Os transformadores de potência elétrica produzem um elevado nível de ruído que em alguns casos gera desconforto à comunidade vizinha. O presente trabalho desenvolve um modelo estrutural de elementos nitos que, com carregamento adequado, é capaz de reproduzir o deslocamento, medido durante a operação, de um transformador de potência elétrica. Este modelo estrutural é utilizado para calcular a redução do deslocamento das superfícies deste transformador decorrentes do emprego de absorvedores dinâmicos de vibração. Este modelo estrutural foi desenvolvido para estimar o número de absorvedores dinâmicos, sua massa e sua localização que permitiria reduzir o ruído acústico emitido por este transformador de potência até alcançar níveis de intensidade de som em comformidade com a legislação brasileira. / Electrical power transformers produce a high level of noise, which, in some cases, generate discomfort to the surrounding community. The present work develops a structural model by the Finite Element Method that, with adequate loading conditions, is capable of reproducing the displacement, measured during operation, of the transformer tank. The structural model has been used to compute the displacement reduction of the transformer surfaces by using dynamic vibration absorbers. The structural model was developed to estimate the number of dynamic absorbers, the mass and localization that could reduce the acoustic noise to levels of intensity of sound in accordance to the Brazilian law.

Os transformadores de potência elétrica produzem um elevado nível de ruído que em alguns casos gera desconforto à comunidade vizinha. O presente trabalho desenvolve um modelo estrutural de elementos nitos que, com carregamento adequado, é capaz de reproduzir o deslocamento, medido durante a operação, de um transformador de potência elétrica. Este modelo estrutural é utilizado para calcular a redução do deslocamento das superfícies deste transformador decorrentes do emprego de absorvedores dinâmicos de vibração. Este modelo estrutural foi desenvolvido para estimar o número de absorvedores dinâmicos, sua massa e sua localização que permitiria reduzir o ruído acústico emitido por este transformador de potência até alcançar níveis de intensidade de som em comformidade com a legislação brasileira. / Electrical power transformers produce a high level of noise, which, in some cases, generate discomfort to the surrounding community. The present work develops a structural model by the Finite Element Method that, with adequate loading conditions, is capable of reproducing the displacement, measured during operation, of the transformer tank. The structural model has been used to compute the displacement reduction of the transformer surfaces by using dynamic vibration absorbers. The structural model was developed to estimate the number of dynamic absorbers, the mass and localization that could reduce the acoustic noise to levels of intensity of sound in accordance to the Brazilian law.

The global mean surface temperature rise was observed in the past century and proved the warming of the earth climate system. Global warming is believed to continue into the next decades due to unprecedented increases in greenhouse gas emissions. As a consequence of global warming, extreme weather scenarios are also expected to occur more frequently. In such a context, it is of vital importance to assess the impacts of climate change on the operational performance of power systems. This thesis investigates the impacts of climate change on the operational performance of power systems. The future climate is simulated based on emission scenarios and is then used as an input to the thermal models of power system components to assess their ratings and ageing, and further the reliability of the system. This research contributes to a number of areas in power system research. In the literature review, the risks that climate change may cause to power systems are identified. The models used for the simulation of future climate are firstly introduced. The weather variables that can be simulated from the models include air temperature, solar radiation, wind speed and direction, soil moisture and soil temperature. Among the models, the one for soil temperature is originally developed in this thesis. Following this, the component thermal models of overhead line, cable and transformer, from different standards are compared and selected. After that, the sensitivity of component ratings to individual weather variables is investigated, as a preliminary study for the later research in this thesis. Then, the impacts of climate change on component ratings (including both static and dynamic rating) are comprehensively and probabilistically assessed. The assessment results indicate the reduction of component ratings due to climate change. The impacts of climate change on system reliability is further examined on the IEEE Reliability Test System. Results demonstrate and quantify the reduction of both component ratings and system reliability, and prove that the dynamic rating can be used to mitigate the reduction. Finally, the preliminary exploration of transformer ageing is carried out and shows an increased ageing rate due to air temperature rises.

No description available.

