<p>Isolationsdiagnostik är ett redskap som är av stor betydelse för underhållsoptimering av elektriska anläggningar. Ett av de möjliga mått på isolationsförsämring som kan användas i diagnosticeringssyfte är partiella urladdningar. Det här examensarbetet beskriver ett modelleringsförsök av ett resistivt-kapacitivt nätverk för simulering av partiella yturladdningar i Matlab. Tyvärr blev försöket misslyckat på grund av ett oväntat stort beroende av högspänningskapacitanser på ytresistiviteten. Ytterligare ett försök genomfördes i COMSOL Multiphysics, ett program baserat på finita elementmetoden ämnat för simuleringar av fysikaliska processer. Den huvudsakliga nackdelen med COMSOL Multiphysics modellen är långa simuleringstider. Det visade sig vara möjligt att simulera urladdningar i COMSOL Multiphysics. Här modellerades ytresistansen med hjälp av ett resistivt skikt. Yturladdningar simulerades genom att ändra det resistiva skiktets konduktivitet. Här upptäcks ytterligare ett problem: mycket långa simuleringstider vid användandet av olinjära konduktivitetsuttryck som beror på det elektriska fältet.</p><p>Alla simuleringar, både i Matlab och COMSOL Multiphysics, utfördes på en dator med Intel dual-core processor: 2.13 GHz, 0.99 GB of RAM.</p> / <p>Insulation diagnostics is a very important tool in optimization of electric installations’ maintenance. One of the possible measures of insulation deterioration that can be used for diagnostic purposes are partial discharges. This thesis work describes an attempt to model a resistive-capacitive network for simulating partial surface discharges in Matlab. Unfortunately this attempt proved to be a failure due to an unexpectedly considerable dependency of high voltage capacitances on surface resistivity. Another attempt described here was performed in COMSOL Multiphysics, a finite-element based program for simulation of physical processes. The main drawback with COMSOL Multiphysics model is long simulation times. It proved to be possible to simulate discharges in COMSOL Multiphysics. Here surface resistance was modeled with the help of a resistive layer. Discharges were simulated by changing conductivity of the mentioned layer. Here another problem was discovered: very long simulation times when using non-linear, electric field dependent expressions for conductivity.</p><p>All the simulations, both in Matlab and COMSOL Multiphysics, were performed on a computer with Intel dual-core processor: 2.13 GHz, 0.99 GB of RAM.</p>

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In comparison with Si-based converters, the emerging Medium Voltage (MV) SiC-based converters can achieve higher blocking voltage capability, lower on-resistance, faster switching speed with less switching related losses and run under higher temperature. Thus, theoretically, it can achieve much higher power density, which becomes very promising for future power transmission and distribution. However, in order to achieve the desired high power density, insulation system of the MV SiC-based converter must be compact. Therefore, challenges for the insulation system gradually appeared, as the insulation size becomes smaller and the Electric field (E-field) intensity significantly increases. Under such high E-field intensity, it is necessary and important to eliminate Partial Discharge (PD) for such power converters, since the converter system is vulnerable to PDs. Developing an insulation design, assessment and online monitoring method to help reach a compact and PD free insulation system for MV SiC-based converters is a goal of this work. General insulation design and assessment guidelines based on experimental PD investigation and physics-based model –Experimental PD investigation is completed for internal void discharge, surface discharge, and point discharge representative coupons under square excitations. Based on the data and the existing knowledge about PD mechanisms, widely accepted PD models are selected. Using these physics-based models, simulation results can demonstrate the major features observed in the experiments. With the experimental data and valid PD models, several general insulation design and assessment guidelines are proposed, which could be further applied during converter prototypes development. Partial Discharge elimination methodology and design examples – By using the laminated bus as the design example, internal void evaluation and analysis method is demonstrated. Then, targeting the internal PD-free design with reasonable insulation thickness, several insulation improvement methods are applied and experimentally verified by using representative coupons. After understanding the possible ways for evaluating and eliminating internal voids, a PCB-based planar bus is designed and fabricated, which shows great insulation improvement after experimental verification. In order to eliminate PDs in the air and shrink the insulation distance, three ways for managing E-field distribution in air are demonstrated by three examples. First, by using the interconnections among the power modules, Rogowski-based current-sensing board, and the laminated bus as an example, E-field distribution can be estimated by Finite Element Analysis (FEA) and its management can be achieved by geometrical modifications. Second, for the one-turn inductor, a methodology is demonstrated that builds a coaxial insulation structure with proper termination technology in order to squeeze air out of the insulation system. Finally, E-field shielding technology is applied along the heatsink edges in order to make the E-field distribution uniform and to shrink the insulation distance between the heatsink and the cooling system. After improving the insulation, this work shrinks the converter unit size by around 50% while maintaining its PD-free status under normal operation conditions. Besides the significant increase in power density and weight reduction, the entire converter system has less ringing and better current-sharing performance due to reductions of the parasitic inductance. Partial Discharge online monitoring via acoustic and photon detection methods –Targeting the online monitoring and even localization of surface discharge for power converter applications, two novel types