Le transformateur de puissance est un équipement essentiel d’un réseau électrique et le plus coûteux dans les postes. Pour augmenter son degré de disponibilité et de fiabilité, il est nécessaire d’appliquer la manœuvre contrôlée afin de diminuer la saturation du noyau lors de l’enclenchement, et donc limiter les courants d’appel. Ces derniers sont asymétriques, d’amplitude élevée, et riches en harmoniques. Ils peuvent causer des effets indésirables comme le disfonctionnement des dispositifs de protections, l’endommagement mécanique des enroulements du transformateur et réduire en général la durée de vie et la qualité des systèmes. Une technique efficace pour réduire ces courants d’appel est de mettre sous tension le transformateur quand le flux dynamique généré par la source est égal à son flux rémanent. Un modèle simplifié du transformateur de puissance est adopté pour l’analyse des phénomènes physiques liés à l’application des manœuvres. Pour évaluer le degré de faisabilité de cette technique, des simulations sont effectuées en utilisant le simulateur de réseau EMTP. Les contraintes requises pour chacun des composants du système de manœuvre contrôlée comme les segments de ligne, les disjoncteurs sont étudiées en détail pour déterminer l’algorithme de calcul de l’instant optimal de manœuvres. Ensuite des tests de validation statistiques sont effectués afin d’évaluer les performances des différentes approches employées. Enfin une étude consacrée à la reconstitution du flux rémanent via un transformateur capacitif de tension (TCT) est menée pour appliquer l’algorithme de manœuvre contrôlée dans les postes en utilisant les équipements de mesure déjà existants. / Power transformers are vital equipment in electrical networks and are the most expensive ones in substations. In order to increase their availability and reliability, controlled switching must be applied for reducing cores saturation during its energization, called “inrush currents”. These inrush currents are asymmetrical, high-magnitude, harmonic-rich, and may cause many undesirable effects such as maloperation of protective relays and fuse, mechanical damage to the transformer winding and generally reduce the lifetime and quality of power systems. An efficient technique to reduce these inrush currents is to energize the transformer when the dynamic flux generated by the source is equal to its residual flux. A simplified model is adopted to analyze the physical phenomena related to the switching applications. In order to assess the feasibility of this technique, numerous simulations have been performed using EMTP simulator. The critical requirements for each component of the controlled switching system such as pieces of line, circuit breakers have been studied in detail in order to determine the best switching instant calculation algorithm. Then statistical validation tests have been conducted to evaluate the performances of its different approaches. Finally a study dedicated to the reconstitution of residual flux using a capacitive voltage transformer (CVT) has been carried on in order to apply the controlled switching algorithm in substations using their existing measurement equipments.

Nesta pesquisa, apresentam-se os principais eventos relacionados com a proteção de transformadores e sua correlação com os distúrbios de qualidade da energia elétrica (QEE). Neste sentido, foi desenvolvido um algoritmo que utiliza a transformada Wavelet (TW) e a lógica Fuzzy (LF) para classificar os eventos transitórios associados à proteção de transformadores. Estes eventos foram observados em um sistema elétrico de potência (SEP) simulado com a utilização do software Alternative Transients Program (ATP). Importa ressaltar que o sistema modelado apresenta transformadores ligados em paralelo, possibilitando o estudo de eventos decorrentes desta situação, como a energização solidária (Sympathetic Inrush). Por este SEP, modelado sobre parâmetros reais, foram simuladas várias situações transitórias, que provocam o aparecimento de correntes diferenciais, sendo estas direcionadas para análise do algoritmo desenvolvido. Afirma-se que, nos testes realizados, o algoritmo proposto apresentou um desempenho satisfatório perante as mais variadas situações a que foi submetido, identificando as causas das correntes diferenciais, sejam proporcionadas por defeitos ou por outras condições de operação aplicadas. / In this research, the main events related to the transformer protection and its correlation with the power quality disturbances (PQ) are presented. In this context, an algorithm based on Wavelet transform (WT) and Fuzzy logic (FL) was developed to classify the transient events associated with the transformer protection. These events were observed in an electrical power system (EPS) simulated using the Alternative Transients Program (ATP) software. It should be emphasized that the modeled system presents transformers connected in parallel, allowing the study of events of this situation, such as sympathetic inrush. For the simulated EPS, modeled based on real parameters, various transients situationswere simulated, causing the appearance of differentials currents which were directed to the analysis. The proposed algorithm showed a satisfactory performance tomany situations, identifying the causes of the differentials currents, either provided by faults or other operation conditions.

