Underground Residential Distribution (URD) power cables are aged due to electrical, thermal, mechanical, and environmental stresses during their service. The recent dielectric conditions of the cables are of much interest for utilities. The existing offline diagnostic method requires forceful disconnection of the URD cable for maintenance. Online recording and Fast Fourier Transform analysis of intentionally created transients in URD is one of the promising method to assess the current condition of the cable. For the bigger goal of developing an online power cable condition assessment, the measurement techniques which are required to be implemented has to be evaluated. In order for implementing the online measurement system, the requirements of the measurement system have to be identified at first. URD system model was simulated using Electro Magnetic Transient Program to identify the characteristics of induced transients. A list of requirements of the measurement system was created based on the simulation results

This thesis proposes the small signal model for the Interline Power Flow Controller (IPFC). Using this model, the damping performance of the IPFC with different power system configuration is investigated and also compared with the AC Transmission System (FACTS) based controllers such as the Unified Power Flow Controller (UPFC). The IPFC and the UPFC in constant power control mode can be viewed as effectively cutting the connected transmission line. This change on the structure of the network results in a significant change on the small signal stability. This thesis also addresses issues regarding the different levels of models that are required for the investigation of the behavior of FACTS. An effective validation approach that uses a minimum sized demonstration platform is proposed. This platform is small enough for detailed EMTP validation, yet large enough to exhibit the range of transient electrical and electromechanical behavior which is the focus for FACTS devices. To demonstrate the approach, the small signal models of the system embedded with the IPFC and the UPFC are developed respectively. The results obtained from small signal analysis are validated with EMTP-type simulation and show a close agreement.

This thesis proposes the small signal model for the Interline Power Flow Controller (IPFC). Using this model, the damping performance of the IPFC with different power system configuration is investigated and also compared with the AC Transmission System (FACTS) based controllers such as the Unified Power Flow Controller (UPFC). The IPFC and the UPFC in constant power control mode can be viewed as effectively cutting the connected transmission line. This change on the structure of the network results in a significant change on the small signal stability. This thesis also addresses issues regarding the different levels of models that are required for the investigation of the behavior of FACTS. An effective validation approach that uses a minimum sized demonstration platform is proposed. This platform is small enough for detailed EMTP validation, yet large enough to exhibit the range of transient electrical and electromechanical behavior which is the focus for FACTS devices. To demonstrate the approach, the small signal models of the system embedded with the IPFC and the UPFC are developed respectively. The results obtained from small signal analysis are validated with EMTP-type simulation and show a close agreement.

Les câbles sont utilisés de plus en plus pour le transport et la distribution de l’électricité en courant alternatif sur des distances de plus en plus longues. La prolifération de fermes éoliennes offshore qui nécessitent d’interconnexions avec le continent a aussi propulsé leur utilisation sous-marine. Modèles de câbles sont disponibles dans le bien connu logiciel Electro Magnetic Transient Program et sont destinés au domaine temporel. Ces modèles sont assemblés en utilisant différentes techniques, mais tous nécessitent une connaissance précise des paramètres des câbles dans le domaine fréquentiel. Dans ce but, pour le calcul des impédances des câbles tripolaires cette thèse propose une méthode qui améliore la prise en compte de la proximité entre tous les conducteurs : il s’agit d’une méthode semi-analytique qui utilise le concept duale de fils minces et sous-conducteurs pour décrire la densité de courant à l’intérieur des conducteurs et le calcul des impédances. L’effet du retour par la mer est aussi analysé et une méthode quasi Monte Carlo est proposé, afin de résoudre les intégrales qui décrivent la formulation des impédances pour le sol à deux couches (la mer et son fond) sur lequel ces câbles sont posés. L’effet du à la présence des couches de semi-conducteur dans les câbles est aussi traité. La méthode de collocation stochastique est aussi décrite et appliquée, afin de prendre en compte la variabilité des paramètres d’entrée. / Cables are extensively used for underground alternating current electricity distribution and progressively over longer distances ; the proliferation of offshore wind farms which require interconnections with the mainland has also increased their use underwater. Models of cables are available in the well-known Electro Magnetic Transient Program software and are designed to the time-domain. These models are assembled using different techniques but all of them need a precise knowledge of the frequency domain parameters of the cables. Accordingly, for the calculation of the impedances of three-core submarine power cables this thesis proposes an improved method to consider the proximity effect between all conductors. The method, which is a semi-analytical, uses the dual concept of thin-wires and sub-conductors to describe the current density inside the conductors and the calculation of the impedances. The effect of the sea return is also analyzed and a quasi Monte Carlo method is proposed, to solve the integrals describing the impedances formulations for the two layer soil (the sea and seabed) upon which the submarine cables are laid. The effect due to the presence of semi-conducting layers in the cables is also treated. The stochastic collocation method is also described and applied, in order to account for the variability of the input parameters.

