TABLE OF CONTENTS The physics and electrical engineering associated with the study of lightning and its impact on electrical equipment is a distinct technical field, with many workers contributing to the current state of knowledge. In the space available here it is only possible to introduce the reader to the subject in the context of EMC testing electronic equipment to withstand the large impulsive electrical transients which lightning creates.
This natural electrical phenomenon has been studied scientifically since Benjamin Franklin, who remarked in 1752 that 'the clouds of a thunder-gust are most commonly in a negative state of electricity, but sometimes are in a positive state'. The details of how the charge separation mechanisms operate and the complex microstruc-ture of lightning discharge formation are still being studied and argued over [47].
While the debate concerning the physics of the phenomenon has continued, it has been necessary to collect actual data on the nature of lightning strokes and their frequency of occurrence around the world such that protection against typical strikes can be engineered into equipments. These data have been analysed statistically to yield a nominal description of the lightning discharge event which has been used as the basis for a number of standards and specifications. One such is DEF STAN 00-35 which gives the standard description of the discharge as:
Risetime
average risetime = 2 ?s
value range = 1 10 ?s
Duration
average duration = 40 ?s
value range = 20 200 ?s
Peak...
