Electric field close to lightning channel in the presence of current reflections from the ground

The extended generalized traveling current source (extended GTCS) return stroke model with current reflections from the ground is used to explain the appearance of an overcompensated positive electric field in most vertical field measurements performed very close to the channel core. As suggested by experiments in triggered lightning conditions or in measurements of simulated return strokes in the laboratory we assumed that the ground reflection coefficient depends on the current magnitude. We separated the channel-base current into two components. The first current component is fast and with a greater peak value, while the second component is slower and with a lower peak. We analysed two return strokes with simultaneously measured channelbase currents and close electric waveforms. A new channel charging function is calculated according to the extended GTCS model, as well as the value of the ground reflection coefficient for the analysed strokes. On the other, the calculated values of the ground reflection coefficients confirm the results reported in other independent studies performed in natural or laboratory conditions. Finally, the concept of the extended GTCS model, that takes into account current pulse reflections from the ground, is proved to be correct. The obtained results can be used for lightning protection as well as for the insulation coordination in the power delivery.