Large electric transformers such as those used in high voltage substations radiate an annoying low frequency hum into nearby communities. Attempts have been made to actively control the noise by placing a large number of loudspeakers as control sources around noisy transformers to cancel the hum. These cancellation systems require a large number of loudspeakers to be successful due to the imposing size of the transformer structures. Thus such systems are very expensive if global noise reduction is to be achieved. The aim of this thesis is to investigate theoretically and experimentally the use of thin perforated panels closely placed to a heavy structure to reduce the radiation of unwanted harmonic noise. These panels can themselves be vibrated to form a control source radiating over a large surface surrounding the primary source. The problem of the equipment overheating inside the enclosure is alleviated because the holes in the panels still allow natural cooling. An initial study is carried out to determine the resonance frequencies of perforated panels. The use of previously determined effective elastic properties of the panels and Finite Element Analysis to theoretically calculate their resonance frequencies is examined. Secondly the attenuation provided by active noise control using perforated panels as control sources is explored by use of a coupled analysis, where the primary source is assumed to influence the radiation of the perforated control panel. This analysis was found to predict poorly the amount of attenuation that could be achieved, so an uncoupled analysis is undertaken, where both the primary and control sources are assumed to radiate independently of each other. Not only does this greatly simplify the theoretical analysis but it also enables prediction of attenuation levels which are comparable to those determined experimentally. The theoretical model is reformulated to enable comparison of the sound power attenuation provided by perforated panel control sources with that of traditional acoustic and structural control sources. Finally, the use of modal filtering of traditional acoustic error sensor signals to give transformed mode (or power mode) sensors is examined. The independently radiating acoustic transformed modes of the panel are determined by an eigenanalysis and a theoretical analysis is presented for a farfield acoustic power sensor system to provide a direct measurement of the total radiated acoustic power. The frequency dependence of the sensor system, and the amount of global sound power attenuation that can be achieved is examined. Experimental measurements are made to verify the theoretical model and show that a sound power sensor implemented with acoustic sensors can be used in a practical active noise control system to increase the amount of attenuation that can be achieved. Alternatively the sound power sensor can be used to reduce the number of error channels required by a control system to obtain a given level of attenuation when compared to traditional error criteria. The power mode sensor analysis is then applied to the perforated panel control system, with similar results. / Thesis (Ph.D.)--Engineering (Department of Mechanical Engineering), 1996.

The use of predicate transformers to model the action of sequential programs has allowed the construction of a refinement calculus for expressing the formal verification of the top-down development of sequential programs. It is shown that predicate transformers may also be used to model real-time processes. The notions of precondition and postcondition in the sequential refinement calculus are replaced by the notions of assumption and effect. In this way the formal development of real-time processes may also be expressed within the refinement calculus. Notations are developed for the specification and implementation of real-time processes within the framework of the refinement calculus. Several case-studies are presented to demonstrate the utility of this approach.

Thesis (Ph.D.)-- University of Adelaide, Dept. of Mechanical Engineering, 2000. / Bibliography: leaves 182-190. Also available electronically.

Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 2000? / Bibliography: leaves 182-190. Also available in print form.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 91-97). Also available on the World Wide Web.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 23, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Scott D. Kovaleski. Vita. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1966. / eContent provider-neutral record in process. Description based on print version record.

