agreement for the two prototypes considered. Measurement of switching surges was done on-site at the wind farm to understand the nature of the transients. Using analysis tools such as FFT and frequency domain severity factor it was possible to understand the impact the nature of these transients would pose on the transformer insulation. Different mitigation techniques which can be used to alleviate the transient overvoltages to within safe levels were investigated. The most notable protection device considered was the RL choke device which offered a significant reduction of the pre-strikes and is virtually transparent under power frequency operation. / MT2017

Orientador: José Alfredo Covolan Ulson / Banca: José Carlos de Melo Vieira Junior / Banca: Renato Crivellari Creppe / Resumo: Os transformadores são equipamentos importantes do sistema elétrico de potência, possuem alto custo e suas falhas tem influência direta na qualidade da energia entregue aos consumidores. Uma das principais causas de falhas em transformadores imersos em líquido isolante, as descargas parciais, advém da degradação física e química do sistema de isolação devido à diversos fatores tais como sobrecarga, cargas não-lineares, chaveamento e superaquecimento. Essas descargas parciais aceleram a degradação do dielétrico do transformador e podem levar à destruição do equipamento, ocasionando elevado prejuízo financeiro. Dessa forma, são necessárias ações de prevenção de falhas causadas por descargas parciais em transformadores, através de métodos de monitoramento e localização. Este trabalho teve por objetivo apresentar um método de localização de descargas parciais em transformadores de potência imersos em óleo mineral isolante utilizando o método de emissão acústica e sistemas inteligentes do tipo redes neurais artificiais e algoritmos genéticos. Foram aplicadas métricas de processamento de sinais aos sinais acústicos gerados a partir de descargas parciais e obtidos através de sensores piezelétricos de baixo custo instalados no lado externo do tanque do transformador. Estas métricas foram utilizadas para treinamento das redes neurais a fim de obter a distância euclidiana entre os sensores e as descargas parciais. Essas distâncias euclidianas foram utilizadas em um sistema não-linear d... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Transformers are important devices of the electric power system, which have high cost and their failures have a direct influence on the power quality delivered to the consumers. One of the main causes of failures in oil-immersed transformers, the partial discharges, comes from the physical and chemical degradation of the insulation system due to several factors such as overload, non-linear loads, switching and overheating. These partial discharges accelerate the degradation of the transformer dielectric and they can lead to the destruction of the equipment, causing high financial losses. Thus, actions are necessary to prevent faults caused by partial discharges in transformers, through monitoring and locating methods. The aim of this work was to present a method for locating partial discharges in oil-immersed power transformers using the acoustic emission method and intelligent systems such as artificial neural networks and genetic algorithms. Signal processing metrics were applied to the acoustic signals generated from partial discharges and obtained by low-cost piezoelectric sensors installed on the external side of the transformer tank. These metrics were used to train the neural networks in order to obtain the euclidean distance between the sensors and the partial discharges. These euclidean distances were used in a nonlinear location system, which was solved through a genetic algorithm in order to obtain the three-dimensional coordinates of the partial discharge. The ana... (Complete abstract click electronic access below) / Mestre

