Field Investigations of Lightning

In the investigation described in this paper, measuerements have been made and statistical data obtained on the multiple character and wave shape of the currents in direct strokes and the currents discharged by lightning arresters. These data, in conjunction with other data on the field performance of arresters, have revealed definite differences between the nature of direct strokes and the currents they produce in arresters. 1. Arrester discharge currents have fewer components than found in direct strokes. Only about 30 per cent were found to be multiple and not over 8 components were recorded, while from 50 to 70 per cent of direct strokes were multiple with as many as 32 components recorded. 2. Components of arrester discharges are of lower crest magnitude. Only 30 per cent of those measured exceeded 1,000 amperes, while for direct strokes 50 per cent exceeded 5,000 amperes. 3. The initial high current portions of the components of arrester discharges do not vary greatly in wave shape and are similar to those of direct strokes, having for both types of discharges times to half value which, in general, lie between 25 and 100 microseconds and average about 50 micro- seconds. 4. The long duration low magnitude portions of direct strokes vary over wide limits, both in magnitude and duration. However, for arrester discharges they are seldom present to any appreciable degree.