Submitted in fulfillment of the requirements for the degree of Master of Engineering, Durban University of Technology, Durban, South Africa, 2017. / Much equipment in the eThekwini Electricity network has been in use for several decades. Failure of this equipment could critically impact electricity supply to customers, and result in high costs associated with loss of load and/or component replacement. The fundamental motive for any power utility is to plan, operate, and maintain power infrastructure such that customers receive reliable electric services at the minimum expense possible. For this dissertation, the Reliability Centered Maintenance (RCM) model was implemented in the eThekwini Electricity network. This model emphasises the importance of long-term planning and allocation of resources over the life time of a transformer, or any other component. RCM is an ongoing process that entails gathering data from operating systems performance, and using this data to improve design, operation, and maintenance of the system. The eThekwini Power network failure statistics for the previous five years were collected and thoroughly analysed to identify critical components associated with higher failure rates, and associated consequences. Upon examination, it was determined that the power transformer is a critical component of the system. The transformer plays a significant role in the power system due to its remarkable effect on overall reliability, in addition to the fact that it is a major cost factor in the power grid. Transformer management comprises of identifying the appropriate type and frequency of maintenance, and the appropriate time to replace the transformer in a cost-effective manner. The Markov model for ascertaining the transformer’s remaining service life was applied on the identified critical transformer. The transformer deterioration process is modelled by representing the oil insulation by discrete stages. Using the Institute of Electrical and Electronics Engineers (IEEE) standard for interpreting the transformer insulation, the transformer under review was found to be at stage two. Further analysis was performed on system unavailability rates versus mean time to first failure (MTTFF). The analyses indicated that the higher the MTTFF, the longer the system availability whereas the lower the MTTFF, the more reduced the system availability. Improving the MTTFF rates of a system will enhance reliability. The effective application of RCM will optimise the maintenance processes with reasonable expenditures. / M

This thesis describes new methods of evaluating the efficiency of three-phase induction machines using synthetic loading. Synthetic loading causes the induction machine to draw full-load current without the need to connect a mechanical load to the machine's drive shaft. The synthetic loading methods cause the machine to periodically accelerate and decelerate, producing an alternating motor-generator action. This action causes the machine, on average over each synthetic loading cycle, to operate at rated rms current, rated rms voltage and full-load speed, thereby producing rated copper losses, iron loss and friction and windage loss. The excitation voltages are supplied from a PWM inverter with a large capacity DC bus capable of supplying rated rms voltage. The synthetic loading methods of efficiency evaluation are verified in terms of the individual losses in the machine by using a new dynamic model that accounts for iron loss and all parameter variations. The losses are compared with the steady-state loss distribution determined using very accurate induction machine parameters. The parameters were identified using a run-up-to-speed test at rated voltage and the locked rotor and synchronous speed tests conducted with a variable voltage supply. The latter tests were used to synthesise the variations in stator leakage reactance, magnetising reactance and the equivalent iron loss resistance over the induction machine's speed range. The run-up-to-speed test was used to determine the rotor resistance and leakage reactance variations over the same speed range. The test method results showed for the first time that the rotor leakage reactance varied in the same manner as the stator leakage and magnetising reactances with respect to current. When all parameter variations are taken into account there is good agreement between theoretical and measured results for the synthetic loading methods. The synthetic loading methods are applied to three-phase induction machines with both single- and double-cage rotors to assess the effect of rotor parameter variations in the method. Various excitation waveforms for each method were used and the measured and modelled efficiencies compared to conventional efficiency test results. The results verify that it is possible to accurately evaluate the efficiency of three-phase induction machines using synthetic loading.

