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xiv ABSTRACT The trend for interc01mection of the electrical systems and the necessity to offer better services to the consumers have increased. The systems have operated more close to the generation capability and transmission limits, therefore, close to the estability frontiers. Then, the implementation of the stability analysis with efficient computing methods has been one o f the main subjects searched in this area. The models used until then are simple and damping effects as frequency load dependency has been disregarded. Aiming to incorporate this dampings effects in the analysis, this work suggest a frequency dependent load model and shows the imp011ant influence of these damping effects in the criticai clearing time, specially in cases in which the system loses synchronism after the first swing. In order to implement this load model it is necessary to preserve the network structure and also to know the frequencies at the load buses. A program was developed following the Ruppe11 [5] proposal that permits the calculation of these frequencies in a way considered precise, however, this method shows itself too slow and reveals the requirement for faster methods. In this work a new, efficient and fast method to estimate the frequencies at the load buses is also proposed. The obtained results are encorageous, and the new method allows to determine the system frequency islands, extending the concept o f coherence, already known for generators, to load buses.The trend for interc01mection of the electrical systems and the necessity to offer better services to the consumers have increased. The systems have operated more close to the generation capability and transmission limits, therefore, close to the estability frontiers. Then, the implementation of the stability analysis with efficient computing methods has been one o f the main subjects searched in this area. The models used until then are simple and damping effects as frequency load dependency has been disregarded. Aiming to incorporate this dampings effects in the analysis, this work suggest a frequency dependent load model and shows the imp011ant influence of these damping effects in the criticai clearing time, specially in cases in which the system loses synchronism after the first swing. In order to implement this load model it is necessary to preserve the network structure and also to know the frequencies at the load buses. A program was developed following the Ruppe11 [5] proposal that permits the calculation of these frequencies in a way considered precise, however, this method shows itself too slow and reveals the requirement for faster methods. In this work a new, efficient and fast method to estimate the frequencies at the load buses is also proposed. The obtained results are encorageous, and the new method allows to determine the system frequency islands, extending the concept o f coherence, already known for generators, to load buses.

Ilhas de frequência e efeitos de amortecimento provocado por cargas dependentes da frequência em estabilidade transitória