As descargas atmosféricas estão entre as principais causas de distúrbios nos sistemas elétricos, provocando sobretensões e ocasionando uma parcela significativa das interrupções não programadas. Tais distúrbios são cada vez mais percebidos pelos consumidores, ocasionando desde o mau funcionamento até a queima de aparelhos e equipamentos eletro-eletrônicos residenciais, comerciais e industriais. Antigamente eletromecânicos, tais aparelhos são atualmente, em grande parte, produzidos com componentes semicondutores, o que os torna mais sensíveis a interferências. As descargas atmosféricas também apresentam um agravante de, salvo raras exceções, não serem registradas nos bancos de dados das concessionárias, ao contrário das operações de manobra, faltas e variações de carga na rede de distribuição. Essa situação contribui para os conflitos cada vez mais freqüentes entre consumidores e empresas de energia a respeito dos pedidos de indenização por danos em aparelhos elétricos (PID). Dada a relevância do tema, muitos estudos têm sido realizados ao longo dos últimos anos, sem entretanto esclarecer todos os aspectos necessários para a minimização desses problemas. Neste trabalho são avaliadas as amplitudes e formas de onda das sobretensões transferidas à rede de baixa tensão via transformador quando da ocorrência de surtos no primário. Esses surtos podem ser oriundos de descargas diretas na rede primária ou decorrentes de descargas em suas proximidades. O estudo visa a obtenção de informações tendo em vista a melhoria do desempenho das redes de distribuição e conseqüentemente a minimização dos danos causados aos consumidores. Nas simulações, realizadas através do programa ATP (“Alternative Transients Program"), são consideradas linhas com configurações típicas, bem como modelos de comprovada validade para representação dos isoladores de média e de baixa tensão e do transformador de distribuição. O trabalho analisa a influência, nas sobretensões, de diversos parâmetros, como por exemplo amplitude e forma de onda da corrente da descarga, ponto da incidência da descarga, resistência de terra e presença de dispositivos de proteção contra surtos. Os resultados apresentados constituem-se em importantes subsídios para a definição de critérios de instalação de dispositivos de proteção contra surtos em redes de baixa tensão. / Lightning discharges are among the main causes of disturbances in electrical systems, causing overvoltages and leading to a significant portion of unscheduled interruptions. Such disturbances are increasingly noticed by consumers, causing from malfunction to the burnt-out of electrical-electronic devices and equipment in homes, businesses and industries. Formerly electromechanical, such devices currently are, in their majority, produced with semiconductors, what makes them more sensitive to interferences. Lightning discharges also present the aggravation of not being recorded in power suppliers’ databases, but for seldom exceptions, as opposed to switching operations, failures and charge variations in the distribution network. This situation contributes for the increasingly frequent conflicts among consumers and power companies regarding indemnity claims due to damages to electrical devices. Given the subject’s significance, many studies have been conducted along the past years, not explaining, however, all the aspects required to minimize those problems. On this work, the amplitudes and waveforms of overvoltages on medium and low voltage lines are evaluated upon the incidence of direct discharges on the primary. The voltages transferred to the low voltage side are also evaluated in case of strikes in the vicinity of the line. The study intends to obtain information in order to achieve a performance improvement of distribution networks and, as a consequence, the reduction of damages to consumers to a minimum. In the simulations conducted through ATP (“Alternative Transients Program"), lines with typical configurations are considered and models of proven validity are used to represent the low and medium voltage insulators and the distribution transformer. The work analyses the effect of several parameters on the overvoltages, such as amplitude and waveform of the stroke current, lightning strike point, grounding resistance and existence of surge protective devices. The results presented constitute an important foundation to define the installation criteria of surge protective devices on low voltage networks.

