Diagnosis of power transformers using return voltage and partial discharge measurements - New methods for measurement data evaluation

Zur Diagnose des Isoliersystems von Leistungstransformatoren kommt eine Vielzahl unterschiedlicher elektrischer und nicht-elektrischer Verfahren zum Einsatz. Jedes dieser Verfahren kann Aufschluss über eine oder mehrere bestimmte Komponenten des komplexen Systems Transformatorisolierung geben. Ein einzelnes Verfahren, das eine Diagnose des Gesamtobjekts zulässt, ist aufgrund der Komplexität des Systems nicht verfügbar. Für eine Beurteilung des Gesamtsystems ist grundsätzlich eine Analyse mit mehreren unterschiedlichen Verfahren erforderlich. Im Rahmen der vorliegenden Arbeit wurden speziell zwei Verfahren untersucht: Rückkehrspannungsmessungen und Teilentladungsmessungen in Transformatoröl. Die Rückkehrspannungsmessung als dielektrisches Diagnoseverfahren, bisher hauptsächlich aus der Kabeldiagnose bekannt, liefert ein integrales Abbild der dielektrischen Eigenschaften der gesamten Transformatorisolierung, während die Teilentladungsdiagnose des Isolieröls zunächst nur Rückschlüsse auf die Ölqualität zulässt, die aber in großem Maße den Zustand des Gesamtsystems widerspiegelt. Beide Verfahren haben gemeinsam, dass die eigentliche Messtechnik mit vergleichsweise einfachen Mitteln aufzubauen ist. Speziell die Rückkehrspannungsmessung ist relativ störsicher, während Teilentladungsmessungen oft unter Laborbedingungen durchgeführt werden. In den letzten Jahren hat allerdings auch die softwaregestützte Störunterdrückung erheblich an Bedeutung gewonnen, wobei durch spezielle Algorithmen Störsignale von Nutzsignalen getrennt werden können. Gegenstand der vorliegenden Arbeit ist in erster Linie die Vorstellung neuer Möglichkeiten zur Auswertung der genannten Verfahren unter Ausnutzung der dargelegten physikalischen Zusammenhänge. Dadurch ist es möglich, aus mit den herkömmlichen Messverfahren gewonnenen Daten zusätzliche Informationen zu erhalten. Speziell im Fall der Rückkehrspannungsmessung, die unter der Bezeichnung "Recovery Voltage Method" bzw. "Polarisationsspektrum" seit längerem von vielen Autoren als für die Transformatordiagnose ungeeignet dargestellt wird, ist eine eingehendere Betrachtung der physikalischen Hintergründe des Verfahrens sinnvoll, da die in der Literatur angezweifelten Messergebnisse in erster Linie auf eine Fehlinterpretation der Messdaten anhand einer ungeeigneten Modellbildung zurückzuführen sind. Teilentladungsmessungen in Isolieröl mit geeigneten inhomogenen Elektrodenanordnungen sollen Rückschlüsse auf die Ölqualität, speziell zumindest qualitativ auf den Gehalt an kurzkettigen Abbauprodukten, ermöglichen. Das Fernziel der Untersuchungen ist die Entwicklung einer Messanordnung zum Einbau in Transformatoren, mit der eine Online-Ölüberwachung durchgeführt werden kann. Zu diesem Zweck werden Parameter gesucht, die eine automatische Auswertung gestatten. Die Arbeit präsentiert zunächst die Theorie und Modellvorstellungen, die den Verfahren zugrunde liegen. Die theoretischen Überlegungen werden anschließend anhand von realen Messergebnissen näher erörtert. Des weiteren werden Vergleiche mit Simulationen und Berechnungen vorgenommen.With the increase of required lifetime of power transformers, diagnostics become more and more important to monitor the condition of the insulation system. There are numerous methods existing for the analysis of different components or parts of the insulation and their electrical and chemical properties. The results of all these methods together should give a complete overview of the condition of the sample. This thesis presents new approaches in measurement data evaluation for two diagnostic methods, the Return Voltage Measurement (RVM) - also known as Recovery Voltage Measurement - and the Partial Discharge (PD) Measurement in the insulating oil. The Return Voltage Measurement is an integral method that is influenced by both the solid and the liquid component of the insulation. In contrast to this, the PD Measurement in transformer oil basically reveals information about the condition of the liquid component. Especially the Return Voltage Measurement is often criticized as not being suitable for transformer diagnostics due to a lack of useful evaluation methods. Most methods that have been known for many years - i.e. especially the Polarisation Spectrum as the most well-known one - do not take the physically relevant processes inside a multi-layer insulation into account and thus give insufficient or even wrong interpretation of the data. The basic mechanism in oil-cellulose insulation systems is the boundary polarization which is the only polarization mechanism - maybe only except charge carrier trapping or space charge processes - that can produce time constants in the range of up to several hundreds of seconds. For the description of boundary polarization processes in a two-component system, the Maxwell equivalent circuit can be used. For this equivalent circuit it is possible to calculate all relevant parameters analytically, even with an additional resistance - e.g. the finite input resistance of the measuring equipment - and capacitance in parallel. The goal of this work is to show that an evaluation of RVM data according to the Maxwell equivalent circuit may reveal additional information about the condition of the insulation - especially that of the cellulose component - that cannot be gained by interpretation based on the commonly used formal equivalent circuit. For the analysis of the condition of the liquid component of the insulation - i.e. in this case the transformer oil - different methods exist that in many cases are relatively intricate and expensive. The simpler methods like e.g. the electric breakdown strength testing often do not reveal much information about the actual overall condition of the oil. The present work compares the partial discharge behavior of transformer oils in different conditions and with different histories of ageing in order to find correlations to the presence of certain degradation products that do not necessarily directly affect the electrical strength of the oil - and that consequently cannot be detected by simple dielectric strength measurements, e.g. a breakdown test - but that may reveal information about the overall condition of the insulation system. Usually those substances can only be detected e.g. by gas chromatography or similar procedures. The basic idea behind the experiments was to find at least a qualitative influence of these substances on partial discharge parameters. In some cases the results could be compared to the results of standard analyses like the Dissolved Gas Analysis. The influence of the concentration of water in the oil was evaluated as well. The partial discharge measurements were performed using a low frequency wide-band band pass filter system as detector. For the evaluation of the partial discharge data, recently developed methods were applied that mainly analyze the shape of the signals generated by the partial discharge detector (Pulse Shape Analysis). The shape of these impulse responses is influenced by short-time sequences of partial discharge events in the range of a few microseconds. The final goal of the experiments was to find methods that allow a quick (maybe even on-line) low-cost analysis that allows a relatively prompt reaction to critical states of the insulation system. The low cost aspect is particularly interesting for smaller and/or less important equipment, where other on-line monitoring methods would be too costly and consequently are usually not applied. The intention is not to replace the standard methods like e.g. the DGA, but rather as a complementary pre-analysis that - in case of the detection of a critical condition - may lead to a warning and subsequently to a further analysis using standard methods

