O ruído acústico produzido pelos transformadores elétricos de potência, instalados em áreas urbanas, gera problemas ambientais e desconforto na população vizinha. Neste trabalho propõe-se desenvolver uma metodologia de projeto para reduzir o ruído dos transformadores com o objetivo de atingir níveis de ruído que a legislação ambiental exige. Um transformador elétrico de potência contém um núcleo, no qual encontram-se as bobinas, dentro de um tanque, ao ativar-se o núcleo e a bobina produz ruído e vibração em todos os componentes do transformador. Para diminuir a vibração e o ruído propõe-se o uso de Absorvedores Dinâmicos (AD) fixados nas paredes do tanque, e amortecedores automotivos ligados à base do tanque. Com os amortecedores procura-se atenuar os deslocamentos da base do tanque impostos pelo núcleo. Este procedimento, isoladamente, diminui a vibração da base do tanque e das paredes do tanque. Adicionalmente, utilizando absorvedores dinâmicos de vibração, projetados e alocados de acordo com resultados de simulações numéricas, é possível reduzir a amplitude de vibração das paredes do tanque. A redução de amplitude de vibração das paredes do tanque leva necessariamente a uma redução do ruído acústico, pois o ruído acústico decorre do acoplamento da vibração das paredes com o ar vizinho. Dados de deslocamento das paredes em condições operacionais, Operational Defection Shape (ODS), foram utilizados para determinar regiões de maior vibração e regiões para alocação dos absorvedores dinâmicos. Os modelos de elementos finitos do tanque, dos absorvedores dinâmicos e o carregamento operacional permitem estimar a redução de ruído e o número e a posição dos absorvedores dinâmicos. / The acoustic noise produced by electric power transformers, installed in urban areas, generates environmental problems and discomfort for the citizens of the neighborhood. The present work proposes a design methodology of devices to reduce the acoustic noise to levels legally accepted. An electric power transformer has a core, where the coils are assembled, inside a tank to active the core and coils make sound and vibration in all transformer component. To reduce vibration and noise it is evaluate the use of Dynamic Absorbers (DA), attached to the walls of the tank, and automotive dampers, attached to the base of the tank. The shock absorbers are intended to attenuate the displacements of the base of the tank imposed by the core of the transformer. This procedure, alone, reduces the vibration amplitude of the base and of the walls of the tank. Additionally, using vibration dynamic absorbers, designed and allocated according to numerical simulations, it is possible to reduce the amplitude of vibration on the walls of the tank. The reduction of the vibration amplitude necessarily leads to a reduction of the acoustic noise, since the acoustic noise is generated through the coupling of the structural vibration and the air in the near field. Operational displacement data, from an Operational Defection Shape (ODS) analysis, were used to determine regions of vibration higher and regions to location of dynamic absorber. Finite elements models of the tank and of the dynamic absorbers and the operational loading allow the estimation of noise reduction and of the number and position of the dynamic absorbers.

Present demagnetization methods for large power system transformers are time consuming and can be dangerous to persons performing demagnetization. The work of this thesis was to develop improved demagnetization methods and to construct an automated instrument that would implement the methods developed. One previously developed method was analyzed for effectiveness. Then, two new methods for demagnetization were developed and also analyzed for effectiveness. An automated test instrument prototype was redesigned to be able to accommodate these methods and to improve the safety of the user. The previously developed method attempts demagnetization based on current flow behavior characteristics. The first new method is a magnetic flux estimation based on saturation time. The second new method is also based on measuring saturation time, modified to account for the variable voltage loss due to wire resistance. The second of the two new methods developed proved to be the most effective for demagnetization and was able to demagnetize a transformer within an error margin of 2%. The instrument designed to perform the demagnetization with this new routine is now in early production stages for an expanded field trial with transformer maintenance teams.

Title: Indonesian-English Neural Machine Translation Author: Meisyarah Dwiastuti Department: Institute of Formal and Applied Linguistics Supervisor: Mgr. Martin Popel, Ph.D., Institute of Formal and Applied Linguis- tics Abstract: In this thesis, we conduct a study on neural machine translation (NMT) for an under-studied language, Indonesian, specifically for English-Indonesian (EN-ID) and Indonesian-English (ID-EN) in a low-resource domain, TED talks. Our goal is to implement domain adaptation methods to improve the low-resource EN-ID and ID-EN NMT systems. First, we implement model fine-tuning method for EN-ID and ID-EN NMT systems by leveraging a large parallel corpus contain- ing movie subtitles. Our analysis shows the benefit of this method for the improve- ment of both systems. Second, we improve our ID-EN NMT system by leveraging English monolingual corpora through back-translation. Our back-translation ex- periments focus on how to incorporate the back-translated monolingual corpora to the training set, in which we investigate various existing training regimes and introduce a novel 4-way-concat training regime. We also analyze the effect of fine- tuning our back-translation models with different scenarios. Experimental results show that our method of implementing back-translation followed by model...

This is a verification of the results of “Smart Grid Protection through Self-Healing” from the publication of Chathurika Chandraratne, et al., that proposes a protection solution for the smart grid. The paper used as reference has as the main focus on three different protections; directional overcurrent protection, overcurrent protection, and transformer protection, which are validated through ETAP software simulation of IEEE- 9 bus and 14 bus electrical power systems, the same used by the author. It was validated after repeated simulation, that just as intended, self-healing increases system agility, and it helped prevent false-tripping14 bus electrical power systems.

