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DEHN – Safety according to Specification
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1a
1b
Fig. 3:
Direct/Close lightning strike:
Lightning strike into the external lightning
protection system, process framework
(in industrial installations), cables etc.
Voltage drop at the impulse earthing
resistance R st
Induced voltage in loops
(kA)
i
2c
100 kA
60 kA
50 kA
1a
R st
IT system
1b
1
L1
L2
L3
PEN
low voltage power
supply system
2a
20 kV
Causes of surges in case of lightning discharges
2
20 μs
200 μs
1
350 μs 600 μs 800 μs 1000 μs
t
2a
2b
2c
2b
Distant lightning strike:
Strike into medium voltage
overhead lines
Surge travelling waves on
overhead lines due to
cloud-to-cloud lightning
Fields of the lightning
channel
Wave form [μs] 10/350 8/20
imax [kA] 100 5
Q [As] 50 0.1
W/R [J/Ω] 6 2.5 10 3 0.4 10
Standard IEC 62305-1 EN 6100-4-5
Fig. 4:
1
Test impulse current for
2
Test impulse current for
lightning current arresters surge arresters
(μs)
To ensure permanent availability of complex power supply and
IT systems even in case of a direct lightning effect, further
surge protection measures for electrical and electronic installations
are necessary in addition to the lightning protection system
of a structure. Taking all causes of surges into consideration
is very important. For this purpose, the lightning protection
zones concept described in IEC 62305-4 is applied (Fig. 5).
A structure is subdivided into different risk zones. These zones
help to define the necessary protection measures, in particular
the lightning and surge protection devices and components.
Part of an EMC-conform lightning protection zones concept is
an external lightning protection system (including air-termination
system, down-conductor system, earthing), equipotential
bonding, spatial shielding and surge protection for the power
supply systems and IT systems. The lightning protection zones
have to be defined according to Table 1.
According to the requirements and loads at the place of installation
of surge protective devices, they are classified into lightning
current arresters, surge arresters and combined lightning
current and surge arresters.
The highest discharge capacity requirements are placed on
lightning current arresters and combined lightning current and
surge arresters used at the transition from lightning protection
zone 0 A to 1 or 0 A to 2.
These SPDs must be able to conduct partial lightning currents
(wave form 10/350 μs) several times without destruction in
order to prevent penetration of destructive partial lightning currents
into the electrical installation of a building.
At the transition from LPZ 0 B to 1 or downstream of the lightning
current arrester at the transition from LPZ 1 to 2 and higher,
surge arresters are used for protection against surges. Their
function is to further reduce both the residual loads of the
upstream protection stages and to limit the induced surges or
surges produced in the installation.
air termination system
ventilation
spatial shield
M
terminal device
The lightning and surge protective measures at the lightning
protection zone boundaries described above apply to both
power supply systems and IT systems to the same extent.
All measures described in the EMC-conform lightning protection
zones concept help to achieve permanent system availability
of a modern infrastructure.
downconductor
system
For more detailed technical information, we will be pleased to
send you our “Lightning Protection Guide”.
l.v. power
supply system
IT system
foundation earth electrode
steel reinforcement
Lightning equipotential bonding
Lightning current arrester (SPD Type 1)
Local equipotential bonding
Surge arrester (SPD Type 2, SPD Type 3)
Lightning equipotential bonding
Lightning current arrester
Local equipotential bonding
Surge arrester
Lightning electromagnetic
pulse
Switching electromagnetic
pulse
Lightning
protection zone
Fig. 5:
EMC-based lightning protection zones concept
www.dehn.de
LEMP protection of structures with electrical and electronic systems
according to IEC 62305-4
Lightning Protection Zone Description
LPZ 0 A Threat by direct lightning strokes, impulse currents up to complete lightning currents
and the entire lightning field.
LPZ 0 B Protected against direct lightning strokes. Threat by impulse currents up to partial
lightning currents and the entire lightning field.
LPZ 1
LPZ 2
Impulse currents are further limited by current distribution and SPDs situated at
the zone boundaries. The lightning field is mostly attenuated by spatial shielding.
Impulse currents are further limited by current distribution and SPDs situated at
the zone boundaries. The lightning field is mostly attenuated by spatial shielding.
Table 1: Definition of lightning protection zones (LPZ)
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