Lors de la réalimentation des auxiliaires d'une tranche nucléaire ou hydraulique, l'étape la plus à risque est la remise sous tension brusque du transformateur à cause des surtensions et courants d'appels générés. Ces phénomènes transitoires engendrent des effets très indésirables autant pour le réseau comme pour le transformateur (efforts électrodynamiques sous les bobinages, vibration du circuit magnétique, bruit et vieillissement prématuré du transformateur.) Le but de ces travaux de thèse est de proposer de nouvelles méthodologies permettant d'évaluer les paramètres mal connus (les valeurs des flux rémanents présents dans le circuit magnétique du transformateur avant sa mise sous tension). Face aux problèmes actuelles pour l'estimer (méthode non directe, dérive, imprécision de la mesure de la tension, etc.), deux nouvelles méthodes basées sur la magnétisation préalable du circuit magnétique (méthode de prefluxing) et sur la mesure des flux de fuites du circuit magnétique (méthode de mesure directe de flux par mesure de l’induction magnétique) sont proposées. / During the re-energization of the auxiliaries of a nuclear or hydraulic power plant, the most dangerous step is the re-energization of the power transformer, because of the temporary overvoltage and inrush currents. These transients phenomenon causes undesirable effects for both network and for the power transformer (electrodynamic forces over the windings, the magnetic circuit’s vibration, noise and the premature aging of the transformer). The goal of these thesis is to suggest new methodologies allowing us to evaluate unknown parameters (the residual flux’s values in the magnetic circuit before transformer’s energization). According to the latest problems in order to evaluate it (no direct method, derivation, voltage measurement error, etc) two new methods based on the previous magnetization of the magnetic circuit (prefluxing method) and on the leakage flux measurement of the magnetic circuit (direct measurement of the flux by measuring the magnetic induction method) are proposed.

Cette thèse présente un nouveau système de stabilisation de la tension batterie spécialement destinés aux véhicules Stop-Start, économique et compact, nommé LVSS (Linear Voltage Stabilization System). Le LVSS se comporte comme une résistance variable et limite le courant à l’aide de transistors MOSFET fonctionnant en mode linéaire. Il permet donc de stabiliser la tension de la batterie pendant le démarrage du moteur à combustion interne (ICE). Un prototype a été conçu et testé sur une voiture. Les résultats ont montré que la tension était stabilisée tout en limitant le courant de démarrage. De plus la solution proposée n’impacte pas sur les performances globales du système Stop-Start et comme les transistors fonctionnent en mode linéaire, cette solution n’émet pas de perturbations CEM. / This thesis presents a new Linear Voltage Stabilization System (LVSS) specially designed for µ-hybrid vehicles using the Stop-Start function. The LVSS stabilizes the battery voltage during the start-up of the Internal Combustion Engine (ICE) limiting the start-up current using parallels MOSFETs working in linear mode. A prototype was developed and tested in a car. Results have shown the battery voltage properly stabilized limiting the start-up current. Furthermore the proposed solution does not impact on the overall performance of the Stop-Start. Main advantages are its small volume, low price and the fact that there is no EMC perturbation as transistors work in linear mode.

The brushed DC motor is a source of electromagnetic emission that may cause interference. The main issues with brushed DC motor are arcing, which occurs between the brushes and commutator, and inrush current. It is possible to decrease the electromagnetic emissions by addressing the source (brushed dc motor) and the installation. The source may be addressed by using filters in the form of X2Y-capacitors on the terminals or ferrites on the cables. The installation does not produce any emission, but it is possible to lower its contribution. This is done by altering the installation like changing the placement of cables and provide good coupling. An effective way of decreasing inrush currents is by using negative-thermal-coefficient (NTC) thermistors. Another measure to improve the EMC properties of the brushed DC motor is to design the motor so that it can trap EM emissions. Some of these parameters are motor house material, end-cap material, vent holes or slots on motor housing, placement of power terminals, crimping tabs and motor enclosure.

