Dissertations / Theses on the topic 'Power transformer inrush current'

Este trabalho apresenta um procedimento completo de simulação da proteção digital diferencial aplicada a transformadores de potência, visando o emprego deste à avaliação do comportamento de relés comercialmente disponíveis. Foi escolhido o software ATP (Alternative Transients Program) como ferramenta para a simulação de distintas situações sobre um sistema diferencial de proteção aplicado a um transformador de 25 MVA. Dentre as ocorrências evidenciadas, destacam-se: situações de faltas internas, faltas externas, situações de energização e energização com falta interna do transformador, condição de sobreexcitação e de saturação de TC (Transformador de Corrente). Cabe comentar que das simulações a real caracterização sobre o relé em teste, fez-se necessário todo um pré-processamento e análise da informação que será convenientemente abordada e justificada no trabalho apresentado, denotando-se um procedimento comum de teste a ser adotado a esta filosofia de proteção. A metodologia e esquema prático adotado trazem uma contribuição importante para a análise laboratorial de modelagens e simulações aplicadas a relés de proteção presentes no mercado e contribui de maneira substancial para os estudos teóricos de possíveis soluções para limitações eventualmente encontradas<br>This dissertation presents a complete procedure of simulation of digital differential protection applied to power transformers, focusing on its use to evaluate of the behavior of commercially available relays. Software ATP (Alternative Transients Program) was chosen as a tool for the simulation of distinct situations in a differential protection system applied to a 25 MVA three-phase transformer. Amongst the evidenced occurrences internal and external fault conditions, energization with or without internal fault of a three-phase transformer, overexcitation and CT (Current Transformer) saturation conditions were distinguished. It should be mentioned that from simulations to the characterization the real situations on the relay in test, a pre-processing and analysis of the information were necessary, and will be justified in the present study, denoting a common test procedure to be adopted to this philosophy of protection

This thesis investigates the impact of resonant overvoltages and their origin. Series and parallel resonances are present in any electrical grid. The frequency of which this resonance occurs is called resonance frequency. For parallel resonance, which is mainly being studied in this thesis, a high impedance peak can be found at the resonance frequency. This impedance peak in conjunction with a harmonic rich current cause a kind of temporary overvoltages called resonant overvoltages. The harmonic content of the current is high following a fault clearing in the grid, due to transformer saturation. The resonance frequency is heavily dependent on the amount of reactance present in the grid, which entail that a change in reactance causes a change in the resonance frequency. The electromagnetic transient tool PSCAD has been used to investigate resonant overvoltages following transformer energization caused by faults and switching in Stockholm. Secondly, a model was created of a grid connecting off-shore wind power to the mainland via long AC submarine transmission cables. These cables, having a high capacitance, lower the resonance frequency. Faults in this model were simulated to investigate the phenomenon of resonant overvoltages in such a grid. This was especially interesting due to Swedens planned expansion of wind power in the Baltic sea. While resonant overvoltages were found in Stockholm they were not deemed significant due to their low magnitude and longevity. However, severe resonant overvoltages were found in the off-shore wind farm model. The worst resonant overvoltages had a maximum amplitude of the 2nd order harmonic voltage of 130 kV which, while eventually damped, were significant for up to 50 periods. Lastly, the phenomenon of an increased resonance frequency during the saturation of a transformer was studied. The most severe resonant overvoltages occured in a model where the frequency scans showed a resonance frequency of 98 Hz. Indicating, caution needs to be had during EMT-studies of resonant overvoltages while choosing what resonance frequency to study.

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<br>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

The present PhD thesis deals with transformer inrush current in offshore grids including offshore wind farms and High Voltage Direct Current (HVDC) transmission systems. The inrush phenomenon during transformers energization or recovery after the fault clearance is one of important concerns in offshore systems which can threaten the security and reliability of the HVDC grid operation as well as the wind farms function. Hence, the behaviour of wind turbines,Voltage Source Converters (VSC) and transformer under the normal operation and the inrush transient mode is analyzed. For inrush current reduction in the procedure of the offshore wind farms start-up and integration into the onshore AC grid, a technique based on Voltage Ramping Strategy (VRS) is proposed and its performance is compared with the operation of system without consideration of this approach. The new methodology which is simple, cost-effective ensures minimization of transformer inrush current in the offshore systems and the enhancement of power quality and the reliability of grid under the transformer energizing condition. The mentioned method can develop much lower inrush currents according to the slower voltage ramp slopes. Concerning the recovery inrush current, the operation of the offshore grid especially transformers is analyzed under the fault and the system restoration modes.The recovery inrush transient of transformers can cause tripping the HVDC and wind farms converters as well as disturbing the HVDC power transmission. A voltage control design based on VRS is proposed in HVDC converter to recover ali the transformers in offshore grid with lower inrush currents.The control system proposed can assure the correct performance of the converters in HVDC system and in wind farm and also the robust stability of the offshore grid.<br>Esta tesis doctoral estudia las corrientes de energización de transformadores de parques eólicos marinos con aerogeneradores con convertidores en fuente de tensión (VSC) de plena potencia conectados a través de una conexión de Alta Tensión en Corriente Continua (HVDC). Las corrientes de energización pueden disminuir la fiabilidad de la transmisión eléctrica debido a disparos intempestivos de las protecciones durante la puesta en marcha o recuperación de una falta. Para la mitigación de las corrientes de energización durante la puesta en marcha del parque esta tesis propone una nueva estrategia basada en incrementar la tensión aplicada por el convertidor del parque eólico en forma de rampa (VRS). Este método persigue energizar el parque eólico con el menor coste y máxima fiabilidad. La tesis analiza diferentes escenarios y diferentes rampas. Otro momento en que las corrientes de energización pueden dar lugar a un disparo intempestivo de las protecciones es durante la recuperación de una falta en la red de alterna del parque eólico marino. Esta tesis extiende la estrategia VRS, utilizada durante la puesta en marcha del convertidor del parque, para los escenarios de recuperación de una falta.

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.

Transformers are essential components facilitating transmission and distribution of electric power. Energisation of transformers, however, can cause core operating at deep saturation region and thereby induce transient inrush currents of high magnitude and with rich harmonics. This can lead to undesirable effects including potential damage to the transformer itself, relay mal-operation, harmonic resonant overvoltages, and reduced power quality in the system (mainly in the form of voltage dips). This thesis investigates voltage dips caused by energising generator step-up (GSU) transformers and two types of generation connection are studied: one is a combine cycle gas turbine (CCGT) plant connected to a 400 kV transmission grid and the other is a large offshore wind farm connected to a 132 kV distribution grid. To carry out the investigation, detailed network models were developed in alternative transients program/electromagnetic transients program (ATP/EMTP) and validated with the help of field measurements. For the connection of generation in the transmission grid, deterministic assessment was conducted to comparatively analyse voltage dips caused by energising large GSU transformers under different energisation conditions and different network conditions; special attention was paid to the energisation cases involving sympathetic inrush between transformers by addressing its prolonging effects on voltage dips, with sensitivity studies further carried out to identify the key influential parameters. In addition, stochastic assessment was conducted by applying Monte Carlo method, which helps identify the dip frequency pattern and the likelihood of reaching the dip magnitude resulted from the commonly agreed worst case energisation condition; their sensitivities to the variation of circuit breaker closing time span, transformer core residual flux, system condition and the number of transformers being energized together were also investigated. Furthermore, possible cost-effective operational approaches to mitigate the voltage dips were explored and compared. For the connection of large offshore wind farm, voltage dips caused by energising wind turbine transformers under different scenarios were assessed; in particular, sympathetic inrush between wind turbine transformers were studied, and the energisation sequence resulting in less sympathetic inrush was deterministically identified and stochastically validated. The simulation results of deterministic studies indicate that, when carrying out energisation of a large GSU transformer in the transmission grid under the commonly agreed worst case energisation condition, the dip magnitude can reach 9.6% and the duration 2.7 seconds; moreover, when coupled with sympathetic inrush, the duration can be prolonged by 136%, lasting for 6.4 seconds. The sensitivity studies show that transformer core saturation inductance is the key parameter determining dip magnitude and transformer copper losses is the key parameter determining dip duration. Stochastic assessment of voltage dips shows that, out of 1000 stochastic dip events, less than 0.5% of the dips can reach the worst case dip magnitude and about 80% are of magnitudes less than 0.6 pu of the worst case dip magnitude; the dip frequency pattern is found to be insensitive to the circuit breaker closing time variation but can be considerably influenced by the residual flux distribution. In terms of mitigation measures, it was proven that, by adjusting tap changer position, applying static var compensator and even opening coupler circuit breaker in the substation, the degree of voltage dip especially the dip duration can be significantly reduced. Contrasting to those observed in the transmission grid, voltage dips resulted from energising wind turbine transformers in large offshore wind farms are of less concern; dip magnitudes are no more than 1% in the case of energising a stand-alone wind turbine transformer. However, sympathetic inrush between wind turbine transformers within one feeder was found to be significant and the energisation sequence resulting in less sympathetic inrush is to separately energise the wind turbine transformer from the one closest to the offshore platform to the one farthest away from the platform.

