The conversion of mechanical energy to electrical energy is done mainly with synchronous generators. They are used in hydropower generators and nuclear plants that presently account for about 80% of the electric energy production in Sweden. Because of the dominating role of the synchronous generators, it is important to minimize the power losses for efficient use of natural resources and for the economies of the electric power companies and their customers. For a synchronous machine, power loss means undesired heat production. In electric machines, there are power losses due to windage, friction in bearings, resistance in windings, remagnetization of ferromagnetic materials, and induced voltages in windings, shields and parts that are conductive but ideally should be non-conductive. The subject of this thesis is prediction of end region magnetic leakage fields in synchronous generators and the eddy current power losses they cause. The leakage fields also increase the hysteresis losses in the end regions. Magnetic flux that takes paths such that eddy current power losses increase in end regions of synchronous generators is considered to be leakage flux. Although only a small fraction of the total magnetic flux is end region leakage flux, it can cause hot spots, discoloration and reduce the service life of the insulation on the core laminations. If unattended, damaged insulation could lead to electric contact and eddy currents induced by the main flux between the outermost laminations. That gives further heating and deterioration of the insulation of laminations deeper into the core. In a severe case, the core can melt locally, cause a cavity, buckling and a short circuit of the main conductors. The whole stator may have to be replaced. However, the end region leakage flux primarily causes heating close to the main stator conductors which makes the damage possible to discover by visual inspection before it has become irrepairable.

Pour réduire les émissions de gaz polluants, les constructeurs automobiles cherchent à mieux contrôler le volume d'air introduit dans le moteur pour optimiser la combustion. Des dispositifs mécaniques ou hydrauliques couplés avec l'arbre à cames sont déjà en place dans certaines voitures et permettent des gains de 8 à 10% sur la consommation de carburant. L'utilisation d'un actionneur électromagnétique à la place de l'arbre à cames (application « camless ») pour commander les soupapes améliore nettement ce gain (15 à 20%). Les travaux de cette thèse consistent à modéliser une structure choisie, pour ensuite l'optimiser. Compte tenu des exigences de notre application et des contraintes d'environnement du moteur thermique, la modélisation doit être à la fois suffisamment précise et rapide pour estimer et améliorer les performances de l'actionneur. Pour la partie statique, nous avons opté pour un modèle réluctant 3D. Obtenu par extension de son homologue 2D, il reste rapide tout en donnant des résultats en accord avec les mesures. En régime transitoire, nous proposons une nouvelle approche analytique de la distribution des courants de Foucault, directement à partir de l'évolution du flux magnétique. L'équation de diffusion comporte alors des conditions aux limites de Neumann. Nous avons traité le cas d'un flux magnétique arbitraire grâce au théorème de Duhamel, ainsi que la saturation du matériau grâce à une approche semi-analytique. / Variable valve actuation is one of automotive constructors' strategies to fulfil environmental queries about emission of pollutant gases. It brings improvement to the thermal engine, and many constructors have their own devices associated to the camshaft, with a gain between 8 and 10% on fuel consumption. The use of camless actuator brings further more gain, from 15 to 20%. The established approach during this thesis consists in modelling a chosen topology of actuator, and next in optimization. However, camless specifications and constraints require fast models, but with correct accuracy. That's why we use 3D permeances network in steady state. That model is obtained from extension of its 2D version. It is still fast and gives results in good agreement with measurements. We proposed a new analytical approach of eddy currents distribution in transient state, directly from the evolution of magnetic flux. Thus we have Neumann's boundary conditions in the diffusion equation. Arbitrary magnetic flux excitation and saturated material (with semi-analytical approach) are considered.

This master thesis deals with the suppression of the skin and proximity effects in high-speed machines. The first part summarizes the general knowledge of high-speed machines. The second part is devoted to the principle and possible suppression of consequences caused by skin and proximity effects. The third part shows the simulation results of models of a synchronous machine with permanent magnets. The results of these simulations reveal the consequences of skin and proximity effects. In addition, design measures are proposed to limit these and other undesirable phenomena to achieve the highest possible efficiency.