In this thesis is described the function and design of the transformer designed on ferromagnetic core, composed of transformer sheets. It is explained a transient inrush current of the transformer. In this work is inserted voltage and current waveforms, designed printed circuit board, serving to reduce the inrush current.

In this thesis is described the function and design of the transformer designed on ferromagnetic core, composed of transformer sheets. It is explained a transient inrush current of the transformer. In this work is inserted voltage and current waveforms, designed printed circuit board, serving to reduce the inrush current.

Hydropower is the most important power balancing resource in the Swedish electrical power system, regulating the power supply to match the load. Consequently, several hydropower plants have periods of stand-by operation where the power production is absent but where several devices within a plant are still active. Such a device is the step-up power transformer, which during stand-by operation still generates no-load energy losses. These losses can accumulate to a considerable amount of energy and costs during the long technical lifetime of the apparatus. One option to minimize these no-load energy losses is by turning the transformer off when its generating unit is in stand-by operation. However, when this transformer operational change has been explained to experts in the field, the most common response has been that a more frequent reenergizing of a transformer leads to higher risks for errors or transformer breakdowns. This study aimed to analytically investigate three effects from this operational change. First, the potential of fatigue failure for the windings due to the increased sequences of inrush current. Secondly, the thermal cycling as a consequence of change in present losses. Lastly, the energy and economic saving potentials for hydropower plants where this operational adjustment is applied. The study used both established as well as analytical tools explicitly created for this study. These were then applied on currently active transformers in different plant categories in Fortum’s hydropower fleet.  The study primarily showed three things. Firstly, risk of fatigue failure due to the increased presence of inrush currents did not affect the transformer’s technical lifetime. Secondly, the thermal cycling changes were slightly larger with absent no-load losses during stand-by operation. The average temperature for the transformer decreased, which in general is seen as a positive indicator for a longer insulation lifetime and thus the transformer’s technical lifetime. Finally, the created frameworks showed the potential of saving energy and money for all plant categories, where the potential grew with the installed production capacity and the stand-by operation timeshare. Despite the simplifications made to describe the complex reality of a transformer operating in a hydropower plant, this thesis contributes to lay a foundation for future investigation of an easy adjustment to avoid unnecessary energy losses and costs for transformers in hydropower plants.

