Στην παρούσα διπλωματική εργασία θα ασχοληθούμε με την ποσοτική καταγραφή και στατιστικοποίηση των αιτίων βλάβης με κριτήριο το Σημείωμα Αποκατάστασης Βλάβης της ΔΕΗ (Σ.Α.Β), στις περιοχές των δήμων Πατρώων, Ερύμανθου και Αιγιάλειας. Οι μετρήσεις αυτές μας δόθηκαν σε ηλεκτρονική μορφή και παρέχουν λεπτομερή αναφορά των βλαβών που υπέστησαν οι εξοπλισμοί Μέσης Τάσης στις εν λόγω περιοχές. Στο πρώτο κεφάλαιο θα προσπαθήσουμε να ορίσουμε και να επεξηγήσουμε κάποιες βασικές έννοιες, ώστε να διευκολύνουμε την μελέτη αυτής της διπλωματικής εργασίας και από έναν μέσο αναγνώστη. Στο δεύτερο κεφάλαιο γίνεται παρουσίαση της μορφής των συστημάτων ηλεκτρικής ενέργειας με ιδιαίτερη έμφαση στο σύστημα διανομής. Παρουσιάζεται η δομή του συστήματος διανομής, τα επιμέρους μέρη και εξαρτήματα από τα οποία αποτελείται καθώς και τα χαρακτηριστικά τους. Στο τέλος παρουσιάζονται δεδομένα και στατιστικά του ελληνικού συστήματος διανομής. Στο τρίτο κεφάλαιο, γίνεται μια σύντομη παρουσίαση των σφαλμάτων και υπερτάσεων που παρουσιάζονται στο σύστημα διανομής καθώς και των μέσων προστασίας που χρησιμοποιούμε προκειμένου να εξασφαλίσουμε την αδιάλειπτη λειτουργία του συστήματος διανομής Στο τέταρτο κεφάλαιο θα παρουσιάσουμε όλες τις βλάβες για όλες τις προαναφερθείσες περιοχές συνολικά και για όλα τα πιθανά αίτια βλάβης. Επίσης θα απεικονίσουμε στατιστικά και συγκριτικά τα αίτια βλάβης της κακοκαιρίας και του κεραυνού για τα έτη 2003 έως 2011 και για τους δήμους Πατρώων, Ερύμανθου και Αιγιάλειας ξεχωριστά. Τέλος ακολουθούν τα τελικά συμπεράσματα που απορρέουν από την επεξεργασία των στοιχείων που διαχειριστήκαμε. / In this diploma work we intend to deal with the quantitative report and statistics of the causes of damages concerning the damage repair document of ΔΕΗ, (Σ.Α.Β.), around the areas of the municipals of Patrai, Erymanthos and Egialia. All these measurements were given to us in electronic form including a detailed report of damages which occurred to the medium voltage equipment in the whole place of Achaia. In the first chapter our effort will be to determine and explain a number of basic concepts, so that the study of this diploma work will be easy understood by an average reader. The second chapter contains the presentation of the form of electric power systems, with special emphasis on the distribution system. It is a presentation of the distribution system structure, the individual parts and devices as well as their features. Data and statistics of the Greek distribution system are presented at the end of the section. The third section is a brief presentation of the faults and overvoltage occurring at the distribution system as well as of the protection measures we use in order to ensure the uninterrupted operation and the integrity of our system. In chapter four what will be presented are the damages of all the above mentioned areas in total, as well as the possible causes of them. Moreover there will be a presentation of damages caused by bad weather and thunder from the year 2003 up to 2011 for the municipals of Patrai, Erymanthos and Egialia separately. All this work will be done through statistics and comparison. At the end we will expose the final conclusions that come from the data we handled.

The burdensome capital cost of urban water distribution systems demands the use of efficient optimization methods capable of finding a relatively inexpensive design that guarantees a minimum functionality under all conditions of operation. The combinatorial and nonlinear nature of the optimization problem involved accepts no definitive method of solution. Adaptive search methods are well fitted for this type of problem (to which more formal methods cannot be applied), but their computational requirements demand the development and implementation of additional heuristics to find a satisfactory solution. This work seeks to employ adaptive search methods to enhance the search process used to find the optimal design of any water distribution system. A first study presented here introduces post-optimization heuristics that analyze the best design obtained by a genetic algorithm--arguably the most popular adaptive search method--and perform an ordered local search to maximize further cost savings. When used to analyze the best design found by a genetic algorithm, the proposed post-optimization heuristics method successfully achieved additional cost savings that the genetic algorithm failed to detect after an exhaustive search. The second study herein explores various ways to improve artificial neural networks employed as fast estimators of computationally intensive constraints. The study presents a new methodology for generating any large set of water supply networks to be used for the training of artificial neural networks. This dataset incorporates several distribution networks in the vicinity of the search space in which the genetic algorithm is expected to focus its search. The incorporation of these networks improved the accuracy of artificial neural networks trained with such a dataset. These neural networks consistently showed a lower margin of error than their counterparts trained with conventional training datasets populated by randomly generated distribution networks.