As descargas atmosféricas estão entre as principais causas de distúrbios nos sistemas elétricos, provocando sobretensões e ocasionando uma parcela significativa das interrupções não programadas. Tais distúrbios são cada vez mais percebidos pelos consumidores, ocasionando desde o mau funcionamento até a queima de aparelhos e equipamentos eletro-eletrônicos residenciais, comerciais e industriais. Antigamente eletromecânicos, tais aparelhos são atualmente, em grande parte, produzidos com componentes semicondutores, o que os torna mais sensíveis a interferências. As descargas atmosféricas também apresentam um agravante de, salvo raras exceções, não serem registradas nos bancos de dados das concessionárias, ao contrário das operações de manobra, faltas e variações de carga na rede de distribuição. Essa situação contribui para os conflitos cada vez mais freqüentes entre consumidores e empresas de energia a respeito dos pedidos de indenização por danos em aparelhos elétricos (PID). Dada a relevância do tema, muitos estudos têm sido realizados ao longo dos últimos anos, sem entretanto esclarecer todos os aspectos necessários para a minimização desses problemas. Neste trabalho são avaliadas as amplitudes e formas de onda das sobretensões transferidas à rede de baixa tensão via transformador quando da ocorrência de surtos no primário. Esses surtos podem ser oriundos de descargas diretas na rede primária ou decorrentes de descargas em suas proximidades. O estudo visa a obtenção de informações tendo em vista a melhoria do desempenho das redes de distribuição e conseqüentemente a minimização dos danos causados aos consumidores. Nas simulações, realizadas através do programa ATP (“Alternative Transients Program”), são consideradas linhas com configurações típicas, bem como modelos de comprovada validade para representação dos isoladores de média e de baixa tensão e do transformador de distribuição. O trabalho analisa a influência, nas sobretensões, de diversos parâmetros, como por exemplo amplitude e forma de onda da corrente da descarga, ponto da incidência da descarga, resistência de terra e presença de dispositivos de proteção contra surtos. Os resultados apresentados constituem-se em importantes subsídios para a definição de critérios de instalação de dispositivos de proteção contra surtos em redes de baixa tensão. / Lightning discharges are among the main causes of disturbances in electrical systems, causing overvoltages and leading to a significant portion of unscheduled interruptions. Such disturbances are increasingly noticed by consumers, causing from malfunction to the burnt-out of electrical-electronic devices and equipment in homes, businesses and industries. Formerly electromechanical, such devices currently are, in their majority, produced with semiconductors, what makes them more sensitive to interferences. Lightning discharges also present the aggravation of not being recorded in power suppliers’ databases, but for seldom exceptions, as opposed to switching operations, failures and charge variations in the distribution network. This situation contributes for the increasingly frequent conflicts among consumers and power companies regarding indemnity claims due to damages to electrical devices. Given the subject’s significance, many studies have been conducted along the past years, not explaining, however, all the aspects required to minimize those problems. On this work, the amplitudes and waveforms of overvoltages on medium and low voltage lines are evaluated upon the incidence of direct discharges on the primary. The voltages transferred to the low voltage side are also evaluated in case of strikes in the vicinity of the line. The study intends to obtain information in order to achieve a performance improvement of distribution networks and, as a consequence, the reduction of damages to consumers to a minimum. In the simulations conducted through ATP (“Alternative Transients Program”), lines with typical configurations are considered and models of proven validity are used to represent the low and medium voltage insulators and the distribution transformer. The work analyses the effect of several parameters on the overvoltages, such as amplitude and waveform of the stroke current, lightning strike point, grounding resistance and existence of surge protective devices. The results presented constitute an important foundation to define the installation criteria of surge protective devices on low voltage networks.