The UK Government has set an ambitious target to achieve 15% of final energy consumption from renewable sources by 2020. High Voltage Direct Current (HVDC) technology is an attractive solution for integrating offshore wind power farms farther from the coast. In the near future, more windfarms are likely to be connected to the UK grid using HVDC links. With the onset of this fairly new technology, new challenges are inevitable. This research is undertaken to help assist with these challenges by looking at possibilities of problems with respect to faster AC/DC interaction modes, especially, on the impact of inrush currents which occur during fault-recovery transients. In addition to that, possible mitigation strategies are also investigated. Initially, the relative merits of different transformer models are analysed with respect to inrush current transient studies. The most appropriate transformer model is selected and further validated using field measurement data. A detailed electro-magnetic-transient (EMT) model of a grid-connected MMC-HVDC system is prepared in PSCAD/EMTDC to capture the key dynamics of fault-recovery transformer inrush currents. It is shown that the transformer in an MMC system can evoke inrush currents during fault recovery, and cause transient interactions with the converter and the rest of the system, which should not be neglected. It is shown for the first time through a detailed dynamic analysis that if the current sensors of the inner-current control loops are placed at the converter-side of the transformer instead of the grid-side, the inrush currents will mainly flow from the grid and decay faster. This is suggested as a basic remedial action to protect the converter from inrush currents. Afterwards, analytical calculations of peak flux-linkage magnitude in each phase, following a voltage-sag recovery transient, are derived and verified. The effects of zero-sequence currents and fault resistance on the peak flux linkage magnitude are systematically explained. A zero-sequence-current suppression controller is also proposed. A detailed study is carried out to assess the key factors that affect the maximum peak flux-linkage and magnetisation-current magnitudes, especially with regard to fault specific factors such as fault inception angle, duration and fault-current attenuation. Subsequently, the relative merits of a prior-art inrush current mitigation strategy and its implementation challenges in a grid-connected MMC converter are analysed. It is shown that the feedforward based auxiliary flux-offset compensation scheme, as incorporated in the particular strategy, need to be modified with a feedback control technique, to alleviate the major drawbacks identified. Following that, eight different feedback based control schemes are devised, and a detailed dynamic and transient analysis is carried out to find the best control scheme. The relative merits of the identified control scheme and its implementation challenges in a MMC converter are also analysed. Finally, a detailed EMT model of an islanded MMC-HVDC system is implemented in PSCAD/EMTDC and the impacts of fault-recovery inrush currents are analysed. For that, initially, a MMC control scheme is devised in the synchronous reference frame and its controllers are systematically tuned. To obtain an improved performance, an equivalent control scheme is derived in the stationary reference frame with Proportional-Resonant controllers, and incorporated in the EMT model. Following that, two novel inrush current mitigation strategies are proposed, with the support of analytical equations, and verified.

This thesis investigates the operation of the current transfonner (CT) when sensing retum-to-zero current pulses in power electronic circuitry. The CT's output signal is nonnally rectified when sensing current pulses and the effects of the different rectification techniques on peak current and average current droop are evaluated. Initially, the various current sensing techniques and their application in power electronics circuits are reviewed. The CT and both diode and synchronous rectification are then reviewed in more detail. Operation of the CT with diode rectification (DR) and natural resetting is investigated. Three operating modes are identified. These are the discontinuous magnetizing current, continuous magnetizing current and discontinuous secondary current modes. The error (droop) in the average output signal obtained is found to be predominantly defined by CT core losses. Coefficients are given for correcting the error due to droop, provided that the discontinuous secondary current mode is avoided. Diode rectification with the dual CT arrangement is also investigated. Operation of the CT with synchronous rectification (SR) and natural resetting is then investigated. The SR topologies possible using a discrete MOSFET are categorized. During experimentation the arrangement used to drive the MOSFET's gate is found to be important if distortion is to be minimized. It also is found that the average current droop is dependent on the oscillatory behaviour of the resetting circuit and has an effectively random component. The magnitude of this component is defined by the voltage drop exhibited by the SR MOSFET's intrinsic anti-parallel diode. SR is then implemented using a commercially available analogue switch. The problems detailed with the use of a discrete MOSFET are largely alleviated. Another benefit is that the increased restriction on maximum duty factor imposed by introducing a discrete MOSFET is also eased. However, whichever SR technique is implemented, an operational amplifier is used and the transient response of this circuit element is important. A method of minimizing droop by indirect sensing of the CT's peak core flux excursion is then presented. A corresponding correcting voltage is applied in series with the CT's output terminals during a current pulse. The magnitude of this voltage is based on the magnitude of the resetting voltage sensed during previous switching cycles. A circuit is implemented and simulated. Experimental results are presented. A switched-mode circuit operating at a frequency higher than that of the main power circuit is then used to apply the correcting voltage with the objective of reducing the power drawn. Again, the circuit is implemented and simulated and experimental results are presented.

This dissertation presents the development of an algorithm for classifying electrical transients in power transformers for protection. Initially the main transient involving power transformers were analyzed, with a special focus on the magnetizing current that occur during energizing equipment, known as inrush currents. Among the studied transient, current inrush are those that present greater difficulty in identification and discrimination by the differential protection, due to its high peak magnitude. In a second moment, was developed a test system implemented in ATP / EMTP software for the simulation of different operating situations of the power transformer, current data being obtained from TCs for analysis. After known the problem and implement a test for acquisition system, we developed an algorithm based on the last samples of the detail coefficients, called Details Signals, from the decomposition of the data of differential phase current using the Discrete Wavelet Transform. The methodology has the objective improve the system for protection of the transformer, becoming one efficient alternative for the identification of transients.<br>Esta dissertação apresenta o desenvolvimento de um algoritmo para classificação de transitórios elétricos em transformadores de potência, para fins de proteção. Inicialmente foram analisados os principais transitórios associados aos transformadores de potência, tendo um foco especial na corrente de magnetização que surge durante a energização do equipamento, conhecida como corrente de inrush. Dentre os transitórios estudados, as correntes de inrush são as que apresentam maior dificuldade de identificação e discriminação por parte da proteção diferencial, devido a sua alta magnitude de pico. Em um segundo momento, foi desenvolvido um sistema teste implementado no software ATP para a simulação das diversas situações de operação do transformador de potência, sendo obtidos dados de correntes a partir dos TCs para análise. Após conhecer o problema e implementar um sistema teste para a obtenção dos dados, desenvolveu-se um algoritmo baseado nas últimas amostras dos coeficientes de detalhes, chamada de Sinais de Detalhes, provenientes da decomposição dos dados de correntes diferenciais das fases por meio da Transformada Wavelet Discreta. A metodologia desenvolvida tem como objetivo melhorar o sistema de proteção do transformador, tornando-se uma alternativa eficiente para a identificação de transitórios.

With deregulation, diagnosis and maintenance of power equipment, especially power transformers, become increasingly important to keep power systems in reliable operation. This dissertation systematically studied two kinds of transformer failure and abnormality cases, and then developed a new Internet based Virtual Hospital (VH) for power equipment to help power equipment diagnosis and maintenance. A practical case of generator-step-up (GSU) transformer failures in a pumped storage plant was extensively studied. Abnormal electrical phenomena associated with GSU transformers, including switching transients and very fast transients (VFT), and lightning, were analyzed. Simulation showed that circuit breaker restriking could be a major cause of transformer successive failures, and current surge arrester configuration did not provide enough lightning protection to GSU transformers. Mitigation of abnormal electrical phenomena effects on GSU transformers was proposed and discussed. The study can be a complete reference of troubleshooting of other similar transformer failures. Geomagnetically induced current (GIC) is another possible cause of transformer abnormality. A simplified method based on the equivalent magnetizing curve for transformers with different core design was developed and validated to estimate harmonic currents and MVar drawn by power transformers with a given GIC. An effective indicator was proposed using partial harmonic distortion, PHD, to show when the transformer begins saturating with the input GIC. The developed method has been applied to a real time GIC monitoring system last year for a large power network with thousands of transformers. A new Internet based Virtual Hospital (VH) for Power Equipment was conceptually developed to share experience of power equipment diagnosis and maintenance, and update the existing diagnostic techniques and maintenance strategies, and a comprehensive information model was developed for data organization, access, and archiving related to equipment diagnosis and maintenance. An Internet based interactive fault diagnostic tool has been launched for power transformers based on dissolved gas analysis (DGA). The above results and findings can help improving power equipment diagnosis and utility maintenance strategies.<br>Ph. D.

The objective of this research is to advance the field of condition monitoring of electrolytic capacitors used in power electronics circuits. The construction process of an electrolytic capacitor is presented. Descriptions of various kinds of faults that can occur in an electrolytic capacitor are discussed. The methods available to detect electrolytic capacitor faults are discussed. The effects of the capacitor faults on the capacitor voltage and current waveforms are investigated through experiments. It is also experimentally demonstrated that faults in the capacitor can be detected by monitoring the capacitor voltage and current. Various ESR estimation based detection techniques available to detect capacitor failures in power electronics circuits are reviewed. Three algorithms are proposed to track and detect capacitor failures: an FFT based algorithm, a system modeling based detection scheme, and finally a parameter estimation based algorithm. The parameter estimation based algorithm is a low-cost real-time scheme, and it is inexpensive to implement. Finally, a detailed study is carried out to understand the failure mechanism of an electrolytic capacitor due to inrush current.