Online Gaming and Personality: Explaining Gamers’ Cheating Intention

Cheating in online games poses a risk to game publishers, as it deters other gamers and reduces revenues. These facts make it essential for game publishers to understand ‘who’ in the sense of gamers with what personalities have cheating intentions. Building on psychology research, we draw on (a) the big five personality traits and (b) the dark triad personality traits to explain how these reflect gamers’ personalities and together lead to cheating intentions. Following a configurational approach (N=192), we reveal two configurations explaining high cheating intention and one explaining low cheating intention. We contribute to online gaming research by revealing that gamers with cheating intentions have specific personalities. We advance information systems (IS) personality research by combining broad and dark triad traits to explain divergent behavior like cheating

Reversible magnetomechanical collapse: virtual touching and detachment of rigid inclusions in a soft elastic matrix

Soft elastic composite materials containing particulate rigid inclusions in a soft elastic matrix are candidates for developing soft actuators or tunable damping devices. The possibility to reversibly drive the rigid inclusions within such a composite together to a close-to-touching state by an external stimulus would offer important benefits. Then, a significant tuning of the mechanical properties could be achieved due to the resulting mechanical hardening. For a long time, it has been argued whether a virtual touching of the embedded magnetic particles with subsequent detachment can actually be observed in real materials, and if so, whether the process is reversible. Here, we present experimental results that demonstrate this phenomenon in reality. Our system consists of two paramagnetic nickel particles embedded at finite initial distance in a soft elastic polymeric gel matrix. Magnetization in an external magnetic field tunes the magnetic attraction between the particles and drives the process. We quantify the scenario by different theoretical tools, i.e., explicit analytical calculations in the framework of linear elasticity theory, a projection onto simplified dipole-spring models, as well as detailed finite-element simulations. From these different approaches, we conclude that in our case the cycle of virtual touching and detachment shows hysteretic behavior due to the mutual magnetization between the paramagnetic particles. Our results are important for the design and construction of reversibly tunable mechanical damping devices. Moreover, our projection on dipole-spring models allows the formal connection of our description to various related systems, e.g., magnetosome filaments in magnetotactic bacteria.Comment: 14 pages, 7 figure

Wird die Rolle von psychischen Erkrankungen beim Suizid überbewertet?