High speed applications demands with a need for lower energy consumption lead to designing new types of bearings. In the last decades magnetic bearing, which would be able to obtain passive stable levitation using regular materials at room temperature, has been searched. This has lead to development of electrodynamic bearing based on eddy currents principle. Currently the electrodynamic bearings are still not fully explored and further research is needed. The aim of the work is to describe the theory about modern magnetic bearing, analysis and design of electrodynamic bearing according to given parameters. The finite element method is used for further analysis and evaluate behaviour of its properties.

The aim of this work is to analyze the methodology for executing examination heat transfer tubes of steam generator by method of eddy currents on EDU, to create the model for the estimate of standard combined uncertainty of efficiency value, quantify the individual components of standard uncertainties, analyse the influence of different components on the expressing of uncertainty, to make the final estimate of standard combined and enlarged uncertainty of efficiency value and as of minor objective to evaluate the suitability of the use of this method .

Die Dynamik von axialen Magnetlagern ist im besonderen Maße von den eingesetzten Materialien abhängig. Axiale Flussverläufe machen eine Blechung von Stator und Rotor unwirksam und hohe induzierte Spannungen rufen im Magnetkreis wirbelstrombedingte Gegenfelder hervor. Zusätzliche kompensierende Magnetisierungsströme lassen den messbaren Strom der Steuerspule dem kraftbildenden Hauptfluss vorauseilen. Durch Einsatz von Pulververbundwerkstoffen lässt sich dieser Effekt reduzieren. Aus mechanischen Gründen wird die rotierende Axiallager-Scheibe in konventionellen Anwendungen dennoch aus Stahl gefertigt. In dieser Diplomarbeit werden alternative Materialien und Ausführungsformen untersucht und die auftretenden Unterschiede im dynamischen Verhalten mit der Eisenkreiszeitkonstante quantifiziert. Neben dem zu Grunde liegenden analytischen Modell soll eine fortgeschrittene Systembeschreibung vorgestellt werden, die das atypische Übertragungsverhalten der Regelstrecke berücksichtigt. Dieses setzt sich aus Differenziergliedern gebrochen-rationaler Ordnung zusammen und bildet ein sogenanntes „Fractional-Order-System“. Die Modelle werden mittels FEM-Simulationen und Experimenten am eigens konstruierten Versuchslager verifiziert. / The dynamics of axial magnetic bearings are characterized by an above-average dependency on the used materials. Axially directed fields render laminated stators and rotors ineffective. High induced voltages inside the magnetic core evoke eddy currents and opposing fields, which are compensated by an additional magnetizing current. Therefore a significant delay between the measurable coil current and the force-related magnetic flux is observed. The use of soft magnetic composites can minimize this effect, though the bearing disk usually is manufactured from conventional steel for mechanical reasons in a wide range of applications. In this diploma thesis alternative materials and embodiments are considered and the occurring differences regarding the dynamic behavior will be quantified by means of the magnetic circuit time constant. Beside its underlying analytical model, an advanced system description is introduced to include the atypical transfer function of the closed loop control system, characterized by so-called Fractional-Order-Derivatives. All models will be verified by FE-analysis and experiments on a newly constructed magnetic bearing.