Geomagnetically induced currents (GIC’s) caused by solar storms or other sources of dc excitation in the presence of ac energization can disturb the normal operation of power transformers. If large enough, they cause half-cycle saturation of a power transformer’s core which could lead to overheating due to excessive stray flux. Finite element matrix (FEM) modelling software is of considerable use in transformer engineering as it is able to solve electromagnetic fields in transformers. For many problems, typically involving only specific parts of a transformer, fairly accurate solutions can be reached quickly. Modelling the effects of GIC or leakage currents from dc systems, however, is more complex because dc components are superimposed on ac in transformers with nonlinear electrical core steel parameters. At the beginning of the investigation, FEM models of different bench-scale laboratory transformers and a 40 MVA three-phase three limb power transformer were investigated, but the results did not sufficiently represent the measurement data due to the application of widely used modelling assumptions regarding the transformer joints. Following the preliminary analyses, practical measurements and FEM simulations were carried out using three industrially made model single-phase four limb transformers (1p4L) without tanks. These test transformers resemble a real power transformer because they have high-quality grain oriented electrical core steel and parallel winding assemblies. Practical laboratory measurements recorded during ac testing were used to calibrate 2D FEM models by adding “equivalent air gaps” at the joints. The implementation of this joint detail helped to overcome the shortcomings of the preliminary FEM simulation. Analyses of the electrical and magnetic responses of the FEM models using simultaneous ac and dc then followed. A refined 3D FEM simulation with more detailed modelling of the core joints of 1p4L model transformers agreed more closely with the practical measurements of ac only no-load conditions. Further, the depiction of stray flux leaving the transformer’s saturated core under simultaneous ac and dc excitation showed an improvement in the approach as measured in the physical model. Saturation inductance (Lsat) is an important parameter for input into mid- to low-frequency lumped parameter transformer models that are used in electromagnetic transients software such as PSCAD/EMTDC, but it is not easily measured and is seldom provided by manufacturers. Some Lsat measurements on the 1p4L test transformers are presented in this thesis, along with some 3D FEM analyses. The measurements and FEM analyses investigated “air core inductance” which represents a transformer without a core, and “terminal saturation inductance” which represents deep saturation due to dc excitation. An important finding in this thesis is that “terminal saturation inductance” is the more useful of the two for topological transformer models investigating realistic GIC excitation. Further to this, a new composite depiction of half-cycle saturation with a multi-parametric relationships supported by measurement and simulation is presented. The main contribution of this thesis is that it gives more accurately the electrical response and distribution of the leakage flux under conditions such as those caused by GIC or other sources of leakage dc excitation, as well as including of joint details in the FEM models through calibration with physical models. This calibration can aid transformer modelling and design in industry for mitigation of the effects of GICs, contributing to improved transformer survival during significant geomagnetic disturbances.

High voltage power supply design presents unique requirements, combining safety, controllability, high performance, and high efficiencies. A new Resonant Self-Tracking Current-Fed Converter (RST-CFC) is investigated as a proof-of-concept of a high voltage power supply particularly for an X-ray system. These systems require fast voltage rise times and low ripple to yield a clear image. The proposed converter implements high-frequency resonance among discrete components and transformer parasitics to achieve high voltage gain, and the self-tracking nature ensures operation at maximum gain while power switches achieve zero-voltage switching across the full load range. This converter exhibits an inherent indefinite short-circuit capability. Theoretical results were obtained through simulations and verified by experimental results through a complete test configuration. Converter topology viability was confirmed through hardware testing and characterization.

Phasor Measurement Units (PMUs) are widely acknowledged as one of the most significant developments in the field of real-time monitoring of power system. By aligning time stamps of voltage and current phasor measurements, which are consistent with Coordinated Universal Time (UTC), a coherent picture of the power system state can be achieved through either direct measurements or simple linear calculations. With the growing number of PMUs installed or planned to be installed in the near future, both utilities and research institutions are looking for novel applications of synchrophasor measurements from these widely installed PMUs. In this dissertation, the author proposes two new PMUs measurements applications: three-phase instrument transformer calibration, and three-phase line parameter calculation with instrument transformers. First application is to calibrate instrument transformers. Instrument transformers are the main sensors used in power systems. They provide isolation between high voltage level of primary side and metering level of the secondary side. All the monitoring and measuring systems obtain input signals from the secondary side of instrument transformers. That means when instrument transformers are not accurate, all the measurements used in power system are inaccurate. The most important job of this dissertation is to explore a method to automatically calibrate all the instrument transformers in the power system based on real-time synchrophasor measurements. The regular instrument transformer calibration method requires the instrument transformer to be out of service (offline) and calibrated by technicians manually. However, the error of instrument transformer changes when environment changes, and connected burden. Therefore, utilities are supposed to periodically calibrate instrument transformers at least once a year. The high labor and economic costs make traditional instrument transformer calibration method become one of the urgent problems in power industry. In this dissertation we introduce a novel, low cost and easy method to calibrate three-phase instrument transformers. This method only requires one three-phase voltage transformer at one bus calibrated in advance. All other instrument transformers can be calibrated by this method as often as twice a day, based on the synchrophasor measurements under different load scenarios. Second application is to calculate line parameters during calibrating instrument transformers. The line parameters, line impedance and line shunt admittance, as needed by utilities are generated by the computer method. The computer method is based on parameters, such as the diameter, length, material characteristics, the distance among transmission line, the distance to ground and so on. The formulas to calculate line parameters have been improved and re-modeled from time to time in order to increase the accuracy. However, in this case, the line parameters are still inaccurate due to various reasons. The line parameters errors do affect the instrument transformers calibration results (with 5% to 10% error). To solve this problem, we present a new method to calculate line parameters and instrument transformers in the same processing step. This method to calibrate line parameter and instrument transformers at the same time only needs one pre-calibrated voltage transformer and one pre-calibrated current transformer in power system. With the pre-calibrated instrument transformers, the line parameter as well as the ratio correction factors of all the other instrument transformers can be solved automatically. Simulation results showed the errors between calculated line parameters and the real line parameter, the errors between calibrated ratio correction factors and the real ratio correction factors are of the order of 10e-10 per unit. Therefore, high accuracy line parameters as well as perfectly calibrated instrument transformers can be obtained by this new method. This method can run automatically every day. High accuracy and dynamic line parameters will significantly improve power system models. It will also increase the reliability and speed of the relay system, enhance the accuracy of power system analysis, and benefit all other researches using line parameters. New methods of calculating line parameter and the instrument transformer calibrations will influence the whole power industry significantly.<br>Ph. D.

Auxiliary power supply (APS) plays a key role in ensuring the safe operation of the main circuit elements including gate drivers, sensors, controllers, etc. in medium voltage (MV) silicon carbide (SiC)-based converter systems. Such a converter requires APS to have high insulation capability, low common-mode coupling capacitance (Ccm ), and high-power density. Furthermore, considering the lifetime and simplicity of the auxiliary power supply system design in the MV converter, partial discharge (PD) free and multi-load driving ability are the additional two factors that need to be addressed in the design. However, today’s state-of-the-art products have either low power rating or bulky designs, which does not satisfy the demands. To improve the current designs, this thesis presents a 1 MHz isolated APS design using gallium nitride (GaN) devices with MV insulation reinforcement. By adopting LCCL-LC resonant topology, the proposed APS is able to supply multiple loads simultaneously and realize zero voltage switching (ZVS) at any load conditions. Since high reliability under faulty load conditions is also an important feature for APS in MV converter, the secondary side circuit of APS is designed as a regulated stage. To achieve MV insulation (> 20 kV) as well as low Ccm value (< 5 pF), a current-based transformer with a single turn structure using MV insulation wire is designed. Furthermore, by introducing different insulated materials and shielding structures, the APS is capable to achieve different partial discharge inception voltages (PDIV). In this thesis, the transformer design, resonant converter design, and insulation strategies will be detailly explained and verified by experiment results. Overall, this proposed APS is capable to supply multiple loads simultaneously with a maximum power of 120 W for the sending side and 20 W for each receiving side in a compact form factor. ZVS can be realized regardless of load conditions. Based on different insulation materials, two different receiving sides were built. Both of them can achieve a breakdown voltage of over 20 kV. The air-insulated solution can achieve a PDIV of 6 kV with Ccm of 1.2 pF. The silicone-insulated solution can achieve a PDIV of 17 kV with Ccm of 3.9 pF.<br>M.S.<br>Recently, 10 kV silicon carbide (SiC) MOSFET receives strong attention for medium voltage applications. Asit can switch at very high speed, e.g. > 50 V/ns, the converter system can operate at higher switching frequency condition with very small switching losses compared to silicon (Si) IGBT [8]. However, the fast dv/dt noise also creates the common mode current via coupling capacitors distributed inside the converter system, thereby introducing lots of electromagnetic interference (EMI) issues. Such issues typically occur within the gate driver power supplies due to the high dv/dt noises across the input and output of the supply. Therefore, the ultra-small coupling capacitor (<5 pF) of a gate driver power supply is strongly desired.[37] To satisfy the APS demands for high power modular converter system, a solution is proposed in this thesis. This work investigates the design of 1 MHz isolated APS using gallium nitride (GaN) devices with medium voltage insulation reinforcement. By increasing switching frequency, the overall converter size could be reduced dramatically. To achieve a low Ccm value and medium voltage insulation of the system, a current-based transformer with a single turn on the sending side is designed. By adopting LCCL-LC resonant topology, a current source is formed as the output of sending side circuity, so it can drive multiple loads importantly with a maximum of 120 W. At the same time, ZVS can use realized with different load conditions. The receiving side is a regulated stage, so the output voltage can be easily adjusted and it can operate in a load fault condition. Different insulation solutions will be introduced and their effect on Ccm will be discussed. To further reduce Ccm, shielding will be introduced. Overall, this proposed APS can achieve a breakdown voltage of over 20 kV and PDIV up to 16.6 kV with Ccm<5 pF. Besides, multi-load driving ability is able to achieve with a maximum of 120 W. ZVS can be realized. In the end, the experiment results will be provided.

