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abstract: This thesis focuses on the influence of a grounded back electrode on the breakdown characteristics. The back electrode is an electrode which attaches at the back side of solid insulation. Insulation with grounded back electrode is a common type of insulation which is adopted in many high voltage power devices. While most of the power equipment work under AC voltage, most of the research on back electrode is focused on the DC voltage. Therefore, it is necessary to deeply investigate the influence of the back electrode under AC applied voltage. To investigate the influence of back electrode, the research is separated into two phases, which are the experiment phase and the electric field analysis phase. In the experiments, the breakdown voltages for both with and without back electrode are obtained. The experimental results indicate that the grounded back electrode does have impact on the breakdown characteristics. Then with the breakdown voltage, based on real experiment model, the electric field is analyzed using computer software. From the field simulation result, it is found that the back electrode also influences the electric field distribution. The inter relationship between the electric field and breakdown voltage is the key to explain all the results and phenomena observed during the experiment. Additionally, the influence of insulation barrier on breakdown is also investigated. Compared to the case without ground electrode, inserting a barrier into the gap can more significantly improve breakdown voltage. / Dissertation/Thesis / M.S. Electrical Engineering 2014

Ester liquids including natural ester and synthetic ester are considered as potential substitutes for mineral oil, due to their good biodegradability and high fire points. Although these liquids have been widely used in distribution and traction transformers, research efforts are required for the purposes of design and manufacture of high voltage and large power transformers which are filled by esters. Indeed, it would be risky to apply esters in large power transformers without thorough understandings of their behaviours in large gaps and/or when combined with pressboard insulation. Therefore, investigations of creepage discharges along the surface of pressboard in esters are vitally important and their behaviours should be compared with those of mineral oils. This thesis is aimed to investigate the creepage discharges along pressboard in esters and mineral oil under ac divergent electric field. Apparent charges, current signals and images of streamer channels were obtained synchronously to identify whether and how the introduction of pressboard surface would influence the inception and propagation of discharges as compared to tests in open gap. When over-stressed by higher voltages, the surface tracking along the pressboard-ester interface, triggered by sustaining creepage discharges, was studied and the evolutions of accompanying creepage discharge patterns were investigated. In these experiments, both esters and mineral oil impregnated pressboards were comparatively studied. The test results indicated that at the inception stage, the presence of pressboard or any other solid types in different liquids under test do not influence the PD inception voltages; in the propagation stage, solid surface tends to promote the development of discharges, especially those occurring in negative half cycles, and shifts more discharges towards the zero-crossing phase angles. This discharge promotion effect is much more evident in esters than in mineral oil, probably because of higher discharge intensity in esters and higher viscosity of esters. The space charge effect and the residual low density channel effect are proved as the mechanisms best explaining the influences of solids on creepage discharges. Under higher voltages, it was found that the impregnated pressboard is susceptible to discharge erosion characterized by “white and carbonized tree-shaped marks”, due to intense discharges occurring on or near the pressboard surface. The “white mark” appears at a lower voltage and propagates more easily on ester impregnated pressboard. The gaseous “white mark” channels will attract the subsequent discharges to follow the same discharge routes; the accumulative energy dissipation in these channels will then result in the carbonization of the channels. Once formed, the surface tree-shaped mark can continue to grow even under reduced voltage levels until it bridges the gap and causes the final flashover.

