Modelos para definição de ondas de corrente e tensão representativas das solicitações de sistemas de distribuição por descargas atmosféricas

Abstract

The perception that distribution system components could be subjected to voltage and current waveforms not specified by currently adopted standards has motivated studies dedicated to investigate the interaction of lightning with distribution networks. In this context, a new return-stroke model was developed. This model, called DNUTL model, represents the lightning channel as a non-uniform transmission line with time-varying parameters. Several analyses were performed aiming at identifying the influence of the spatial and temporal variation of both the channel resistance and capacitance on the return-stroke current, on associated electromagnetic fields and on lightning-induced voltages on overhead lines. The obtained results indicate that the DNUTL model is able to reproduce all features typically observed in lightning electromagnetic fields. With the application of the DNUTL model, it was also possible to confirm that, in certain conditions, simplified return-stroke models can be successfully applied in the calculation of lightning-induced voltages. Aiming at performing evaluations on complex network configurations including the effect of non-linearities, a methodology to calculate lightning-induced voltages in time domain applying the Alternative Transients Program (ATP) was proposed and implemented. This methodology adopts the coupling model of Taylor/Agrawal and allows the use of any return-stroke model to predict the incident electromagnetic field. In addition, models able to represent the behavior of system components when subjected to lightning surges were also implemented in the ATP platform. Some of them, like the transformer and insulator models, were found in the literature. Others, such as the simplified grounding model and the current waveforms dedicated to represent typical features of first and subsequent strokes measured at Morro do Cachimbo Station, were originally proposed in this thesis. With the aid of the implemented models, investigations were carried out in order to provide an estimate of the influence of several parameters on lightning surges developed in a typical distribution system. The obtained results, apart illustrating the effects of direct strikes and lightning-induced voltages on the evaluated system, contributed to characterize the performance of medium voltage surge arresters in terms of associated currents and energies. This allowed a preliminary assessment of the validity of waveforms recommended by currently adopted standards to evaluate the performance of protective devices in laboratory.