Page 25 - 35_DS702_E_2014_Lightning_Protection_Guide

Maximum values Minimum values
(dimensioning criteria) (dimensioning criteria)
Light- Light- Minimum Probability that the
ning pro- Maximum Probability that the ning pro- peak actual lightning
tection peak value of actual lightning current tection value current is greater Rolling
level the lightning is smaller than the level of the than the minimum sphere
current maximum peak value of lightning peak value of the radius
the lightning current
current lightning current
I 200 kA 99 % I 3 kA 99 % 20 m
II 150 kA 98 % II 5 kA 97 % 30 m
III 100 kA 95 % III 10 kA 91 % 45 m
IV 100 kA 95 % IV 16 kA 84 % 60 m
Table 2.7.1 Maximum lightning current parameter values and their Table 2.7.2 Minimum lightning current parameter values and their
probabilities probabilities

Tables 2.7.1 and 2.7.2 show the assignment of the lightning
protection levels to the maximum and minimum values of the Place of installation of the
high-current shunt of the
lightning current parameters.
research group ALDIS at the
top of the tower
2.8 Lightning current measurements
for upward and downward flashes Place of installation of the
Rogowski coils of the mobile
In general, it is assumed that downward flashes (cloud-to- detection system at the top
earth flashes) place a greater stress on objects hit by light- platform
ning than upward flashes (earth-to-cloud flashes), particularly
with regard to short strokes. In the majority of cases, down-
ward flashes are to be expected in flat terrain and near low
structures. If, however, structures are situated in an exposed
location and / or are very high, upward flashes typically occur.
The parameters defined in the lightning protection standards
generally apply to upward and downward flashes. In case of
upward flashes, especially the long stroke with or without su- Place of installation
perimposed impulse currents must be considered. of the data loggers
A more exact determination of the lightning current para meters and evaluation units
and their mutual dependence for upward and downward
flashes is in preparation. Therefore, lightning current measure-
ments for scientific fundamental research are performed on
different lightning measuring stations throughout the world.
Figure 2.8.1 shows the lightning measuring station oper-
ated by the Austrian research group ALDIS on the Gaisberg
mountain near Salzburg / Austria. Since 2007, DEHN has been
performing lightning current measurements on this measuring
station by means of a mobile lightning current detection unit.
The results of these comparison measurements basically con-
firm the lightning current parameters as described in the lat- Figure 2.8.1 Lightning current measurements by the Austrian lightning
est IEC 62305-1 (EN 62305-1) standard. The high number of research group ALDIS and DEHN at the ORS transmission
superimposed impulse currents in case of upward flashes is mast on top of the Gaisberg mountain near Salzburg

24 LIGHTNING PROTECTION GUIDE www.dehn-international.com