Lightning strokes in field and laboratory — III

LIGHTNING research is classified here for convenience into three main divisions. First, there are the meteorological and physical processes which give rise to the lightning stroke proper. Second, we have the characteristics of the lightning stroke as these appear at the point of incidence of the stroke to electric lines, to protective systems, and to earth. And third, comes that branch of the art connected with the development of these characteristics over electric circuits and their effects on electrical apparatus. This paper deals with the second division of lightning research. It is essentially a continuation of a previous report¹ and presents the results of investigations carried on particularly through 1937 to 1940. The first part of the paper covers data and findings which pertain to the long-duration low-current components of lightning. The relative frequency of occurrence of these long-duration components is discussed. From these studies, we find that the electric charge of lightning discharges ranges from a few to 200 coulombs. Higher values are not entirely precluded but they would be rare. The second part of the paper refers to the type of component characteristics for lightning-stroke discharge prevalent to earth and to electric systems (figure 20). The method of analysis in these investigations consists in comparing the physical effects on objects tested in the laboratory to the field data on similar objects that have been hit by lightning, such as lightning rods, ground wires, conductors of power and communication lines, coaxial cables, metal sheets, and other objects. The degree, nature, and amount of fusion on the metal is determined by ordinary measurements as well as by means of macrographs and micrographs of the objects affected.