A distributed transmission line model of cloud-to-ground lightning return stroke: Model verification, return stroke velocity, unmeasured currents and radiated fields

摘要

Among the various models for lightning return strokes (LRS) that exist, the lossy distributed transmission line (DLCR) model, it is shown herein, is a dependable, comprehensive and accurate model. The model contains inductance (L), capacitance (C), and the heat-loss resistance (R). Recently, many alternative models have been proposed, and the adequacy of the DLCR model (DLCRM) has been questioned because of some shortcomings in the previously reported DLCRM simulation results. This paper corrects some of these shortcomings, such as correct representation and computation of the LRS current pulse wavefront, and the special nature of the attachment point at the earth end. In this paper where the DLCRM model proposed is a self-consistent model, within the assumptions stated and justified, it is shown that the LRS velocity predicted by the DLCRM is about fifty to seventy percent less than the velocity of light (for example, c/3). The velocity determined from the DLCRM presented here agrees with the measured LRS velocity, and captures also the drop in velocity as the LRS moves away from the segments away from the ground. When considering both the physical principles and observations of the earth flash lightning return stroke (LRS), the DLCRM yields results that are consistent with lightning measurements. The DLCRM may be used to obtain important engineering parameters which are not easily measured; one such example is the very high rate of rise of currents on a submicrosecond timescale (for example, 98 kA/μs), whereas the microsecond rate of rise of current may be a tenth of the submicrosecond values. Relating the computed electric and magnetic fields radiated by the LRS currents obtained from the DLCRM shows the correlation between the LRS current waveforms and the electromagnetic field waveforms at different distances from the LRS channel. Moreover, for unbranched first and subsequent return strokes, the model’s electrical parameters such as inductance (L), capacitance (C) and resistance (R) values may be calculated from basic principles, with the assumptions made clearly defined and justified. Among the various models for lightning return strokes, the lossy transmission line model (the DLCRM) remains the most dependable when considering both the physical principles and measurements that provide a consistent and self-contained justification for the LCR model.