Current differential protection principle is superior in terms of sensitivity and speed of operation in comparison with other protection principle used in power systems. From the last five decades, various current differential protection schemes are widely used to protect busbars, transformers, and short-transmission lines. The deployment of high capacity microwave and optical fiber technologies redefined the line protection systems by facilitating the use of current differential protection schemes for long transmission lines. The common application issue of these schemes is mis-operation due to current transformer (CT) saturation during close-in external faults. Moreover, transformer differential protection schemes face mis-trip due to inrush current during energization. The techniques presented in the literature to address those issues, de-sensitize protection function and increase the time of operation. A comprehensive fault discrimination algorithm and an inrush current detection algorithm are highly demanded for current differential protection schemes. The purpose of this dissertation is to optimize the performance of differential schemes applied to protect busbar, transformer and line. This research derives the mathematical model of saturated secondary current of CT and introduces the concept of Partial Operating Current (POC). Based on these mathematical developments, the characteristics of POC are identified for all three types of differential zones like busbar, transformer and line protection. A new inrush current blocking algorithm is developed for transformer differential protection. A new time-domain CT saturation detection algorithm is also proposed. Based on these new developments, three separate differential schemes are designed for busbar, transformer, and line protection, respectively. The proposed schemes provide complete immunity against the mis-operations due to CT saturation during close-in external faults and transformer inrush current without sacrificing the sensitivity for internal faults. The speed of operation is also improved. The model for each scheme is built in Matlab platform and the performance is validated using the test system simulated in Electro-Magnetic Transient Program (EMTP) for all possible fault scenarios. Documented results show the improved performance of the proposed schemes when compared to traditional differential schemes in terms of reliability, sensitivity, selectivity, and speed

In order to satisfy the huge demand energy transmission in future, the DC grid concept is proposed based on voltage sourced converter (VSC) HVDC and modular multilevel converter (MMC) HVDC technologies. It provides an attractive approach for long distance power transmission such as offshore renewable energy transmission in Europe. However, there are two main obstacles in the DC grid development. The first obstacle is the DC fault detection and selective isolation. Under severe fault condition, the DC grid is desired to isolate the healthy and faulty part which implies the whole grid system will operate normally during the fault. The second obstacle is the voltage stepping in DC grid system. The high power converter is desired to achieve high voltage stepping ratio yet must be cost-effective. In this thesis, an IGBT-based DC/DC converter employing an internal inductor-capacitor-inductor (LCL) passive circuit is presented to overcome above two obstacles. The proposed converter can achieve high voltage stepping without internal AC transformer implying smaller converter size and it is also designed to have reasonable efficiency in high power application. In addition, the converter has good response even under extreme fault conditions. The IGBT-based LCL DC/DC converter design procedure and performance under fault condition is investigated based on the theoretical studies initially. The converter is modelled on PSCAD platform under normal/fault operation and the simulation results are used for converter efficiency calculation and fault analysis. The advantages of IGBT-based LCL DC/DC converter are demonstrated by comparing with other two high power DC/DC converter topologies. A low power level prototype of LCL DC/DC converter is built following the design principle. The hardware results are used to verify the theoretical conclusions. The VSC converter is defenceless to DC faults in DC grid application. In order to overco The VSC converter is defenceless to DC faults in DC grid application. In order to overcome this major drawback, a fault tolerant VSC converter employing LCL passive circuit is studied in this thesis. The LCL VSC converter design principle is presented by analysing the converter equations. The converter model is developed on PSCAD platform under normal/fault operation. An advanced control method is designed based on developed MATLAB analytical model to improve the LCL VSC converter stability. The advantages of LCL VSC converter are presented by comparing with its performance with conventional L-VSC converter considering efficiency and fault response. A fault tolerant DC grid topology employing LCL VSCs and using low speed protection is also investigated in this thesis. The simple mechanical DC circuit breakers are used at DC bus bars and at connecting points of each DC cable. A comprehensive protection scenario including DC cable differential protection, DC bus bar protection and back up protection is employed to protect the whole DC grid against any probable DC faults. An accurate DC cable model is adopted for a four-terminal DC grid which is modelled on PSCAD platform. The advantage and feasibility of this method in DC fault protection is investigated based on the developed grid model.

Current transformer saturation will cause the secondary current distortion. When saturation occurs, the secondary current will not be linearly proportional to the primary current, which may lead to maloperation of protection devices. This thesis researches and tests two detecting methods: Fast Fourier Transform (FFT) and Wavelet Transform based methods. Comparing these two methods, FFT has a better performance in steady state saturation, and Wavelet Transform can determine singularity to provide the moment of distortion. The Jiles-Atherton (J-A) theory of ferromagnetic hysteresis is one approach used in electromagnetics transient modeling. With decades of development, the J-A model has evolved into different versions. The author summarizes the different models and implements J-A model in both MATLAB and Simulink.

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.

Transformadores de potência são dispositivos que requerem atenção especial devido a sua grande importância ao sistema elétrico de potência no qual ele está conectado. Geralmente relés diferenciais são utilizados como proteção primária em transformadores de potência. Nestes relés, a corrente diferencial é comparada com um nível de ajuste e caso ocorra uma falta interna, o transformador deverá ser desconectado do restante do sistema. Entretanto, a simples detecção da presença de uma corrente diferencial não é suficiente para distinguir faltas internas de outras situações que também podem produzir tal corrente. Tais situações surgem durante a energização dos transformadores, devido a saturação dos transformadores de corrente, entre outras, as quais podem resultar em uma incorreta atuação da proteção. Uma rápida e correta discriminação entre faltas internas e outras situações é um dos desafios da moderna proteção de transformadores de potência. A respeito da identificação de faltas internas ou situações de energização, além da mencionada lógica diferencial é acrescentado uma subrotina baseada na restrição de harmônicas. Neste método, a corrente de energização é reconhecida através da presença de uma segunda harmônica obtida por filtros de Fourier. No entanto, o método de filtragem pode algumas vezes retardar a operação da proteção. Além disto, uma componente de segunda harmônica pode também estar presente durante uma falta interna. Este trabalho propõe a utilização da transformada Wavelet - uma poderosa ferramenta matemática - empregada como um meio rápido e eficiente de analisar as formas de onda de transformadores de potência e como uma alternativa a tradicional transformada de Fourier. Os sinais das correntes diferenciais são processados pelas transformadas discretas Wavelet, visando obter uma discriminação entre ambas situações (energização e falta). Um nível de limiar é utilizado após a decomposição Wavelet do sinal para discriminar entre as situações descritas. A janela de dados utilizada para este propósito pode ser variada. Para testar o algoritmo proposto, as simulações de energização e falta foram implementadas, utilizando o programa ATP (\"Alternative Transient Program\"). Em situações onde a janela de dados é reduzida para 1/4 de ciclo o critério de discriminação pode ser otimizado utilizando a transformada discreta de Wavelet auxiliada com técnicas de reconhecimento de padrões. Este trabalho apresenta a utilização de redes neurais artificiais para tal finalidade como exemplo. Resultados encorajadores são apresentados sobre a capacidade de discriminação para as situações descritas assim como a rapidez de resposta quando comparados aos métodos tradicionais.<br>Power transformers are devices that require special maintenance and care due to their importance to the electrical system to which they are connected. Generally, differential relays are used for the primary protection of large transformers. In such relays, differential currents are compared to a threshold and in the case of an internal fault, the transformer should be disconnected from the rest of the system. However, a simple detection of a differential current is not sufficient to distinguish internal faults from other situations that also produce such a current. Some of these situations appear during transformer energization (inrush currents), CT (current transformer) saturation, among others, which can result in an incorrect trip. A correct and fast distinction of internal faults from the other situations mentioned is one of the challenges for modern protection of power transformers. Concerning the identification of internal faults as opposed to inrush currents, the approach tarditionally used is the aforementioned differential logic together with harmonic restraint. In this method, transformer inrush current due to energization is recognized on the basis of second harmonic components obtained by Fourier filters. However, the filtering method can sometimes delay the protection process. In addition to this, a second harmonic component can also be present during internal faults. This work proposes Wavelet transform - a powerful mathematical tool - employed as a fast and effective means of analyzing waveforms from power transformers, as an alternative to the traditional Fourier transform. The differential signals are processed by discrete Wavelet transform to obtain the discrimination between both situations (inrush and fault). A threshold level is utilized after the Wavelet decomposition to discriminate the situations describeb. The time window used for such purpose can be varied. In order to test proposed algorithm, simulations of fault and inrush currents in a power transformer were implemented using ATP ( \"Alternative Transient Program\") software. When the time window is reduced to only 1/4 of the cycle the discrimination criteria should be optimized using a pattern recognition technique to aid the Discrete Wavelet transform. This study shows as a sample for this purpose the use of artificial neural networks. Very encouraging results are presented concerning the capacity of discrimination of the described situations as well as the speed of response when compared to the traditional method.

