Tall-Structure Lightning Return-Stroke Models

从电气工程师的角度来看，回击是闪电中最重要的事件，因为它造成了电力和电信网络的大部分破坏和干扰。为了确定这些场，必须建立雷电回击（LRS）模型。同时测量雷电电流、伴随电磁场和雷电通道特性是定量评价雷电回击模型以及建立和评价新模型的必要条件。这种基于实验的验证和开发方法将增强我们对LRS过程的理解，有助于制定可更成功地用于闪电探测算法的模型，并允许开发更复杂的防雷措施。加拿大国家电视塔，以其极高的高度，提供了世界上进行这项调查的最佳选择之一。到1991年，有五个测量站同时运作，记录所有有关的闪电参数，包括塔上的回冲电流及其在塔以北2公里处产生的电磁场。在过去的几年里，加拿大国家电视塔及其附属的闪电通道一直由一系列级联的均匀传输线（TL）段来代表。在该模型中，考虑了连续增长的回冲程通道前方的电流反射。根据测量电流确定了CN塔三个主要结构不连续处的反射系数。通过比较应用特定LRS模型计算的电磁场与距离发射塔2公里处测量的电磁场，对该模型进行了定量评价。虽然这个比较验证了这个TL模型的优点，但使用均匀TL段显然是一个近似值，因为闪电电流路径的每一层（高架物体和通道）到地的距离是不同的。申请人计划将闪电电流路径建模为一系列非均匀传输线，每条传输线都有随高度变化的特征阻抗。

From the point of view of electrical engineers, the return stroke is the most important event in a lightning flash, as it causes most of the destruction and disturbance in electrical and telecommunication networks. In order to determine these fields, a lightning return-stroke (LRS) model must be constructed. Simultaneous measurement of the lightning current, its associated electromagnetic field, and lightning channel characteristics are necessary for the quantitative evaluation of lightning return-stroke models, and for the construction and evaluation of new models. This experimentally-based verification and development method will enhance our understanding of the LRS process, help in the formulation of models that can be used more successfully in lightning detection algorithms, and permit the development of more sophisticated measures for lightning protection. The CN Tower, with its extreme height, presents one of the best options in the world to carry out this investigation. By 1991, five measurement stations were in operation to simultaneously record all relevant lightning parameters, including the return-stroke current at the tower and its generated electromagnetic (EM) field 2 km north of the tower. Over the past several years, the CN Tower and the attached lightning channel have been represented by a series of cascaded uniform transmission line (TL) segments. In this model, current reflections at the front of the continuously growing return-stroke channel were taken into consideration. Reflection coefficients at CN Tower's three major structural discontinuities were determined from the measured current. A quantitative evaluation of this model was carried out by comparing the EM field, computed by applying a particular LRS model and that measured 2 km away from the tower. Although this comparison verified the merits of this TL model, the use of uniform TL segments is clearly an approximation since the distance to ground of each level of the lightning current path (the elevated object and the channel) is different. The applicant is planning to model the lightning current path as a series of non-uniform transmission lines, each having its characteristic impedance that varies with height.