The deployment of Renewable Energy (RE)-based generation has experienced a sustained global growth in the recent decades, driven by many countries' interest in reducing greenhouse gas emissions and dependence on fossil fuel for electricity generation. This trend is also observed in remote off-grid systems (isolated microgrids), where local communities, in an attempt to reduce fossil fuel dependency and associated economic and environmental costs, and to increase availability of electricity, are favouring the installation of RE-based generation. This practice has posed several challenges to the operation of such systems, due to the intermittent and hard-to-predict nature of RE sources. In particular, this thesis addresses the problem of reliable and economic dispatch of isolated microgrids, also known as the energy management problem, considering the uncertain nature of those RE sources, as well as loads. Isolated microgrids feature characteristics similar to those of distribution systems, in terms of unbalanced power flows, significant voltage drops and high power losses. For this reason, detailed three-phase mathematical models of the microgrid system and components are presented here, in order to account for the impact of unbalanced system conditions on the optimal operation of the microgrid. Also, simplified three-phase models of Distributed Energy Resources (DERs) are developed to reduce the level of complexity in small units that have limited impact on the optimal operation of the system, thus reducing the number of equations and variables of the problem. The proposed mathematical models are then used to formulate a novel energy management problem for isolated microgrids, as a deterministic, multi-period, Mixed-Integer Nonlinear Programming (MINLP) problem. The multi-period formulation allows for a proper management of energy storage resources and multi-period constraints associated with the commitment decisions of DERs. In order to obtain solutions of the energy management problem in reasonable computational times for real-time, realistic applications, and to address the uncertainty issues, the proposed MINLP formulation is decomposed into a Mixed-Integer Linear Programming (MILP) problem, and a Nonlinear programming (NLP) problem, in the context of a Model Predictive Control (MPC) approach. The MILP formulation determines the unit commitment decisions of DERs using a simplified model of the network, whereas the NLP formulation calculates the detailed three-phase dispatch of the units, knowing the commitment status. A feedback signal is generated by the NLP if additional units are required to correct reactive power problems in the microgrid, triggering a new calculation MINLP problem. The proposed decomposition and calculation routines are used to design a new deterministic Energy Management System (EMS) based on the MPC approach to handle uncertainties; hence, the proposed deterministic EMS is able to handle multi-period constraints, and account for the impact of future system conditions in the current operation of the microgrid. In the proposed methodology, uncertainty associated with the load and RE-based generation is indirectly considered in the EMS by continuously updating the optimal dispatch solution (with a given time-step), based on the most updated information available from suitable forecasting systems. For a more direct modelling of uncertainty in the problem formulation, the MILP part of the energy management problem is re-formulated as a two-stage Stochastic Programming (SP) problem. The proposed novel SP formulation considers that uncertainty can be properly modelled using a finite set of scenarios, which are generated using both a statistical ensembles scenario generation technique and historical data. Using the proposed SP formulation of the MILP problem, the deterministic EMS design is adjusted to produce a novel stochastic EMS. The proposed EMS design is tested in a large, realistic, medium-voltage isolated microgrid test system. For the deterministic case, the results demonstrate the important connection between the microgrid's imbalance, reactive power requirements and optimal dispatch, justifying the need for detailed three-phase models for EMS applications in isolated microgrids. For the stochastic studies, the results show the advantages of using a stochastic MILP formulation to account for uncertainties associated with RE sources, and optimally accommodate system reserves. The computational times in all simulated cases show the feasibility of applying the proposed techniques to real-time, autonomous dispatch of isolated microgrids with variable RE sources.

