Power system generators are interconnected in a distributed network to allow sharing of power. If one of the generators cannot meet the power demand, spare power is diverted from neighbouring generators. However, this approach also allows for propagation of electric disturbances. An oscillation arising from a disturbance at a given generator site will affect the normal operation of neighbouring generators and might cause them to fail. Hours of production time will be lost in the time it takes to restart the power plant. If the disturbance is detected early, appropriate control measures can be applied to ensure system stability. The aim of this study is to improve existing algorithms that estimate the oscillation parameters from acquired generator data to detect potentially dangerous power system disturbances. When disturbances occur in power systems (due to load changes or faults), damped oscillations (or &quotmodes") are created. Modes which are heavily damped die out quickly and pose no threat to system stability. Lightly damped modes, by contrast, die out slowly and are more problematic. Of more concern still are &quotnegatively damped" modes which grow exponentially with time and can ultimately cause the power system to fail. Widespread blackouts are then possible. To avert power system failures it is necessary to monitor the damping of the oscillating modes. This thesis proposes a number of damping estimation algorithms for this task. If the damping is found to be very small or even negative, then additional damping needs to be introduced via appropriate control strategies. This thesis presents a number of new algorithms for estimating the damping of modal oscillations in power systems. The first of these algorithms uses multiple orthogonal sliding windows along with least-squares techniques to estimate the modal damping. This algorithm produces results which are superior to those of earlier sliding window algorithms (that use only one pair of sliding windows to estimate the damping). The second algorithm uses a different modification of the standard sliding window damping estimation algorithm - the algorithm exploits the fact that the Signal to Noise Ratio (SNR) within the Fourier transform of practical power system signals is typically constant across a wide frequency range. Accordingly, damping estimates are obtained at a range of frequencies and then averaged. The third algorithm applied to power system analysis is based on optimal estimation theory. It is computationally efficient and gives optimal accuracy, at least for modes which are well separated in frequency.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-04-12T19:44:42Z No. of bitstreams: 1 brunomontesanoschettino.pdf: 4192681 bytes, checksum: 0df0705f39a6ff58697ec7dc00759256 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-04-24T03:29:36Z (GMT) No. of bitstreams: 1 brunomontesanoschettino.pdf: 4192681 bytes, checksum: 0df0705f39a6ff58697ec7dc00759256 (MD5) / Made available in DSpace on 2016-04-24T03:29:36Z (GMT). No. of bitstreams: 1 brunomontesanoschettino.pdf: 4192681 bytes, checksum: 0df0705f39a6ff58697ec7dc00759256 (MD5) Previous issue date: 2015-12-08 / Este trabalho propõe um método para detectar a saturação dos núcleos dos transformadores de corrente (TCs) utilizados na proteção de sistemas elétricos de potência (SEPs), além de promover a compensação de seus efeitos através da correção do sinal de corrente secundária distorcido pela saturação. Técnicas de processamento de sinais baseadas no filtro diferenciador de segunda ordem de Savitzky-Golay são utilizadas para localizar os pontos de transição entre partes do sinal de corrente distorcidas e não distorcidas pela saturação. Em seguida, um processo de estimação baseado no critério dos mínimos quadrados que utiliza exclusivamente amostras do sinal contidas nas regiões não distorcidas é efetuado, extraindo os parâmetros necessários à promoção da correção do sinal. As influências do ruído e dos desvios de frequência de operação do SEP foram analisadas, tendo sido desenvolvidos e incorporados meios adaptativos para mitigar seus efeitos. Os algoritmos desenvolvidos foram implementados em MATLAB e a avaliação de desempenho foi realizada utilizando sinais extraídos de simulações de falta ocorridas em um sistema modelado em um simulador digital em tempo real (RTDS). Os resultados indicaram que o método proposto atingiu desempenho satisfatório, independente dos parâmetros do TC e dentro de uma ampla gama de cenários da falta analisados. Além disso, o método mostrou-se robusto em relação ao ruído e eficiente na mitigação dos erros provocados pelos desvios de frequência. Ainda, os recursos técnicos e computacionais necessários para sua execução indicam que o método proposto é passível de implementação nos atuais dispositivos de proteção disponibilizados pela indústria. / This work proposes a method for detecting the saturation of the current-transformer cores used in the protection of electric power systems and promote the compensation for its effects by correcting the secondary current signal distorted due to the saturation. Signal processing techniques based on the second order differentiator Savitzky-Golay filter are used for locating the transition points between distorted and undistorted parts of the current signal. Then, an estimation process based on the least squares criteria that uses exclusively signal samples included in the undistorted regions is performed, extracting the parameters needed for the signal correction. The influences of the noise and the frequency offset were analysed, and adaptive means to mitigate their effects were developed and incorporated. The developed algorithms were implemented in MATLAB and performance evaluation was performed using the signals taken from fault simulations in a system modeled on a real time digital simulator (RTDS). The results indicated that the proposed method reaches a satisfactory performance, regardless of the CT parameters and within a wide range of analysed fault scenarios. Moreover, the method showed to be robust relative to the noise and effective in mitigating the errors due to the frequency offsets.