Polychlorinated biphenyls (PCBs) are toxic and persistent anthropogenic contaminants. Concern on their adverse health effects has led to their regulation in air, water and/or soil in addition to sludge. Hence, removal of PCBs in various matrices, including transformer oils (TO) is a priority. This study aims to investigate PCB-118 and Aroclor 1254 toxicity and dechlorination by varying certain critical experimental components including electron donor (sludge or fatty acids), inocula (unacclimated or acclimated culture) and the doses of PCB and TO under anaerobic conditions. Anaerobic toxicity assays (ATA) reactors, lab-scale anaerobic batch digesters and sediment microcosms were used for this purpose. Increase in PCB-118 and TO doses affected anaerobic digester performance by negatively influencing methanogenesis, while favoring dechlorination only with the increase in PCB-118 dose. Up to 22% PCB-118 removal was attained with unacclimated culture. Studies with acclimated cultures showed Grasse River (GR) sediment to be the most active when compared to Fox River and Baltimore Harbor sediments. In GR sediment microcosms, PCB-118 and Aroclor 1254 removal efficiencies decreased when TO was present (1%), while 10% TO inhibited PCB dechlorination. Waste activated sludge was shown to be an effective electron donor, similar to fatty acids. Aroclor 1254 dechlorination was dechlorinated through removal of flanked meta and para chlorines, however, dechlorination pathways appeared to differ according to the presence/absence of TO. No ortho or unflanked chlorines were removed. Molecular tools (qPCR and DHPLC) were used to confirm the presence of active PCB dechlorinators. Dechlorination of PCBs was shown to be growth-linked.

As in all other electrical equipments it is essential to estimate the temperature distribution in transformer components in the design stage and during the operation since temperatures above thermal limits of these components might seriously damage them. Thermal models are used to predict this vital information prior to actual operations. In this study, a three dimensional model based on the Finite Element Method (FEM) is proposed to estimate the temperature distribution in the three phase, SF6 gas insulated-cooled power transformer. This model can predict the temperature distribution at the specific discredited locations in the transformer successfully.

As in all other electrical equipments it is essential to estimate the temperature distribution in transformer components in the design stage and during the operation since temperatures above thermal limits of these components might seriously damage them. Thermal models are used to predict this vital information prior to actual operations. In this study, a three dimensional model based on the Finite Element Method (FEM) is proposed to estimate the temperature distribution in the three phase, SF6 gas insulated-cooled power transformer. This model can predict the temperature distribution at the specific discredited locations in the transformer successfully.

Transformers are very important parts of any electrical network, and their size increase so does their price. Protecting these important devices is a daunting task due to the wide variety of operating conditions. This thesis develops a new protection scheme based on state estimation.The foundation upon which our protection scheme is built is the modeling of the single phase transformer system of equations. The transformer equations are composed of polynomial and differential equations and this system of equations involving the transformer's electrical quantities are modeled into a system of equations such that highest degree of each of the system's equations is quadratic―in a process named Quadratization and then integrated using a technique called Quadratic integration to give a set of algebraic companion equations that can be solved numerically to determine the health of the transformer.

A power transformer is one of the most important and expensive components in any power system. Power transformers can be exposed to a wide variety of abnormal conditions and faults. Internal turn-to-turn faults are the most difficult types of faults to detect within the power transformer. The IEEE Standards documents have revealed that there is no one standard way to protect all power transformers against minor internal faults such as turn-to-turn faults and at the same time to satisfy basic protection requirements: sensitivity, selectivity, and speed.<p> This thesis presents a new, simple and efficient protection technique which is based on negative sequence currents. Using this protection technique, it is possible to detect minor internal turn-to-turn faults in power transformers. Also, it can differentiate between internal and external faults. The discrimination is achieved by comparing the phase shift between two phasors of total negative sequence current. The new protection technique is being studied via an extensive simulation study using PSCAD®/EMTDC 1 software in a three-phase power system and is also being compared with a traditional differential algorithm.<p> Relay performance under different numbers of shorted turns of the power transformer, different connections of the transformer, different values of the fault resistances, and different values of the system parameters was investigated. The results indicate that the new technique can provide a fast and sensitive approach for identifying minor internal turn-to-turn faults in power transformers.

Power systems are protected by numerical relays that detect and isolate faults that may occur on power systems. The correct operation of the relay is very important to maintain the security of the power system. <p>Numerical relays that use voltage measurements from the power system provided by coupling capacitor voltage transformers (CCVT) have sometimes difficulty in correctly identifying a fault in the protected area. The fundamental frequency voltage phasor resulting from these CCVT measurements may result in a deviation from the true value and therefore may locate this phasor temporarily in the incorrect operating region. This phasor deviation is due to the CCVT behavior and the CCVT introduces spurious decaying and oscillating transient signal components on top of the original voltage received from the power system in response to sudden voltage changes produced during faults. Most of the existing methods for estimating the voltage phasor do not take advantage of the knowledge of the CCVT behavior that can be obtained from its design parameters.<p>A new least squares error method for phasor estimation is presented in this thesis, which improves the accuracy and speed of convergence of the phasors obtained, using the knowledge of the CCVT behavior. The characteristics of the transient signal components introduced by the CCVT, such as frequencies and time constants of decay, are included in the description of the curve to be fitted, which is required in a least squares fitting technique. Parameters such as window size and sampling rate for optimum results are discussed.<p>The method proposed is evaluated using typical power systems, with results that can be compared to the response if an ideal potential transformer (PT) were used instead of a CCVT. The limitations of this method are found in some specific power system scenarios, where the natural frequencies of the power system are close to that of the CCVT, but with longer time constants. The accuracy with which the CCVT parameters are known is also assessed, with results that show little impact compared to the improvements achievable.