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Made available in DSpace on 2014-10-09T12:40:44Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:41Z (GMT). No. of bitstreams: 1 02752.pdf: 9313866 bytes, checksum: e570b355f24e91b0efa7ade917c2797b (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Due to limitation of economics and legislation, the power system is not allowed serious accident on modern social. In order to enhance system reliability, many types of special protection systems (SPS) have been implemented by utilities around the world. One of the main concerns in the design of an SPS is whether the designed system can achieve the reliability requirement. Currently, the literature that discusses the SPS reliability issue is scarce. In this thesis, a comparison of several techniques suitable for performing reliability assessment of SPS is presented. Discussed reliability models include using reliability block diagram, fault tree analysis, Markov modeling and Monte Carlo simulations. In order to understand the uncertainty effects of input data on the calculated system reliability, Monte Carlo Sampling method is utilized in this study to take the input parameters uncertainty into account in the system modeling. To deal with the problem of not being able to reach the reliability requirement after uncertainty analysis, a sensitivity analysis is proposed to analyze the importance of the components involved in the system. Sensitivity analysis can be used to identity the most effective component in the enhancement the SPS reliability. A Taipower SPS is used in this thesis to explain the proposed reliability assessment methods.

abstract: This research work describes the design of a fault current limiter (FCL) using digital logic and a microcontroller based data acquisition system for an ultra fast pilot protection system. These systems have been designed according to the requirements of the Future Renewable Electric Energy Delivery and Management (FREEDM) system (or loop), a 1 MW green energy hub. The FREEDM loop merges advanced power electronics technology with information tech-nology to form an efficient power grid that can be integrated with the existing power system. With the addition of loads to the FREEDM system, the level of fault current rises because of increased energy flow to supply the loads, and this requires the design of a limiter which can limit this current to a level which the existing switchgear can interrupt. The FCL limits the fault current to around three times the rated current. Fast switching Insulated-gate bipolar transistor (IGBT) with its gate control logic implements a switching strategy which enables this operation. A complete simulation of the system was built on Simulink and it was verified that the FCL limits the fault current to 1000 A compared to more than 3000 A fault current in the non-existence of a FCL. This setting is made user-defined. In FREEDM system, there is a need to interrupt a fault faster or make intelligent deci-sions relating to fault events, to ensure maximum availability of power to the loads connected to the system. This necessitates fast acquisition of data which is performed by the designed data acquisition system. The microcontroller acquires the data from a current transformer (CT). Mea-surements are made at different points in the FREEDM system and merged together, to input it to the intelligent protection algorithm that has been developed by another student on the project. The algorithm will generate a tripping signal in the event of a fault. The developed hardware and the programmed software to accomplish data acquisition and transmission are presented here. The designed FCL ensures that the existing switchgear equipments need not be replaced thus aiding future power system expansion. The developed data acquisition system enables fast fault sensing in protection schemes improving its reliability. / Dissertation/Thesis / M.S. Electrical Engineering 2011

