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Total Solution to Earthing & Lightning Protection |
9AKK106354A3360
10
Electronic systems protection
Introduction
Lightning currents as a result of direct lightning strikes
are represented by the simulated 10/350 μs waveform
with a fast rise time and long decay that replicates the
high energy content of direct lightning.
Direct lightning can inject partial lightning currents of the
10/350 μs waveform into a system where a structure with a
structural Lightning Protection System (LPS) receives a direct
strike (Source S1) or where lightning directly strikes an
overhead service line (Source S3).
Remote or indirect lightning flashes near the structure
(Source S2) or near a connected service to the structure
(Source S4) of up to 1 km radius away (and hence far more
common) are represented by the 8/20 μs waveform. Induced
surges from direct lightning flashes and switching sources are
also represented by this waveform.
With a much shorter decay or fall time relative to the 10/350 μs
waveform, the 8/20 μs waveform presents significantly less
energy (for an equivalent peak current) but is still devastating
enough to damage electrical and electronic equipment.
IEC/BS EN 62305-1 recognizes that failure of internal
systems (Damage Type D3) due to Lightning Electromagnetic
Impulse (LEMP) is possible from all points of strike to the
structure or service - direct or indirect (all Sources: S1, S2,
S3 and S4).
To ensure continuous operation of critical systems even in the
event of a direct strike, SPDs are essential and are suitably
deployed, based on the source of surge and its intensity using
the Lightning Protection Zones (LPZ) concept within
IEC/BS EN 62305-4.
1 Illustration of lightning current flow from a direct strike to a structure (Source S1) | 2 Illustration of lightning current flow from a direct strike to a nearby
service (Source S3) | 3 Illustration of lightning current flow from a direct strike near the structure (Source S2) | 4 Illustration of lightning current flow from
lightning flashes near connected services (Source S4)
1
2
3
4
Damped current
waveshape
(8/20 µs)
Ground Level
Structural
LPS
10/350 µs
surge current
(
I
imp
)
Ground Level
8/20 µs
surge
current
Ground
Level
Induced Surges/
Overvoltages
8/20 µs surge current Strike up to 1 km away
8/20 µs
Ground Level
10/350 µs
surge current
(
I
imp
)
(
I
imp
)
2
(
I
imp
)
2