Towards a partial discharge free insulation system for the More Electrical Transportation

Currently, electric motor manufacturers install a ground and turn insulation capable of withstanding normal operating voltages without exceeding the dielectric strength of the air. If the electric field generated during operation exceeds this characteristic quantity, there are pre-discharge phenomena, which accelerate the degradation of the insulation and therefore lead to a shortening of the useful life of the machine. The main objective of this thesis was to develop a model capable of determining the so-called Partial Discharge Inception Voltage for random-wound machines and to facilitate the design of their electrical insulation system. In addition to this, an in-depth study was carried out on how to improve the qualification process of electric motors and actuators intended for use in the world of More Electric Transportation. First, it was considered how to effectively test the insulation systems of random-wound electrical machines to prove that they are PD-free. Subsequently, the impact of thermo-mechanical stress due to frequent speed and torque variations was studied. Finally, the impact of partial discharges on insulation at different altitudes was investigated to better understand the potential risk these can have on the correct operation of the machine, since it is easier to trigger them at pressures above sea level. Ultimately, this thesis seeks to provide various tools for a complete study of the reliability of the insulation system of an electric random-wound motor (or actuator) applied to the transport sector, with particular regard to preventing the partial discharge triggering. Nevertheless, a general approach has been adopted that can be extended to the study of other low-voltage machines, such as dry-type high-frequency transformers or hairpin motors.Attualmente, i produttori di motori elettrici installano isolamenti di terra e di spira in grado di sopportare le normali tensioni di funzionamento senza superare la rigidità dielettrica dell'aria. Se il campo elettrico generato durante il funzionamento supera questa quantità caratteristica, si verificano fenomeni di pre-scarica che accelerano l'invecchiamento del materiale e quindi portano ad un accorciamento della vita utile della macchina. L'obiettivo principale di questa tesi è quello di sviluppare un modello in grado di determinare la cosiddetta Tensione di Innesco delle Scariche Parziali (PDIV) per macchine a filo avvolto e di facilitare la progettazione del loro sistema di isolamento elettrico. Oltre a questo, è stato condotto uno studio approfondito su come migliorare il processo di qualificazione dei motori elettrici e degli attuatori destinati ad essere utilizzati nel mondo del More Electric Transportation. In primo luogo, si è considerato come testare efficacemente i sistemi di isolamento delle macchine elettriche a filo avvolto per dimostrare che sono privi di scariche parziali. Successivamente, è stato studiato l'impatto delle sollecitazioni termo-meccaniche dovute alle frequenti variazioni di velocità e di coppia. Infine, si è analizzato l'impatto delle scariche parziali sull'isolamento a diverse altitudini per comprendere meglio il potenziale rischio che queste possono avere sul corretto funzionamento della macchina, poiché è più facile innescarle a pressioni sopra il livello del mare. In definitiva, questa tesi cerca di fornire vari strumenti per uno studio completo dell'affidabilità del sistema di isolamento di un motore (o attuatore) elettrico a filo avvolto applicato al settore dei trasporti, con particolare riguardo alla prevenzione dell'innesco delle scariche parziali. Tuttavia, è stato adottato un approccio generale che può essere esteso allo studio di altre macchine a bassa tensione, come i trasformatori a secco ad alta frequenza o i motori hairpin

Assessment Techniques to Ensure Reliable Electrical Insulation for More Electric Transportation

Partial discharge testing of complete, low-voltage induction machines and dry-type convertor transformers for the More Electric Transportation is discussed. The current standard (i.e. IEC 60034-18-41, 60317-0-1 and 61378\u20131) offers very few answers to the new challenges posed to the insulating systems reliability of these increasingly electrified electrical machines. Based on tests performed on different kind of specimens and the literature, the most promising assessment technique to ensure a reliable insulation is based on optical sensors. In addition, this work seeks to give some precise, but simple, indications on how to take into account the effect of altitude and high frequency in the qualification of an insulation system for More Electric Transportation and the limits of the different standards involved are highlighted

Mémoire et recyclage dans Visages Villages d’Agnès Varda : autoportrait de la vieillesse d’une réalisatrice et de son dispositif cinématographique

