Navegando por Autor "Leal, Mônica Maria"
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Artigo Improved traditional directional protection by using the stationary wavelet transform(Elsevier, 2018-08-09) Leal, Mônica Maria; Costa, Flávio Bezerra; Campos, João Tiago Loureiro SousaThis paper proposes a directional protection with phase, positive sequence, negative sequence, and zero sequence units by using the scaling coefficients of the real-time stationary wavelet transform (RT-SWT). As directional protection activators, the wavelet coefficients are used for fast detection of the fault inception time, whereas the scaling coefficients are used to provide backup activators in accordance with the overcurrent protection. Evaluations prove the feasibility to rebuild the traditional directional protection by using RT-SWT. However, the proposed wavelet-based directional protection provided better performance and faster operating time than the conventional one based on the discrete Fourier transform (DFT). As new functionalities, the wavelet-based negative sequence unit can be used to detect three-phase faults, even with severe voltage sags without memory strategies, which is not possible with the conventional protection. In addition, the proposed protection was implemented in hardware in order to demonstrate its practical feasibilityArtigo Mathematical development of the sampling frequency effects for improving the two-terminal traveling wave-based fault location(Elsevier, 2020-02) Costa, Flávio Bezerra; Lopes, F. V.; Silva, K. M.; Dantas, Karcius Marcelus Colaço; França, R. L. S.; Leal, Mônica Maria; Ribeiro, R. L. A.This paper presents a deep analysis of sampling frequency effects on the classical two-terminal traveling wavebased transmission line fault location method performance, demonstrating that these effects can be represented by well-defined regions (in the format of lozenges) in a time-space plane. Thereby, it is demonstrated that the classical method estimates the fault location in predefined points due to sampling frequency-associated time resolution. Furthermore, faults at the same location can be randomly estimated in different predefined locations depending on the fault inception time, resulting in location uncertainties. Nevertheless, the proposed time-space lozenges support a probabilistic analysis in order to consider the sampling frequency effects by adding a probabilistic search field component to the classical fault location formulation which indicates the region in which the fault took place with 100% of certainty regarding the sampling frequency effects. Therefore, this paper also proposes an improvement on the classical method by considering the effects of the sampling frequency. The proposed approach was evaluated by means of digital simulations and validated experimentally in laboratory by the application of faults along a 1 km long cableDissertação Proteção de sobrecorrente direcional utilizando transformada wavelet(2017-01-23) Leal, Mônica Maria; Costa, Flávio Bezerra; ; http://lattes.cnpq.br/7510091283933216; ; http://lattes.cnpq.br/5926057964306833; Lopes, Felipe Vigolvino; ; http://lattes.cnpq.br/3155646870666658; Oliveira Júnior, José Josemar de; ; http://lattes.cnpq.br/4263696954174963; Fernandes, Marcelo Augusto Costa; ; http://lattes.cnpq.br/3475337353676349; Ribeiro, Ricardo Lúcio de Araújo; ; http://lattes.cnpq.br/6628177274865696Tradicionalmente, a principal proteção utilizada nos sistemas elétricos de potência à nível de distribuição é a proteção de sobrecorrente, devido sua simplicidade e baixo custo. No entanto, com a recente inserção de geradores distribuídos no sistema, o sentido do fluxo de potência pode ser variado de acordo com o local de ocorrência da falta, sendo insuficiente, para algumas aplicações, avaliação apenas das amplitudes das correntes de falta. Então, um módulo direcional pode ser adicionado para fornecer informação do sentido de ocorrência da falta, se à frente ou reversa ao ponto de medição das correntes e tensões. Portanto, propõe-se nesta dissertação de mestrado a reconstrução das unidades de sobrecorrente direcional de fase, de sequência positiva, negativa e zero baseadas na transformada wavelet discreta redundante, com a qual é possível recriar as unidades de sobrecorrente clássicas por meio das energias dos coeficientes escala das correntes e as unidades direcionais clássicas por meio dos coeficientes escala das tensões e correntes, o que otimiza a proteção pois não conta com alguns inconvenientes provenientes da transformada de Fourier discreta. Para avaliação do método proposto, foi utilizando o sistema de 30 barras do IEEE com geração distribuída, assim como, o sistema de 230 kV do IEEE à parâmetros distribuídos.Tese Wavelet-based directional protection supported by a wavelet-based fault classifier(Universidade Federal do Rio Grande do Norte, 2020-08-10) Leal, Mônica Maria; Costa, Flávio Bezerra; ; ; Ribeiro, Ricardo Lúcio de Araújo; ; Lopes, Felipe Vigolvino; ; Vieira Júnior, José Carlos de Melo; ; Strunz, Kai;Fast and accurate protections are required to ensure the safety of the power system. In this research, a new directional protection based on wavelet transfom is described by using only the first wavelet decomposition level. The scaling coefficients are used in replacement of the Fourier transform in order to recreate the conventional directional protection. The torque equations were mathematically redefined in the wavelet domain by using sampled voltages and currents. Regarding the protection activation, the wavelet coefficients are used for fast detection of fault-induced transients (wavelet activators) in order to reduce the relay operating time, whereas the scaling coefficients are used for backup activation in accordance with the overcurrent protection (wavelet overcurrent activators). Evaluations have proved the feasibility to rebuild the conventional directional protection by using the real-time stationary wavelet transform (RT-SWT), which has provided better performance and faster operating time than the conventional protection based on the discrete Fourier transform (DFT). As new functionalities to the directional protection, the wavelet-based negative sequence unit can be used to identify the fault directionality to three-phase faults, even with severe voltage sags without memory strategies, which is not possible with the conventional protection. In addition, a real-time fault classification method using the real time boundary stationary wavelet transform (RT-BSWT) applied to modal components of the Clarke transform was developed to support the directional protection. The proposed classifier uses a simple threshold-based logic flow and requires three-phase current measurements from only one terminal. Furthermore, by using the wavelet coefficients energy of RT-BSWT, this classifier is fast and accurate due to the extraction of high-frequency components and the border effect. The fault classifier results have shown it is accurate and fast to identify all of the ten fault types successfully supporting the directional protection needs.