The concept of More Electric Aircraft, where is to utilize the electrical power to drive more or all aircraft subsystem instead of conventional combination of pneumatic, hydraulic, mechanical and electrical power, can be recalled to World War II. It has been proven to have more advantages for decades in terms of energy efficiency, environmental issues, logistics and operational maintenance. It can also enhance aircraft weight, volume and battle damage reconfigurability.Thanks to the new electronics technologies and the emergence of new materials, It becomes feasible for high power density electrical power components to drive the majority of aircraft subsystem. However, sustaining the transmission of hundreds of kilowatts of electrical power at low voltages is not feasible owing to the penalties incurred due to high cable weights and voltage drop may become critical. It is very easy to come up with the solution of the increase of voltage. However, higher voltage will introduce other problems such as the reliability of insulation coordination on the aircraft due to the increased probability of electrical discharge. For aircraft designers, it is very important to understand the rules of insulation coordination on the aircraft including determining clearance and creepage distances, and also have a clear investigation of the phenomena and mechanism of electrical discharges. Past research has identified a number of the concerns of operating electrical systems at higher voltages in an aerospace environment, especially for dimensioning of clearances. However, there is little study on dimensioning of creepage distances and relevantly flashover and electrical tracking on solid insulating material surfaces. This thesis firstly discusses the rules for determining clearances and creepage distances. The experimental validation work was done for breakdown in air gap and on the solid insulating material surfaces under dry condition so that some standard recommended values can be evaluated not only with theoretical values such Paschen's law. Suggestions of application of those standards were provided. Secondly, the complex electrical discharge under wet condition on solid insulating material surfaces was discussed. A mathematical model to predict this type of electrical failure -electrical tracking (the electrical discharges on solid insulation materials which will lead to physical damage in the materials) with the consideration of different environmental conditions including air pressure, ambient temperature, and pollution degrees was developed. A series of electrical tracking tests were carried out on organic materials to find out the mechanism of electrical tracking and validate the finding by the mathematic model. Finite element analysis simulations were also conducted to find out the background thermal transfer mechanism to support our explanation of those phenomena of electrical tracking. Different test techniques have ben developed for specific impact factors. Finally, the suggestions for utilization of the standards and feasible test techniques for electrical tracking under wet conditions were provided.

- Luft- und Kriechstreckenberechnung in 3D-CAD-Daten - Neue, umfassendere Funktionalität in CCX - CCX löst Spark Analysis Extension ab - AutoCrea - Mehr Sicherheit im Entwurf von elektronischen Komponenten - Rasante Beschleunigung in der Geometrieauslegung zur Vermeidung von Risiken durch Luft- und Kriechstrecken - Deutliche Wertschöpfung schon in der Produktentwicklung in der Auslegung von elektronischen Komponenten

Elektrische Baugruppen enthalten Netze unterschiedlicher Spannung, zwischen denen sich Kurzschlüsse entweder durch Funkenüberschlag durch die Luft (Luftstrecke) oder über die Oberflächen von Isolatoren (Kriechstrecke) bilden können. AutoCrear bietet eine robuste und effiziente softwarebasierte Analyse aller Luft- und Kriechstrecken auf CAD Daten elektrischer Baugruppen. Entwickler von elektrischen Baugruppen steht damit erstmals ein robustes Werkzeug zur Verfügung, um sämtliche Normverletzung bereits in der Designphase zu erkennen und gezielt zu beseitigen, sowie eine umfassende und einheitliche Dokumentation hinsichtlich Luft- und Kriechstrecken zu erstellen und damit den Produktionsprozess massiv zu optimieren. AutoCrear ist eine Standalone-Lösung, die den kompletten Workflow einer Luft- und Kriechstreckenanalyse in einem einzigen Programm vereint.

