Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, June 2004. / Thesis advisor(s): Robert Ashton. Includes bibliographical references (p. 73-74). Also available online.

Unsupervised models can provide supplementary soft constraints to help classify new, "target" data since similar instances in the target set are more likely to share the same class label. Such models can also help detect possible differences between training and target distributions, which is useful in applications where concept drift may take place, as in transfer learning settings. This contribution describes two general frameworks that take as input class membership estimates from existing classifiers learnt on previously encountered "source" data, as well as a set of cluster labels from a cluster ensemble operating solely on the target data to be classified, and yield a consensus labeling of the target data. One of the proposed frameworks admits a wide range of loss functions and classification/clustering methods and exploits properties of Bregman divergences in conjunction with Legendre duality to yield a principled and scalable approach. The other approach is built on probabilistic mixture models and provides additional flexibility of distributed computation that is useful when the target data cannot be gathered in a single place for privacy or security concerns. A variety of experiments show that the proposed frameworks can yield results substantially superior to those provided by popular transductive learning techniques or by naively applying classifiers learnt on the original task to the target data. / text

Η παρούσα διπλωματική εργασία πραγματεύεται τη μελέτη και κατασκευή ενός μετατροπέα συνεχούς τάσης σε εναλλασσόμενη (αντιστροφέας) που προορίζεται για τη σύνδεση ενός φωτοβολταϊκού πλαισίου στο δίκτυο χαμηλής τάσης. Η εργασία εκπονήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών του Πανεπιστημίου Πατρών. Αρχικά, παρουσιάζονται, συνοπτικά, πληροφορίες για τη φωτοβολταϊκή τεχνολογία και για τους τρόπους διασύνδεσής τους με την κατανάλωση ή το δίκτυο. Στη συνέχεια, γίνεται αναφορά στον αντιστροφέα της διπλωματικής εργασίας. Πιο συγκεκριμένα, μελετάται ένας διαφορικός αντιστροφέας τύπου boost, ένα χαρακτηρισμό που τον οφείλει στην δυνατότητα, να επιτευχθεί μέσω αυτού εναλλασσόμενη τάση εξόδου με ενεργό τιμή μεγαλύτερη της συνεχούς τάσης εισόδου. Ο μετατροπέας αυτός αποτελείται στην ουσία από δύο επιμέρους μετατροπείς dc-dc τύπου boost, με τη συνδυασμένη λειτουργία των οποίων επιτυγχάνεται η επιθυμητή μετατροπή. Η ονομαστική ισχύς για την οποία πραγματοποιείται ο σχεδιασμός του μετατροπέα είναι ίση με 250W. Με δεδομένα τα μεγέθη ρευμάτων και τάσεων, καθώς και των κυματώσεων στα ρεύματα των πηνίων και στις τάσεις των πυκνωτών, υπολογίστηκαν οι τιμές των στοιχείων, βάσει των οποίων έγιναν οι προσομοιώσεις. Κατόπιν, δοκιμάστηκαν σε προσομοίωση διάφορες μορφές ελέγχου του αντιστροφέα, με μόνη ικανοποιητική αυτή του έλεγχου με ολίσθηση στο πεδίο καταστάσεων. Αυτός ήταν και ο έλεγχος που τελικά επιλέχθηκε για τη διάταξη που μελετήθηκε, γι’ αυτό και γίνεται αναλυτική περιγραφή του ελέγχου αυτού. Λόγω των απαιτήσεών του αποφασίστηκε ο έλεγχος να υλοποιηθεί χωρίς χρήση μικροελεγκτή, αλλά με χρήση αποκλειστικά ολοκληρωμένων αναλογικών κυκλωμάτων. Ακολουθεί η περιγραφή της διαδικασίας σχεδίασης και κατασκευής του μετατροπέα που έγινε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας και παρουσιάζονται τα επιμέρους στοιχεία και οι συνδεσμολογίες που χρησιμοποιήθηκαν. Τέλος, περιγράφονται τα πειράματα που πραγματοποιήθηκαν και παρατίθενται τα αποτελέσματα που προέκυψαν, αποδεικνύοντας την ορθή λειτουργία της διάταξης. Επίσης, εξάγονται τα ανάλογα συμπεράσματα. / In this diploma thesis, a Power Inverter in order to connect an Alternating Current-Photovoltaic (AC-PV module) to the low voltage grid is analyzed, designed and manufactured. The work was carried out in the Laboratory of Electrical and Mechanical Energy Conversion at the Department of Electrical and Computer Engineering of the Polytechnic School, University of Patras, Greece. At first, some data and information concerning the photovoltaic technology are presented as well as the connection modes of a PV system or module. Secondly, the operation and structure of the inverter is described. Specifically, a differential output boost inverter is examined, the title of which is derived from its ability to produce an output voltage larger than the input voltage. In fact, this converter consists of two boost dc-dc converters, the combined operation of which achieves the desirable operation of the inverter. The nominal power of the inverter is chosen to be equal to 250W. Depending on the expected values of the currents and voltages, as well as on the ripple voltages of the capacitors and the ripple currents of the inductors, the component values were calculated. The following step was to simulate the operation of the converter under different control techniques. The only control method with satisfying results which was eventually applied to the inverter was the sliding mode control, so it is extensively described. Due to its requirements, this control technique was implemented without using a microcontroller, but only using analog integrated circuits. The design and implementation of the inverter is then described along with the selected components and some individual circuits. Finally, the results of the conducted experiments are presented, the good operation of the setup is confirmed and the related conclusions are derived.

