The Influence of the Prestrike on Transmission-Line Lightning Performance

Abstract
1. The paper presents an analysis of the voltage-time and current-time relations to be expected on transmission lines based on the prestrike theory of the companion paper.1 2. The prestrike current is correlated with the AIEE2 return stroke current. The amplitudes of the two currents are found to be of the same order of magnitude. 3. The prestrike current waveform is influenced by the electric circuit characteristics of the stricken structure, and is found to have very high time rates of change as compared to the AIEE2 stroke current. 4. Calculated data on tower-top crest voltages and their durations are presented for a range of transmission-line design parameters. 5. The severity of the prestrike varies approximately as the square of the tower height, over the usual range of tower heights. 6. The prestrike theory predicts much higher tower-top potentials than the AIEE method, for equal stroke intensities and zero tower footing resistance. 7. Consideration of conclusions 5 and 6 in combination suggests that the poor lightning performance of some lines is due to the prestrike phenomena. 8. The presented data on prestrike waveforms are suggestive of the response required of recording devices to confirm this theory. 9. A calculation method was developed which permits the long-time analysis of numerous cases by digital computer procedures.

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