Electrical assemblies contain networks of varying voltages between which short circuits can form either by sparkover through the air (clearance) or across the surfaces of insulators (creepage). AutoCrear offers a robust and efficient software-based analysis of all clearances and creepage distances on CAD data of electrical assemblies. For the first time, developers of electrical assemblies have a robust tool at their disposal to detect all standard violations already in the design phase. A comprehensive and uniform documentation regarding clearance and creepage distances is automatically created. AutoCrear is a standalone solution that combines the complete workflow of a clearance and creepage distance analysis in a single programme. / Elektrische Baugruppen enthalten Netze unterschiedlicher Spannung, zwischen denen sich Kurzschlüsse entweder durch Funkenüberschlag durch die Luft (Luftstrecke) oder über die Oberflächen von Isolatoren (Kriechstrecke) bilden können. AutoCrear bietet eine robuste und effiziente softwarebasierte Analyse aller Luft- und Kriechstrecken auf CAD Daten elektrischer Baugruppen. Entwickler von elektrischen Baugruppen steht damit erstmals ein robustes Werkzeug zur Verfügung, um sämtliche Normverletzung bereits in der Designphase zu erkennen. Es wird automatisch eine umfassende und einheitliche Dokumentation hinsichtlich Luft- und Kriechstrecken erstellt. AutoCrear ist eine Standalone-Lösung, die den kompletten Workflow einer Luft- und Kriechstreckenanalyse in einem einzigen Programm vereint.

The wheel-rail contact mechanics and dynamics that are of great importance to the railroad industry are evaluated by applying statistical methods to the large volume of data that is collected on the VT-FRA state-of-the-art roller rig. The intent is to use the statistical principles to highlight the relative importance of various factors that exist in practice to longitudinal and lateral tractions and to develop parametric models that can be used for predicting traction in conditions beyond those tested on the rig. The experiment-based models are intended to be an alternative to the classical traction-creepage models that have been available for decades. Various experiments are conducted in different settings on the VT-FRA Roller Rig at the Center for Vehicle Systems and Safety at Virginia Tech to study the relationship between the traction forces and the wheel-rail contact variables. The experimental data is used to entertain parametric and non-parametric statistical models that efficiently capture this relationship. The study starts with single regression models and investigates the main effects of wheel load, creepage, and the angle of attack on the longitudinal and lateral traction forces. The assumptions of the classical linear regression model are carefully assessed and, in the case of non-linearities, different transformations are applied to the explanatory variables to find the closest functional form that captures the relationship between the response and the explanatory variables. The analysis is then extended to multiple models in which interaction among the explanatory variables is evaluated using model selection approaches. The developed models are then compared with their non-parametric counterparts, such as support vector regression, in terms of "goodness of fit," out-of-sample performance, and the distribution of predictions. / Master of Science / The interaction between the wheel and rail plays an important role in the dynamic behavior of railway vehicles. The wheel-rail contact has been extensively studied through analytical models, and measuring the contact forces is among the most important outcomes of such models. However, these models typically fall short when it comes to addressing the practical problems at hand. With the development of a high-precision test rig—called the VT-FRA Roller Rig, at the Center for Vehicle Systems and Safety (CVeSS)—there is an increased opportunity to tackle the same problems from an entirely different perspective, i.e. through statistical modeling of experimental data. Various experiments are conducted in different settings that represent railroad operating conditions on the VT-FRA Roller Rig, in order to study the relationship between wheel-rail traction and the variables affecting such forces. The experimental data is used to develop parametric and non-parametric statistical models that efficiently capture this relationship. The study starts with single regression models and investigates the main effects of wheel load, creepage, and the angle of attack on the longitudinal and lateral traction forces. The analysis is then extended to multiple models, and the existence of interactions among the explanatory variables is examined using model selection approaches. The developed models are then compared with their non-parametric counterparts, such as support vector regression, in terms of "goodness of fit," out-of-sample performance, and the distribution of the predictions. The study develops regression models that are able to accurately explain the relationship between traction forces, wheel load, creepage, and the angle of attack.

This master’s thesis is dedicated to the design of an experimental rig that allows investigation of causes for noise during tram’s passing of a track curve and the developement of means to mitigate this noise. The opening section of this thesis contains theoretical background for the tribological mechanics of wheel-rail contact with emphasis on the process of noise generation, followed by an overview of laboratory tst rigs with similar purpose. Design itself is centered around the implementation of the dynamic model of wheel-rail contact using real tram wheel. Resulting test rig allows measurement of the adhesion characteristic in tangential and lateral directions and recording of the generated noise while an angle of attack is set.