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Protected area
Area exposed strike
Electrogeometric lightning model/rolling sphere method
2. The protec-
tion methods, which are specified more detail in
IEC/EN 62305-3 and IEC/EN 62305-4, only offer ef-
fective protection against lightning strikes whose cur-
rent technical values are the area between the max-
imum and minimum peak current values defined by
the lightning protection class (see following table). Their reproducible effectiveness could not be
proven recognised scientific methods. Connecting discharges are launched
towards the tip the stepped leader from various
points such trees, houses and antennas.
The lightning current must intercepted and arrested
by the lightning protection system. The air-termination systems
provide optimal impact point and are connected to
the earthing system via the conductors.1. This ball will referred
to here the “rolling sphere”.
The rolling sphere rolls over the
building; everywhere makes con-
tact possible impact point for
the lightning. The radius the
rolling sphere depends the lightning protection
class the buildings that are protected. case direct
strike, the lightning protection system protects the
building against fire.
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59
Chapter The external lightning protection system
.
Other, theoretical models, which only allow small
areas with greater peak current values than named in
IEC/EN 62305-1, may not used for planning a
lightning protection system recognised the stand-
ard. The air-termination systems form protective
spaces, the necessary size which can determ-
ined using, for example, the “rolling sphere method”. For lightning
currents, this creates conductive path into the
ground. is
therefore necessary protect all points the sur-
face ball with the radius the striking distance,
and with the tip the stepped leader its centre,
against direct lightning strike.1 Rolling sphere method
Charge separation causes potential difference
between the clouds and the ground, producing a
stepped leader. the
point where the interception discharge first reached
by the tip the stepped leader, strike occurs.1.
The rolling sphere radius, together with the minimum
current peak values relative the appropriate light-
ning protection class, form the electrogeometric mod-
el (EGM), which the only physically recognised ba-
sic model for the creation lightning protection
concept according IEC/EN 62305-1
