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Voltage sags are one of major concerns in power quality, as they cause serious malfunction of a large number of apparatuses. There are a number of reasons for voltage sags in distribution networks: there is some evidence, however, that in electrical systems located in regions with high value of isokeraunic level, lightning can cause the majority of voltage sags. Data from lightning location systems, which provide an estimation of both lightning flash location and return-stroke current amplitude, can then be used to understand whether lightning is indeed the real cause of circuit breaker operation during thunderstorms-which means, in turn, of voltage sags-or not. Due to the complexity of the problem, the information coming from LLS (lighting location and estimate of lighting current amplitude) are, in general, not enough to infer the origin for voltage sags. It is necessary to suitably integrate them with data from system monitoring, e.g. relevant to the intervention of circuit breakers in primary substations, and with simulation results from of accurate models for computing lighting-induced voltages on complex power networks.