Distributionsförluster är en viktig faktor i fjärrenergisystem. Genom att optimera förluster i sådana system, kan både ekonomiska och miljömässiga aspekter uppfyllas. Tyvärr finns det ringa information om rörförluster i fjärrkylasystem. Föreliggande studie fokuserar på förluster i ett fjärrkylanät genom att både använda ett R-nätverk och FEM simuleringsmodeller. Ett R-nätverksmodell bestående av termiska konduktanser har utvecklats genom analytiska ekvationer och simuleringar med FEM har utfört för validering av modellen. Därefter har ett fjärrkylanätverk som konstrueras i Gävle, analyserats. Undersökningen omfattar 15 olika rördiametrar i tre utföranden (dubbelrör med två symmetriska och en osymmetrisk värmeisolering) och i tre förläggningsdjup (0,8; 2 och 4 meter) för en säsong om 7 månader (April t o m Oktober). Särskilt utreds ökningen av temperaturen hos framledningsmediet, där matningsrören förlagts i en å mitt i staden om en sträcka av 1 km. Den maximala förlusten under säsongen, bland alla rörkonfigurationer, motsvarar 2 % av den totala levererade energin. Slutligen konstateras att kombinationen av isolerad framledningsrör och oisolerade returrör verkar som en gångbar investering, ekonomiskt och tekniskt, men kan inte användas i hela nätet eftersom stora delar har redan byggts med oisolerade plaströr. R-nätverksmodellen, som visades vara effektiv och pålitlig i undersökningen, kan som beräkningsverktyg, framförallt för dimensionering och för att uppskatta energiförluster. / Distribution losses are a very important factor in district energy systems. By optimizing the losses in such a system, both economical and environmental aspects can be fulfilled. Unfortunately, there is few information regarding losses for district cooling systems. This study focuses on losses in district cooling networks by using both R-network and FEM simulation models. A R-network model composed of thermal conductances has been developed through analytical equations and simulations have been performed for validation. Afterwards, an in-progress construction project of a district cooling network from the city of Gävle, Sweden, is analyzed. The assessment consists of 15 pipe diameters in three configurations (two symmetric cases and one asymmetric), at three ground laying depths (0.8, 2 and 4 meters) for a duration of 7 months (April to October). A particular case in which the main distribution pipes from and to the plant are submerged in the city’s river for a distance of 1 km is investigated in order to estimate the temperature increase of the supply water. A maximum cooling loss below 2% of the total delivered energy during the season for any network configuration resulted from the calculation. Finally, the mixed pipes array seems to be a feasible investment both economically and technically but it cannot be used for the entire network spread since a part of the network has been already built with the non-insulated plastic pipes. The R-network model proved to be effective and reliable in the analysis which provides confidence that it can serve as a solid foundation for a calculation tool - primarily for design purposes and also for estimating energy loss.

This study gives a description about the development of a computer model, RealPipe, which relates genetic algorithm (GA) to the well known problem of least-cost design of water distribution network. GA methodology is an evolutionary process, basically imitating evolution process of nature. GA is essentially an efficient search method basically for nonlinear optimization cases. The genetic operations take place within the population of chromosomes. By means of various operators, the genetic knowledge in chromosomes change continuously and the success of the population progressively increases as a result of these operations. GA optimization is also well suited for optimization of water distribution systems, especially large and complex systems. The primary objective of this study is optimization of a water distribution network by GA. GA operations are realized on a special program developed by the author called RealPipe. RealPipe optimizes given water network distribution systems by considering capital cost of pipes only. Five operators are involved in the program algorithm. These operators are generation, selection, elitism, crossover and mutation. Optimum population size is found to be between 30-70 depending on the size of the network (i.e. pipe number) and number of commercially available pipe size. Elitism rate should be around 10 percent. Mutation rate should be selected around 1-5 percent depending again on the size of the network. Multipoint crossover and higher rates are advisable. Also pressure penalty parameters are found to be much important than velocity parameters. Below pressure penalty parameter is the most important one and should be roughly 100 times higher than the other. Two known networks of the literature are examined using RealPipe and expected results are achieved. N8.3 network which is located in the northern side of Ankara is the case study. Total cost achieved by RealPipe is 16.74 percent lower than the cost of the existing network / it should be noted that the solution provided by RealPipe is hydraulically improved.

