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Observation of lightning current by using Rogowski coils started in February 2012 at Tokyo Skytree, which is a 634-m-high freestanding broadcasting tower. Electromagnetic field waveforms have been also observed by calibrated capacitive antennas at several tens of kilometers from the tower. Simultaneously observed lightning current and electric field waveforms are reproduced by using an electromagnetic model of a return stroke over lossy ground with the help of NEC-4. Lightning channel models with inclination are reconstructed from observed images. Consequently, it turns out that the electromagnetic field waveforms are affected by the geometrical shape of a lightning channel, current refractions in the tower, ground conductivity, and current wave velocity in the lightning channel. NEC-4 is quite useful for such analysis of lightning strokes hitting high structures. [ABSTRACT FROM AUTHOR]

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]