Page 10 - Planning_Lightning_Protection

DEHN Distance Tool:
Separation distances

Basic Version: Conventional calculation as per Distance Edition: Calculation according to nodal
IEC 62305-3 analysis
To prevent damage caused by lightning strikes, specific In the Basic Version of the DEHN Distance Tool software,
protection measures must be taken. Knowledge in the the separation distance is calculated with the help of an
field of lightning research allowed to constantly further Excel table. The Basic Version can be upgraded to the
develop the method of calculating the separation distance. Distance Version which allows to calculate the separation
The current IEC 62305-3 standard points out that distance by means of nodal analysis.
roof-mounted structures be located in the protected zone
using air-termination rods or elevated air-termination Nodal analysis is a method for network analysis used in
systems (elevated ring conductor or spanned cables). To electrical engineering. A constant earthing resistance is
this end, the calculated separation distance s must be kept. assumed for the calculation (type B earth electrode).
Nodal analysis provides more exact results than a conven-
The following general equation is used to calculate s: tional calculation according to the IEC 62305-3 standard.
k
c
s = k · · l (m)
i k
m
where
• k depends on the selected class of LPS
i
• k depends on the electrical insulation material
m Lightning Protection System
according to IEC 62305-3
• k depends on the (partial) lightning current flowing
c
through the air-termination systems and down
conductors

• l is the length along the air-termination system or air-termination system down-conductor system earth-termination system separation distances lightning equipotential bonding
down conductor from the point where the separation
distance is to be determined to the nearest equipoten-
tial bonding point or the earth-termination system.
The length l can be disregarded in structures with continu-
ous metal roofs acting as natural down conductor.

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