Resumo: Neste trabalho a metaheurística GRASP é utilizada para resolver o problema de reconfiguração de sistemas de distribuição de energia elétrica modelado como um problema de programação não linear binário misto. O objetivo é minimizar as perdas de potência ativa do sistema sujeito a restrições físicas e operacionais do sistema de distribuição. As variáveis binárias do problema representam a abertura e/ou fechamento de chaves de interconexão existentes nos ramos do sistema e as variáveis contínuas representam as tensões nodais e ângulos das tensões nodais. Na metodologia utilizada todas as chaves de interconexão do sistema de distribuição estão fechadas no início do processo e a cada passo da fase construtiva do GRASP um ramo é desconectado do sistema e um fluxo de carga é resolvido. Na fase de melhoria, tendo em vista que a solução da fase construtiva é um sistema radial, foi utilizado a cada iteração um fluxo de carga especializado para sistemas radiais. Para garantir que o sistema de distribuição opere de forma radial, foi introduzido na metodologia de solução uma rotina na qual é verificada a formação de laços e a conectividade do sistema em cada iteração das fases de construção e de melhoria local. São apresentados testes realizados utilizando os sistemas de 14, 33, 84,119 e 136 barras para avaliar a eficiência e robustez da metodologia proposta. Os resultados obtidos foram comparados aos resultados encontrados na literatura com o objetivo de validar a proposta deste trabalho / Abstract: In this work the GRASP is used to solve the problem of reconfiguring systems for electricity distribution modeled as a nonlinear programming problem of binary mixture. The goal is to minimize the power losses of the system subject to physical constraints and operating the distribution system. The problem of binary variables represents the opening and/or closing braces interconnecting branches existing in the system and the continuous variables represent the nodal voltages and angles of nodal voltages. In the methodology used to interconnect all the keys of the distribution system are closed at the beginning of the process and every step of the constructive phase of GRASP a branch is disconnected from the system and a load flow is solved. In the improvement phase, given that the solution of the constructive phase is a radial system was used at each iteration a load flow for radial systems specialist. To ensure that the distribution system operates in a radial manner, was introduced into the solution methodology is a routine in which verified the formation of linkages and connectivity of the system in each iteration of the phases of construction and local improvement. Tests are presented using the systems 14, 33, 84, 119 and 136 bus to evaluate the efficiency and robustness of the proposed methodology. The results were compared to results from the literature in order to validate the proposal of this work / Orientador: Rubén Augusto Romero Lázaro / Coorientador: Marina Lavorato de Oliveira / Banca: Marcos Julio Rider Flores / Banca: Eduardo Nobuhiro Asada / Mestre

abstract: In the deregulated power system, locational marginal prices are used in transmission engineering predominantly as near real-time pricing signals. This work extends this concept to distribution engineering so that a distribution class locational marginal price might be used for real-time pricing and control of advanced control systems in distribution circuits. A formulation for the distribution locational marginal price signal is presented that is based on power flow sensitivities in a distribution system. A Jacobian-based sensitivity analysis has been developed for application in the distribution pricing method. Increasing deployment of distributed energy sources is being seen at the distribution level and this trend is expected to continue. To facilitate an optimal use of the distributed infrastructure, the control of the energy demand on a feeder node in the distribution system has been formulated as a multiobjective optimization problem and a solution algorithm has been developed. In multiobjective problems the Pareto optimality criterion is generally applied, and commonly used solution algorithms are decision-based and heuristic. In contrast, a mathematically-robust technique called normal boundary intersection has been modeled for use in this work, and the control variable is solved via separable programming. The Roy Billinton Test System (RBTS) has predominantly been used to demonstrate the application of the formulation in distribution system control. A parallel processing environment has been used to replicate the distributed nature of controls at many points in the distribution system. Interactions between the real-time prices in a distribution feeder and the nodal prices at the aggregated load bus have been investigated. The application of the formulations in an islanded operating condition has also been demonstrated. The DLMP formulation has been validated using the test bed systems and a practical framework for its application in distribution engineering has been presented. The multiobjective optimization yields excellent results and is found to be robust for finer time resolutions. The work shown in this report is applicable to, and has been researched under the aegis of the Future Renewable Electric Energy Delivery and Management (FREEDM) center, which is a generation III National Science Foundation engineering research center headquartered at North Carolina State University. / Dissertation/Thesis / Ph.D. Electrical Engineering 2012