[Truncated abstract] This thesis studies current sensing techniques that are designed to meet the requirements for the next generation of power converters. Power converters are often standardised, so that they can be replaced with a model from another manufacturer without an expensive system redesign. For this reason, the power converter market is highly competitive and relies on cutting-edge technology, which increases power conversion efficiency and power density. High power density and conversion efficiency reduce the system cost, and thus make the power converter more attractive to the customer. Current sensing is a vital task in power converters, where the current information is required for monitoring and control purposes. In order to achieve the above-mentioned goals, existing current sensing techniques have to be improved in terms of cost, power loss and size. Simultaneously, current information needs to be increasingly available in digital form to enable digital control, and to allow the digital transmission of the current information to a centralised monitoring and control unit. All this requires the output signal of a particular current sensing technique to be acquired by an analogue-to-digital converter, and thus the output voltage of the current sensor has to be sufficiently large. This thesis thoroughly reviews contemporary current sensing techniques and identifies suitable techniques that have the potential to meet the performance requirements of the next-generation of power converters. After the review chapter, three novel current sensing techniques are proposed and investigated: 1) The usefulness of the resistive voltage drop across a copper trace, which carries the current to be measured, to detect electrical current is evaluated. Simulations and experiments confirm that this inherently lossless technique can measure high currents at reasonable measurement bandwidth, good accuracy and low cost if the sense wires are connected properly. 2) Based on the mutual inductance theory found during the investigation of the copper trace current sense method, a modification of the well-known lossless inductor current sense method is proposed and analysed. This modification involves the use of a coupled sense winding that significantly improves the frequency response. Hence, it becomes possible to accurately monitor the output current of a power converter with the benefits of being lossless, exhibiting good sensitivity and having small size. 3) A transformer based DC current sense method is developed especially for digitally controlled power converters. This method provides high accuracy, large bandwidth, electrical isolation and very low thermal drift. Overall, it achieves better performance than many contemporary available Hall Effect sensors. At the same time, the cost of this current sensor is significantly lower than that of Hall Effect current sensors. A patent application has been submitted. .... The current sensing techniques have been studied by theory, hardware experiments and simulations. In addition, the suitability of the detection techniques for mass production has been considered in order to access the ability to provide systems at low-cost.

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.

Massive deployment of wireless IoT (Internet of Things) devices makes replacement or recharge of batteries expensive and impractical for some applications. Energy harvesting is a promising solution, and various designs are proposed to harvest power from ambient resources including thermal, vibrational, solar, wind, and RF sources. Among these ambient resources, AC powerlines are a stable energy source in an urban environment. Many researchers investigated methods to exploit this stable source of energy to power wireless IoT devices. The proposed circuit aims to harvest energy from AC powerlines with a wide input range of from 10 to 50 A. The proposed system includes a wake-up circuit and is capable of cold-start. A buck-boost converter operating in DCM is adopted for impedance matching, where the impedance is rather independent of the operation conditions. So, the proposed system can be applied to various types of wireless sensor nodes with different internal impedances. Experimental results show that the proposed system achieves an efficiency of 80.99% under the powerline current of 50 A.<br>M.S.<br>Nowadays, with the magnificent growth of IoT devices, a reliable, and efficient energy supply system becomes more and more important, because, for some applications, battery replacement is very expensive and sometimes even impossible. At this time, a well-designed self-contained energy harvesting system is a good solution. The energy harvesting system can extend the service life of the IoT devices and reduce the frequency of charging or checking the device. In this work, the proposed circuit aims to harvest energy from the AC power lines, and the harvested power intends to power wireless sensor nodes (WSNs). By utilizing the efficient and self-contained EH system, WSNs can be used to monitor the temperature, pressure, noise level and humidity etc. The proposed energy harvesting circuit was implemented with discrete components on a printed circuit board (PCB). Under a power line current of 50 A @ 50 Hz, the proposed energy harvesting circuit can harvest 156.6 mW, with a peak efficiency of 80.99 %.

Renewable energy is harnessed from continuously replenishing natural processes. Some commonly known are sunlight, water, wind, tides, geothermal heat and various forms of biomass. The focus on renewable energy has over the past few decades intensified greatly. This thesis contributes to the research on developing renewable energy technologies, within the wind power, wave power and marine current power projects at the division of Electricity, Uppsala University. In this thesis grid connection of permanent magnet generator based renewable energy sources is evaluated. A tap transformer based grid connection system has been constructed and experimentally evaluated for a vertical axis wind turbine. Full range variable speed operation of the turbine is enabled by using the different step-up ratios of a tap transformer. This removes the need for a DC/DC step or an active rectifier on the generator side of the full frequency converter and thereby reduces system complexity. Experiments and simulations of the system for variable speed operation are done and efficiency and harmonic content are evaluated.  The work presented in the thesis has also contributed to the design, construction and evaluation of a full-scale offshore marine substation for wave power intended to grid connect a farm of wave energy converters. The function of the marine substation has been experimentally tested and the substation is ready for deployment. Results from the system verification are presented. Special focus is on the transformer losses and transformer in-rush currents. A control and grid connection system for a vertical axis marine current energy converter has been designed and constructed. The grid connection is done with a back-to-back 2L-3L system with a three level cascaded H-bridge converter grid side. The system has been tested in the laboratory and is ready to be installed at the experimental site. Results from the laboratory testing of the system are presented.<br>Wind Power<br>Wave Power<br>Marine Currnet Power

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.

This Thesis addressed the challenge of ensuring balanced currents in the phases of a multi-kW, interleaved dc-dc converter by means of closed-loop digital control. The Thesis examines uniformly-sampled, valley-current, peak-current and average-current control for a dual interleaved boost converter with inter-phase transformer which might form part of the power train of an electric vehicle. Also, an enhancement of the average-current control is investigated in which the transistor duty-ratio is updated more rapidly, which allows an improvement of approximately ten times in the response speed of the system. Based on the theoretical analysis, the average-current control methodology was determined to be the most suitable technique for this type of converter as it ensures well-balanced phase currents over a wide range. To provide a basis for control system analysis and design for interleaved converters, a modelling methodology is developed based on a combination of multi-rate data-sampled theory and a small-signal averaged converter model. The model is shown to represent accurately the interaction between the interleaved phases, revealing a reduced stability range compared with a non-interleaved converter. The modelling and control methods are validated using switched and average value simulations obtained with the SABER software and by experimental results from a 25 kW, 30 kHz converter prototype. The control techniques were implemented on a Texas Instruments TMS320F28335 digital signal controller.

За даними номінальних потужностей обладнання було визначено розрахункове навантаження методом коефіцієнту попиту. Обрані перерізи провідників силових живлючих кабелів, проводів силової розподільчої мережі за допомогою метода найбільшого допустимого струму. Всі провідники узгоджені з відповідними апаратами захисту. Розраховано струми короткого замикання, з огляду на значення яких було обрано апарати захисту. Проведено моделювання аварійних режимів, з метою розглянення їх впливів на мережу. Розраховано економічну ефективність модернізованого обладнання для значодження часу окупності приладів.

This project develops the required guidelines to assure stable and accurate operation of Power-Hardware-in-the-Loop implementations. The proposals of this research have been theoretically analyzed and practically examined using a Real-Time Digital Simulator. In this research, the interaction between software simulated power network and the physical power system has been studied. The conditions for different operating regimes have been derived and the corresponding analyses have been presented.

The objective of the research is to develop a cost-effective high-power bi-directional dc/dc converter with low total-device ratings, reduced system parasitic effects, and a wide input/output range. Additional objectives of the research are to develop a small-signal model and control methods, and to present performance characterizations. Device stresses in the proposed topology are controlled to maintain minimal levels by varying the duty ratio and phase-shift angle between the primary and the secondary bridges, which results in a low total-device rating, when compared to conventional bi-directional dc/dc topologies. In the proposed topology, soft switching, which reduces power loss, can be realized under specific operating conditions. When the condition that causes minimal device stress is satisfied, zero-voltage switching (ZVS) can be obtained. In the research, ZVS capability is explored for a wide range of voltage conditions as well as for the minimal device-stress condition. The performance characterization includes verifying the soft-switching regions and power-loss estimation. Another part of the thesis is the controller design of the converter. Small-signal models and feedback controllers are developed, and the controllers are experimentally validated. Because in the isolated high-frequency converters, transformer saturation is an important issue, a method to prevent transformer saturation is proposed and experimentally validated.

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.<br>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.

Goal of this semestral thesis is to design power converter which is to be used for measurement. The converter consists of two forward converters in push-pull topology. The converter is to behave as a constant current source with maximum open-circuit voltage of 1000V. Maximum current is 5A. The current range is split into three sub-ranges, to meet the strict requirements on ripple current. The range of currents is 0-5A. The operating frequency of converter is 34KHz. The converter will be charged using two portable electric generators with output voltage 230V.