The aim of this thesis is a modification of the distribution network (DS) of the city of Brno to ensure power supply in the required quantity and quality for end consumers. Calculation of steady - state operation of distribution network (DS) of Brno is performed in the programme PAS DAISY Off-Line v.4.00 Bison. On the basis of available data (dispatching scheme, load current of stem lines and reserved power of wholesale customers) we will analyze the steady-state of network. We will find out which of the 110/22 kV transformer stations, cable and overhead lines are overloaded and perform network adjustments to ensure safe and reliable operation by 2015. We will identify in which year we will need to build a new power node in the northern part of Brno. The conclusion is focused on technical and economic evaluation of proposed alternative network arrangements.

The thesis addresses the conceptual design and implementation of the switched-mode power supply having the adjustable dc voltage output up to 25V and current output up to 15A. The half-bridge topology is used for this supply. Design features and quantities are simulated in PSpice and Micro-Cap simulation tools. The thesis covers the simulation results, assembly data and the results measured on the implemented functional sample.

The thesis deals with the design of a transformer station for the outgoing power of cogeneration unit with an electric capacity of up to 1 MW. The thesis describes the design procedure of individual devices such as a transformer with a nominal ratio 22/0,4 kV, high voltage switchgears and low voltage switchgears. With the proper selection of the transformer, along with the technical parameters, the economic benefits that come from its purchasing and operating costs with the transformer operation are also considered. Based on this, the economic comparison of selected types of oil transformers during 20 years is also developed. Another part of the thesis deals with HV and LV switchgears, which are dimensioned according to shortcircuit conditions in the transformer station. In conclusion this work deals with the grounding of a transformer station and design protection in accordance PPDS.

No description available.

In this project an experimental setup is designed to investigate the effect of intermittent load patterns in combination with moisture content on cellulose ageing. It is done by exposing groups of samples to different intermittent load patterns with varying frequency. A literature review is done on transformer insulation system and cellulose degradation. Various technical solutions to different aspects of the experimental design are reviewed. The final experimental setup is explained with the primary focus being on the hardware and programming of the controlling system. The controlling system consists of a Data Acquisition (DAQ) system from National Instruments and is programmed in LabVIEW. The controlling system is examined in two investigative tests where it performed satisfactorily. Three load patterns are developed. This project suggests how to prepare the samples and what direct- and indirect tests to apply to the insulation system for future analysis.Over the years, a considerable amount of scientific work has been devoted to understanding paper ageing in order to improve transformer diagnostics and investments for utility owners. However, transformer loading guidelines of today do not take intermittent load in combination with moisture content into account [1] [2]. Previous work suggests that the thermal models may be improved by looking into the effects of moisture content [3].The primary aim of the proposed experimental setup is to investigate whether an intermittent load pattern in combination with moisture content have a considerable detrimental effect on cellulose ageing. The intent is to contribute with new knowledge about transformer diagnostics and long-term possibly improve the current thermal models used for Dynamic Transformer Rating (DTR) which do not take this phenomenon into account. This would in particular benefit transformers with typically intermittent load patterns, e.g. a transformer connected to a wind farm or photovoltaic panels. Increasing renewable energy installations increase the need for developing the thermal models in the transformer loading guidelines to take unconventional load profiles into account. / I det här projektet utformas ett experiment för att undersöka inverkan av intermittenta lastmönster i kombination med fukthalt på åldrande av cellulosa. Detta görs genom att utsätta provgrupper för olika lastmönster med varierande frekvens. En litteraturgenomgång görs på transformatorisoleringssystem och nedbrytning av cellulosa. Olika tekniska lösningar för olika aspekter av experimentets design ses över. Den slutliga utformningen av experimentet förklaras med fokus på hårdvara och programmering av kontrollsystemet. Kontrollsystemet består av ett system för datainsamling från National Instruments och programmeras i LabVIEW. Kontrollsystemet utvärderas i två undersökande test där det förfor på ett tillfredsställande sätt. Tre lastmönster till experimentet har tagits fram. Det här projektet föreslår hur man förbereder proverna och vilka direkta och indirekta test som kan göras för framtida analyser.Under åren har en betydande mängd vetenskapligt arbete ägnats åt att förstå pappersåldring för att förbättra transformatordiagnostik och investeringsunderlaget för nätägare. De industriella standarderna tar dock inte hänsyn till intermittent belastning i kombination med fukthalt [1] [2]. Tidigare arbete föreslår att de termiska modellerna möjligen kan förbättras genom att undersöka effekterna av fukthalt [3].Det huvudsakliga målet med den föreslagna experimentella uppställningen är att undersöka huruvida ett intermittent belastningsmönster i kombination med fukthalt har en betydande inverkan på pappersåldrandet. Föresatsen är att bidra med ny kunskap om transformatordiagnostik och för att om möjligt långsiktigt förbättra de nuvarande termiska modellerna som används till dynamiska lastbarhetsmodeller för transformatorer. Detta skulle särskilt gynna transformatorer med typiskt intermittenta belastningsmönster, t ex en transformator ansluten till en vindkraftpark eller solcellspaneler. Ökande antal av anläggningar för förnybar energi ökar behovet av att utveckla de termiska modellerna för att ta hänsyn till okonventionella lastprofiler.

