Current and electromagnetic field associated with lightning-return strokes to tall towers

An analysis of electric and magnetic fields radiated by lightning first and subsequent return strokes to tall towers is presented. The contributions of the various components of the fields, namely, static, induction, and radiation for the electric field, and induction and radiation for the magnetic field are illustrated and discussed. It is shown in particular that the presence of a tower tends, in general, to increase substantially the electric and magnetic field peaks and their derivatives. This increase is mainly caused by the presence of two oppositely propagating current wavefronts originating from the tower top and by the very high propagation velocity of current pulses within the tower, and depends essentially on the wavefront steepness of the channel-base current. Because of the last factor, the increase of the field magnitudes is found to be significantly higher for subsequent return strokes, which are characterized by much faster risetimes compared to first return strokes. The presented results are consistent with experimental observations of current in lightning strokes to the Toronto CN Tower and of the associated electric and magnetic fields measured 2 km away. These findings partially explain the fact that subsequent return strokes characterized by lower current peaks but higher front steepnesses and return stroke speeds may result in higher field peaks. The results obtained have important implications in electromagnetic (EM) compatibility. It is found that lightning strokes to tall metallic objects lead to increased EM field disturbances. Also, subsequent return strokes are to be considered an even more important source of EM interference than first return strokes. Indeed, EM fields from subsequent strokes are characterized by faster fronts and additionally, they may reach greater peaks than first strokes. Lastly, findings of this study emphasize the difficulty of extracting reliable lightning return stroke current information from remote EM field measurements using oversimplified formulae.

[1]  Vladimir A. Rakov,et al.  On the empirical formula of Willett et al. relating lightning return‐stroke peak current and peak electric field , 1992 .

[2]  Wasyl Janischewskyj,et al.  Electromagnetic field radiation model for lightning strokes to tall structures , 1996 .

[3]  Farhad Rachidi,et al.  Experimental validation of a modification to the Transmission Line model for LEMP calculation , 1989 .

[4]  Vladimir A. Rakov,et al.  Lightning subsequent-stroke electric field peak greater than the first stroke peak and multiple ground terminations , 1992 .

[5]  K. Berger.  Parameters of lightning flashes , 1975 .

[6]  R. H. Golde.  Lightning and tall structures , 1978 .

[7]  J. C. Willett,et al.  Submicrosecond intercomparison of radiation fields and currents in triggered lightning return strokes based on the transmission-line model , 1989 .

[8]  M. Ianoz,et al.  On lightning return stroke models for LEMP calculations , 1988 .

[9]  J. C. Willett,et al.  Submicrosecond field variations during the onset of first return strokes in cloud‐to‐ground lightning , 1996 .

[10]  M. Uman,et al.  The electromagnetic radiation from a finite antenna , 1975 .

[11]  M. Ianoz,et al.  Influence of a lossy ground on lightning-induced voltages on overhead lines , 1996 .

[12]  Farhad Rachidi,et al.  On the influence of elevated strike objects on directly measured and indirectly estimated lightning currents , 1998 .

[13]  Wasyl Janischewskyj,et al.  Statistics of lightning strikes to the Toronto Canadian National Tower (1978-1995) , 1997 .

[14]  Vladimir A. Rakov,et al.  Transient response of a tall object to lightning , 2001 .

[15]  Farhad Rachidi,et al.  Statistical analysis of magnetic fields due to CN Tower multistroke flashes , 1998 .

[16]  Wasyl Janischewskyj,et al.  Simultaneous measurement of lightning parameters for strokes to the Toronto Canadian National Tower , 1995 .

[17]  M. Ianoz,et al.  Modified Transmission Line model for LEMP calculations. Effect of the return stroke velocity decreasing and elevated strike object on close fields , 1992 .

[18]  Farhad Rachidi,et al.  Analyse du champ électromagnétique dû à une décharge de foudre dans les domaines temporel et fréquentiel , 1988 .

[19]  Kenneth L. Cummins,et al.  The U.S. National Lightning Detection NetworkTM and Applications of Cloud-to-Ground Lightning Data by Electric Power Utilities , 1998 .

[20]  Farhad Rachidi,et al.  Extension of two return stroke models to consider the influence of elevated strike objects on the lightning return stroke current and the radiated electromagnetic field: comparison with experimental results , 1996 .

[21]  Farhad Rachidi,et al.  On the Master, Uman, Lin, Standler and the Modified Transmission Line Lightning return stroke current models , 1990 .

[22]  C. Leteinturier,et al.  Current and electric field derivatives in triggered lightning return strokes , 1990 .

[23]  Vladimir A. Rakov,et al.  Review and evaluation of lightning return stroke models including some aspects of their application , 1998 .

[24]  Richard E. Orville,et al.  An experimental test of the 'transmission-line model' of electromagnetic radiation from triggered lightning return strokes , 1988 .

[25]  W. David Rust,et al.  Photoelectric return-stroke velocity and peak current estimates in natural and triggered lightning , 1989 .

[26]  Farhad Rachidi,et al.  Determination of lightning currents from far electromagnetic fields , 1993 .

[27]  Gerhard Diendorfer,et al.  An improved return stroke model with specified channel-base current , 1990 .