Siemens GPS1000 Radio Clock 2XV9450-1AR82 - Manual (Page 13)

User Manual SICLOCK GPS1000
Order numberr 2XV9450-1AR82-BA Version 2.0 13
4. Lightning Protection
When exterior antennas are used in industrial areas, a reliable lightning protection is of the utmost importance
for operating the system safely.
The installation of a lightning protection unit alone is not sufficient. The antenna and antenna cable must be in-
stalled in such a way that a direct stroke of lightning or flashover in these parts is not possible. Otherwise it
would not be possible to prevent the destruction of parts of the unit.
4.1. Lightning Theorie
Recordings made with high speed cameras have shown that lightning does not cover the distance between the
storm cloud and the point of striking at a continuous and constant speed but travels intermittently at intervals on
average of 20 to 40 meter in length. Between these lightning advancing distances there are holding points of a
few microseconds, where further energy is built up (see Fig. 6).
The possible locations of the subsequent holding points lie within a sphere (here called ball of lightning) around
the previous holding point with 20 to 40 meter radius. The last holding point is reached when parts of the earth’s
surface or other grounded parts extend into the ball of lightning. The lightning then strikes in the point of this
structure closest to the last holding point
Fig 6: The course of a lightning stroke