Protection against lightning overvoltages in resonant grounded power distribution networks

• Procedure for the estimation of the annual number of lightning events causing concomitant faults in more than one phase conductor of an overhead line.
• The procedure takes into account all the main factors that have a significant influence on line insulation flashovers.
• The calculation of the surges takes into account the effects of the utility frequency voltage.
• Several results obtained for both the case with and without protection means are presented and discussed.

AES Sul, a Brazilian electric distribution utility, has recently started a project focused on the installation of neutral resonant grounding devices at the medium voltage side of some substation transformers previously operated with solid grounded neutral. As a consequence of the expected increase of the voltage in the sound conductors during phase to ground faults, all the surge arresters must be replaced with ones with increased rating. In order to minimize the number of required surge arresters, a procedure has been developed for the estimation of the annual number of lightning events causing concomitant faults in more than one phase conductor. The paper describes the procedure, which takes into account all the main factors that have a significant influence on line insulation flashovers caused by lightning, and presents results obtained for the case of an overhead line with and without protection means.