Abstract :
C. M. Foust (General Electric Company, Schenectady, N. Y.): Mr. Bell has called attention to the fact that when incoming currents at the tower tip are added, the sum is usually greater than outgoing currents. These incoming currents flow in along the ground wires and up through the tower structure. The outgoing currents under consideration are usually those flowing up through the lightning rod. An explanation which seems reasonable to account for the differences has to do with multiple strokes. Multiple-discharge lightning strokes have been recorded many times by various investigators using both oscillographic and photographic methods and the general understanding now is that about 25 per cent of all cloud-to-ground strokes are of the multiple-discharge nature. While it has not been demonstrated experimentally, still it is reasonable to assume that each discharge of a multiple-discharge stroke is associated with the discharge of a particular cloud area. Particular cloud areas are located in different positions as regards the transmission line and the point of contact of the lightning stroke. Assuming that a first discharge gives overhead ground wire and ground currents flowing into the tip of the lightning rod from one direction, and that another discharge because of the different location of the cloud area participating gives overhead ground wire and ground currents flowing in from the opposite direction, it is obvious that the two in-flowing discharge currents will not be simultaneous. In such a case the magnetic links on the lightning rod will record only the maximum value of current which will not be the sum of the in-flowing currents.