of sensors have been proposed and fabricated. In order to verify the concepts, one example with experimental results has been given for each type of sensor. The experimental data demonstrates that such sensors can be placed inside the converter and online monitoring can be realized for surface or corona discharges by capturing either the acoustic signal or the photons that are generated by discharge events. / Doctor of Philosophy / A unproper designed insulation system can take more than 50% volume of Medium Voltage (MV) SiC-based converters and have significant internal or external Partial Discharge (PD), which can not only accelerate the insulation aging but also risk to multiple aspects of the converter system. Therefore, developing an insulation design, assessment and online monitoring method to help reach a compact and PD free insulation system for MV SiC-based converters is a goal of this work. Experimental PD investigation is completed for internal void discharge, surface discharge, and point discharge representative coupons under square excitations. Several general insulation design and assessment guidelines are proposed based on the experimental PD investigation and physics-based explanations, which are further applied during converter prototypes development. Then, PD elimination methodology is developed and demonstrated by design examples. By using the laminated bus as an example, internal void evaluation and analysis method is demonstrated. Then, targeting the internal PD-free design with reasonable insulation thickness, several insulation improvement methods are applied and experimentally verified by using representative coupons. In order to eliminate PDs in air and shrink the insulation distance, three ways for managing E-field distribution in air are demonstrated by three examples. First, by using the interconnections among the power modules, Rogowski-based current-sensing board, and the laminated bus as an example, E-field distribution can be estimated by Finite Element Analysis (FEA) and its management can be achieved by geometrical modifications. Second, for the one-turn inductor, a coaxial insulation structure with proper termination technology in order to squeeze air out of the insulation system is demonstrated. Finally, E-field shielding technology is applied along the heatsink edges in order to make the E-field distribution uniform and to shrink the insulation distance between the heatsink and the cooling system. After improving the insulation, this work shrinks the converter unit size by around 50% while maintaining its PD-free status under normal operation conditions. Besides the significant increase in power density and weight reduction, the entire converter system has less ringing and better current-sharing performance due to reductions of the parasitic inductance. Targeting the PD online monitoring for power converter applications, two novel types of sensors have been proposed and fabricated. In order to verify the concepts, one example with experimental results has been given for each type of sensor. The experimental data demonstrates that such sensors can be placed inside the converter and online monitoring can be realized for surface or corona discharges by capturing either the acoustic signal or the photons that are generated by discharge events.

The main goal of this thesis was to study plasma generated by surface discharge and its application in volatile organic compound destruction. Introduction of this thesis deals with the issue of volatile organic compound. The term of volatile organic compound was defined and explained. Summary of the most important sources of volatile organic compound emissions and possible technics for their elimination was presented. This thesis drew attention on negative aspects of volatile organic compounds on human organism and on the whole environment. The problems of surface discharge and its possible application in various branches are known only few years therefore construction of plasma reactor itself was the first independent step of this work. The plasma reactor was consisted of electrode, which was created from the series of metal stripes each other separated by dielectric barrier. On the surface of the electrode, discharge was regulated and distributed. For the reason of technical limits experiment time was limited up to one minute. The experimental part describes reactor for surface discharge and other parts of apparatus in which degradation volatile organic compound was carried out. Nitrogen was used as carrier gas and it was mixed with air before entering into the reactor. Samples of compounds after degradation process were taken from reactor for the subsequent analysis. Analysis of the products proceeded in a gas chromatogram linked to mass spectrometer. The decomposition products were adsorbed in the SPME filaments or in sorption tubes. The decomposition products were analysed also through the mean of Testo 350 M/XL. This apparatus provided the information on the concentration of small molecules such as CO, H2, NO, NO2 and CxHy Hexane, cyclohexane and xylene were used as VOC examples. Analysis of GC-MS showed decomposition products of hexane, cyclohexane and xylene. The decomposition products were especially various alcohols, ketones, aldehydes and benzene compounds. The apparatus Testo 350 M/XL was unable to detect any CxHy, only large quantity of NO2. This thesis was further focused on possible factors which could have an influence on degradation of compounds, for example input power or different flow of oxygen. It was found that increasing power declined the removal efficiency. The maximum removal efficiency was 87 % for degradation of hexane at the lowest input power. Next part of this thesis was focused on diagnostics of plasma generated in the surface discharge form. The optical emission spectroscopy has been chosen as the best method for plasma characterisation. By this method, various important discharge parameters can be determined, e.g. vibration and rotation temperature. The obtained numeric value of rotation temperature was 840±80 K and vibration temperature was 1880±140 K. The obtained results may be used as a fundament for further study of VOC decomposition in surface discharge.