No description available.

No description available.

Generators in an interconnected power system normally remain in synchronism with one another. However, severe faults that lead to loss of heavily loaded generators or large load blocks can cause oscillations in the generator rotor angles that are large enough to result in a pole slip in which a generator, or a group of generators, loses synchronism with the rest of the power system. When a generator pole slips and falls out-of-step with the power system, the generator and system voltages sweep past one another at a slip frequency, producing a pulsating current, which can be greater than a three-phase fault at the generator terminals. An out-of-step generator should therefore be isolated from the power system to prevent damage to the generator, generator transformer and the turbine. This dissertation analyses the dynamic performance of generator-pole-slip protection during various stable and unstable power swing events. For the purpose of this dissertation, the Siemens 7UM622 machine protection relay is used to test the response of generator-pole-slip protection. This is done in two stages, firstly, within the DigSilent PowerFactory software by modelling the Siemens 7UM622 relay and then applying simulated time domain stable and unstable power swing conditions to the relay model to evaluate its response. Secondly, the actual 7UM622 hardware relay is injected with currents and voltages, which are produced during the time domain pole-slip simulations to determine if the relay hardware device operates in accordance with the Siemens relay technical manual. The power system analysed in the dissertation was heavily interconnected and a generator pole slip was rather unlikely. If an unlikely generator pole slip were to occur when the system is operating in a normal configuration (all power station outgoing feeders in service), the generator-pole-slip protection was able to detect and disconnect the generator after a single pole-slip cycle. v The critical fault clearing time decreases when an outgoing power station feeder is out of service (n-1 contingency) and therefore the probability of a generator pole slip increases. If a generator pole slip occurs when operating the network under a n-1 contingency, the pole-slip system electrical centre is usually located within the transmission network. In practice, the generator-pole-slip protection settings that are implemented at the power station do not reach into the transmission network (zone 2 disabled). Therefore, if a pole slip were to occur under a n-1 contingency, the generator-pole-slip protection would not be able to detect this condition. The zone 2 generator-pole-slip protection should rather reach into the transmission network, but the trip should only be issued after the third or fourth pole-slip cycle to allow the transmission line out-of-step protection sufficient time to separate the network into islands. The pole-slip function of the Siemens 7UM622 relay model within DigSilent PowerFactory operated in accordance with the Siemens relay technical manual and can be used in future to optimise and test generator-pole-slip protection settings. In the majority of cases, the Siemens 7UM622 relay hardware device operated in accordance with the Siemens relay technical manual. The only time that the relay operated incorrectly was when the measured impedance trajectory of a three-phase fault lingers on the inside and outside edge of the pole-slip impedance characteristic before exiting the pole-slip impedance characteristic. The stable and unstable power swing COMTRADE files that were generated for the tests performed in this dissertation can be used in future to test the generator-pole-slip protection at Kendal power station since it is rather difficult to test the pole-slip protection function properly without a COMTRADE file. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.

