Transient surges: the largest voltage peaks in the low-voltage
consumer network are caused by lightning discharges. The high energy
content of lightning surges when a direct strike hits the external
lightning protection system or a low-voltage over-head line usually
causes - without internal lightning and surge protection - total
outage of the connected consumers and damage to the insulation. Yet
induced voltage peaks in building installations and energy or data
supply cables can also reach many times the nominal operating
voltage. Switching surges, too, which in fact do not cause such high
voltage peaks as lightning discharges but occur much more
frequently, can result in immediate system failure.
As a rule,
switching surges amount to two to three times the operating voltage,
lightning surges on the other hand can sometimes reach 20 times the
nominal voltage value and transport a high energy content. Often,
failures occur only after a time delay the aging process of
electronic components in the affected devices triggered by smaller
transients causes insidious damage. A number of different protection
measures are required. These depend on the exact cause and/or impact
point of the lightning discharge.
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Direct lightning strike into a building |
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Switching Surges in the Low-Voltage System
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if a lightning strike hits the external lightning protection
system or earthed roof structures capable of carrying lightning
current (e.g roof antenna), the lightning energy can be safely
diverted in advance to the ground potential. However, this has not
yet been done with a lightning protection system alone: due to its
impedance the building's entire earthing system is raised to a
high potential. This potential increase causes the lightning
current to be split over the building's earthing system and also
over the power supply systems and data cables to the adjacent
earthing systems (adjacent building, low-voltage transformer).
Threat value : up to 200 kA (10/350) potential.
Switching surges are caused by switch-on and switch-off
operations, by switching inductive and capacitive loads and by
interrupting short-circuit currents. Particularly when production
plants, lighting systems or transformers are switched off,
electrical equipment located in close proximity can be damaged.
Threat value : several kA (8/20) .
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Direct Lightning Strike into a Low Voltage
Overhead Line |
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Coupling of Surges Through Local or Remote Lightning
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A direct lightning strike into a low-voltage over-head line or
data cable can couple high partial lightning currents in an
adjacent building. Electrical equipment in buildings at the end of
the low-voltage over-head line are at particular risk of damage
caused by surges. Threat value : up to 100 kA(10/350)
Even if lightning protection and surge protection equipment is
installed, a local lightning strike creates additional high
magnetic fields, which in turn induce high voltage peaks in line
systems. Inductive of galvanic coupling can cause damage within a
radius of up to 2km around the lightning impact point. Threat
value: several kA (8/20)
