Datasheet

II-2015, www.findernet.com
26
E
7P SERIES
Surge Protection Device (SPD)
7P
SERIES
PROTECTING PHOTOVOLTAIC (PV) SYSTEMS AGAINST LIGHTNING
Installation characteristics
[U
OCSTC
] PV voltage: Open circuit voltage, measured under standardized
test conditions, of the PV module, panel, array, or the DC side of the
photovoltaic inverter. prEN50539-12.
[I
SCSTC
]: Short-circuit current: Short-circuit current, measured under
standardized test conditions, of the PV module, panel, array, or photovoltaic
inverter. prEN50539-12.
[U
CPV
] SPD Maximum continuous operating voltage: Must be equal
or greater than to 1.2 times U
OCSTC
in all conditions of radiation and
temperature. prEN50539-11, prEN50539-12.
[I
SCPV
]: Maximum prospective short-circuit current from the power system
for which the SPD, in conjunction with the disconnectors specified, is
rated. EN50539-11.
System installation
Photovoltaic systems are generally located external to a building and can
be subjected to the direct or indirect effects of lightning.
Whilst the installation of photovoltaic panels on the roof does not, in
itself, increase the risk of direct lightning, the only practical way to protect
against the effects of a direct lightning strike would be the use of a
lightning protection system (LPS).
The indirect effects of lightning can however, be mitigated by the
appropriate use of Surge Protection Devices (SPD). These indirect effects
occur when lightning strikes in proximity to the structure and where
magnetic induction creates an overvoltage in the conductors – a danger
to both people and equipment. In particular, the DC cables of a PV system
would be exposed to the high conducted and radiated disturbances
caused as a result of the lightning currents. In addition, overvoltages in PV
systems are not only of atmospheric origin. It is also necessary to consider
overvoltages due to switching on electrical networks connected to them.
These overvoltages can also damage both the inverter and the PV panels,
and this explains the need to protect the inverter on both DC and AC sides.
Photovoltaic system on a building without a lightning protection
system (LPS)
As an example, Figure 10 represents a simplified photovoltaic system
placed on a building without lightning rod. In such a system, the protection
against lightning must be considered at the following points of installation:
- DC input of the inverter
- AC output of the inverter
- Low voltage supply network
At the DC input to the inverter SPDs specific for photovoltaic systems must
be installed, according to the PV system voltage. At the inverter AC output,
type 2 surge arresters must be installed suitable for the type of system.
At the point of connection to the LV supply network, install type 2 surge
arresters suitable to the type of system (TT, TN). In more complex systems,
it might be necessary to introduce additional SPDs. DC side: if the distance
between the inverter and PV modules exceeds 10 m, it is necessary to
replicate and install the SPD as close as possible to the PV modules.
Figure 10: Example of a photovoltaic system located on a building without
LPS, protected on the DC side by an SPD with U
OCSTC
=420V, and on
the AC side by a 7P.22, specific for TT systems.
Photovoltaic system on a building with a lightning protection system
(LPS)
Where an LPS exists it is good practice to install the photovoltaic panels in
the area protected by the lightning rod.
In addition it is necessary to realize a good equipotential bonding system,
which must be positioned as close as possible to the entry point of LV
supply into the structure. The LPS, the SPD and all metal parts have to be
connected to this equipotential system.
SPD protection on the DC depends on the safety distance (referred in
EN50539-12:12-2012).
Note that under EN62305 installation of a Type 1 SPD is mandatory at the
point of delivery of the AC electricity supply, whether or not the building
has LPS (with or without solar panels).