In the scientific literature, it is often said that 90% of all suicides are the consequences of a~mental illness. Nevertheless, recent reports and comments cast doubt on this view and point out that such a~limitation might hamper effective suicide prevention. In this overview we will outline and discuss important results on how often suicides are the consequence of mental illnesses and whether the association between mental illnesses and suicide might be overestimated.Mental illnesses and especially affective disorders increase the risk of suicide by 30 to 50~times. Nevertheless, they explain only a~certain percentage of all suicides. Observational and treatment studies indicate that mental illness is only one factor of several that lead to suicide. Among other factors are relationship problems, drug abuse, severe somatic illnesses, job problems, financial worries or juridical threats.Suicidal behaviour is an indicator of deep unhappiness but not necessarily caused by a~mental illness. Many persons with mental illnesses do not show suicidal behaviour. On the other hand, not all people who take their own lives have a~mental illness. This has significant consequences for universal and indicated prevention of suicide. ZUSAMMENFASSUNG Die Aussage, dass Suizide zu 90 % Folge psychischer Erkrankungen sind, wird häufig in der wissenschaftlichen Literatur zitiert. Neuere Analysen und Kommentare ziehen das aber in Zweifel und betonen die Notwendigkeit, vielfältigere Ursachen für Suizidereignisse zu beachten, auch um die Prävention von Suiziden nicht auf das Erkennen und Behandeln psychischer Erkrankungen zu reduzieren. Das Ziel dieser Übersichtsarbeit ist die Darstellung und Bewertung wichtiger empirischer Befunde zu der Frage, ob die Rolle psychischer Störungen beim Suizid überbewertet wird.Psychische Störungen erhöhen das Risiko eines Suizides um das bis zu 30- bis 50-Fache gegenüber der Allgemeinbevölkerung, dennoch wird dadurch nur ein Teil aller Suizide erklärt. Aus Beobachtungs- und Therapiestudien ergeben sich deutliche Hinweise, dass psychische Störungen nur ein Faktor unter mehreren sind, die zu Suizid führen. Eine Rolle spielen beispielsweise auch Beziehungsprobleme, Substanzmissbrauch, Belastungen durch schwere körperliche Erkrankungen, akute Krisen im Beruf, Probleme mit Finanzen und juristische Belastungen.Suizidales Verhalten weist auf eine tiefe Unzufriedenheit hin, aber nicht notwendigerweise auf eine psychische Erkrankung. Viele Menschen mit einer psychischen Erkrankung zeigen kein suizidales Verhalten und nicht alle Menschen, die sich ihr Leben nehmen, haben eine psychische Erkrankung. Diese Erkenntnisse haben erhebliche Konsequenzen für die universale und indizierte Prävention von Suiziden

Model Adaptation and Optimization for the Evaluation and Investigation of Novel Amine Blends in a Pilot-plant Scale CO2 Capture Process under Industrial Conditions

Carbon capture processes are highly energy intensive and the main driving force during the process design is the necessity to reduce the energy consumption for the solvent regeneration. The energy efficiency of absorption desorption processes is driven by the plant design and operation conditions, but also to a large extent by the choice of the scrubbing liquid (Wang et al., 2011). Absorbent screening for CO2 capture is timeconsuming and costly. Apart from the energy efficiency, aspects such as loading capacity and robustness towards industrial impurities and disturbances have to be investigated before designing a large-scale plant and optimally operating it. In this contribution, a systematic approach is presented to carry out evaluation tests for a novel solvent in an industrial pilot-plant and at the same time to determine an optimal operation point with maximum energy efficiency. The three-step approach is based on the assumption that for a novel absorbent little to no thermodynamic data is available. Hence, the investigation is solely based on simulation data from similar solvents and experimental data on the novel one. Monoethanolamine (MEA) still is widely used as reference absorbent for removing CO2. Consequently, simulation data and the properties of MEA are taken as a baseline for the general performance and behaviour of amine-based absorbents. As a first step, data from rigorous simulations is used to develop a surrogate model describing the general behaviour of a carbon capture process for MEA. Subsequently, pilot-plant-scale experiments are carried out to investigate the application of MEA in practice. Secondly, the surrogate model is then updated to account for the plant characteristics as given by the experimental data for MEA. Finally, by means of the MEA-based data-driven model, the new solvent is experimentally investigated. By successive approaches the surrogate model’s maximum in energy efficiency is identified and repeatedly updated for the novel solvent’s experimental behaviour. In terms of the energy efficiency and based on this workflow the performance of the novel solvent is compared with MEA