Page 193 - 35_DS702_E_2014_Lightning_Protection_Guide

previous definitions of these safety distances d s/1 and d s/2 were k I w
often incorrectly assigned to LPZ 1 and LPZ 2. H = h f /max m in A/m
1/f /max
d s/1 Safety distance in case of a spatial shield of LPZ 1 if d w ( d r)
lightning current flows into this spatial shield (The
spatial shield of LPZ 1 produces a magnetic field. In ¨ Caused by the first negative stroke:
this case, no shielding factor can be assigned:
¨ Only in case of a direct lightning strike (S1) to the k I w
shield of LPZ 1.) H = h fn/max m in A/m
d s/2 Safety distance in case of spatial shields if no lightning 1/fn/max d w ( d r)
current flows into these spatial shields (the shielding
factor defines the attenuation of H n to H n+1 ):
¨ Caused by the subsequent strokes:
¨ Applies to all spatial shields of LPZ 1 or higher in
case of nearby lightning strikes (S2) k I w
or H = h s/max m in A/m
1/s/max
¨ Applies to all internal spatial shields of LPZ 2 or d w ( d r)
higher in case of direct lightning strikes (S1) or
nearby lightning strikes. where
Therefore, Germany suggested editorial changes for the future I f/max is the maximum value of the first positive stroke
revision of the EN 62305-4 lightning protection standard. The current in accordance with the LPL in A;
following new designations should be used in the future:
I fn/max is the maximum value of the first negative stroke
¨ d s/1 becomes d DF in case of direct lightning strikes to the current in accordance with the LPL in A;
shield of LPZ 1;
¨ d s/2 becomes d SF when using the shielding factor SF. I s/max is the maximum value of the subsequent stroke
currents in accordance with the LPL in A.
Consequently, the formulas for calculating the safety distances
must be adapted accordingly. Note: The magnetic field is reduced by a factor of 2 if a
meshed equipotential bonding network in accordance with 5.2
Calculation of the magnetic field strength in case of of the IEC 62305-4 (EN 62305-4) standard is installed.
a direct lightning strike
The magnetic field strength H 1 at a certain point in LPZ 1 is These values of the magnetic field are only valid in the safety
calculated as follows:
volume V s inside the grid-like shield with a safety distance d s/1
k I w from the shield (Figure 7.3.3):
H = h 0 m in A/m
1 w SF
d w ( d r) d = m
s/1 for SF 10 in m
10
where
d r is the shortest distance between the point considered d = w for SF < 10 in m
and the roof of the shielded LPZ 1 in m; s/1 m
d w is the shortest distance between the point considered where
and the wall of the shielded LPZ 1 in m;
SF is the shielding factor in dB determined using the
I 0 is the lightning current in LPZ 0 A in A; equations in Table 7.3.1;
—
k h is the configuration factor, typically k h = 0.01 in 1/√m; w m is the mesh size of the grid-like shield in m.
w m is the mesh size of the grid-like shield of LPZ 1 in m.
Note: Experimental results of the magnetic field inside a grid-
The result of this formula is the maximum value of the mag- like shield around LPZ 1 show that the magnetic field strength
netic field in LPZ 1 (observe notes 1 and 2): close to the shield is less than that resulting from the equa-
¨ Caused by the first positive stroke: tions above.

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