Determination of lightning currents from far electromagnetic fields: Effect of a strike object

• Published in: Journal of electrostatics Vol. 65; no. 5; pp. 289 - 295
• Main Authors: Bermudez, J.L., Rachidi, F., Janischewskyj, W., Shostak, V., Rubinstein, M., Pavanello, D., Hussein, A.M., Chang, J.S., Paolone, M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2007
• Subjects: Electromagnetic fields; Lightning; Return stroke current; Return stroke models; Strike object; Tall towers; Return stroke current; Return stroke models; Tall towers; Electromagnetic fields; Lightning; Strike object
• ISSN: 0304-3886; 1873-5738
• DOI: 10.1016/j.elstat.2006.09.007

We discuss in this paper the influence of the presence of an elevated strike object on the peak of the lightning return stroke current determined from remote field measurements. We develop analytical expressions relating the lightning return stroke channel-base current and the far electromagnetic field for different specific cases, namely, (1) ground-initiated return strokes (classical transmission line (TL) model), (2) ground-initiated return strokes including possible reflections at ground level, (3) tall strike objects for which the current's zero-to-peak time is smaller than the travel time along the object, and (4) electrically short strike objects. It is shown that for tall structures, the field enhancement relative to a return stroke initiated at ground level is expressed through a factor equal to k tall = [ 1 + c / v ( 1 - 2 ρ t ) ] / ( 1 - ρ t ) , where v and c are the return stroke front speed and the speed of light in vacuum, respectively, and ρ t is the top reflection coefficient. For very short towers and/or very slow return stroke current wavefronts, when the condition t f ⪢ h / c applies, expressions relating the far electromagnetic field and the return stroke current were also derived. For case (2), return strokes initiated at ground level, the field enhancement relative to a return stroke initiated at ground level, case (1), is expressed through a factor equal to k short = ( 1 + ( c / v ) ρ ch – g ) / ( 1 + ρ ch – g ) , where ρ ch–g represents the reflection coefficient between the lightning channel and the grounding impedance.