Page 361 - 35_DS702_E_2014_Lightning_Protection_Guide

I [kA]
total current
current flowing through the
type 1 arrester (spark gap)

current flowing
through the varistor
of the terminal equipment

reduction of the impulse time
“wave breaker function”
t [ms]

Figure 9.17.7 Spark-gap-based type 1 arrester (typical characteristic
curve)

I [kA]
total current
Figure 9.17.6 Prewired hybrid box for 48 V d.c. outdoor installa- current flowing through the
tions with DEHNguard type 2 arrester varistor of the terminal equipment
energy conversion
Customised solutions for 48 V d.c. remote radio in the type 2 arrester
heads / units (type 2 arresters)
Type 2 assembly systems as per IEC 61439-1 (EN 61439-1) /
IEC 61439-2 (EN 61439-2) are also used depending on the
protection philosophy of mobile network operators and current flowing through
system manufacturers, technical specifications and country- the type 1 arrester (MOV)
specific conditions. Varistor-based type 2 arresters with an
extremely low voltage protection level such as DEHNguard t [ms]
DG S 75 FM protect terminal equipment and are used for
RRH / RRU installations with a nominal voltage up to 48 V Figure 9.17.8 Varistor-based type 1 arrester (typical characteristic
curve)
d.c.
Figure 9.17.6 shows a prewired type 2 assembly sys-
tem in the form of a hybrid box (d.c. box) for indoor Comparison of the protective effect of spark-gap-
and outdoor installations. The lockable glass-fibre re- based type 1 arresters with that of varistor-based
inforced (GRP) enclosure with an IP 66 degree of pro- type 1 arresters
tection provides space for up to and including six Energy coordination with terminal equipment to be pro-
RRHs / RRUs. All incoming and outgoing lines up to tected is an important advantage of spark gaps used in type
48 V d.c. are wired on terminal blocks. This provides sig- 1 arresters (10/350 µs) over MOVs (metal oxide varistors).
nificant installation benefits for the installer, in particular
in case of mast installation and retrofitting. For data com- A so-called “wave breaker function” is achieved by the fast trig-
munication, the d.c. hybrid box houses up to 12 LC Duplex gering of the spark gap within a matter of microseconds, mean-
adapters that accept the prewired glass fibre cable from the ing that almost no current flows into the terminal equipment to
technical equipment room. These adapters are connected to be protected after the spark gap has ignited (Figure 9.17.7).
the RRHs / RRUs via so-called jumper cables by the most di- Thus, a relatively small amount of energy enters the terminal
rect path. Easy-to-install accessories such as wall and mast equipment even in case of extremely high impulse currents.
brackets with tensioning strap ensure easy and fast instal- This energy, however, is uncritical for the protective circuit in-
lation. tegrated in the input of the terminal equipment.

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