Thermal systems involve multiple components assembled to store or transfer heat for power, cooling, or insulation purpose, and this research focuses on modeling the performance of two novel thermal systems that are capable of functioning in environments subjected to high heat fluxes. The first investigated thermal system is a cascaded thermoelectric generator (TEG) that directly converts heat into electricity and offers a green option for renewable energy generation. The presented cascaded TEG allows harvesting energy in high temperatures ranging from 473K to 973K, and being a solid-state device with no moving parts constitutes an excellent feature for increase device life cycle and minimum maintenance in harsh, remote environments. Two cascaded TEG designs are analyzed in this research: the two-stage and three-stage cascaded TEGs, and based on the findings, the two-stage cascaded TEG produces a power output of 42 W with an efficiency of 8.3% while the three-cascaded TEG produces 51 W with an efficiency of 10.2%. The second investigated novel thermal system is a thermal protection system inspired by the porous internal skeleton of the cuttlefish also known as cuttlebone. The presented bio- inspired thermal protection has excellent features to serve as an integrated thermal protection system for spacecraft vehicles including being lightweight (93% porosity) and possessing high compressive strength. A large amount of heat flux is generated from friction between air and spacecraft vehicle exterior, especially during reentry into the atmosphere, and part of the herein presented research involves a thermomechanical modeling analysis of the cuttlebone bio-inspired integrated thermal protection system along with comparing its performance with three conventional structures such as the wavy, the pyramid, and cylindrical pin structures. The results suggest that the cuttlebone integrated thermal protection system excels the best at resisting deformation caused by thermal expansion when subjected to aerodynamic heat fluxes. / Doctor of Philosophy / Operating engineering systems in extremely hot environments often decreases systems' reliability, life cycle, and creates premature failure. This research investigates two novel thermal systems capable of functioning in high temperatures including a cascaded thermoelectric generator (TEG) and a bio-inspired thermal protection system. The first evaluated novel thermal systems is a cascaded TEG that directly converts waste heat into power, and being a solid-state device with no moving parts forms an excellent feature for device life cycle improvement and minimum maintenance in harsh, remote environments. The research findings show that the designed cascaded TEGs can produce power when subjected to high temperatures ranging from 473K to 973K. The remaining part of the research presented in this dissertation models the thermomechanical performance of a lightweight structure, which is inspired by the internal skeleton of the cuttlefish, also knows as the cuttlebone. The cuttlefish's natural ability to support high-deep sea pressure translates into possessing high compressive strength, and when added the fact of being lightweight (up to 93% porosity), the cuttlebone forms an excellent candidate to serve as integrated thermal protection for spacecraft vehicles. The last part of the presented research discuss the thermomechanical analysis of the cuttlebone when subjected to high aerodynamics heat flux generated from friction between the air and spacecraft vehicle exterior, and it was found that the cuttlebone structure resists deformation associated with the steep temperature gradient experienced by the spacecraft vehicle during travel.

Τα πλοία αποτελούν πιθανό στόχο ενός κεραυνικού πλήγματος. Η μελέτη και η προσομοίωση ενός κεραυνού σε δύο διαφορετικά πλοία για διάφορα σημεία πτώσης έγινε με χρήση του προγράμματος Vector Fields Opera 3D Cobham. Στο κεφάλαιο 1, γίνεται μία συνοπτική παρουσίαση των ηλεκτρικών ατμοσφαιρικών φαινομένων που οδηγούν στην εμφάνιση του κεραυνού. Επίσης, παρουσιάζονται τα διάφορα είδη κεραυνικών πληγμάτων, οι ισοδύναμες κυκλωματικές αναπαραστάσεις αυτών και η συχνότητα πτώσης κεραυνών. Στο κεφάλαιο 2, αναφέρονται οι διάφορες μέθοδοι υπολογισμού πεδιακών μεγεθών και γίνεται μια πιο εκτενής αναφορά στη μέθοδο των πεπερασμένων στοιχείων. Ακολούθως, παρουσιάζεται το πρόγραμμα Opera 3D στο οποίο έγινε η προσομοίωση του κεραυνού. Γίνονται αναφορές στης εξισώσεις και τον αλγόριθμο που χρησιμοποιεί το πρόγραμμα για τον υπολογισμό των ηλεκτρομαγνητικών μεγεθών του εκάστοτε προβλήματος. Στο κεφάλαιο 3, παρουσιάζονται οι προσομοιώσεις που πραγματοποιήθηκαν με το συγκεκριμένο πρόγραμμα. Αρχικά αναφέρεται η προσέγγιση του κεραυνικού πλήγματος με στόχο να προσαρμοσθεί στις δυνατότητες του προγράμματος. Στη συνέχεια αναφέρονται τα δύο μοντέλα πλοίων που χρησιμοποιήθηκαν (USS Somerset, HMS Albion) και τα σημεία τα οποία επιλέχθηκαν να πληγούν από κεραυνό. Επιλέχθηκαν τέσσερα σημεία σε κάθε πλοίο (πλώρη, πρύμνη, δύο κορυφές) και εφαρμόσθηκε η οριακή συνθήκη της μέγιστης τιμής του ρεύματος ενός χαρακτηριστικού κεραυνού. Σαν αποτέλεσμα προέκυψε η πυκνότητα ηλεκτρικού ρεύματος, για τις διάφορες περιπτώσεις, στο σύνολο της επιφάνειας του πλοίου και της θάλασσας. Στο κεφάλαιο 4, σχολιάζονται οι διαφορές που προέκυψαν στα δύο διαφορετικά πλοία καθώς και στα διαφορετικά σημεία πλήγματος. Επίσης παρουσιάζονται οι κανονισμοί προστασίας πλοίων, ανθρώπων και συσκευών που πρέπει να τηρούνται. Τέλος, με χρήση της μεθόδου κυλιόμενης σφαίρας γίνεται μία εκτίμηση της προστασίας έναντι κεραυνών στο κάθε πλοίο. / Naval ships are possible targets of a lightning strike. A study and simulation of a lightning strike in two different ships for different stress points is executed with Vector Fields Opera 3D Cobham. In chapter one, an overview of electrical atmospheric phenomena that lead to the appearance of lightning is given. Also, there are presented various kinds of lightning strikes, equivalent circuit representation of lightning current and frequency lightning maps. In chapter 2, various methods of calculating electromagnetic fields are presented and a more extensive report on the finite element method is described. Furthermore, the Opera 3d program is described, which simulates the lightning strike. The equations that are computed, the algorithm and the methods of calculating the electromagnetic field of Opera 3d are fully analyzed. In chapter 3, the performed simulations are presented. Firstly, the lightning approach is described. The approach was made in order to adapt to the capabilities of the program. Two ships with different dimensions (USS Somerset, HMS Albion) are designed. For the solution of the electromagnetic problem the lightning strike is approximated with the peak value of a standard strike waveform and the current density results are analyzed over the ship for four different stress points. In chapter 4, the differences that resulted from the two different ship’s simulations and different striking points are described. Several regulations of ship, human, electric devices, protection against lightning are presented and must be observed. Finally, using the rolling sphere method, lightning protection in each vessel is estimated.

