Reverse Current Through Defective Modules - Steca Grid 20000 Installationsanleitung

EN
To keep the maximum current allowed of 25 A at the DC Circuit breaker contacts, observe the fol-
lowing input assignments. The power of the PV generator must be uniformly distributed over all
inputs. The maximum DC current at the input across all connections may not be exceeded.
Figure No. 4
3 PV connecting lines  inputs 1, 3 and 5 or inputs 2, 4 and 6
4 PV connecting lines  inputs 1, 3, 5 and 6 or inputs 2, 3, 5 and 6
If several PV connecting lines are available, the connections can be made as desired.

3.6 Reverse Current through Defective Modules

Reverse currents are fault currents that only occur in PV systems comprising parallel strings. Given
short circuits of individual modules or cells in a module, or a double ground fault, the open circuit
voltage of the string in question can drop (e.g. due to defective modules or parts of modules) so far
that the intact parallel strings will drive a reverse current through the defective string. This may
result in strong heating and therefore to a destruction of the string.
What is more, the reverse current may cause secondary damage.
To prevent such damage to PV systems, appropriate precautionary measures should be taken.
There are the following two cases:
1. The PV system is designed such that the reverse current which is flowing in case of a
failure and consists of the sum of the short-circuit currents of all intact strings in the
worst case does not result in the destruction of the damaged string and therefore in sec-
ondary damage either. The decisive factor here is the current carrying capacity of the
system components (connectors, lines) and the reverse current carrying capacity of the
modules. The appropriate data can be found in the manufacturer's data sheet. In this
case, it is not necessary to take any further measures.
2. The PV system is designed such that the reverse current flowing in case of a failure ex-
ceeds the destruction limit. In this case, each string must be separately protected by a
string fuse connected in series with the other string fuses. In case of a failure, this iso-
lates the string from the intact strings so that destruction is prevented.
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PV generator connector StecaGrid 20000 3ph and 23000 3ph
748.508 | Z01 | 2013-06-10