An Eight-Year Investigation of Lightning Currents and Preventive Lightning Protection on a Transmission System

1. The recording of lightning currents with surge-crest-ammeter links began in 1934. In the ensuing years through 1942, 5,501 bracket records have been obtained from transmission towers aggregating 13,227 tower-years of exposure. There have been 54 sets of records from lightning arresters, obtained during 155 bank-years of experience. 2. Based on an eight-year period of record in one case and a five-year period in the other, two similar 220-kv lines running in a generally north-south direction experienced the same average number of strokes per year within approximately seven per cent. Two similar 66-kv lines lying in an east-west direction experienced the same average number of strokes, within about three per cent, during a seven-year period. 3. A 132-kv line, having about the same span lengths as a 220-Kv line but lying in a more or less northwest-southeast direction within about two miles of a river throughout its length, experienced on the average about 40 per cent more strokes per unit length than the 220-kv line during an eight-year period. 4. The maximum number of strokes recorded on one of the transmission lines in one year was 4.9 times the minimum number recorded in another year. The maximum number on this line occurred in the same year that the minimum number occurred on a comparable line. 5. The strokes in single years to a line deviated up to 89 per cent from the seven- or eight-year averages.