Nesta dissertação, discorre-se sobre manobra sincronizada de disjuntores. Entre as atividades desenvolvidas para a sua elaboração estão a análise de transitórios causados por manobras em capacitores, reatores e linhas de transmissão, estudos de sobretensão e estudos para a determinação de instantes favoráveis às manobras, sob o ponto de vista de diminuição de sobretensões. Completa a dissertação a especificação de equipamento de sincronismo que, a partir de medições em tempo real de variáveis elétricas - que interferem nas sobretensões - e de variáveis climáticas - que interferem no tempo de acionamento dos contatos dos disjuntores - calculam o tempo de atraso necessário para o fechamento elétrico em instantes mais convenientes. / The scope of this dissertation is the study of synchronized switching of circuit breakers. The transients caused by capacitor, reactor and transmission line switching are analyzed, for overvoltage evaluation and to determined the favorable time in the wave that leads to smallest overvoltages. Finally the specification of an equipment is produced. The equipment acquire, in real time, the values of electrical variables (current and voltages) the ambient temperature and oil pressure in the circuit breaker operating mechanism, voltage in the auxiliary system and assign a delay in the breaker switching time in order to control overvoltages.

Nesta dissertação, discorre-se sobre manobra sincronizada de disjuntores. Entre as atividades desenvolvidas para a sua elaboração estão a análise de transitórios causados por manobras em capacitores, reatores e linhas de transmissão, estudos de sobretensão e estudos para a determinação de instantes favoráveis às manobras, sob o ponto de vista de diminuição de sobretensões. Completa a dissertação a especificação de equipamento de sincronismo que, a partir de medições em tempo real de variáveis elétricas - que interferem nas sobretensões - e de variáveis climáticas - que interferem no tempo de acionamento dos contatos dos disjuntores - calculam o tempo de atraso necessário para o fechamento elétrico em instantes mais convenientes. / The scope of this dissertation is the study of synchronized switching of circuit breakers. The transients caused by capacitor, reactor and transmission line switching are analyzed, for overvoltage evaluation and to determined the favorable time in the wave that leads to smallest overvoltages. Finally the specification of an equipment is produced. The equipment acquire, in real time, the values of electrical variables (current and voltages) the ambient temperature and oil pressure in the circuit breaker operating mechanism, voltage in the auxiliary system and assign a delay in the breaker switching time in order to control overvoltages.

This thesis analyses the controlled switching methods applied to modern SF6 type circuit breakers for the purpose of reducing switching overvoltages. Main emphasis is placed on controlled switching methods applied at extra high voltage level, since the cost of failures caused by switching overvoltages is highest in this voltage level. After a brief introduction about circuit breakers in general, switching overvoltages and controlled switching methods are analysed. Also a case study about controlled switching of an unloaded overhead line is provided, and success of controlled switching method is evaluated.

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.

Switching of shunt reactors and capacitor banks is known to cause a very high rate of rise of transient recovery voltage across the circuit breaker contacts. With improvements in circuit breaker technology, modern SF6 puffer circuits have been designed with less interrupter per pole than previous generations of SF6 circuit breakers. This has caused modern circuit breakers to operate with higher voltage stress in the dielectric recovery region after current interruption. Catastrophic failures of modern SF6 circuit breakers have been reported during shunt reactor and capacitor bank de-energisation. In those cases, evidence of cumulative re-strikes has been found to be the main cause of interrupter failure. Monitoring of voltage waveforms during switching would provide information about the magnitude and frequency of small re-ignitions and re-strikes. However, measuring waveforms at a moderately high frequency require plant outages to connect equipment. In recent years, there have been increasing interests in using RF measurements in condition monitoring of switchgear. The RF measurement technique used for measuring circuit breaker inter-pole switching time during capacitor bank closing is of particular interest. In this thesis, research has been carried out to investigate switching transients produced during circuit breaker switching capacitor banks and shunt reactors using a non-intrusive measurement technique. The proposed technique measures the high frequency and low frequency voltage waveforms during switching operations without the need of an outage. The principles of this measurement technique are discussed and field measurements were carried out at shunt rector and capacitor bank installation in two 275 kV air insulated substations. Results of the measurements are presented and discussed in this thesis. The proposed technique shows that it is relatively easy to monitor circuit breaker switching transients and useful information on switching instances can be extracted from the measured waveforms. Further research works are discussed to realise the full potential of the measuring technique.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / A busca por soluções mitigatórias, no que tange aos efeitos das sobretensões transitórias atreladas às manobras de energizações e religamentos das linhas de transmissão, contemplam um tema desafiador e com fortes impactos sobre a coordenação de isolamento dos sistemas elétricos. Muito embora o reconhecimento de propostas clássicas e comerciais para a atenuação destes fenômenos, outras possibilidades, certamente, ainda são meritórias de destaque e investigações. Neste contexto, a presente dissertação encontra-se alicerçada na exposição dos fundamentos físicos e matemáticos de uma estratégia baseada em chaveamentos controlados, cujos instantes para o religamento da linha são pré-programados. A avaliação computacional da eficácia da metodologia é realizada utilizando o simulador ATP, no qual são efetuados estudos em um sistema elétrico típico submetido à curtos-circuitos sucedidos por desligamentos e subsequentes religamentos, sob a ação da tecnologia aqui focada e na ausência da mesma. / The search for mitigation solutions, with respect to the effects of overvoltages linked to the energization and reclosing maneuvers of transmission lines include a challenging subject with strong impact on the insulation coordination of electrical systems. Although the recognition of classical and commercial proposals to mitigate these phenomena, other possibilities are certainly still worthwhile highlighting and investigations. In this context, the present work is grounded in the exposure of the physical and mathematical foundations of a strategy based on controlled switchings, whose moments to the line reclosing are pre-programmed. The computational evaluation of the effectiveness of the methodology is made using the ATP simulator, which are studies in a typical electrical system subjected to the action of short-circuits fallowed by shutdowns and subsequent reclosing, under the action of technology here focused and lack thereof. / Dissertação (Mestrado)