Cálculo de sobretensões causadas por descargas atmosféricas indiretas em linhas de distribuição aéreas considerando falhas de isolamento

Abstract

In this work it is evaluated the effect of lightning-induced voltages on a singlephase overhead line considering flashovers. For calculating lightning-induced voltages, a direct time-domain approach was used in which the ground was assumed as a perfect conductor. The coupling of the incident lightning electromagnetic fields with the illuminated line was made with Agrawals model. The model was implemented in theMODELS routine available in ATP (Alternative Transients Program) using a formulation based on the method of characteristics. To evaluate the occurrence of flashovers caused by lightning-induced overvoltages on overhead lines, an insulator model based on the integration method wasimplemented in ATP. Three different methodologies were tested to determine the parameters to be used in this model: one based on the solution of non-linear equations using Newtons method, other based on the minimum variance method proposed by Ancajima et al., and finally a third methodology based on Hilemans approach. The three methods above were tested and validated through comparisons with V-t curvesobtained from laboratory tests with distribution line insulators. It was also considered in the analyses the simplified method proposed by the IEEE to estimate the flashover rate of overhead distribution lines due to lightning-induced overvoltages. Finally, to evaluate the effect of lightning-induced voltages considering flashovers, an actual single-phase, medium-voltage distribution line containing transformers, surge arresters, and consumer loads was implemented. Sensitivityanalyses were performed to evaluate the effect of different parameters on the resulting overvoltages, namely the lightning current waveform, the insulator model, the stroke location, the front time of the lightning current, and the effect of surge arresters. The obtained results indicate the importance of considering adequate insulator models to evaluate lightning-induced voltages on distribution lines.