Technical Application Papers No.10 Photovoltaic plants - ABB

The disconnection of the inverter must be possible both
on the DC side as well as on the AC side so that maintenance
is allowed by excluding both the supply sources
(grid and PV generator) (CEI 64-8/7).
On the DC side of the inverter a disconnecting device
shall be installed which can be switched under load,
such as a switch-disconnector. On the AC side a general
disconnecting device shall be provided. The protective
device installed at the point of connection with the grid
can be used; if this device is not close to the inverter, it is
advisable to position a disconnecting device immediately
on the load side of the inverter.
6.4 Protection against overvoltages
The PV installations, since they usually are outside the
buildings, may be subject to overvoltages of atmospheric
origin, both direct (lightning striking the structure) as well
as indirect (lightning falling near to the structure of the
building or affecting the energy or signaling lines entering
the structure) through resistive or inductive coupling.
The resistive coupling occurs when lightning strikes the
electrical line entering the building. The lightning current,
through the characteristic impedance of the line,
originates an overvoltage which may exceed the impulse
withstand voltage of the equipment, with consequent
damaging and fire hazard.
The inductive coupling occurs because the lightning
current is impulsive and therefore it generates in the surrounding
space an electromagnetic field highly variable.
As a consequence, the variation in the magnetic field
generates some overvoltages induced on the electric
circuits nearby.
In addition to the overvoltages of atmospheric origin,
the PV plant may be exposed to internal switching overvoltages.
6.4.1 Direct lightning
6.4.1.1 Building without LPS12 Generally, the erection of a PV plant does not change
the outline of a building and therefore the frequency of
the fulminations; therefore no specific measures against
the risk of fulmination are necessary (CEI Guide 82-25,
II ed.) (Figure 6.3).
12 Lightning Protection System: it is constituted by the protective systems both external
(detectors, lightning conductors and ground electrodes) as well as internal (protective
measures in order to reduce the electromagnetic effects of the lightning current entering
the structure to be protected).
Figure 6.3
On the contrary, in case the PV installation changes
significantly the outline of the building, it is necessary
to reconsider the frequency of fulminations on it and
consequently to take into consideration the necessity of
realizing an LPS (CEI Guide 82-25 II ed.) (Figure 6.4).
Figure 6.4
6.4.1.2 Building with LPS
In case of presence of a protection system against atmospheric
discharges13 , if the PV plant does not alter
the outline of the building and if the minimum distance d
between the PV plant and the LPS plant is higher than the
safety distance s (EN 62305-3) other additional measures
13 It is advisable that the protection grounding plant is connected to that for the protec-
tion against lightning.
Photovoltaic plants
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6 Protection against overcurrents and overvoltages