Poly (co iso-butyl vinyl ether-alt-maleic anhydride), an alternating copolymer, was synthesised. For this class of copolymers the formation of an electron-donor complex is invoked to explain their microstructure in which the two comonomers strictly alternate. Due to its polarity, this copolymer constitutes a potential additive for imparting hydrophilic properties to a hydrophobic matrix. In order to obtain narrow molecular weight polymers and study the relation between the molecular weight of this additive and its ability to migrate to the host polymer surface, chain transfer agents were introduced in the system and also the Reversible Addition-Fragmentation chain Transfer (RAFT) process was employed. Free radical polymerisation was first carried out to allow for a comparison with the RAFT process and kinetics of copolymerisation was studied by NIR-FTIR and 1H NMR spectroscopy in order to analyse the rate of reaction of each comonomer. Dibenzyl trithiobenzoate, 3-benzyl sulfanyl thiocarbonyl sulfanyl-propionic acid and dibenzyl trithiobenzoate were used as RAFT agents. Results demonstrate that only benzyl dithiobenzoate is able to control the molecular weight of this copolymer and decrease its polydispersity index; possible reasons laying behind this result are discussed. It was also found that, in particular in the presence of benzyl dithiobenzoate, poly(iso-butyl vinyl ether) forms. This is an unusual phenomenon considering that the free radical polymerisation affords alternating copolymers and that iso-butyl vinyl ether is a monomer that polymerises through the cationic process. Experiments were carried out in various solvents in an attempt to counteract this side reaction, but no appreciable correlation between the properties of the solvents and the formation of homopolymer were found. Various hypothesis are considered, however it is likely that, in the conditions adopted, the presence of the RAFT agents alters the equilibrium constant of complex formation favouring the synthesis of the homopolymer. In addition to this side???reaction also inhibition of the copolymerisation reaction was at times encountered and an investigation into this phenomenon was also conducted.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Includes bibliographical references (p. 169-182) Also available in print.

Thesis (M.Eng.)--Memorial University of Newfoundland, 1999. / Bibliography: leaves 111-113.