CAPES; CNPQ; FINEP; FA; SETI / Este trabalho tem como objetivo implementar, caracterizar, calibrar e testar um acelerômetro óptico biaxial para o monitoramento de vibrações em máquinas elétricas. São apresentados os métodos convencionais de sensoriamento e sistemas ópticos para a análise de vibrações. O acelerômetro proposto tem como elemento sensor as redes de Bragg em fibra óptica, onde a oscilação da massa inercial provoca a alteração do comprimento de onda de Bragg conforme o deslocamento da base do sensor. O acelerômetro óptico biaxial permite a medição da aceleração em duas direções ortogonais, onde a frequência natural para o eixo x é 747,5 Hz e para o eixo y é 757,5 Hz, podendo assim realizar medições com sensibilidade constante até aproximadamente um terço dessas frequências. A caracterização em resposta em frequência denominado massa dinâmica, foi obtido com os ensaios experimentais utilizando o martelo de impacto e o atuador eletromecânico. Este último ensaio permitiu que o acelerômetro fosse exposto a uma excitação harmônica de 10 Hz a 750 Hz. A comparação da resposta obtida com o acelerômetro piezoelétrico utilizado como referência e o sistema óptico possibilitou obter a curva de sensibilidade em pm por g ao longo da frequência de análise. A análise em frequência está em consonância com a NBR 60034-14 a qual especifica os limites de vibração para máquinas elétricas girantes quando desacopladas de qualquer carga ou acionamento. Os ensaios realizados para validar a resposta do acelerômetro óptico biaxial para o monitoramento das frequências de vibrações em máquinas elétricas, foram desenvolvidos em três momentos. Primeiro foi analisado um grupo-gerador de 500 kVA no Hospital Pequeno Príncipe em Curitiba. Segundo foi utilizado um motor de indução conectado a um inversor de frequência e por último foi analisado um motor de indução operando com o rotor com a barra quebrada, onde foi acoplado um gerador síncrono para prover a carga ao motor. / The means focus of this study is to implement, characterize, calibrate and test of a biaxial optical fiber accelerometer for vibration monitoring in electrical machines. The conventional methods of the sensing as well as the optical systems for analysis of the vibrations are presents. The accelerometer proposed uses fiber Bragg gratings to measure the displacement of the na inertial mass, where cause the change of Bragg wavelength relatively to a displacement of the support base. The biaxial optical accelerometer allows the measurement of the acceleration in two ortogonal directions, where the natural frequency for the x-axis is 747,5 Hz and for y-axis is 757,5 Hz, being able to perform measurements with constant sensitivity up to one third of these frequencies. The characterization in frequency response called dynamic mass was obtained with the experimental tests using the impact hammer and electromechanical actuator. The last test allowed the accelerometer was exposed to a harmonic excitation of the 10 Hz to 750 Hz. The comparison of the response between the optical system and the piezoelectric accelerometer used as reference allowed to get the sensibility in pm by g regarding the analysis of the frequency. The analysis frequency is in line with the NBR 60034-14 wich specifies the limits of the vibration for rotating electrical machines when uncoupled from any load or drive. The tests perfomed to validate the response of the biaxial optical accelerometer for a monitoring of the vibration frequencies in electrical machines were developed in three moments. First it was tested a group-generator, 500 kVA at the Hospital Pequeno Príncipe in Curitiba. Second was used an induction motor connected to a frequency inverter and finally was analyzed na operating induction motor with broken rotor bar where was also used a synchronous generator to provide the load for motor.

Orientadores: Ernesto Ruppert Filho, Alfeu Joãozinho Sguarezi Filho / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-23T13:09:28Z (GMT). No. of bitstreams: 1 Trindade_FilipeSarmento_M.pdf: 4372801 bytes, checksum: 51cf6a93426e65669c049bef356ed0a2 (MD5) Previous issue date: 2013 / Resumo: Nas últimas décadas, a crescente necessidade de novas fontes limpas e renováveis de energia elétrica provocou um grande interesse por meios alternativos às usinas elétricas convencionais. Entre eles, o aproveitamento da energia eólica. Nesse contexto, o gerador de indução de rotor bobinado tem sido bem utilizado com turbinas eólicas em todo o mundo devido à possibilidade de conexão do seu estator diretamente à rede elétrica e à possibilidade de controle das potências ativa e reativa através de conversores eletrônicos de potência conectados aos terminais do seu rotor, o que diminui a potência dos conversores para até 30% da potência nominal do gerador elétrico. Assim, a presente dissertação objetiva propor o controle das potências ativa e reativa do gerador elétrico com o uso de controladores por modos deslizantes utilizando a técnica de orientação de campo pelo fluxo do estator para realizar o controle independente dessas potências. Primeiramente, compara-se o desempenho do controlador proposto com o tradicional controle de potências por controladores PI, através de simulações computacionais da conexão do gerador à rede elétrica através de duas topologias de conversores: com apenas os terminais do estator conectados à rede elétrica e com os terminais do rotor também conectados através de conversores em anti-paralelo (back-to-back). Finalmente, o controlador por modos deslizantes foi implementado fisicamente em uma bancada experimental com apenas os terminais do estator do gerador conectados à rede elétrica para comprovação da proposta / Abstract: In the last decades, the increasing need for new clean and renewable sources of electric energy