It is important for electric power companies to maintain grounding resistances adequately for the safety of the public. But they have difficulty in managing those grounding systems because vast amounts of grounding electrodes are installed in distribution lines. Based on the statistical data of surge currents through lightning arrestors and electrical surges in customers, a rated value of the grounding resistance for lightning arrestors on distribution lines was specified in the 1960's. TEPCO had conducted field research to measure the waveforms of surge voltage and current in order to rationalize the lightning protection design of distribution lines. And the authors proposed a lightning-surges analysis model based on the observation data. In this study, a lightning surge analysis for the rationalization of the grounding system was carried out by means of the EMTP. The calculated results suggest that a practical grounding design is possible. That can be useful for the Electric Power Companies to manage grounding systems.
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