The insulation lifetime of power cables is determined by several factors. One of the most important of these is the occurrence of partial discharge (PD) at the dielectric. The ability to detect and locate a PD source is limited by attenuation of the high frequency PD pulses as they propagate through the cable to the sensor. Therefore it is necessary to understand the high frequency response of such cables. The ultimate aim of this thesis is to develop an accurate frequency-dependent cable model for detecting and locating degraded insulation regions on power cables, caused by partial discharge activities. Numerical methods can calculate field distribution in the vicinity of a cavity of non-standard shape which generates PDs, and is difficult to calculate by analytical methods. The simulated results show the important influence of the shape of cavity on the electric stress within it. The cavity stress enhancement increases as the permittivity of the dielectric increases. The increase is greater for cavities with large diameter to thickness ratios. A cavity with its axis parallel to the applied field direction has a higher stress enhancement. In addition the stress distribution in the cavity is smaller for spherical cavities than for cylindrical types. The research results show that the semi-conducting layers response voltage increases as frequency increases. This indicates that the semi-conducting layers can have high sensitivity for detection of partial discharge signals and this may be a useful feature to incorporate in the design of cables and in the application of cable models. By using ATPDraw, FEM and EMTP-RV techniques, three different types of cable models are developed. The simulated results give a good agreement with the measured results on the single and three phase power cable. The developed cable model can use for reconstruction of PD source signal by using the receiving signal captured at the cable ends. It is important to use the true pulse shape because it is characteristic of the PD type and location. An investigation into the possibility of detecting different PD patterns and signals when conducting PD tests using different sensor bandwidths is also presented in this thesis. The occurrence of discharge activity was created by an artificial defect manufactured in the single core cable insulation. The artificial defect generated internal discharge and was used to investigate the PD signal propagation on cross-linked polyethylene (XLPE) cable. Capacitance coupled external sensors have been applied for the PD detection measurements and the results show that these external sensors have a number of advantages compared to high frequency current transformer (HF-CT) sensors for the detection of PD pulses. In addition, development of a method to detect cross-coupling of PD signals between phases of a three core cable and location of the PD source on the three phase cable. In order to visualize recorded data gained by PD measurement of three phase cable under test, the 3PARD diagram was used. Each data pulse is assigned to a single dot in the (scatter plot) diagram. The measured results show that the 3PARD diagram allowed the user to identify the fault between phases with PD location. The model used for reconstruction which includes the effect of semicon material in the losses provides accurate reproduction of the propagation characteristics of high frequency PD pulses and the thesis work had used such a model to reconstruct PD waveforms of site PDs from the measured signal for the first time. The use of the original waveform is important for PD identification and location in the practical situation.

Η αντικεραυνική προστασία των αιολικών πάρκων αποτελεί ένα πρόβλημα με αρκετές ιδιαιτερότητες λόγω της μορφής και της τοποθέτησης αυτών των κατασκευών σε σημεία όπου είναι ευάλωτα σε κεραυνικά πλήγματα. Για αυτό τον λόγο, έχουν αναπτυχθεί διάφορες μέθοδοι για την προστασία των ανεμογεννητριών και διεξάγονται έρευνες για την αποτελεσματικότητα αυτών. Μία από τις μεθόδους που χρησιμοποιούνται είναι και η διασύνδεση των πλεγμάτων γείωσης των ανεμογεννητριών. Αντικείμενο, λοιπόν, της παρούσης εργασίας είναι η εξομοίωση της μεταβατικής συμπεριφοράς ενός συστήματος γείωσης ενός αιολικού πάρκου το οποίο αποτελείται από τέσσερεις ανεμογεννήτριες. Τα πλέγματα γείωσης των ανεμογεννητριών συνδέονται μέσω αγωγών γείωσης, με σκοπό την καταγραφή της συμπεριφοράς της τάσης σε διάφορα σημεία των πλεγμάτων. Στη συνέχεια, πραγματοποιείται σύγκριση των κυματομορφών των τάσεων στα διάφορα σημεία καθώς και σύγκριση για διαφορετικές διεγέρσεις και τιμές της ειδικής αντίστασης του εδάφους, στο χώρο όπου τοποθετούνται οι γειωμένοι αγωγοί διασύνδεσης. Επίσης γίνεται σύγκριση της συμπεριφοράς του διασυνδεδεμένου μέσω αγωγών γείωσης συστήματος με ένα σύστημα στο οποίο η διασύνδεση των γεννητριών γίνεται μέσω αγωγών οι οποίοι ακουμπάνε στο έδαφος. Για την εξομοίωση των συστημάτων γείωσης, χρησιμοποιήθηκε το μοντέλο της κυκλωματικής προσέγγισης σύμφωνα με το οποίο τα ηλεκτρόδια γείωσης παριστάνονται μέσω κατανεμημένων τμημάτων, τα οποία αποτελούνται από εν σειρά επαγωγές και αντιστάσεις, καθώς και εγκάρσιες αγωγιμότητες και χωρητικότητες. Το ισοδύναμο κύκλωμα δημιουργήθηκε στο πρόγραμμα εξομοίωσης ηλεκτρομαγνητικών φαινομένων EMTP και οι τιμές των διαφόρων μεγεθών υπολογίστηκαν με τη βοήθεια του Microsoft Excel. / Lightning protection of wind farms is a complex problem because of the shape and the placement of these structures in places where lightning strikes are very common. That's why many different methods for the protection of wind turbines have been developed and researches are done for their effectiveness. One of these methods uses the interconnection of the wind turbine's grounding grids for protection. In this thesis, a transient analysis of a grounding interconnected system of a wind farm, consisting of four wind turbines, is being conducted. The grounding grids of each wind turbine are interconnected through buried conductors for the recording of the voltage behaviour in different nodes of the grounding grids. Additionally, a comparison of the voltage waveforms in different nodes is being conducted, as well as a comparison for different injected currents and values of soil resistivity in the place where the interconnecting conductors are being placed. A comparison of the behaviour of an interconnected system using conductors placed on the ground is also being conducted. For the simulation of the grounding systems, the model of circuit approach was used. According to this, the grounding electrodes are modeled using series resistors and inductors and transverse conductivities and capacitancies. The equivalent circuit was created in the electromagnetic phenomena programm EMTP and the parameter values were calculated with the use of Microsoft Excel.