caused a great interest in alternative means to conventional power plants. Among them, the use of wind energy. In this context, the doubly-fed induction generator has been widely used with wind turbines worldwide due to the possibility of connecting its stator terminals directly to the electric power grid and its active and reactive power control possibility through electric power converters connected to its rotor terminals, which reduce the converters power capacity for up to 30% of the generator rated power. Thus, this dissertation aims to propose the generator active and reactive power control using sliding mode controllers using field-oriented control to perform independent power control. First, the performance of the proposed controller with the traditional PI power control controllers is compared through computer simulations connecting the generator to the electric grid through two converter topologies: with only the stator terminals connected to the grid and with the rotor terminals also connected to the grid through a back-to-back converter. Finally, the sliding mode controller was implemented on a laboratory assembly with only the generator stator terminals connected to the grid to prove the proposal / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

This thesis proposes innovative methods to extract information embedded in the frequency and time domain response of the transformer winding, and utilizes them to suggest solutions to a few tasks that have until now been thought difficult, if not impossible, to resolve. Pursuing this philosophy originated from the basic under- standing that the response of any physical system (behaving largely as a linear time invariant system) has embedded information that characterizes it completely. So, the prerequisite is to evolve ways to extract this information from measured responses. Once that is done, a variety of interesting applications can be envisaged. The two applications considered in this thesis are- •Investigate indirect measurement of the series capacitance of a transformer winding using the measured frequency or time domain response •Explore the possibility of increasing the physical resolution of the ladder network used to model a fully interleaved-disk winding In the former application, since direct measurement of series capacitance is impossible, alternatives based on indirect measurement were also not attempted. Similarly, in the latter application, the upper limit is known to be fixed by the number of distinctly observable peaks in the magnitude frequency response, so the question of increasing this limit was also never explored. Solutions to these tasks are proposed after a systematic analysis of frequency/time domain responses of a winding, initially modeled as a lumped parameter ladder network, to extract correlations that exist between them and winding parameters, and finally examine how these relations can be exploited together with the measured responses. Each of the five chapters is dedicated to describe the solution to one task. In each chapter, analytical formulation is presented first, followed by experimental results. Good agreement with the predicted results demonstrates its practicability. In final summary, indirect measurement of the series capacitance of a winding and en- hancing physical resolution of a ladder network model to represent a fully interleaved- disk winding was successfully demonstrated and they are the main contributions of this thesis.

Orientador: Walmir de Freitas Filho / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-24T08:26:46Z (GMT). No. of bitstreams: 1 Salles_NewtonJosede_D.pdf: 8861113 bytes, checksum: 46fbfc4ed40c793e3b012449f77b88ab (MD5) Previous issue date: 2013 / Resumo: Recentemente, o ilhamento intencional, ou seja, a operação isolada de uma parte do sistema elétrico de potência que pode ser alimentada localmente por geradores distribuídos, tem representado um grande interesse para as empresas concessionárias de energia elétrica. Tamanho interesse deve-se à capacidade destes geradores em assegurar a redução do tempo de indisponibilidade do fornecimento de energia elétrica, aumentando a confiabilidade das cargas pertencentes ao sistema ilhado. O sucesso da prática do ilhamento intencional é o conhecimento prévio de todas as contingências possíveis que podem resultar em operação ilhada, quer sejam situações de manutenções programadas ou mesmo a perda de subestações de distribuição ou linhas de transmissão de alta tensão. Neste cenário, uma prática comum é utilizar o(s) gerador(es) síncrono(s) distribuído(s) para alimentar o sistema ilhado e garantir a regulação da frequência e da magnitude da tensão, com a atuação do regulador de velocidade e do regulador de tensão, respectivamente. Um dos aspectos mais importantes que deve ser considerado no planejamento do sistema elétrico de potência é o desempenho do sistema de proteção, uma vez que os ajustes dos dispositivos de proteção não são flexíveis o suficiente para acomodar a operação antes e depois de detectado o ilhamento. Neste contexto, esta tese de doutorado apresenta duas contribuições principais: (1) apresentar um estudo detalhado de viabilidade técnica para a realização do ilhamento intencional ¿ dado que o autor deste trabalho é um engenheiro experiente em uma das mais bem conceituadas concessionárias brasileiras, entende-se que o detalhamento destes estudos é de extrema importância para a academia; (2) desenvolver modelos de modernos relés digitais de proteção nos ambientes MATLAB/Simulink, ATP/ATPDraw e ANATEM e utilizar estes modelos em esquemas de proteção suficientemente flexíveis para permitir a viabilidade do ilhamento intencional de geradores síncronos distribuídos. Na avaliação do desempenho de dispositivos de proteção para a formação do ilhamento, são utilizados