The aim of this paper is to study, with an intersectional approach, the tendency of Agnès Varda’s films to seek to adopt a different gaze, and to deconstruct stereotypical representations of women’s old age. This study will focus on Varda’s penultimate film, Visages Villages, in which she explores being an ageing artist who is practicing the old art of cinema, an art that is now disappearing. Particular attention will be paid to one of the film’s final scenes, in which Varda evokes the Grande Galerie of the Louvre. It is Varda’s intention, this paper will argue, to propose cinema as a medium particularly suited to representing old age. Thanks to editing, cinema – like the museum – is capable of being a place to conserve all the material traces that time has left behind.L'objectif de cet article est d'étudier la tendance des films d’Agnès Varda à chercher à adopter un regard différent, et à déconstruire les représentations stéréotypées de la vieillesse des femmes. Cette étude se concentre sur l’avant-dernier film de Varda, Visages Villages, dans lequel elle interroge le fait d'être une artiste vieillissante, pratiquant un art ayant vieilli avec elle, le cinéma, art selon elle en crise et en voie de disparition. En particulier, l’article analyse l'une des dernières scènes du film, où Varda parcourt la Grande Galerie du Louvre, voulant nous proposer le cinéma comme lieu privilégié de représentation de la vieillesse parce que celui-ci est capable de devenir, à la manière d’un musée, un lieu de conservation de toutes les traces matérielles que le temps a laissées derrière lui

Ultrasonic force microscopy on 'poly(vinyl alcohol)/SrTiO3' nano-perovskites hybrid films

Atomic Force Microscopy (AFM) and Ultrasonic Force Microscopy (UFM) have been applied to the characterization of composite samples formed by SrTiO 3 (STO) nanoparticles (NPs) and polyvinyl alcohol (PVA). The morphological features of the STO NPs were much better resolved in UFM than in contact-mode AFM topography. For high STO concentrations the individual STO NPs formed nanoclusters, which gathered in microaggregates. The STO aggregates, covered by PVA, exhibited no AFM frictional contrast, but were clearly distinguished from the PVA matrix using UFM. Similar aggregation was observed for NPs in the composite samples than for NPs deposited on top of a flat silicon substrate from a milliQ water solution in the absence of polymer. In the hybrid films, most STO nanoparticles typically presented a lower UFM contrast than the PVA matrix, even though stiffer sample regions such as STO should give rise to a higher UFM contrast. STO NPs with intermediate contrast were characterized by an UFM halo of lower contrast at the PVA/STO interface. The results may be explained by considering that ultrasound is effectively damped on the nanometer scale at PVA/ STO interfaces. According to our data, the nanoscale ultrasonic response at the PVA/STO interface plays a fundamental role in the UFM image contrast

Partial Discharge Phenomena in Electrical Machines for the More Electrical Aircraft. Part II: Impact of Reduced Pressures and Wide Bandgap Devices

This paper focuses on the inception of partial discharges within the insulation system of electrical actuators used for the More Electrical Aircraft (MEA). Since these machines should operate in the absence of Partial Discharges (PDs), the dependence of the PD Inception Voltage (PDIV) on voltage impulses typical of wide bandgap (SiC) devices is investigated at both 1 bar, reduced pressures close to those typical of aircraft cruising altitudes (150 mbar – 200 mbar) or lower (down to 5 mbar). Propagation issues are not dealt with here as results were obtained working on insulation models consisting of couples of wires twisted together (twisted pairs), thus knowing exactly the potential differences between all points of the insulation model. The results show that the rise times and the switching frequencies associated with wide bandgap devices have little impact on the PDIV. A model able to predict the PDIV of the turn/turn insulation of random wound motors (the most vulnerable part of the insulation) at different pressures is proposed. The model is also able to deal with temperature changes, with limitations that depend on the type on insulation systems

La basilica portiana e S. Vittore al Corpo: un punto di vista archeologico

peer reviewe

Canonical explorations of 'Tel' environments for computer programming

This paper applies a novel technique of canonical gradient analysis, pioneered in ecological sciences, with the aim of exploring student performance and behaviours (such as communication and collaboration) while undertaking formative and summative tasks in technology enhanced learning (TEL) environments for computer programming. The research emphasis is, therefore, on revealing complex patterns, trends, tacit communications and technology interactions associated with a particular type of learning environment, rather than the testing of discrete hypotheses. The study is based on observations of first year programming modules in BSc Computing and closely related joint-honours with software engineering, web and game development courses. This research extends earlier work, and evaluates the suitability of canonical approaches for exploring complex dimensional gradients represented by multivariate and technology-enhanced learning environments. The advancements represented here are: (1) an extended context, beyond the use of the ‘Ceebot’ learning platform, to include learning-achievement following advanced instruction using an industrystandard integrated development environment, or IDE, for engineering software; and (2) longitudinal comparison of consistency of findings across cohort years. Direct findings (from analyses based on code tests, module assessment and questionnaire surveys) reveal overall engagement with and high acceptance of collaborative working and of the TEL environments used, but an inconsistent relationship between deeply learned programming skills and module performance. The paper also discusses research findings in the contexts of established and emerging teaching practices for computer programming, as well as government policies and commercial requirements for improved capacity in computer-science related industries