With the continued proliferation of access and the usage of the internet, the field of web learning is continuously growing in order to automate and improve parts of our experience on the web. Research in web learning has often lagged behind its counterparts in Natural Language Processing (NLP), novel methods often reach adoption in web learning research with a delay. Web pages are more complex in both content and structure, as they are semi- structured documents divided into sections, often containing a combination of images, text, and markup. For humans, this is not difficult to understand, as we are familiar with the structure of web pages and in fact are often aided by the styling and markup of the pages. However for machine learning algorithms, this structure and mixture of content poses several challenges which are not similar in nature to comparable documents in NLP problems. Transformer models have shown significant performance gains on a multitude of tasks ranging from NLP to image processing. This thesis studies the usage of alternative and novel approaches to encoding positional information of nodes in a HyperText Markup Language (HTML) Document Object Model (DOM) tree in order to enable effective use of transformer models on web page data. The problem studied was a HTML element classification problem, specifically the task of extracting product data from a product web page. Three positional encodings for tree structured data were studied: Breadth First Search (BFS), Depth First Search (DFS), and novel tree positional encodings. These encodings resulted in 3 trained transformer models which were compared to a baseline transformer model trained with no positional encoding in order to measure the change in performance that the encodings produced. The analysis of the results show that the BFS and DFS encodings increased model performance across all measured metrics (precision, recall, f1-score, accuracy) by up to 1% in absolute performance. The novel tree positional encodings resulted in worse model performance across all metrics measured. The results show that transformers benefit from certain tree positional encodings of the HTML elements, and further research should be done to see how these positions can be effectively encoded for transformer models to process web pages. / Med den fortsatta spridningen av åtkomst och användningen av internet växer området för webbinlärning kontinuerligt för att automatisera och förbättra vår erfarenhet på nätet. Forskning inom webbinlärning har ofta släpat efter dess motsvarigheter inom NLP, nya metoder når oftast webbinlärningsforskning med försening. Webbsidor är mer komplexa i både innehåll och struktur än text dokument, eftersom de är halvstrukturerade dokument indelade i sektioner, som ofta innehåller en kombination av bilder, text och stil. För människor är detta inte svårt att förstå, eftersom vi är bekanta med strukturen på webbsidor och faktiskt ofta får hjälp av utformningen och uppdelningen av sidorna. Men för maskininlärnings algoritmer är strukturen och blandningen av innehåll en utmaning som inte liknar jämförbara dokument i NLP. Transformer modeller har visat flera prestandaförbättringar på en mängd uppgifter som sträcker sig från NLP till bildbehandling. Denna uppsats studerar användningen av alternativa och nya metoder för kodning av positionsinformation för noder i ett HTML DOM träd för att möjliggöra effektiva användningen av transformer modeller på webbsidadata. Problemet som studerades var ett HTML elementklassificeringsproblem, specifikt uppgiften att extrahera produktdata från en produktsida. Tre positionskodningar för trädstrukturerade data har studerats: BFS, DFS och träd positionskodningar. Dessa kodningar resulterade i tre tränade transformer modeller som jämfördes med en modell tränad utan någon positionskodning för att mäta förändringen i prestanda som kodningarna producerade. Analysen av resultaten visar att BFS och DFS kodningarna ökade modellprestanda över alla uppmätta mått (precision, accuracy, f1-score) med upp till 1% i absolut prestanda. De nya trädpositionskodningarna resulterade i sämre modellprestanda över alla mått mätt. Resultaten visar att transformer modellererna drar nytta av vissa trädkodningar för HTML-elementen, och ytterligare undersökningar bör göras för att se hur dessa positioner av datan effektivt kan kodas för transformer modeller för att bearbeta webbsidor.