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equipotential surface

Figure 9.19.11 Surge protective device in a monitoring generator
junction box
Type 1 a.c. SPDs
Type 2 PV SPDs equipotential
and puts the entire unit into a safe state (Figure 9.19.10). surface
Thus, DEHNcombo YPV SCI … (FM), which is installed at the Partial lightning currents
inverter and in the generator junction box (GJB), reliably pro-
tects PV generators up to 1000 A without backup fuse (Figure Figure 9.19.12 Lightning current distribution in case of free field
PV systems with string inverter
9.19.11). DEHNcombo YPV SCI is available for 600 V, 1000 V
and 1500 V. If string monitoring systems are used, the float-
ing remote signalling contacts for condition monitoring of the potential bonding conductor between the local earth poten-
SPDs can be integrated in these monitoring systems. tial of the PV array hit by lightning and the remote equipo-
The combination of the numerous technologies integrated in tential surface of the infeed transformer. The only difference
the DEHNcombo YPV SCI combined arrester prevents damage from plants with central inverters is that in case of PV systems
to the surge protective device due to insulation faults in the PV with string inverters the partial lightning currents flow into
circuit, minimises the risk of fire of an overloaded arrester and the a.c. lines. Therefore, type 1 arresters are installed on the
puts the arrester in a safe electrical state without disrupting a.c. side of the string inverters and on the low-voltage side
the operation of the PV system. Thanks to the protective cir- of the infeed transformer. Table 9.19.1 shows the minimum
cuit, the voltage-limiting characteristic of varistors can now be discharge capacity of type 1 SPDs depending on the SPD tech-
fully used in the d.c. circuits of PV systems. In addition, the ar- nology. Type 2 SPDs such as DEHNcube YPV SCI are sufficient
rester minimises numerous small voltage peaks. Thus, the SCI for the d.c. side of string inverters. If an earth-termination sys-
technology increases the service life of the bypass diodes and tem according to Supplement 5 is installed, the string invert-
the d.c. inputs of the inverters. ers and the PV array connected to them form a local equipo-
tential surface so that it is not to be expected that lightning
PV power plants with decentralised string inverters currents are injected into the d.c. lines since the arresters limit
If PV power plants with decentralised string inverters are induced interference. They thus also protect the modules in
used, most of the power cables are installed on the a.c. side. close proximity from surges. Several a.c. outputs of these out-
The inverters are installed in the field underneath the module door inverters are collected and stored in a.c. boxes. If type
racks of the relevant solar generators. Due to the proximity to 1 arresters such as DEHNshield … 255 are installed there,
the modules, the inverter assumes typical functions of genera- these devices protect all inverter outputs up to a distance of
tor junction boxes. 10 m (conducted). Further a.c. field cables are routed into the
Supplement 5 of the German DIN EN 62305-3 standard de- operations building where the powerful type 1 and type 2
scribes that the lightning current distribution is influenced DEHNventil combined arrester protects the electrical equip-
by the power cables (string or central inverter). In addition ment for the grid connection point. Other equipment such
to Supplement 5, Figure 9.19.12 exemplarily shows the as the grid and plant protection, alarm panel or web server
lightning current distribution in case string inverters. If string which is located less than 10 m (conducted) from this SPD is
inverters are installed, the power cables are also used as equi- also protected.

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