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SPDs for Information Technology Systems
Cate- Type of Impulse Impulse Minimum quan- Test
gory test voltage current tity of impulses for
C1 0.5 kV or 0.25 kA or 300
1 kV, 1.2/50 μs 0.5 kA, 8/20 μs
C2 steep 2 kV, 4 kV, 1 kA, 2 kA 10
rate of or 10 kV, or 5 kA,
rise 1.2/50 μs 8/20 μs
C3 ≥ 1 kV, 10 A, 25 A 300
1 kV/μs or 100 A,
10/1000 μs
Surge arrester
D1 high ≥ 1 kV 0.5 kA, 1 kA 2
energy or 2.5 kA, *)
10/350 μs
General
The surge protection components of the arresters do not contain any
radioactive isotopes and consist of at least one voltage-limiting or voltage-switching
component and, in some cases, also of additional overcurrent-limiting
components. Multi-stage arresters must be designed without
blind spots. This means that it must be ensured that the different protection
stages are fully coordinated with one another. Otherwise the protection
stages will not reliably trip and cause faults in the protective
device.
Arrester selection
The following must be observed when selecting arresters:
– Protective effect [Yellow/Line SPD class (discharge capacity and voltage
protection level)]
– System parameters (system voltage, nominal current and transmission
parameters)
– Installations environment (design, connection conditions and approvals)
The selection guide according to interface/signal on pages 158 to 176
facilitates the selection of the right arrester.
Relevant product standard for arresters:
IEC / EN 61643-21
Low-voltage surge protective devices – Part 21: Surge protective devices
connected to telecommunications and signalling networks – Performance
requirements and testing methods
Discharge capacity
According to IEC / EN 61643-21 arresters must be tested with at least
one impulse voltage and impulse current from the above table with the
specified quantity of impulses. Further tests may be performed – even
with different impulse values or quantities. The max. voltage protection
level measured during the test(s) at the output of the device is specified
as voltage protection level U p . Category C represents particularly interference
pulses with a steep rate of rise and low energy, while interference
pulses of category D are supposed to simulate high energy loads
caused by injected partial lightning currents. The relevant category is
specified in the technical data of the arresters [see discharge capacity
(I n , I imp ) and voltage protection level (U p )].
*) Lightning current arrester / Combined lightning current and surge arrester
Voltage and current impulses (preferred values) for determining the voltage-limiting
characteristics (excerpt from Table 3 of IEC / EN 61643-21)
Immunity of terminal equipment to be protected
When testing arresters for electromagnetic compatibility (EMC), electrical
and electronic equipment (devices) must have a certain immunity
against conducted pulse interferences (surges). The requirements on the
immunity and the test set-up are described in EN 61000-4-5.
Since the devices are used in different electromagnetic environments,
they must have different immunities. The immunity of a device depends
on the test level. To classify the different immunities of terminal equipment,
test levels are subdivided into four different levels (1 to 4). Test
level 1 places the lowest requirement on the immunity of terminal equipment.
The test level is specified in the arrester documentation or can be
requested from the manufacturer of the arrester.
Test levels
according to EN 61000-4-5
Corresponds to charging voltage
of the test generator
1 0.5 kV
2 1 kV
3 2 kV
4 4 kV
Protective effect of arresters
Yellow/Line arresters for use in information technology systems are able
to limit conducted interference to a safe level so that the immunity of the
terminal equipment is not exceeded. For example, an arrester with a letthrough
value below the EMC test values of the terminal device must be
selected for a terminal device tested with test level 2:
Impulse voltage < 1 kV in combination with an impulse current of some
amperes (depending on the coupling network).
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