Isolationsdiagnostik är ett redskap som är av stor betydelse för underhållsoptimering av elektriska anläggningar. Ett av de möjliga mått på isolationsförsämring som kan användas i diagnosticeringssyfte är partiella urladdningar. Det här examensarbetet beskriver ett modelleringsförsök av ett resistivt-kapacitivt nätverk för simulering av partiella yturladdningar i Matlab. Tyvärr blev försöket misslyckat på grund av ett oväntat stort beroende av högspänningskapacitanser på ytresistiviteten. Ytterligare ett försök genomfördes i COMSOL Multiphysics, ett program baserat på finita elementmetoden ämnat för simuleringar av fysikaliska processer. Den huvudsakliga nackdelen med COMSOL Multiphysics modellen är långa simuleringstider. Det visade sig vara möjligt att simulera urladdningar i COMSOL Multiphysics. Här modellerades ytresistansen med hjälp av ett resistivt skikt. Yturladdningar simulerades genom att ändra det resistiva skiktets konduktivitet. Här upptäcks ytterligare ett problem: mycket långa simuleringstider vid användandet av olinjära konduktivitetsuttryck som beror på det elektriska fältet. Alla simuleringar, både i Matlab och COMSOL Multiphysics, utfördes på en dator med Intel dual-core processor: 2.13 GHz, 0.99 GB of RAM. / Insulation diagnostics is a very important tool in optimization of electric installations’ maintenance. One of the possible measures of insulation deterioration that can be used for diagnostic purposes are partial discharges. This thesis work describes an attempt to model a resistive-capacitive network for simulating partial surface discharges in Matlab. Unfortunately this attempt proved to be a failure due to an unexpectedly considerable dependency of high voltage capacitances on surface resistivity. Another attempt described here was performed in COMSOL Multiphysics, a finite-element based program for simulation of physical processes. The main drawback with COMSOL Multiphysics model is long simulation times. It proved to be possible to simulate discharges in COMSOL Multiphysics. Here surface resistance was modeled with the help of a resistive layer. Discharges were simulated by changing conductivity of the mentioned layer. Here another problem was discovered: very long simulation times when using non-linear, electric field dependent expressions for conductivity. All the simulations, both in Matlab and COMSOL Multiphysics, were performed on a computer with Intel dual-core processor: 2.13 GHz, 0.99 GB of RAM.

Ce travail s'intéresse aux effets mécaniques créés par les décharges de surface et à leur efficacité comme actionneur. Une géométrie particulière d'électrodes permet de créer de manière pulsée un filament linéaire de plasma et de le chauffer très rapidement par effet Joule (à raison de plusieurs Joules en moins d'une microseconde). Ce chauffage rapide entraîne la formation d'ondes de choc qui peuvent interagir avec l'écoulement ambiant.Nous étudions le comportement électrique de la décharge de surface afin d'évaluer l'énergie déposée dans le filament de plasma par effet Joule. Pour ce faire, nous réalisons une étude paramétrique sur la configuration du circuit et nous déterminons les principaux paramètres qui pilotent la dynamique de la décharge. Différents modèles de résistance sont utilisés dans un code de simulation du circuit électrique, et leurs prédictions du courant et du dépôt d'énergie sont confrontées aux mesures expérimentales.Des mesures spectroscopiques dans différentes configurations de circuit donnent accès à certaines propriétés de la décharge comme la densité électronique, qui atteint des valeurs de 2x1018 cm-3. Le rayon du canal est également mesuré par imagerie rapide. Les ondes de chocs créées par la décharge de surface sont visualisées en imagerie Schlieren pour plusieurs configurations de circuit. Ces ondes de chocs créent une impulsion proportionnelle à l'énergie déposée dans la décharge. Nos développons un modèle de choc pour décrire la trajectoire du choc et pour calculer l'impulsion communiquée par la décharge de surface. Le modèle est en bon accord avec les mesures expérimentales et la décharge de surface a une efficacité mécanique de 0.12mNs/J pour notre configuration d'étude. Nous terminons cette étude en comparant cet actionneur potentiel avec d'autres actionneurs courants et proposons plusieurs pistes pour de futurs travaux. / In this study, we investigate the mechanical effects generated by pulsed surface discharges and their efficiency as an actuator. Using a specific electrode configuration, it is possible to create a short-lived, pulsed, rectilinear plasma channel and to heat it up rapidly (several Joules in less than a microsecond) through Joule heating. This fast energy deposition causes the formation of shock waves that can then interact with the surrounding flow.We study the electrical behavior of the pulsed surface discharge to assess the energy deposited in the plasma channel through Joule heating. To do so, we perform a parametric study on the circuit configuration and identify the main parameters driving the discharge dynamics. Several resistance models are implemented in a numerical description of the electrical circuit and their predictions of the current and deposited energy are compared with experimental measurements.Spectroscopic measurements in different circuit configurations give access to some of the plasma properties such as the electron number density that can reach values up to 2x1018 cm-3. Fast imaging also gives insight into the plasma channel radius. The shock waves generated by the pulsed surface discharge in different circuit configurations are visualized through Schlieren imaging. These shock waves generate an impulse that increases linearly with the energy deposited in the discharge. We develop a shock model to describe the shock trajectory and to compute the impulse imparted by the pulsed surface discharge. The model is in good agreement with our measurements and the pulsed surface discharge is found to have a mechanical efficiency of 0.12 mNs/J for our setup configuration. We conclude this study by comparing the proposed pulsed surface discharge actuator with other common designs and offer some directions for future studies.