Kungälv Energi äger och ansvarar idag över Kungälv Kommuns elnät. Med en ökande befolkningsmängd ställs allt högre krav på elnätet och framför allt leveranssäkerheten. Med kalla vintrar och stort energibehov ger detta upphov till en svårare situation gällande leveranssäkerhet. I nuläget har Kungälv Energi två mottagarstationer, en 130/10kV-station espektive 130/20kV-station. 30/10kV-stationen börjar närma sig en gräns där effektbehovet närmar sig den maximala istributionskapaciteten. Därför fastställs en plan för att kunna klara av effektbehovet vid averi på en av två 130/10kV-transformatorer i mottagarstationen M1. Resultatet av rapporten visar att tillräcklig kapacitet finns i närliggande fördelningsstationer för att klara av reservdrift under hög belastning utan att några övriga komponenter skadas. Rapporten behandlar främst effektflöden för att kontrollera att dessa ej överskrider transformatorernas, ledningarnas och kablarnas märkeffekt. I flertalet fall har även faktorer för nödbelastning räknats med vilket resulterar i att samtliga linjer hos Kungälv Energi klarar av den ökade belastningen. Upptäckta flaskhalsar i nätet har uppmärksammats och delgetts samt förslag till förändringar för att förhindra framtida problem.<br>Kungälv Energi owns and is responsible of Kungälv municipality's electricity grid. With an increasing population and increasing demands on the grid and especially security of supply. With cold winters and large energy gives rise to a more difficult situation regarding security of supply. Currently, Kungälv Energi two receiving stations, a 130 / 10kV station and 130 / 20kV station. 130 / 10kV station is approaching a point where power demand is approaching the maximum distribution capacity. Therefore sets out a plan to cope with the power demand at the failure of one of two 130 / 10kV transformers of the receiving station M1. The results of the report shows that sufficient capacity is available in nearby distribution stations to cope with the emergency operation under high loads without any other components damaged. The report deals primarily with power flows to check that they do not exceed transformers, lines and cables rated power. In the majority of cases have also factors for distress load been counted with, which gives the result that all lines of Kungälv Energi can handle the increased load. Detected bottlenecks in the network have been highlighted, communicated and proposed changes to Kungälv Energi to prevent future problems.

Master‘s thesis is focused on current instrument transformers, current sensors and low power current transformers. Discussion is made on advantages and disadvantages of each measuring principle. Low power current transformers is then designed and manufactured. Manufactured LPCT is then measured for accuracy class. Results are then compared.

Šio darbo tyrimo tikslas – ištirti elektros energijos apskaitos prietaisų, indukcinių ir elektroninių, charakteristikas. Buvo atlikta informacijos šaltinių analizė apie indukcinių ir elektroninių elektros energijos skaitiklių ir srovės matavimo transformatorių parametrus, apsprendžiančius jų charakteristikas. Remiantis informacijos šaltinių apibendrinimu suformuota hipotezė: ne visos elektroninių elektros energijos prietaisų charakteristikos geresnės už indukcinių elektros energijos apskaitos prietaisų charakteristikas. Suformuoti tyrimo uždaviniai: ištirti elektroninių ir indukcinių elektros energijos prietaisų paklaidų priklausomybes nuo apkrovos srovės, galios koeficiento, eksploatacijos laiko, pasvyros kampo ir srovės matavimo transformatorių srovinės paklaidas. Padarytos išvados, nurodomas naudotos literatūros sąrašas.<br>The aim of this paper is to investigate the electricity metering devices, i.e. inductive and electronic, characteristics. It was made the analysis of the sources about the inductive and electricity meters and current transformers for measuring the parameters that define their characteristics. According to sources of information was formed the hypothesis: not all electronic power devices characteristics are better than inductive energy metering devices characteristics. The study objectives are to investigate experimentally the electronic and inductive power devices values of the load current, power factor, operating time, against an adverse list angle and current measuring transformer errors stream. Findings are discussed; the list of references is presented.

It is known from the literature that conventional voltage and current transformers measure inaccurate values for voltage and current harmonics which are parts of power quality. Maximum bandwidth of conventional current transformers, which are used in electricity transmission and distribution systems, is 1.5-2 kHz and it is lower for conventional voltage transformers. Also, it is known that<br>voltages in some frequency spectrum are measured higher and voltages in another frequency spectrum are measured lower by the conventional voltage transformers. Furthermore, because of the phase shift of fundamental component caused by the conventional current and voltage transformers, losses and efficiency can not be calculated accurately. In this work, through the simultaneous measurements taken at the same feeder by both conventional transformers and new technology measurement transformers<br>amplitude and phase shift errors which are caused by conventional transformers depending on frequency and so harmonics, are examined and evaluated. Amplitude coefficients and phase shifts are determined for different types of conventional transformers to be able to calibrate measurement deviation. Through this work, measured data by conventional transformers will be accurate and realistic in terms of harmonic components. This matter is important to determine whether the accurate limits which will be set in the future possibly concerning with harmonics and interharmonics, are surpassed or not<br>also for punitive sanction.

Geomagnetic disturbances that result from solar activities can affect technological systems such as power networks. They may cause DC currents in power networks and saturation of the core in power transformers that leads to destruction in the transformer performance. This phenomena result in unwanted influences on power transformers and the power system. Very asymmetric magnetization current, increasing losses and creation of hot spots in the core, in the windings, and the metallic structural parts are adverse effects that occur in transformers. Also, increasing demand of reactive power and malfunction of protective relays menaces the power network stability. Damages in large power transformers and blackouts in networks have occurred due to this phenomenon. Hence, studies regarding this subject have taken the attention of researchers during the last decades. However, a gap of a comprehensive analysis still remains. Thus, the main aim of this project is to reach to a deep understanding of the phenomena and to come up with a solution for a decrease of the undesired effects of GIC. Achieving this goal requires an improvement of the electromagnetic models of transformers which include a hysteresis model, numerical techniques, and transient analysis. In this project, a new algorithm for digital measurement of the magnetic materials is developed and implemented. It enhances the abilities of accurate measurements and an improved hysteresis model has been worked out. Also, a novel differential scalar hysteresis model is suggested that easily can be implemented in numerical methods. Two and three dimensional finite element models of various core types of power transformers are created to study the effect of DC magnetization on transformers. In order to enhance the numerical tools for analysis of low frequency transients related to power transformers and the network, a novel topological based time step transformer model has been outlined. The model can employ a detailed magnetic circuit and consider nonlinearity, hysteresis and eddy current effects of power transformers. Furthermore, the proposed model can be used in the design process of transformers and even extend other application such as analysis of electrical machines. The numerical and experimental studies in this project lead to understanding the mechanism that a geomantic disturbance affects power transformers and networks. The revealed results conclude with proposals for mitigation strategies against these phenomena.<br><p>QC 20150210</p>

Este trabalho tem como objetivo apresentar um algoritmo de proteção diferencial de geradores baseado em Redes Neurais Artificiais (RNAs), que seja robusto e confiável em situações onde os algoritmos padrões podem apresentar dificuldades, como no caso, da saturação de TCs. O algoritmo desenvolvido é constituído por dois módulos principais: a) um módulo de detecção da saturação dos transformadores de corrente (TCs) empregados na proteção diferencial de geradores e; b) um módulo de correção das formas de onda distorcidas devido à saturação dos TCs. Os módulos utilizam RNAs para detectar e corrigir situações onde haja saturação dos TCs, a fim de evitar a má operação da proteção diferencial. O algoritmo foi desenvolvido em ambiente Matlab e validado com base nos dados da modelagem e simulações de um sistema elétrico utilizando o software Alternative Transients Program (ATP).<br>This work has as objective to present an algorithm for differential protection of generators based on Artificial Neural Networks (ANN), which is robust and reliable in situations where standard algorithms fail, as in the case of Current Transformer (CT) saturation. The algorithm developed consists of two main modules: a) a module to detect saturation of CTs used in differential protection of generators and; b) module to correct distorted waveforms due to CT saturation. The modules use ANNs to detect and correct situations where there is saturation of CTs in order to avoid misoperation of the differential protection. The algorithm was developed using Matlab software and validated based on data modeling and simulations of a power system using the Alternative Transients Program (ATP) software.

Сірик, О. М. Підвищення ефективності функціонування ПС 35/10 кВ "Киселівка" АТ "Чернігівобленерго" : випускна кваліфікаційна робота : 141 "Електроенеретика, електротехніка та електромеханіка" / О. М. Сірик ; керівник роботи Р. О. Буйний ; НУ "Чернігівська політехніка", кафедра електричної інженерії та інформаційно-вимірювальних технологій. – Чернігів, 2021. – 126 с.<br>Об’єкт дослідження даного проекту – підстанція напругою 35/10 кВ «Киселівка». Предмет дослідження – ефективність роботи обладнання ПС 35/10 кВ «Киселівка» при умові перспективного збільшення електричного навантаження. Мета роботи – покращення основних техніко-економічних показників роботи ПС 35/10 кВ «Киселівка». Виконано заміну існуючого морально та фізично застарілого силового обладнання ПС 35/10 кВ «Киселівка».<br>The object of research of this project is a 35/10 kV substation «Kiselivka». The subject of the research is the efficiency of the equipment of the 35/10 kV substation «Kiselivka» under the condition of perspective increase of electric load. The purpose of the work is to improve the main technical and economic performance of the 35/10 kV «Kiselivka» substation. The replacement of the existing morally and physically obsolete power equipment of the 35/10 kV substation «Kiselivka» was performed.

Онопрієнко, О. С. Реновація обладнання підстанції 35/10 кВ «Іваниця» : випускна кваліфікаційна робота : 141 "Електроенеретика, електротехніка та електромеханіка" / О. С. Онопрієнко ; керівник роботи В. М. Безручко ; НУ "Чернігівська політехніка", кафедра електричної інженерії та інформаційно-вимірювальних технологій. – Чернігів, 2021. – 128 с.<br>Об’єкт дослідження даного проєкту – підстанція напругою 35/10 кВ «Іваниця». Предмет дослідження – ефективність роботи ПС 35/10 кВ «Іваниця» при умові інтенсивного збільшення електричного навантаження. Мета роботи – покращення основних техніко-економічних показників роботи ПС 35/10 кВ «Іваниця». Виконано заміну існуючого морально та фізично застарілого основного силового обладнання ПС напругою 35/10 кВ.<br>The object of research of this project is a substation with a voltage of 35/10 kV «Ivanytsia». The subject of research is the efficiency of 35/10 kV substation «Ivanytsia» under the condition of intensive increase of electric load. The purpose of the work is to improve the main technical and economic performance of the 35/10 kV substation «Ivanytsia». The replacement of the existing morally and physically obsolete main power equipment of the 35/10 kV substation was performed.