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Οι μετασχηματιστές αποτελούν ένα από τα σημαντικότερα στοιχεία ενός Συστήματος Ηλεκτρικής Ενέργειας. Κατά συνέπεια, ο συνεχής έλεγχος της σωστής λειτουργίας, της απόδοσης, των καταπονήσεων και των απωλειών των μετασχηματιστών είναι ζωτικής σημασίας. Στην παρούσα διπλωματική, ύστερα από μια εκτενή αναφορά στους μετασχηματιστές και στα βασικά χαρακτηριστικά τους, επικεντρωνόμαστε στις απώλειες, την προστασία καθώς και το διαγνωστικό έλεγχο των μεγάλων μετασχηματιστών ελαίου. Τέλος αναφέρουμε, από τα δεδομένα και τα συμπεράσματα μας, ποια είναι η πιο συχνά χρησιμοποιούμενη διαγνωστική μέθοδος, καθώς και πως μπορεί να επιτευχθεί για μεγαλύτερη ασφάλεια και αξιοπιστία, σε συνδυασμό με χαμηλό κόστος. Κεφάλαιο 1: Αναφέρεται, αρχικά ο ρόλος των μετασχηματιστών, για την κατανόηση του περιγράφονται οι αρχές λειτουργίας και τα κατασκευαστικά του στοιχεία. Στην συνέχεια επικεντρωνόμαστε στην περίπτωση που η γραμμή μιας εκ των τριών φάσεων τροφοδοσίας του μετασχηματιστή διακόπτεται. Αναλύουμε τα διαδοχικά βήματα προσδιορισμού των τάσεων του δευτερεύοντος τυλίγματος και κατά συνέπεια τον προσδιορισμό της φάσης του πρωτεύοντος που δεν τροφοδοτείται με τάση. Κεφάλαιο 2: Αναφέρονται οι απώλειες και τα προβλήματα των μετασχηματιστών που προκύπτουν εξαιτίας κάποιων σφαλμάτων κατά τη λειτουργία τους ή απλά με την πάροδο των ετών. Τονίζεται η σημασία της μόνωσης των μετασχηματιστών σε σχέση με τη λειτουργική τους κατάσταση και της διάρκειας ζωής τους. Κεφάλαιο 3: Παρατίθενται και αναλύονται οι πιο διαδεδομένες μέθοδοι για την παρακολούθηση και τη διάγνωση σφαλμάτων στους μετασχηματιστές. / Transformers are very important elements of the power grid. Consequently, the continuous observation of their proper functioning, their attribution, and their losses is vital. In this thesis, following an extensive reference to transformers and basic features, losses, protection and diagnostic analysis of large oil transformer are emphasized. Finally, we approached, according to our data and our conclusions, the most commonly used diagnostic method, in order to achieve security and reliability in combination with low cost. Chapter 1: firstly, we mentioned the role of transformers, in order to understand that, we described their operating principles and their component parts. Then we focused if one line of the three phases of AC power, being interrupted. We analyzed the successive steps to determine the voltages of the secondary windings and thus determine the phase of the primary windings which aren’t under voltage. Chapter 2: there are listed the transformer's losses and problems because of the errors, during their operation or just because of the normal aging. Stressed the importance of transformers’ isolation, in relation to their functional status and the duration of their life. Chapter 3: Listed and analyzed the most common methods for observation and fault diagnosis in transformers.

D.Ing. / In the field of power electronics, the relentless demand for higher efficiencies, lower costs and ever-decreasing volume and profile have driven the development of many innovative technologies. Planarization and hybridization have become a substantial part of present system integration methodology. With the subsequent size reduction, the effects of layout and component parasitics are becoming vital issues in the development of innovative structures. The component ‘parasitics’ can be considered dimensional effects of the component structure that are not considered during the design process. The concept of electromagnetic integration is aimed at the utilization and modification of these dimensional effects. This leads to an integrated structure that fulfills multiple electromagnetic functions with the potential for improved power density, efficiency and reliability. In this dissertation, a family of electromagnetically integrated passives is presented. The related electromagnetic modeling and design approach of these complex electromagnetic structures is presented through a case study of L-L-C-T structures. The development of a sufficiently accurate, yet simplified electromagnetic model for design purposes is presented for the case study. With the electromagnetic model as basis, a comprehensive electromagnetic loss model is created. The electromagnetic design and loss models are combined into a design evaluation program. The graphical output of this design evaluation program allows for rapid selection of improved designs based on external cost criteria. This led to numerous insights into the relationships between the design variables. Through modification of the program, some fundamental limits of the integration approach are addressed. A case study design for a 1MHz, 500W dc-dc converter was considered to evaluate the design program. To assess the accuracy of the electromagnetic modeling, three L-L-C-T prototypes are constructed and experimentally tested. The construction process presented improved power density by 80% over previous processes. The electromagnetic component parameters for three prototypes were within 10% of the required design values, while the electromagnetic loss model estimations were within measurement error. The design evaluation program was enlisted in the design of two of these prototypes. This resulted in a 100% further improvement in power density (480W/in3 or 29.3W/cm3) compared to the original prototype without a loss in efficiency.