During the second half of 2015, Sweden experienced the largest inflow of asylum-seekers in its history. Almost 163,000 people sought asylum in 2015, whereof approximately 70,000 children. The influx challenged the reception system and severe child protection concerns such as disappearances and sexual exploitation of unaccompanied minors were identified. Half of the children that arrived in 2015 came with families but this group have received less attention so far. The aim of this study was to explore the child protection systems around asylum-seeking and returning children in families by identifying child protection concerns and existing gaps in the services provided to this target group. Fourteen semi-structured interviews with twenty individuals belonging to various stakeholder groups such as staff at asylum accommodations, social workers, parents and, volunteer and staff from civil society organisations were conducted in two municipalities in Skåne, Sweden. The data was analysed using thematic analysis and the results are discussed in regards to the Protective Environment Framework. The results suggest that children in migration, with families, face multiple protection concerns in Sweden. Significant gaps exist in the services provided to these children and there are large disparities between accommodation centres. Many accommodations fail to provide a child-friendly environment and gender separated sanitation facilities. Furthermore, the results point out the importance of increasing competence of child protection among actors, and to increase preventive measure directed towards the parents in order to ensure a protective and safe environment for children.

The pyrolysis mechanics of Phenolic Impregnated Carbon Ablators (PICA) makes it a valued material for use in thermal protection systems for spacecraft atmospheric re-entry. The present study of the interaction of pyrolysis gases and char with plasma gases in the boundary layer over PICA and its substrate, FiberForm, extends previous work on this topic that has been done in the UVM 30 kW Inductively Coupled Plasma (ICP) Torch Facility. Exposure of these material samples separately to argon, nitrogen, oxygen, air, and carbon dioxide plasmas, and combinations of said test gases provides insight into the evolution of the pyrolysis gases as they react with the different environments. Measurements done to date include time-resolved absolute emission spectroscopy, location-based temperature response, flow characterization of temperature, enthalpy, and enthalpy flux, and more recently, spatially resolved and high-resolution emission spectroscopy, all of which provide measure of the characteristics of the pyrolysis chemistry and material response. Flow characterization tests construct an general knowledge of the test condition temperature, composition, and enthalpy. Tests with relatively inert argon plasmas established a baseline for the pyrolysis gases that leave the material. Key pyrolysis species such as CN Violet bands, NH, OH and Hydrogen Alpha (Hα) lines were seen with relative repeatability in temporal, spectral, and intensity values. Tests with incremental addition, and static mixtures, of reactive plasmas provided a preliminary image of how the gases interacted with atmospheric flows and other pyrolysis gases. Evidence of a temporal relationship between NH and Hα relating to nitrogen addition is seen, as well as a similar relationship between OH and Hα in oxygen based environments. Temperature analysis highlighted the reaction of the material to various flow conditions and displayed the in depth material response to argon and air/argon plasmas. The development of spatial emission analysis has been started with the hope of better resolving the previously seen pyrolysis behavior in time and space.