Page 26 - Reliable_System_Solutions

radius = 45 m

S
3 (k m 1) +24.5 m top edge roof superstructure
mesh
L = 5 m h = 2.5 m
1
1
S
2 (k m 0.5) +22 m top edge of the roof
between roof S top edge of the roof
superstructure 1
and air-termination
rod
down-conductor
n = 4

15 m
17 m
building

Design procedure
Isolated air-termination systems for protecting roof

superstructures in consideration of standards concerning
the observance of separation distances

According to the state of the art of lightning protection systems, Building data Step 1:
large roof superstructures should be protected by isolated air- Building height: h = 22 m
termination systems in case of direct lightning strokes. Electrical Number of down-conductors: n = 4 units Determine the length of the aluminium air-termination rod
isolation of the lightning protection system from conductive ! Height of roof superstructure: h 1 = 2.5 m via the protective angle method or rolling sphere method.
parts of the building construction (metal construction parts, Class of LPS: III Step 2:
reinforcement, etc.) and isolation from electrical conductors in Building length: 17 m (maximum distance
the building prevent lightning currents from flowing through between down-conductors Calculate the separation distance to determine the position
control and supply lines as well as interference / destruction of c = 17 m) of the air-termination rod.
sensitive electrical and electronic installations. Building width: 15 m

In accordance with the current DIN EN 62305-3 standard, air- The roof superstructure is supposed to be protected by an
termination rods and/or elevated air-termination systems (ring Roof superstructure directly connected to the air-termination system!!! isolated air-termination rod.
conductors or spanned cables) should be installed taking the
calculated separation distance into account in order to protect 1. Calculation k c (building): 4. Comparison s 3 (k m 1)
roof superstructures on buildings against lightning strokes. between roof superstructure and
Three methods can be used for the determining the arrangement k c = 1 3 c
and position of air-termination systems: ! 2 • n + 0.1 + 0.2 • h air-termination rod (k 1):
m
– Rolling sphere method 1 3 17 s 3 (k m 1) = s’ 2 (L1) + s 1
– Protective angle method k c = 2 • 4 + 0.1 + 0.2 • 22 = 0.41
– Mesh method. 1
s’ 2 (L1) = 0.04 • • (5 + 2.5) = 0.60 m
0.5
The mesh size, the radius of the rolling sphere and the protective 2. Calculation of s top edge of the roof
1
angle depend on the class of LPS. The rolling sphere method as (side strike): s 3 (k m 1) = 0.60 m + 0.72 m = 0.66 m
universal design method should be used particularly for is not maintained!!! 2
geometrically complicated applications. A risk analysis in
accordance with DIN EN 62305-2 has to be carried out to s = k i • k c • L (m) with s
5. Comparison s 2 (k m 0.5) 3 (k m 1)
determine the class of LPS. When using the protective angle k m
method, the protective angle of an air-termination system s 2 (k m 0.5) = 1.12 m > s 3 (k m 1) = 0.66
depends on the selected class of LPS of the lightning protection s 1 = 0.04 • 0.41 • 22 = 0.72 m
system and the height of the air-termination system above the 0.5
area to be protected. 3. Calculation of s between roof Legend: n = total numer of down-conductors
2
superstructure and air-termination rod c = maximum distance between one down-conductor and the next
h = distance (or height) between ring conductors.
(k 0.5):
m
ok 1
s 2 (L1) = 0.04 • • 5 = 0.40 m
is maintained!!! 0.5
s
s 2 (k m 0.5) = s 1 s 2 (L1) 2 = 0.72 m + 0.40 m = 1.12 m Calculation programmes under www.dehn.de
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