Ce travail de thèse porte sur le développement et l’optimisation de capteurs dans le cadre du contrôle non destructif (CND) par courants de Foucault (CF). Le manuscrit présente plusieurs réalisations de capteurs CF souples gravés sur film Kapton. Un premier volet décrit l’évaluation des paramètres électromagnétiques (conductivité électrique σ et perméabilité magnétique µ) des matériaux typiquement rencontrés en CND par CF. Des méthodes conventionnelles pour estimer σ et µ ont été investiguées et mises en œuvre : il s’agit de la méthode à quatre pointes et du perméamètre. Néanmoins, ces méthodes présentent des difficultés pratiques au regard de l’état de surface (peinture, corrosion,…) et de la géométrie de l’échantillon. Deux capteurs ont donc été conçus : le premier composé d’une bobine d’émission et d’une bobine de réception afin d’évaluer la conductivité des matériaux purement conducteurs, puis le second composé d’un bobinage émetteur et d’une GMR pour évaluer la perméabilité magnétique. La conception des motifs et des résultats expérimentaux sont présentés dans le manuscrit. Le second volet décrit le développement d’un imageur CF flexible statique. L’imageur est un capteur multiélément composé de 576 récepteurs disposés en matrice permettant d’inspecter la surface d’une pièce sans déplacement du capteur par rapport à cette dernière. Le contrôle par l’imageur statique permet d’obtenir une image pixélisée de la surface sous le capteur. L’imageur a été optimisé de manière à détecter un défaut surfacique d’au moins 1 mm de long et d’orientation donnée quel que soit son emplacement vis-à-vis des bobines réceptrices. La conception du capteur et son évaluation expérimentale sont donnés dans le manuscrit. / The work of this thesis focuses on the development and the optimization of probes for non-destructive testing (NDT) by Eddy Currents (EC). The manuscript presents several achievements of flexible EC probes engraved on Kapton film. The first part describes the evaluation of the electromagnetic parameters (electrical conductivity σ and magnetic permeability µ) of materials typically encountered in NDT by EC. Conventional methods to estimate σ and μ have been investigated and implemented: it is the four-point probe and the permeameter. However, these methods present practical difficulties relating to the surface condition (paint, corrosion,…) and the sample geometry. Two probes have therefore been designed: the first is composed of a transmitting and a receiving coil in order to evaluate the conductivity of purely conductive materials, and the second is composed of a transmitter coil and a GMR for evaluate the magnetic permeability. Design patterns and experimental results are presented in the manuscript. The second part describes the development of a flexible static EC imager. The imager is a multielement probe composed of 576 receivers arranged in a matrix allowing to inspect the surface of a structure under test without moving the probe relative to the sample surface. The inspection by the static imager provides a pixelated image of the surface under the probe. The imager has been optimized to detect a surface defect of at least 1 mm long of given orientation regardless of its location relative to the receiver coils. The design of the probe and its experimental evaluation are given in the manuscript.

The continuously increasing demand for connecting electric grids with remote renewable energy sources such as wind power and photovoltaic cells has rekindled interest in high voltage direct current (HVDC) multi-terminal networks. Although HVDC networks have numerous benefits, their adoption relies entirely on the availability of HVDC circuit breakers which, compared to traditional alternating current circuit breakers, have to operate in a time frame of milliseconds. This thesis deals with the design of ultra-fast electro-mechanical actuators based on the so-called Thomson coil (TC) actuator. The simulation of a (TC) actuator constitutes a multi-physical problem where electromagnetic, thermal, and mechanical aspects must be considered. Moreover, it is complex since all those variables are co-dependent and have to be solved for simultaneously. As a result, a multi-physics simulation model that can predict the behavior and performance of such actuators with a high degree of accuracy was developed. Furthermore, other actuator concepts were also investigated and modeled in light of searching for a drive with a superior efficiency. The theory behind the force generation principles of two different types of ultra-fast electromechanical actuators, the TC and the double sided coil (DSC), were compared by the use of static, frequency, and comprehensive transient multi-physics finite element simulation models. Although, simulation models serve as a powerful tool for modeling and designing such state of the art actuators, without validation, they are weak and prone to errors since they rely on approximations and simplifications that might not always hold. Therefore, a prototype was built in the laboratory and the model was validated experimentally. Finally, it is important to note that the drives in this thesis are intended to actuate metallic contacts. As such, their behavior and performance upon mechanical loading was studied. Furthermore, some scaling techniques were applied to boost their performance and efficiency. / <p>QC 20130422</p>

