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Possible total current I max of the PV system = Operating current + reverse current tripping time of the

PV fuse depends on the
I N I reverse
available current
900 A 0.1 s
string 1 DC+ reverse
operating ... current
current string 10

string 1 DC-
... risk of arcing
string 10

generator junction box (GJB)

6.5 min

∞
100 A

PV fuse
100 % 75 % 50 % 25 % 25 % 50 % 75 % 100 %
125 A gPV
available solar energy (depending on the time of day)
Figure 9.19.7 PV system with I max of 1000 A: Prospective short-circuit current at the PV arrester depending on the time of day

(d.c. and a.c.), data and equipotential bonding conductors after some minutes (Figure 9.19.7). Therefore, surge protec-
must be routed together as far as practicable. tive devices installed in generator junction boxes must be de-
signed for the possible total current consisting of the operating
Surge protection measures for PV power plants current and the reverse current and ensure automatic discon-
Surge protective devices (SPDs) (Figure 9.19.6) must be in- nection without arcing in case of overload (I SCPV > I max of the
stalled to protect the electrical systems in PV power plants. PV system).
In case of a lightning strike to the external lightning protec-
tion system of a free field PV system, high voltage impulses
are induced on all electrical conductors and partial lightning
currents flow into all sort of park cables (d.c., a.c. and data ca- U [V]
bles). The magnitude of the partial lightning currents depends PV generator
on, for example, the type of earth-termination system, soil re- U OC U OC
sistivity on site and the type of cables. In case of power plants
with central inverters (Figure 9.19.6), extended d.c. cables
are routed in the field. Annex D of Supplement 5 of the Ger- U LB = f (i)
man DIN EN 62305-3 standard requires a minimum discharge operating
capacity I total of 10 kA (10/350 µs) for voltage-limiting type 1 conventional point
d.c. SPDs. d.c. source
SPDs with a sufficiently high short-circuit current rating I SCPV ,
which is determined by means of the EN 50539-11 standard I [A]
and must be specified by the manufacturer, must be used. This I SC
also applies with respect to possible reverse currents.
In PV systems with central inverters, fuses protect from reverse Figure 9.19.8 Source characteristic of a conventional d.c. source
versus the source characteristic of a PV generator.
currents. The maximum available current depends on the ac- When switching PV sources, the source characteristic
tual solar radiation. In certain operating states, fuses only trip of the PV generator crosses the arc voltage range.

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