modelos de relés digitais de proteção desenvolvidos durante o mestrado do autor, bem como novos modelos de relés. Os novos modelos de relés foram desenvolvidos para serem usados em ambientes de análise de transitórios eletromecânicos e eletromagnéticos, como o MATLAB/Simulink, ATP/ATPDraw e ANATEM, constituindo uma poderosa ferramenta de análise e simulação, pois permitem que as interações entre o sistema de proteção e a dinâmica do sistema sejam visualizadas no domínio do tempo. Palavras-chave: Geração distribuída, ilhamento intencional, proteção / Abstract: Nowadays, the utilities have strong interest in practicing the intentional islanding, i.e., the islanded operation of part of the electrical power system fed by distributed generators. This interest is resulted by the capacity of distributed generators to decrease outages and, therefore, to increase system reliability. The success of intentional islanding practice relies on the previous knowledge of all the possible contingencies which may result in islanded operation. These contingencies may be scheduled maintenances or even the loss of distribution substations or transmission lines. Under these circumstances, a common practice is to use the distributed synchronous generators to feed the islanded system and to assure the voltage frequency and magnitude control with the speed governor and voltage regulator actuation, respectively. One of the most important aspects that must be considered in electric power systems planning is the performance of protection system, since the relay settings are not flexible enough to assure the suitable operation before and after the islanding occurrence. In this context, this work has two main contributions: (1) to present a detailed study of intentional islanding technical feasibility ¿ the author is a senior engineer at one of the most important Brazilian utilities, as a result the presentation of how to perform these studies in detail is extremely important for Academy; (2) to develop modern digital relays models using time domain simulation tools such as MATLAB/Simulink, ATP/ATPDraw and ANATEM and to use these models in sufficiently flexible protection schemes to achieve successful intentional islanding operations with synchronous generators. The evaluation of protection systems performance for the intentional islanding practice explore the implemented digital relays models in time domain simulations performed using MATLAB/Simulink, ATP/ATPDraw and ANATEM. This option is an important analysis tool that allows the evaluation of the interaction between protection system and system dynamics during the time. Key-words: Distributed generation, intentional islanding, protection / Doutorado / Energia Eletrica / Doutor em Engenharia Elétrica

This work is dedicated to faulty induction motors. These motors are often used in industrial applications thanks to their usability and their robustness. However, nowadays optimisation of production becomes so critical that the conceptual reliability of the motor is not sufficient anymore. Motor condition monitoring is expanding to serve maintenance planning and uptime maximisation. Moreover, the use of drive control sensors (namely stator current and voltage) can avoid the installation and maintenance of dedicated sensors for condition monitoring.<p><p>Many authors are working in this field but few approach the diagnosis from a detailed and clear physical understanding of the localised phenomena linked to the faults. Broken bars are known to modulate stator currents but it is shown in this work that it also changes machine saturation level in the neighbourhood of the bar. Furthermore, depending on the voltage level, this change in local saturation affects the amplitude and the phase of the modulation. This is of major importance as most diagnosis techniques use this feature to detect and quantify broken bars. For stator short-circuits, a high current is flowing in the short-circuited coil due to mutual coupling with the other windings and current spikes are flowing in the rotor bars as they pass in front of the short-circuited conductors. In the case of rotor eccentricities, the number of pole-pairs and the connection of these pole-pairs greatly affect the airgap flux density distribution as well as the repartition of the line currents in the different pole-pairs.<p><p>These conclusions are obtained through the use of time-stepping finite element models of the faulty motors. Moreover, circuit models of faulty machines are built based on the conclusions of previously explained fault analysis and on classical Park models. A common mathematical description is used which allows objective comparison of the models for representation of the machine behaviour and computing time.<p><p>The identifiability of the parameters of the models as well as methods for their identification are studied. Focus is set on the representation of the machine behaviour using these parameters more than the precise identification of the parameters. It is shown that some classical parameters can not be uniquely identified using only stator measurements.<p><p>Fault detection and identification using computationally cheap models are compared to advanced detection through motor stator current spectral analysis. This last approach allows faster detection and identification of the fault but leads to incorrect conclusions in low load conditions, in transient situations or in perturbed environments (i.e. fluctuating load torque and unideal supply). Efficient quantification of the fault can be obtained using detection techniques based on the comparison of the process to a model.<p><p>Finally, the work provides guidelines for motor supervision strategies depending on the context of motor utilisation. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished