The DC casting process used for the production of cast aluminium alloy products intended for processing by rolling, extrusion or forging is an economically important process with approximately 10 million tonnes of DC cast product being produced annually world wide [1]. Process productivity, particularly with respect to elimination of casting defects and hence process scrap is an important factor to DC cast product producers. The literature reporting the DC casting process, particularly with respect to the formation of defects on the cast surface, is reviewed and the mechanisms for the formation of such defects examined. A universally understood and accepted explanation was found for only one of the normal surface defects encountered in practice. A number of samples of commercially cast DC products were subject to detailed cast surface examination, particularly surface microstructures. The results of this examination and the literature survey identified molten metal surface tension as a possible contributing factor affecting the molten metal meniscus stability within the DC casting mould. Meniscus instability is linked with the formation of surface defects. The literature on surface tension of aluminium alloys provided only limited information hence the surface tension of a range of binary and ternary alloys, including commercial alloys was determined, producing data hitherto not available. Of the common alloying elements used in commercial aluminium alloys, iron and magnesium were found to significantly reduce the surface tension. Surface fracture also resulted in a reduction in surface tension for the majority of alloys tested. The surface tension data is combined with mould thermal and physical model calculations to propose a mechanism for the formation of the cast surface defects. The model proposes a maximum stable size for the meniscus according to the alloy and mould conditions. Conditions outside these limits result in meniscus instability and the formation of cast surface defects. The model suggests possible operating changes that may reduce the incidence of surface defect formation. The work also identifies a number of areas requiring further investigation before major practical process changes aimed at cast surface defect elimination, may be formulated.

This thesis provides a coherent history of Celtic ideas in the modern era. Combining intellectual and cultural history in a transnational framework, it has two main aims. The first is to chart the transformation of perceptions of the Celts from those of a sought-after European ancestor to those of a marginalised people living on the ‘fringes’ of western Europe over the longue durée of 1700-1900. The second aim is to illustrate the wider intellectual, cultural, and political ramifications of this protracted ideological shift. I examine the scholarship of antiquarians, historians, philologists, race scientists, and other intellectuals of all stripes, before investigating how Celtic cultural nationalist movements grew out of these ideas and remained anchored in them. With the racialisation of nations and the cultural shift wherein the nation became a salient political consideration in the period c.1780-c.1820, Celtic ideas were no longer mere passive descriptors of nations, their particular pasts, and their places within wider European history, but active connectors of peoples with both their history and their supposed national destiny. Developments in scholarship combined with the changing imperatives of national thought led to the emergence of an archetypal Celtic image around 1830, where ‘the Celts’ became usefully politicised by both English chauvinists and Celtic nationalists alike. This era also saw the beginnings of Pan-Celticism, where race, far from being used to castigate the Celts, became a central pillar around which members of the different Celtic nations rallied. Tracing Celtic ideological vicissitudes over this longue durée serves as a case-study for how national thought and its conceptual relatives evolved over the eighteenth and nineteenth centuries, following the early-modern squabbles over Celtic ancestry through to the early-twentieth century Pan-Celtic movement, the version of Celticism we have inherited more or less intact today.

Voltage-Sourced Converter High Voltage Direct Current (VSC-HVDC) transmission technology has received great interest and experienced rapid development worldwide because of its compact size, ability to connect two asynchronous AC systems and ability to connect to weak AC grids. It is expected that VSC-HVDC will play a significant role in future power transmission networks. Multi-Terminal Direct Current (MTDC) networks are even being established based on VSC-HVDC and these have great potential to support conventional AC transmission networks. However, such DC networks are vulnerable to any DC side short-circuit fault. DC protection issues must be tackled to enable the development of MTDC networks. This thesis conducts some of the underpinning research for such DC protection studies. As a first step to conduct the protection study, a detailed four-terminal VSC-HVDC system is developed in PSCAD/EMTDC, which consists of both two-level converters and MMC devices. Based on this high fidelity four-terminal system model, a thorough analysis is conducted for the two-level converter and the MMC systems under different fault scenarios. Based on this, a basic understanding of the converter systems' natural responses to these fault scenarios is obtained. Apart from using a DC circuit breaker to isolate a DC fault, there may be other devices which could potentially be used for DC protection. After the fault analysis, a study is conducted to search for any other DC protection equipment which could help the DC breaker isolate a DC fault. Different types of fault current limiters (FCLs) are reviewed and compared. It is found that the resistive type superconducting FCL (SCFCL) has the potential to be usefully employed for DC protection. Next, a DC fault detection and location strategy study is performed. This thesis conducts a detailed study of different DC fault detection and location strategies using a much higher fidelity model than previous studies. After reviewing different fault detection methodologies, it is found that wavelet transforms presently might be the best option for DC protection. The continuous wavelet transform (CWT) is then extensively tested under different DC faults and transient scenarios to prove its robustness, as this method has not been extensively studied in the previous literature. In the end, by using the CWT and placing the SCFCLs in series with DC circuit breakers, the performance of the SCFCLs under a DC side pole-to-pole fault is examined. This study shows that the SCFCL can help reduce the fault current seen by a DC breaker. In the end, a DC system fault recovery study is performed. Different methods are proposed and studied to examine the impact they have on the converter system's DC fault recovery process. A novel bump-less control is proposed to help the system achieve a good fault recovery response.

During four years of Vichy rule and German Occupation, French cinema audiences were exposed to a multiplicity of filmed propaganda. Documentary films formed an important part of the cinema experience in the dark years, and from March 1943 were made obligatory in cinemas across the entire French nation. The documentaries produced, commissioned, funded and sanctioned by the cinema section of the Vichy propaganda ministry, the Secrétariat Général à l’Information (SGI), were, though, distinct from any other propaganda produced by the Vichy authorities. Far from promoting exclusionary and potentially divisive themes like anti-Semitism and collaboration, Vichy documentary films throughout all four years of Occupation projected an image of life under Pétain which was frequently idealised and represented a more moderate approach than that taken in radio or poster propaganda. Drawing on themes which had been the subject of popular support before the Occupation, in particular the family, the Empire and French international standing, along with popular symbols like the tricolore and the Marseillaise, these films ignored the upheavals of the defeat and exode of June 1940 and instead seemed to suggest that life continued as it had done before the creation of the Vichy regime. This thesis examines for the first time the continuity of themes from before the Occupation in Vichy documentary film and investigates why documentaries were so distinct from the content and approach of other Vichy-produced propaganda, especially radio and posters. By examining career trajectories and interests of those responsible for documentary production, the thesis sheds new light on the motivations of Vichy’s functionaries. The close examination of the nature of the themes and values from before the Occupation conveyed in Vichy documentary film therefore advances our knowledge regarding the competing ideas and interests at work in the dark years of Occupation.

The aerospace and marine sectors are currently using or actively considering the use of DC networks for electrical distribution. This has several advantages: higher VA rating per unit volume of cable and ease of generator connections to the network. In these systems the generators are almost exclusively ac generator (permanent magnet or wound field synchronous) that are linked to the dc network via an electric converter that transforms the ac generator output voltage to the dc rail voltage.The main objective of this project is to develop a Homopolar DC Generator (HDG) that is capable of generating pure DC voltage and could therefore remove the need for an electric converter and ease connection issues to a dc electrical distribution network. The project aim is to design, build and test a small technology demonstrator, as well as electromagnetic modeling validation.In Chapter 1, the initial generator concepts proposed to fulfill the aforementioned requirements of DC generator are presented, as well as an obscurity in electromagnetic induction law faced at the beginning of this project. Also the advantages, disadvantages and different applications of Homopolar DC Generators are covered in Chapter 1. In Chapter 2, Faraday's law of induction and the ways of using it properly are discussed using some example. The preliminary design calculations to construct the prototype HDG are presented in Chapter 3. Also the prototype construction and assembly procedure are discussed in this chapter. In this project, magnetostatics and current flow Finite Element (FE) simulations were used to assess the prototype HDG. In Chapter 4, the results of 2D and 3D-FE simulation are presented; furthermore the limitations of the FE simulations to assess the HDG performance are included. In Chapter 5, the results of the practical tests are demonstrated and assessed, as well as comparison between some of the results obtained practically and those obtained using FE-modeling. Using sliding contacts in the HDG is obligatory so some definitions corresponding to electrical contact resistances are given in Chapter 5. Final chapter is conclusions including the results assessments, future works to design, simulation and construction of the HDG.

Master’s thesis deals with the design concept of DC/DC convertor usable for a backup source with supercapacitors. The paper describes the theoretical knowledge of supercapacitors technology, principle of basic DC/DC convertors and their use in electrical energy storage systems. The thesis contains a description of the designed backup power system and its properties, which has been measured.

This diploma thesis deals with design and subsequent realization of DC / DC converter for supply of matrix LED fields for the automotive industry. Such a converter must be able to supply a current of several Amperes and a voltage of the order of tens of Volts. Matrix headlights are currently being developed by a number of automotive companies. These headlamps allow independently to control the intensity of light incident on different objects or people who are in front of a car. In addition to the front headlamps the matrix LED lights are also used in the rear and signaling lights. Here it serves mainly to create different animations that have no function except the overall enhancement appearance of the vehicle. All of these lights need power units that will be suitable to regulate current flowing into various combinations of LEDs illuminated.

This master´s thesis puts mind to choice and suggestion of suited type of DC/DC tension converter for power supply of power LED. It shows comparison of available types of accumulators in The Czech Republic and types of DC/DC converters used in construction of the sample. The choice of available source of energy is subordinated to final weight and size of a battery. There are also some explicit requirements for the smallest possible size and highest effictivity. So the choice is aimed only for converters with a simple coil and minimum numbers of switching elements to realize the converter, for example by SMT technology. One of many possibilities is LTC3453 circuit, which is described in this thesis, assembled and measured. On the basis of this circuit the next two samples are assembled. Here I try to suppress problems from previous circuit and expand it´s possibilities by adding the control of luminance via the microcontroller ATtiny. Then is introduced the basic description of flashlight Petzl MYO XP which is available in stores.

The aim of this diploma thesis is to study the resonant converters operation. This paper is concretely specialized to design and implementation the LLC resonant converter with output power about 350 watts. LLC resonant converter is prospective solution for similar applications. The general advantages are that the power MOSFETs are working on zero voltage switching condition, which reduce the switching loss and improve EMI performance. The detailed design for the LLC resonant tank characteristics presented in this paper, which fully guarantees the ZVS condition. This study is based on replacing the rectifier and load by an equivalent resistance applies the first harmonics approximation and the assumption that the current trough the diodes of the output rectifier has a sinusoidal waveform.

Although arc flash has been a concern amongst the electrical industry for many years, it is only relatively recently that standards by the IEEE have been established on calculating the amount of energy behind an arc flash event. However, these standards only apply to AC systems, where extensive testing and research have been performed. Although the NFPA has provided recommendations on how to calculate the incident energy for DC arc flash events, these have not become the defining standard like those seen for AC. One equation outlined in the NFPA70E, the Maximum Power Method, does provide engineers with a formula to calculate DC arc flash incident energy but as the NFPA states this can be quite conservative. However, the NFPA70E also mentions a Detailed Arcing Current and Energy Calculations Method which contains formulas proposed by various researchers who conducted their own DC arc flash testing but there is scarce info on how these methods compare to the Maximum Power Method. This paper will investigate the relative power of two of the formulas proposed in the alternate method, the results from Stokes/Oppenlander and the results from Paukert, over a variety of parameters that affect DC arcing power. These will then be compared to relative power of the Maximum Power Method, as well as the relative power of the AC equations formed from measurements. Although the results in this paper are not aiming to be a defining standard, the aim is to provide engineers with information on when one methodology is more suitable to use for a given set of certain parameters.