In this thesis a two-stage AC/DC/DC power converter is designed and implemented. The AC/DC input stage of the converter consists of the two&amp<br>#8211<br>phase interleaved boost topology employing the average current mode control principle. The output stage consists of a zero voltage switching phase shifted full bridge (ZVS&amp<br>#8211<br>PS&amp<br>#8211<br>FB) DC/DC converter. For the input stage, main design goals are obtaining high input power factor, low input current distortion, and well regulated output dc voltage, and obtaining these attributes in a power converter with high power density. For the input stage, the interleaved structure has been chosen in order to obtain reduced line current ripple and EMI, reduced power component stresses, and improved power density. The control of the pre&amp<br>#8211<br>regulator is provided by utilizing a new commercial monolithic integrated circuit, which provides interleaved continuous conduction mode power factor correction (PFC). The output stage is formed by utilizing the available prototype hardware of a ZVS&amp<br>#8211<br>PS&amp<br>#8211<br>FB DC/DC converter and mainly the system integration and controller design and implementation studies have been conducted. The converter small signal model is derived and utilizing its transfer function and employing voltage loop control, the output voltage regulator has been designed. The output voltage controller is implemented utilizing a digital signal processor (DSP). Integrating the AC/DC preregulator and DC/DC converter, a laboratory AC/DC/DC converter system with high overall performance has been obtained. The overall system performance has been verified via computer simulations and experimental results obtained from laboratory prototype.

Este trabalho apresenta a proposta de um sistema completo de proteção diferencial de transformadores de potência, aplicando-se as técnicas de Redes Neurais Artificiais (RNAs). O esquema proposto busca a classificação do sistema de proteção como um problema de reconhecimento e reconstrução de padrões, representando um método alternativo aos algoritmos convencionais. Vários fatores como, por exemplo, as situações de energização do transformador e a saturação dos transformadores de corrente, podem causar uma má operação do dispositivo de proteção. Com o objetivo de melhoramento na proteção digital de transformadores de potência, desenvolveu-se um sistema de proteção diferencial, incluindo dispositivos com base em RNAs, em substituição à filtragem harmônica de sinais existente no algoritmo convencional. Em complementação, esquemas de reconstrução das ondas distorcidas provenientes da saturação dos TCs são também propostos e adicionados ao algoritmo final de proteção, sendo esses comparados ao algoritmo convencional de proteção diferencial de transformadores. Com a referida adição de ferramentas de inteligência artificial a um algoritmo completo de proteção diferencial de transformadores, obteve-se uma solução bastante precisa e eficiente, capaz de responder em um tempo reduzido, se comparada aos métodos convencionais.<br>This work proposes a complete differential protection system for power transformers, applying the Artificial Neural Network (ANN) theory. The proposed approach treat the classification of the protection system as a problem of pattern recognition and as an alternative method to the conventional algorithms. Several factors such as, for example, transformer energization and CT saturation can cause an inadequate operation of the protection relay. With the objective of improving the power transformer digital protection, a complete protection system was developed, including an ANN-based device in substitution to harmonic filters, in use in the conventional algorithm. Some approaches concerning the reconstruction of the distorted signals caused by the CTs saturation are also proposed. These routines are added to the final protection algorithm and they are compared to the conventional algorithm for power transformer protection. With the use of artificial intelligence tools in a complete power transformer protection algorithm, one intends to obtain a very precise, fast and efficient solution, if compared to the conventional methods.

Виконано аналіз режимів роботи підстанції напругою 35/10 кВ та вибір основного електричного обладнання на ній. На основі вихідних даних про об’єкт дослідження, проведений вибір силових трансформаторів, вакуумних вимикачів, обмежувачів перенапруги, вибір схеми електричних з’єднань, розрахунок струмів короткого замикання та заземлення. За результатами проведених розрахунків зроблено вибір електрообладнання, апаратури релейного захисту та автоматики. В розділі охорони праці проведений розрахунок заземлення. В економічному розділі наведено розраховані основні показники економічної ефективності.

This thesis deals with a power flow control in the electric power system. An overview of FACTS devices is introduced; their basic characteristics as well as examples of their application are discussed. A significant part of this thesis investigates phase shifting transformers (PST´s), which seem to be suitable for implementation in the transmission system of the Czech Republic. The PST´s are useful devices that control active power flows on cross-border lines and regulate unwanted and unexpected power flows. Basic types and characteristics of the PST´s are discussed. In chapter 7 is designed laboratory task that should validate the regulatory capabilities of the transformer PST. Designs of models of individual parts of this laboratory task are presented. In the last part of this thesis the regulation effect of the PST is validated in the GLF/AES program.

This diplom thesis theoretically deals about principle of pulse welding current source. Work explains operation principle of the single acting transmit converter used in realized construction and mention the others examples of converters types. Goal of the work is design individual parts of source : input filter, pulse transformer, output inductor and power semiconductors components. Thesis also contains description of the regulation circuitry of the converter, auxiliary power supply and pre-driver for power transistors. If everything will be all right prototype of the source will be assembled and measured. Results will be compared with theoretical assumptions.

This master’s thesis engages in project of outgoing transformer unit for the photovoltaic power station. It describes project and its design documentation what conducts to practising of construction. It has compared investing to more expansive transformer what has lower loss. It describes charges of operation’s transformer in twenty years. It leads project of cable low voltage. It compares whether is better to use aluminium or cupric cables. Project is led with respect for investment costs and minimum of operation loss.

This thesis is about to introduce the development of switched power supply with output voltage of 5,5 kV and power of 4,3 kW. This thesis directly follows the outputs of two previous semester projects. Main task is about to finish the development of remaining printed circuit boards and perform launching of all parts of developed power supply. Next necessary task is about to assemble a functional prototype of the supply using the developed parts, performing a series of measurement supply’s parameters and creating of technical documentation of mechanical part. There are all stages of supply’s development included in this thesis. From the first part, that describes various types of converters, through the design of all the supply’s parts, to final implementation of functional prototype. There are the results of measurement supply’s parameters at the end of this thesis.