Σκοπός της εργασίας είναι η μελέτη φαινομένων υπερτάσεων σε δίκτυα σύνδεσης ανανεώσιμων πηγών ενέργειας με τη χρησιμοποίηση του προγράμματος ΕΜΤΡ. Μέσω της ιδιαίτερης αναφοράς σε αιολικά συστήματα γίνεται λεπτομερής εξομοίωση για δυναμικές και διακοπτικές υπερτάσεις, υπερτάσεις χειρισμών, καθώς και κεραυνικές υπερτάσεις. / The purpose of this study is the presentation and analysis of overvoltages occurring in the network interconnection of renewable energy resources. Through the detailed reference of wind power systems, the thorough study of lighting,dynamic and switching overvoltages is presented.

The following work presents a graphical pre-processor software as an alternative version of the Electromagnetic Transients Program (ATP-EMTP). It was developed to aid in the analysis of electromagnetic transients in power substations. The software has been developed using Java programming language and it was named Alternative Transients Program Substation Analysis (ATP-SA). Amongst its functionalities, it can be highlighted the representation of precursory events of electromagnetic transients in the ATP-EMTP standard, data predefinition for the modeling of these events, simulation configuration with compatible values in reference to the transient phenomena to be studied and management simulation through a databank. The transients to be considered are: occurrence and clearance of faults, transformer inrush, Transient Recovery Voltage (TRV) in circuit-breakers, circuit-breaker switching and lightning surges. The software aids in the simulation of transients occurred by these events in both deterministic and stochastic ways. In addition, to show its potentialities, examples of application are presented in a real power system simulations. Hence, with the use of the mentioned software, it is expected to support in subsidies and safety with respect of operations in substations, as well to aid in defect prevention, loss of equipment and potential shutdowns. This work is the main theme of a Research and Development (R&D) project developed by the Laboratory of Analysis and Protection of Power Systems, in the Power System and Energy Research Center, in a partnership along with the State Company of Generation and Transmission of Electric Energy of the Rio Grande do Sul State. / Este trabalho apresenta a implementação de um software pré-processador gráfico para a versão alternativa do ElectroMagnetic Transient Program (ATP-EMTP), desenvolvido para auxiliar a análise de transitórios eletromagnéticos em subestações de potência. Este software, concebido em linguagem de programação Java, recebeu a denominação de Alternative Transients Program Substation Analysis (ATP-SA). Dentre suas funcionalidades, está a representação de eventos precursores de transitórios eletromagnéticos no padrão ATP-EMTP, predefinição de dados para modelagem destes eventos, parametrização da simulação com valores compatíveis com o fenômeno analisado e gerenciamento de simulações através de um banco de dados. Os eventos contemplados pelo software compreendem: ocorrência e eliminação de curtos-circuitos, energização de transformador, Tensão de Restabelecimento Transitória (TRT) em disjuntores, manobras de abertura e fechamento de disjuntores e descargas atmosféricas. O software fornece suporte a simulação de transitórios provocados por estes eventos de forma determinística ou estocástica. Para demonstrar estas potencialidades, abordam-se exemplos aplicados sobre um sistema elétrico real. Com a utilização do software desenvolvido, espera-se fornecer subsídio e segurança para a realização de operações em subestações, bem como auxiliar a prevenção de falhas, perda de equipamentos e desligamentos. O presente trabalho é parte integrante de um projeto de Pesquisa e Desenvolvimento (P&D), desenvolvido pelo Laboratório de Análise e Proteção de Sistemas Elétricos do Centro de Estudos em Energia e Sistemas de Potência (LAPES-CEESP) da UFSM, em parceria com a Companhia Estadual de Geração e Transmissão de Energia Elétrica (CEEE-GT) do Rio Grande do Sul.