Esta dissertação apresenta um modelo aproximado de rede desenvolvido para análise de sistemas de distribuição em regime permanente. O modelo é detalhado do ponto de vista matemático e teórico considerando a representação dos elementos em derivação da rede (cargas e geradores) e dos limites operacionais empregando aproximações lineares. A modelagem linear permite determinar de forma simples os valores das tensões e correntes do sistema, podendo ser empregada em problemas de otimização relacionados ao planejamento e expansão de sistemas de distribuição. A representação da carga considera a influência da variação da tensão, fator determinante nas redes de distribuição. Também é considerada a inclusão de geração distribuída (GD) sendo implementada para diferentes modos de operação, permitindo ainda a minimização das perdas para a barra onde a GD está alocada. Para validar a abordagem proposta, os resultados do modelo apresentado foram comparados em termos de tensões, correntes e perdas com resultados obtidos com o modelo convencional de fluxo de carga, solucionado pelo algoritmo de varredura. Os testes foram realizados em dois sistemas de distribuição conhecidos, um de 70 barras e um de 135 barras. Para o sistema de 70 barras foi avaliado o uso de diferentes modos de operação da GD. Finalmente, para o sistema de 135 barras foram comparados os resultados do modelo proposto com o fluxo de carga convencional caracterizando a GD como uma barra de tensão controlada (PV) para diversos valores de injeção ativa na barra selecionada. As conclusões confirmam a validade e as vantagens que o modelo desenvolvido neste trabalho proporciona. / This work presents an approximate model developed to the analysis of electrical distribution systems at steady state. Both mathematical and theoretical details are given considering the representation of the shunt elements (loads and generators) and the operating limits of the network, using linear approximations. The linear modeling adopted resulted in a simple way to determine the values of the voltages and currents of the system; further the model can be applied to optimization problems related to optimal operation and expansion planning of distribution systems. The load representation considers the influence of voltage variations, which play an important role in the distribution networks. This work also considers the inclusion of distributed generation (DG), which is assessed under several modes of operation, including one mode which allows to minimize the losses at the node where the DG is located. To validate the proposed approach, the results for two example networks, given in terms of voltages, currents and losses, were compared with corresponding results obtained with conventional load flow model, solved by the backward-forward sweep method. The examples networks used to test and validate the model are known distribution systems, one having 70 and the other 135 nodes. Regarding the system with 70 nodes, the inclusion of DG was studied for several operational modes. Finally, the system of 135 nodes were used to compare the results of the proposed model with the results of the conventional load flow; in this case, the GD was characterized as a controlled-voltage bar (PV) for various levels of active power injection into the bar where the GD is located. The conclusions show the validity and advantages of the proposed model.

Monitoring of abnormal events in a distribution feeder by using a single technique is a challenging task. Many abnormal events can cause unsafe operation, including a high impedance fault (HIF) caused by a downed conductor touch ground surface, an incipient fault (IF) caused by partial breakdown to a cable insulation, and a circuit breaker (CB) malfunction due to capacitor bank de-energization to cause current restrikes. These abnormal events are not detectable by conventional protection schemes. In this dissertation, a new technique to identify distribution feeder events is proposed based on the complex Morlet wavelet (CMW) and on a decision tree (DT) classifier. First, the event is detected using CMW. Subsequently, a DT using event signatures classifies the event as normal operation, continuous and non-continuous arcing events (C.A.E. and N.C.A.E.). Additional information from the supervisory control and data acquisition (SCADA) can be used to precisely identify the event. The proposed method is meticulously tested on the IEEE 13- and IEEE 34-bus systems and has shown to correctly classify those events. Furthermore, the proposed method is capable of detecting very high impedance incipient faults (IFs) and CB restrikes at the substation level with relatively short detection time. The proposed method uses only current measurements at a low sampling rate of 1440 Hz yielding an improvement of existing methods that require much higher sampling rates.

abstract: Several music players have evolved in multi-dimensional and surround sound systems. The audio players are implemented as software applications for different audio hardware systems. Digital formats and wireless networks allow for audio content to be readily accessible on smart networked devices. Therefore, different audio output platforms ranging from multispeaker high-end surround systems to single unit Bluetooth speakers have been developed. A large body of research has been carried out in audio processing, beamforming, sound fields etc. and new formats are developed to create realistic audio experiences. An emerging trend is seen towards high definition AV systems, virtual reality gears as well as gaming applications with multidimensional audio. Next generation media technology is concentrating around Virtual reality experience and devices. It has applications not only in gaming but all other fields including medical, entertainment, engineering, and education. All such systems also require realistic audio corresponding with the visuals. In the project presented in this thesis, a new portable audio hardware system is designed and developed along with a dedicated mobile android application to render immersive surround sound experiences with real-time audio effects. The tablet and mobile phone allow the user to control or “play” with sound directionality and implement various audio effects including sound rotation, spatialization, and other immersive experiences. The thesis describes the hardware and software design, provides the theory of the sound effects, and presents demonstrations of the sound application that was created. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2016