Estimation of the Equivalent Impedance of Lightning Return-Stroke Channel From Current Waveforms Measured at Tall Towers

• Published in: IEEE transactions on electromagnetic compatibility 2024-08, Vol.66 (4), p.1168-1175
• Main Authors: Hasegawa, Masahiro, Kutsuna, Koki, Baba, Yoshihiro, Nagaoka, Naoto, Tsuboi, Toshihiro, Rakov, Vladimir A.
• Format: Article
• Language: English
• Subjects: Channel estimation; Current measurement; Finite-difference time-domain (FDTD) method; Impedance; Lightning; lightning equivalent impedance; lightning return-stroke channel; lightning return-stroke current; lightning surge; Permeability; Poles and towers; tall tower; Voltage measurement
• ISSN: 0018-9375; 1558-187X
• DOI: 10.1109/TEMC.2024.3409719

Two waveforms of current measured at a height of 497 m of the 634 m high Tokyo Skytree and three waveforms of current measured at a height of 533 m of the 540-m high Ostankino tower have been reproduced in simulations using the finite-difference time-domain method in the two-dimensional cylindrical coordinate system. The lightning return-stroke channel is represented by a dielectric-coated vertical conductor. The dielectric coating has high relative permeability, such as 20, 40, or 60, and serves to reduce the propagation speed of current wave along the channel-representing vertical conductor and to increase its equivalent impedance relative to that of the vertical conductor without dielectric coating. The channel-representing vertical conductor and the tall tower are excited by a voltage source inserted between them. A procedure to determine the output waveform of the voltage source from measured current waveforms has been developed. The magnitudes of measured initial current peaks ranged from 5 to 12 kA. The equivalent impedance of the lightning return-stroke channel has been inferred to be roughly 800 to 900 Ω.