Submitted by Edisangela Bastos (edisangela@ufpa.br) on 2014-01-13T19:13:15Z No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Tese_IdentificacaoCorrentesInrush.pdf: 2054419 bytes, checksum: 36597eb5c3f5ca05153702c4e53b98db (MD5) / Approved for entry into archive by Ana Rosa Silva(arosa@ufpa.br) on 2014-01-15T13:17:40Z (GMT) No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Tese_IdentificacaoCorrentesInrush.pdf: 2054419 bytes, checksum: 36597eb5c3f5ca05153702c4e53b98db (MD5) / Made available in DSpace on 2014-01-15T13:17:40Z (GMT). No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Tese_IdentificacaoCorrentesInrush.pdf: 2054419 bytes, checksum: 36597eb5c3f5ca05153702c4e53b98db (MD5) Previous issue date: 2013 / A principal dificuldade encontrada na proteção diferencial de transformadores de potência é a correta distinção entre as correntes de inrush e as correntes de faltas internas. Tradicionalmente os relés diferenciais executam esta tarefa utilizando a técnica de restrição por harmônicos baseada na premissa de que as correntes de inrush possuem alta concentração de componentes harmônicas de segunda ordem, contudo essa técnica nem sempre é eficaz. O presente trabalho tem como objetivo apresentar a proposta de duas novas metodologias capazes de realizar a identificação e distinção entre as correntes de inrush das correntes de faltas internas na proteção diferencial de transformadores de potência através de metodologias que não dependem do conteúdo de harmônicos do sinal da corrente diferencial. A primeira metodologia proposta, denominada de método do gradiente da corrente diferencial, é baseada no comportamento do vetor gradiente, obtido através da diferenciação numérica do sinal da corrente diferencial. O critério de distinção utilizado é baseado no desvio padrão do ângulo do vetor gradiente que apresenta comportamento diferenciado para correntes de inrush e correntes de curto-circuito. A segunda metodologia proposta é baseada na capacidade de reconhecimento e classificação de padrões das redes neurais de Mapeamento Auto-organizável de Kohonen. Como padrão de entrada e de treinamento da rede neural é utilizado um vetor contendo quatro níveis do espectro do desvio padrão do ângulo do vetor gradiente da corrente diferencial nas três fases do transformador de potência. A eficácia dos métodos foi testada através da simulação de diversas situações de faltas internas e correntes de inrush, incluindo situações de “Sympathetic Inrush”, em um transformador de potência usando o software EMTP/ATP e através da implementação do algoritmo em MATLAB®, apresentando resultados altamente promissores. / A principal dificuldade encontrada na proteção diferencial de transformadores de potência é a correta distinção entre as correntes de inrush e as correntes de faltas internas. Tradicionalmente os relés diferenciais executam esta tarefa utilizando a técnica de restrição por harmônicos baseada na premissa de que as correntes de inrush possuem alta concentração de componentes harmônicas de segunda ordem, contudo essa técnica nem sempre é eficaz. O presente trabalho tem como objetivo apresentar a proposta de duas novas metodologias capazes de realizar a identificação e distinção entre as correntes de inrush das correntes de faltas internas na proteção diferencial de transformadores de potência através de metodologias que não dependem do conteúdo de harmônicos do sinal da corrente diferencial. A primeira metodologia proposta, denominada de método do gradiente da corrente diferencial, é baseada no comportamento do vetor gradiente, obtido através da diferenciação numérica do sinal da corrente diferencial. O critério de distinção utilizado é baseado no desvio padrão do ângulo do vetor gradiente que apresenta comportamento diferenciado para correntes de inrush e correntes de curto-circuito. A segunda metodologia proposta é baseada na capacidade de reconhecimento e classificação de padrões das redes neurais de Mapeamento Auto-organizável de Kohonen. Como padrão de entrada e de treinamento da rede neural é utilizado um vetor contendo quatro níveis do espectro do desvio padrão do ângulo do vetor gradiente da corrente diferencial nas três fases do transformador de potência. A eficácia dos métodos foi testada através da simulação de diversas situações de faltas internas e correntes de inrush, incluindo situações de “Sympathetic Inrush”, em um transformador de potência usando o software EMTP/ATP e através da implementação do algoritmo em MATLAB®, apresentando resultados altamente promissores.

Hydropower is the most important power balancing resource in the Swedish electrical power system, regulating the power supply to match the load. Consequently, several hydropower plants have periods of stand-by operation where the power production is absent but where several devices within a plant are still active. Such a device is the step-up power transformer, which during stand-by operation still generates no-load energy losses. These losses can accumulate to a considerable amount of energy and costs during the long technical lifetime of the apparatus. One option to minimize these no-load energy losses is by turning the transformer off when its generating unit is in stand-by operation. However, when this transformer operational change has been explained to experts in the field, the most common response has been that a more frequent reenergizing of a transformer leads to higher risks for errors or transformer breakdowns. This study aimed to analytically investigate three effects from this operational change. First, the potential of fatigue failure for the windings due to the increased sequences of inrush current. Secondly, the thermal cycling as a consequence of change in present losses. Lastly, the energy and economic saving potentials for hydropower plants where this operational adjustment is applied. The study used both established as well as analytical tools explicitly created for this study. These were then applied on currently active transformers in different plant categories in Fortum’s hydropower fleet. The study primarily showed three things. Firstly, risk of fatigue failure due to the increased presence of inrush currents did not affect the transformer’s technical lifetime. Secondly, the thermal cycling changes were slightly larger with absent no-load losses during stand-by operation. The average temperature for the transformer decreased, which in general is seen as a positive indicator for a longer insulation lifetime and thus the transformer’s technical lifetime. Finally, the created frameworks showed the potential of saving energy and money for all plant categories, where the potential grew with the installed production capacity and the stand-by operation timeshare. Despite the simplifications made to describe the complex reality of a transformer operating in a hydropower plant, this thesis contributes to lay a foundation for future investigation of an easy adjustment to avoid unnecessary energy losses and costs for transformers in hydropower plants