Τα μονωτικά υλικά αποτελούν συνήθη πρακτική στο σχεδιασμό μονωτικών διατάξεων για εξοπλισμό Υψηλής Τάσης. Χαρακτηριστική περίπτωση αποτελεί η μόνωση των τυλιγμάτων Μετασχηματιστών Υψηλής Τάσης, όπου γίνεται συνδυαστική χρήση ενός κύριου μονωτικού μέσου (υγρής φύσης μονωτικό έλαιο) και δευτερευόντων (συνθετικά λεπτά φύλλα στερεής φύσεως που καλύπτουν τα τυλίγματα). Σε τέτοιου τύπου περιπτώσεις, όπου το ένα μονωτικό μέσο κυριαρχεί, οι διεπιφάνειες παίζουν καθοριστικό ρόλο, καθώς λόγω της εκεί συσσώρευσης φορέων φορτίου και άλλων ανομοιογενειών αλλάζει τη διηλεκτρική συμπεριφορά της συνδυαστική μόνωσης, με τρόπο όχι ως σήμερα εξακριβωμένο. Στόχος της παρούσας διπλωματικής είναι η διερεύνηση των επιδράσεων της εισαγωγής συνθετικού μονωτικού διαφράγματος εντός διακένου που μονώνεται από ειδικό λάδι και καταπονείται υπό γραμμικά αυξανόμενη AC τάση. Για τον λόγο αυτό χρησιμοποιήθηκε η συσκευή BAUR Oil Tester DTA 822-129-1, κομμάτι του ηλεκτρομηχανολογικού εξοπλισμού του εργαστηρίου Υψηλών Τάσεων. Επίσης η παραγωγή γραμμικά αυξανόμενης (με σταθερό ρυθμό 2 kVrms/s) AC τάσης, καθώς και η μέτρηση της τάσης διάσπασης έγιναν από τη συσκευή αυτή. Η ίδια πειραματική διαδικασία ακολουθήθηκε για συνδυασμούς ενός λαδιού ανοιχτού χρώματος με 2 διαφράγματα ιδίου τύπου από 3 διαφορετικούς τύπους (κατά δομή ή κατά πάχος ή και τα δύο) διαφραγμάτων – ήτοι συνθετικό χαρτί NOMEX 0.15mm & 0.25mm , και HYPERTHERM 0.37mm ενώ ΝΟΜΕΧ 0.15 mm δοκιμάστηκε σε συνδυασμό με ένα δεύτερο λάδι σκούρου χρώματος. Για λόγους δυνατότητας σύγκρισης δοκιμάστηκε το λάδι σκούρου χρώματος μόνο του (χωρίς διαφράγματα) και με ένα διάφραγμα. Τα αποτελέσματα και η διαγραμματική τους απεικόνιση με τις απαραίτητες παρατηρήσεις, δίνονται στην παρούσα εργασία και βασιζόμενοι σε αυτά δώσαμε και ανάλογα συμπεράσματα. Έτσι προέκυψε πως η συνδυαστική χρήση μονωτικού ελαίου και συνθετικών διαφραγμάτων μπορεί να επηρεάσει περισσότερων του ενός διηλεκτρικών μεγεθών. Η διηλεκτρική αντοχή, προσδιοριζόμενη από τη μέση τιμή της τάσης διάσπασης των δοκιμίων, παρουσιάζει σημαντικές μεταβολές. Τα διαφράγματα από χαρτί NOMEΧ παρουσιάζουν μια σχετικά σταθερή συμπεριφορά ενώ το HYPERTHERM επιδεικνύει πτωτική τάση της διηλεκτρικής του αντοχής. Το σκέτο λάδι εμφανίζει μέση τιμή διηλεκτρικής αντοχής χαμηλότερη και πιο σταθερή. Λιγότερο αναμενόμενη, ήταν η προκύπτουσα μείωση του σχετικού σφάλματος της συνδυαστικής μονωτικής διάταξης, μέγεθος που χαρακτηρίζει το στοχαστικό χαρακτήρα του συστήματος. Καλύτερα συνεργαζόμενα με το μονωτικό λάδι απεδείχθησαν τα διαφράγματα χαρτιού NOMEX 0.15 / Insulating materials are common in the design provisions for insulating high-voltage equipment. An example is the insulation of windings Transformer High Voltage, which is combined using a principal material of isolation (insulating oil liquid nature) and secondary (synthetic foil solid nature covering the windings). In this case where a material of isolation dominates, the surfaces has a special role, there due to accumulation of electrical load and other entities heterogeneity changes the dielectric behavior of the combination of insulation, so far as not verified. The objective of this diplomatic mission is to investigate the effects of the introduction of synthetic aperture in the insulating gap of special insulated from oil-stressed and under linearly increasing AC voltage. For this reason, we used the device BAUR Oil Tester DTA 822-129-1, part of the electromechanical equipment of the High Voltage Laboratory. Also, the production increased linearly (with constant rate of 2 kVrms / s) AC voltage and measuring the voltage division performed by the device. The same experimental procedure was followed for a combination of oil (type light color) with 2 paper with same type of 3 different types (in structure or thickness or both) bulkhead – i.e. synthetic paper NOMEX 0.15mm & 0.20mm, and HYPERTHERM 0.37mm -. The same bellows tested in combination with half oil dark color. For reasons of comparability tested oil dark color only (without paper) and with only one paper . The results and their diagrammatic representation with the necessary comments are given in this work and based on them and we have similar conclusion. This showed that the combined use of insulating oil and synthetic aperture can affect more than one dielectric sizes. The dielectric strength, determined by the mean breakdown voltage of essays, introduced important changes..ΝΟΜΕΧ shows less stability than HYPERTHERM and give more stable and lower dielectric strength. Less expected, but perhaps more important, was the resulting reduction of the error of combined insulating device, size characterizing the stochastic nature of the system. Better partner with the insulating oil proved the paper thick NOMEX 0.15.