Os transformadores para instrumentos (TIs) são equipamentos essenciais para a realização das funções de medição e de proteção nos sistemas elétricos de potência. O mau funcionamento dos TIs nos sistemas de proteção pode provocar tanto atuações indevidas como falhas de operação e, em ambos os casos, acarretará prejuízos à concessionária ou a terceiros, podendo, ainda, serem gerados danos materiais ou pessoais. Quando os transformadores de corrente (TCs) ou de potencial (TPs) estão instalados em sistemas de medição para faturamento e não funcionam com a precisão necessária, milhares ou milhões de reais podem ser perdidos por ano, seja por quem vende a energia, seja por quem a compra. O presente estudo, analisa a viabilidade (ou possibilidade) da utilização de TIs ópticos no sistema elétrico de potência brasileiro. Foram realizados comparativos técnicos e econômicos entre os TIs convencionais e os ópticos, sendo que no aspecto econômico são analisadas situações em que maus funcionamentos (ou falhas) dos TIs convencionais podem causar prejuízos às concessionárias. São apresentados levantamentos de dados indicativos das quantidades de TIs em uso e dos preços de aquisição desses equipamentos. Também é apresentado o resultado de uma enquete que avaliou o grau de familiaridade que os engenheiros do setor elétrico brasileiro tem com a tecnologia de TIs ópticos. O trabalho apurou que os TIs ópticos demonstram superioridades técnicas e econômicas frente aos TIs convencionais, mas que, para que eles sejam utilizados mais amplamente nas subestações, além de uma maior divulgação dos mesmos por parte de seus fabricantes, ainda são necessários esforços de adaptação e/ou aplicação de novas tecnologias que facilitem a conexão dos TIs ópticos aos sistemas de proteção e medição em uso. O trabalho indica também que esse problema, no futuro, deverá ser eliminado com a natural modernização das subestações e com a implantação de redes de comunicação aderentes à norma IEC 61850-9-2. / The instruments transformers (ITs) are essential equipment to perform the measurement and protection functions in electrical power systems. The malfunctioning of ITs in protection systems can cause undue actuations as well as operation failures and, in both cases, the utilities or third parties will face financial losses and, also, personal or material damages can be generated. When current transformers (CTS) or potential transformers (PTs) are used for revenue metering applications and do not work with the necessary precision, thousands or millions of reais may be lost per year, either by those who sell energy, or by whom purchase it. This study examines the viability of optical ITs applications in brazilian electric power systems. Technical and economical comparisons between conventional and optical ITs were carried out, and economic aspects of situations in which malfunctions (or failures) of conventional ITs can cause financial losses to utilities are discussed. Data about quantities and prices of conventional ITs in use in Brazil are shown. Also, results of a research evaluating the familiarity of engineers working in electric power utilities with the optical ITs technology are presented. The study found that optical ITs have shown technical and economical superiorities over conventional ITs, but, in order to be widely used in substations there are still needed adaptation efforts and/or application of new technologies that facilitate the connection of optical ITs to protection and measurement systems already in use. The present work also indicates that this problem, in the future, should be eliminated by natural modernization of substations and the installation of communication networks compliant to the IEC 61850-9-2 standard.

Este trabalho apresenta uma proposta para cálculo da correção do fator de construção de núcleos de transformadores de potência, devido à influência das perdas na região das juntas magnéticas. Esse fator permite corrigir o valor de perdas em vazio no núcleo, obtido das curvas do fabricante das chapas de aço-silício, e sua determinação, até o momento, tem sido baseada, sobretudo, em estimativas empíricas e estatísticas. A correção proposta para esse fator é baseada no cálculo das perdas magnéticas na região das juntas, cálculo esse obtido a partir de uma simulação computacional do transformador pelo Método de Elementos Finitos. Com esse fator de correção, foi possível melhorar a precisão do cálculo de perdas em vazio, aproximando-o mais dos valores experimentais. Foram estudados dois tipos de juntas magnéticas, com e sem step-lap, e três dimensões de entreferro; em seguida, foi analisada a influência desses parâmetros no fator de construção. As simulações foram realizadas por um programa comercial que utiliza o Método de Elementos Finitos em duas dimensões. / This work presents a suggestion to calculate a correction factor of building factor in a core of power transformers, due to influence of losses in the magnetic junctions. This factor allows correcting the value of no load loss in the core, obtained from steel manufacturers, and their determination, up to now, it has been based, especially, in empirical and statistics estimates. The correction suggested to this factor is based in magnetic losses calculations in junction region, calculation which was obtained from a computer simulation of the transformer by Finite Element Method. Having this correction factor, could the accuracy of the calculation of no load loss, be improved, setting of the experimental value closer. Two types of magnetic joints, with and without step-lap, and three of gap were studied; then, it was examined the influence of these parameters in the building factor. The simulations were run by commercial software which uses finite element method in two dimensions.

Transformadores de potência são equipamentos essenciais no sistema elétrico de potência, alterando os níveis de tensão para interligar os sistemas de geração, transmissão e distribuição de energia elétrica. Neste trabalho são relacionados e descritos os principais modos de falha normalmente verificados em transformadores, associados ao levantamento estatístico que compõe um banco de dados elaborado a partir de perícias realizadas entre os anos de 2.000 e 2.008 para companhias seguradoras. É apresentada e desenvolvida uma análise de falhas verificadas em cerca de uma centena de transformadores com diferentes tipos de aplicação, classes de tensão e níveis de potência. O objetivo do estudo é contribuir com um melhor entendimento de causas de falhas e os tipos de transformadores mais suscetíveis a cada uma delas. / Power transformers are essential equipment in the electric system by changing the voltage levels in order to connect generation, transmission and distribution systems of electric energy. In this study are related and described the most common failure modes in transformers, associated with the statistical statement that makes up a database developed from expertise held between the years 2000 and 2008 for insurance companies. It is presented and developed an analysis of failures found in around a hundred transformers with different types of application, classes of voltage and power levels. The objective of the study is to contribute to a better understanding of the causes of failures and the transformers types most susceptible to each one.