A magnetostrictive material elongates when it is subjected to a magnetic field. This effect can then be used to design powerful actuators. The department of electromagnetic engineering has been working with magnetostricitve material and their applications since the 1980s and is presently engaged in a project focusing on magnetostrictive transducer utilisation for the aeronautic field. The focus of the presented work has been to develop and improve methods and tools supporting the development of magnetostrictive actuators. The axial-radial model was previously developed at the department and is well suited for circular cross sections of magnetostrictive rods. It is, however, common to laminate the magnetostrictive rods resulting in rectangular cross sections. The use of Cauer circuits allows modelling of the shielding effect. This shielding effect results in non-homogenous magnetisation and stress in both rectangular and circular cross sections of the rod. A model based on Cauer circuits, including a hysteresis model based on experimental data, was developed during the project. Furthermore, it is demonstrated how figures of merit and the use of finite element methods can be used to find optimised designs in a systematic and computational efficient way. The modified generalised Fabry factor and the magnetisation inhomogeneity coefficient are two proposed new figures of merit. A Magnetostricitve material is characterised through an experimental procedure. Usually, magnetostrictive material exhibit large hysteresis. An important part of the material characterisation is the post-processing of the measurement data, including a de-hysterisation procedure. In the thesis, a de-hysterisation method which ensures energy consistent data is presented. Energy consistent material data is essential to achieve energy consistent simulations of magnetostrictive systems. It is also demonstrated how the knowledge at the department can be utilised in international projects. In an ongoing project, the department is engaged in two sub tasks. In one of these sub tasks a high torque actuator is to be developed for the helicopter industry. The developed magnetostrictive models are used to perform system simulations of such actuator systems. In the other sub task a device for power harvesting from vibrations is analysed. It has now been shown how to adapt the load impedance in order to extract maximal electric power from the device. / QC 20101115

[pt] Esta dissertação apresenta um projeto de sistema portátil de localização de corpos estranhos metálicos não ferromagnéticos por meio de mapeamento magnético. O sistema baseia-se na indução de correntes parasitas no corpo estranho por um estágio de excitação e na medição por um magnetômetro GMI comercial de elevada resolução (25 pT). A topologia do instrumento é baseada no desacoplamento dos estágios de excitação e medição, com uma configuração que produz linhas de campo magnético primário elevadas na região do corpo estranho e tênues na região do sensor. Esta característica supera as limitações de um instrumento previamente desenvolvido, permitindo aumentar o campo magnético primário de excitação sem saturar o magnetômetro. O projeto é baseado em simulações computacionais, considerando dois tipos de excitação e duas orientações para o eixo de sensibilidade do magnetômetro. Diretrizes internacionais para os limites de exposição à radiação não-ionizante, aspectos biometrológicos, construtivos e elétricos também foram levados em consideração no projeto. A análise de desempenho das configurações mais promissoras confirmou a viabilidade do instrumento de medição proposto, otimizando a operação linear do magnetômetro durante o procedimento de medição e contribuindo para a futura construção de um protótipo de sistema de medição completo, com características de desempenho e segurança asseguradas para a aplicação biomédica pretendida. / [en] This dissertation presents a portable system for the localization of nonferromagnetic foreign metal bodies by magnetic mapping. The system is based on the induction of eddy currents in the foreign body by an excitation stage and the measurement by a high resolution commercial GMI magnetometer (25 pT). The instrument topology is based on the decoupling of the stages of excitation and measurement, with a configuration that produces a high primary magnetic field in the foreign body region and a weak one in the sensor region. This feature surpasses the limitations of a previously developed instrument, allowing to increase the primary excitation magnetic field without saturating the magnetometer. The project is based on computational simulations, considering two types of excitation and two orientations for the magnetometer sensitivity axis. International guidelines for exposure limits to non-ionizing radiation, biometrological, constructive and electrical aspects were also taken into consideration in the project. The performance analysis of the most promising settings confirmed the viability of the proposed measurement instrument, optimizing the linear operation of the magnetometer during the measurement procedure and contributing to the future construction of a complete measurement system prototype, with performance and safety characteristics ensured for the intended biomedical application.