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For the analysis of back‐flashover phenomena of transmission lines, accurate evaluation of flashover occurrence at arcing horns is necessary. In this paper, parallel gap flashover phenomena are studied theoretically in the following conditions: (i) the gap lengths are different, and (ii) after one of the gaps flashes overs, there remains some residual voltage. The formulae for the occurrence probabilities of concurrent flashover on these conditions are introduced. Based on the analysis, application to the analysis of multiphase flashover is discussed. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Recently, very tall structures with heights more than several hundred meters have been constructed all over the world and observation of lightning has been made. The striking characteristics obtained from these observations are reviewed, and conventional and new shielding models are discussed. In addition, future themes of studies to be carried out are proposed. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Nine electric power companies in Japan have been collecting lightning data with lightning location systems. Five years of the lightning data (2009-2013) are summarized and analyzed in this paper. The recent annual number of lightning flashes of which the current is more than 10 kA in Japan is around 1 million. The variations of lightning occurrence characteristics by areas, seasons, and so on, are clarified. Meteorological conditions that may affect lightning occurrence are also discussed. Furthermore, we show that there is a clear correlation between the number of lightning strikes and the outage rate of transmission lines. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Application of Bayes' theorem for the evaluation of diagnostic results of electric facilities is described. A concept of risk assessment method based on the diagnosis results is proposed and the effects of various parameters on the risk are clarified. Based on these results, a rational renewal scheme using diagnostic results is proposed. In addition, the prior probability based on the data of actual facilities is investigated and it is found that the data available so far is insufficient and more data are required for the detailed analysis. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

The lightning occurrence characteristics around Tokyo Skytree are investigated with Japan Lightning Detection Network, and the results are evaluated with observation data by the Rogowski coils installed at a height of 497 m and by cameras set around Tokyo Skytree. After the construction of Tokyo Skytree, the apparent density of detected strokes near Tokyo Skytree increases, but without lightning strokes to Tokyo Skytree, the density of detected strokes around Tokyo Skytree seems to be roughly constant. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Concurrent flashover characteristics with three gaps in parallel are analyzed theoretically considering the statistical characteristics of time to flashover of a gap. The analysis shows that the concurrent flashover phenomena are likely to occur if the overvoltage ratio is large even if there are three gaps. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]