The International Thermonuclear Experimental reactor (ITER), the world’s largest experimental facility in the realm of nuclear fusion for energy production, requires two Neutral Beam Injectors (NBI) rated for the total power of 33 MW for plasma heating and current drive. The ITER NBI includes an ion source which can produce 40 A of D¯ ions beams for 3600 s, accelerated at the energy of 1 MeV. The requirements for the ITER NBI are quite demanding and have never been achieved before all together in a single device. This specifically called for a development of the ITER Neutral Beam Test Facility (NBTF) called PRIMA (Padova Research on ITER Megavolt Accelerator) to carry out an international R&D program for the achievement of the ITER NBI requirements and the optimization of the operation in advance of the future use in ITER. The facility will host two experiments, SPIDER (Source for the Production of Ions of Deuterium Extracted from RF plasma), the full-size prototype of ITER RF ion source, and MITICA (Megavolt ITER Injector and Concept Advancement), the full-scale prototype of the ITER heating NBI. The NBTF in Padova, Italy, is ready, MITICA is currently under construction and SPIDER has been in operation since beginning of June 2018. The NBI ion source was initially based on filament type arc source, while for ITER the inductively coupled (IC) radio frequency (RF) ion source have been finally chosen in 2007. This is because RF sources present several advantages with respect to arc solutions; they have fewer parts and require less maintenance. In these ion sources, radio frequency plasma is generated at the frequency of 1 MHz and is characterized by high RF power density and low operational pressure (around 0.3 Pa). In the last decades, IC ion sources have been developed, studied and experimented at the Max-Planck-Institut für Plasmaphysik (IPP) in Garching, Germany. The most recent one is ELISE (Extraction from a Large Ion Source Experiment), which is able to operate with both Hydrogen and Deuterium gas species and has half the size of ITER NBI source. Other accompanying activities have been recently launched at Consorzio RFX, Padova, Italy within the ITER NBI work program; one of them is a relatively small ion source called NIO1 (Negative Ion Optimization 1) working at 2 MHz, developed in order to gain experience on ion source operation and to study specific physics and engineering topics on a more flexible and accessible device than the SPIDER and MITICA. In addition, a small experimental test facility called HVRFTF (High Voltage Radio Frequency Test Facility) based on a high voltage resonance circuit that feeds a couple of electrodes in vacuum has been started at Consorzio RFX in 2014 to address and study the voltage holding capability of the RF components in the ion source at 1 MHz. The research endeavor during the three years of my PhD was carried out in the frame of the RF R&D task of the NBTF work-program at Consorzio RFX and during the mobility periods at the IPP. I have had the opportunity to work on two main lines: the first was dedicated towards the study of the RF power transfer efficiency of IC RF ion sources and the development of suitable models that will permit to explore possible improvements (in the future). In fact, the higher the efficiency, the lower can be the feeding power to the ion source and this may lead to a lower requirement both for cooling and for electrical insulation of the RF circuit components installed on the source. I have studied and analyzed several plasma heating mechanisms (like ohmic and stochastic heating in particular) and I have developed an electrical model which is responsible for describing the power transfer to the plasma. The first approach was based on a transformer model, and then a multi current filament model has been developed. This model is capable to account for the currents in the passive metallic structure within the driver region of the ion source and with this; it is able to overcome the main limitation of the transformer model. Furthermore, I have integrated all the models to develop a novel methodology to evaluate the efficiency of the RF power transfer to the hydrogen plasma in a cylindrical source. Then, I have implemented the methodology in a MATLAB® code and applied it to the driver of ELISE and NIO1 ion sources showing the results in terms of plasma equivalent resistance and power transfer efficiency obtained as a function of applied frequency and plasma parameters (electron density and gas pressure). The second part of my work was directed towards the design, construction and set-up of the HVRFTF. I gave an important contribution in terms of the electrical characterization of the RF resonance circuit components (mainly the two solenoid coupled inductor), thermal analysis of the electrodes placed inside the vacuum vessel, analyses and design of an efficient shielding from the electro-magnetic radiations foreseen during the operation of the test facility. All this contributed towards the success in the set-up of the test facility which is now in operation. The thesis is structured as follows: Chapter 1 and 2 are introductory chapters on the present energy scenario in the world, the role of the thermo-nuclear fusion and the main fusion experimental device called ITER. The requirement of additional heating systems in ITER along with the description of Neutral beam injection (NBI) system and relevant ion sources (SPIDER, ELISE and NIO1) are presented in these chapters. Then, the thesis is divided into two main parts: Part 1 – From Chapter 3 to Chapter 6 - describes my work on the power transfer efficiency to the plasma of the inductively coupled radio frequency ion sources. Part 2 – From Chapter 7 to chapter 10 - summarizes first the aim of the HVRFTF then reports my contribution to its design and set-up. Lastly, the overall conclusion highlighting the most significant results obtained from the research described in both the parts of the thesis is discussed and a further possible research activity is highlighted for the future work. Throughout the journey of the PhD, I have had the opportunity to grow and acquire different research competences ranging from conceptual studies, modeling activities, practice on several numerical codes and also experimental work, in an international context.<br>Il reattore sperimentale ITER, il più grande esperimento nel settore della produzione di energia da fusione nucleare, richiede di essere equipaggiato con due sistemi d’iniezione di fasci di particelle neutre (chiamato ITER NBI nel seguito), caratterizzati da una potenza complessiva di 33 MW, per contribuire al riscaldamento del plasma e controllo della relativa corrente. ITER NBI comprende una sorgente di ioni negativi che può produrre un fascio di ioni di deuterio accelerati all’energia di 1 MeV, per una durata di 3600 s. L’insieme dei requisiti richiesti ad ITER NBI non sono mai stati raggiunti contemporaneamente nello stesso esperimento. Ciò ha motivato lo sviluppo di un’infrastruttura sperimentale: “the ITER Neutral Beam Test Facility (NBTF)”, chiamata anche PRIMA (Padova Research on ITER Megavolt Accelerator), che ha lo scopo di portare avanti un progetto di ricerca internazionale finalizzato alla dimostrazione della possibilità di raggiungere i requisiti specificati per ITER NBI e alla crescita di conoscenza e competenza nella sperimentazione, prima dell’uso futuro in ITER NBTF ospiterà due esperimenti: SPIDER (Source for the Production of Ions of Deuterium Extracted from an RF plasma), il prototipo a piena scala della sorgente a ioni negativi di ITER NBI, e MITICA (Megavolt ITER Injector and Concept Advancement), il prototipo a piena scala dell’intero ITER NBI. NBTF è stata completata ed ha sede a Padova, in Italia; MITICA è attualmente in costruzione e SPIDER è in operazione dall’inizio di giugno 2018. La sorgente di ioni scelta inizialmente per ITER NBI era del tipo ad arco, ma dal 2007 il progetto dell’NBI è stato sviluppato considerando sorgenti di ioni prodotti in un plasma generato secondo il principio dell’accoppiamento induttivo a radiofrequenza (RF). Queste sorgenti presentano diversi vantaggi rispetto alle sorgenti ad arco: hanno un numero minore di componenti e richiedono minor manutenzione. Le sorgenti RF di ITER NBI operano alla frequenza di 1 MHz, sono caratterizzate da una densità di potenza piuttosto elevata e basso valore di pressione del gas all’interno della camera (0,3 Pa circa). Queste tipologie di sorgenti ioniche sono state studiate e sviluppate negli ultimi decenni presso il Max-Planck-Institut für Plasmaphysik (IPP), dove sono stati realizzati e testati diversi dispositivi sperimentali. Il più recente di essi, chiamato ELISE (Extraction from a Large Ion Source Experiment), è caratterizzato da dimensioni pari a metà di quelle previste per la sorgente ionica di ITER NBI. Altre attività sperimentali di supporto alla ricerca e sviluppo in questo settore sono state avviate presso il Consorzio RFX; una di queste consiste nella realizzazione di una sorgente a ioni negativi relativamente piccola, chiamata NIO1 (Negative Ion Optimization 1), che lavora alla frequenza di 2 MHz, sviluppata per fare esperienza sul funzionamento di sorgenti di ioni negativi e studiare problematiche specifiche di interesse per ITER NBI in un apparato sperimentale molto più flessibile ed accessibile rispetto a SPIDER e MITICA. Inoltre, la realizzazione di un ulteriore dispositivo sperimentale, chiamato HVRFTF (High Voltage Radio Frequency Test Facility), basato su un circuito risonante in alta tensione che polarizza una coppia di elettrodi in vuoto, è stata avviata presso il Consorzio RFX nel 2014 per studiare specifiche problematiche relative alla tenuta della tensione in vuoto di componenti del circuito a radiofrequenza della sorgente di ioni a 1MHz. Il lavoro di ricerca durante i tre anni del mio PhD è stato portato avanti nell’ambito del programma di ricerca e sviluppo sulle sorgenti ioniche a radiofrequenza presso il Consorzio RFX, e durante i periodi di “mobility” presso il laboratorio IPP. Ho avuto l’opportunità di approfondire due tematiche principali: la prima era indirizzata allo studio dell’efficienza del trasferimento di potenza al plasma delle sorgenti di ioni tipo IC RF e allo sviluppo di modelli allo scopo di esplorare in futuro possibili miglioramenti. Infatti, maggiore è l’efficienza, minore è la potenza richiesta al generatore e ciò comporta requisiti meno severi per il sistema di raffreddamento e sollecitazioni inferiori in termini di tensione elettrica applicata. Ho studiato i diversi meccanismi di riscaldamento del plasma (come il riscaldamento ohmico ed in particolare il riscaldamento stocastico) ed ho studiato come descrivere il trasferimento di potenza ad un plasma di idrogeno. Il primo modello sviluppato si basa sullo schema del trasformatore; successivamente ho contribuito significativamente a sviluppare un modello “a multi filamenti” di corrente. Questo modello riproduce le correnti indotte nelle strutture passive presenti nella regione del driver della sorgente di ioni ed è in grado di superare le limitazioni del modello del trasformatore. Ho integrato tutti i modelli per sviluppare una nuova metodologia per la stima dell’efficienza del trasferimento di potenza nei plasmi di idrogeno generati in sorgenti cilindriche. Ho poi implementato la metodologia in MATLAB®, applicandola ai casi delle sorgenti ioniche di ELISE e NIO1, presentando i risultati ottenuti in termini di stima della resistenza equivalente di plasma e di efficienza del trasferimento di potenza come funzione della frequenza applicata e dei parametri di plasma (densità elettronica e pressione del gas). La seconda parte del mio lavoro si è svolta nell’ambito dello sviluppo della HVRFTF. Ho dato importanti contributi che sono consistiti nella caratterizzazione dei componenti del circuito risonante a radiofrequenza (in particolare dell’induttore composto da due solenoidi accoppiati magneticamente), nelle analisi termiche degli elettrodi posti nella camera da vuoto, nelle analisi e progetto di un sistema di schermatura efficace delle radiazioni elettromagnetiche generate dall’operazione dell’esperimento. Tutto ciò ha contribuito al positivo completamento dell’apparato sperimentale, attualmente in funzione. La tesi è strutturata come segue: I capitoli 1 e 2 sono di tipo introduttivo sull’attuale scenario energetico, sul ruolo della fusione termonucleare controllata e del principale esperimento internazionale ITER. In questi capitoli inoltre sono presentati i requisiti del sistema di riscaldamento del plasma di ITER, la descrizione del sistema di iniezione di neutri (NBI) e delle sorgenti ioniche di interesse (SPIDER, ELISE e NIO1). Poi, la tesi è suddivisa in due parti: Parte 1- dal capitolo 3 al capitolo 6- che tratta del lavoro che ho svolto sul problema dell’efficienza del trasferimento induttivo di potenza al plasma nelle sorgenti ioniche. Parte 2 - dal capitolo 7 al capitolo 10- che riassume lo scopo della “HVRFTF” e descrive il mio contributo al suo progetto e realizzazione. Infine, nelle conclusioni ho discusso i più significativi risultati ottenuti dal lavoro di ricerca presentato nelle Parti 1 e 2 di questa tesi evidenziando i possibili sviluppi futuri. Durante il percorso del dottorato di ricerca, ho avuto l'opportunità di crescere e acquisire diverse competenze di ricerca che vanno dagli studi concettuali, alle attività di modellizzazione, alla pratica su diversi codici numerici e anche al lavoro sperimentale, in un contesto internazionale.