Observation and Analysis of Incident Surge Voltage Waveforms in Substations by Winter Lightning

This paper presents the observation results of surge waveforms in substations and the frequency components of such waveforms. In the Higashikanazu 77 kV power system, distribution transformers were damaged three times by winter lightning. In particular, almost the same parts were damaged at the No. 3 transformer in Katayamazu substation. To investigate the cause of the transformer failures, observation apparatus were installed at four substations in the Higashikanazu power system. Approximately 490 waveforms of incident surge were measured during the observed period. In 11 cases, simultaneous measurements of the incident surge waveforms at the four substations were achieved. By the analysis of the observed waveforms, the specific frequency components were found. From the investigation of theoretical and analytical approaches, it became clear that these frequency components depended on the power system configuration. By comparing the specific frequency components of the observed waveforms and the natural frequency components of the transformer, it was clearly shown that the overvoltages due to the internal resonance phenomena were the cause of failures. As a result, the internal resonance phenomena should be considered in the design of transformers, and the specific frequency components should be also estimated by the theoretical and analytical approaches