Investigation on the Sources of Reflection at the Junction of Tall Grounded Object and Lightning Channel

Validity of circuit‐based models for air‐cored helical windings at high‐frequency regimes

“…The numerical EM code (NEC) is a public domain software to evaluate the full‐wave solution in the frequency domain. Owing to the inaccuracies introduced during the inversion to the time domain [18], a direct time‐domain solution of the EFIE is highly desirable. A time‐domain methodology presented [24] uses quadratic interpolation function in time as well as space.…”

“…It may be noted here that any transmission‐line‐based model would impose a transverse EM (TEM) mode of propagation. As detailed in [18], to realise a TEM mode, the following conditions are to be fulfilled: (i) there should be two conductors (or a conductor and the ground) carrying equal and opposite charge (hence current); (ii) the separation distance between them should be much smaller than wavelengths of interest, except for a few selected cases; and (iii) applied excitation should support the TEM mode. The authors have shown the presence of non‐TEM modes (transverse magnetic mode specifically) during the propagation of fast rising currents as encountered in VFTO and PD [19].…”

Investigation on the Interaction of Secondary Current Pulses with the Main Wavefront

“…This approximation neglects the TM mode of current propagation on TGO and hence, the corresponding modification of reflection coefficients with the frequency contents of the current [31,33]. Nevertheless, it is still adequate for the intended task of ascertaining the dynamics at the main wavefront for the secondary current pulses.…”

“…The same was employed in the present work for an initial estimation. However, it is observed that for TM mode, the reflection can be a function of frequency components of the incident current [31,33] and therefore, use of actual current draws some merits. Hence, the analysis is repeated with injected secondary current whose temporal variation is set to follow For the analysis, a 2.5 km long monopole of 2.5 mm radius is considered.…”

“…These observations are in line with that reported in our earlier work [30] wherein a Gaussian excitation was employed. The quantification of this reflection is rather difficult due to: (i) reflection at the junction is frequency dependent [31,33] and (ii) the current wave propagates with attenuation and dispersion (which can be seen in Fig. 7).…”