Fronius IG Plus 35 - Criteria for the Proper Selection of String Fuses; General; Effects of Using Underrated Fuses; Fuse Recommendations - Application Example

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Criteria for the Proper Selection of String Fuses
Criteria for the
Proper Selec-
tion of String
Fuses
The following criteria must be fulfilled for each solar module string when
using fuse protection:
-I
N
> 1.5 x I
SC
-I
N
< 2.00 x I
SC
-U
N
>/= 600 V DC
- Fuse dimensions: Diameter 10.3 x 35 - 38 mm
I
N
Nominal current rating of fuse
I
SC
also STC, short circuit current for standard test conditions according
to solar module datasheet
U
N
Nominal voltage rating of fuse
Effects of
using underra-
ted fuses
In underrated fuses, the nominal current value is less than the short circuit
current of the solar module.
Effect:
The fuse may trip in intensive lighting conditions.
Fuse Recom-
mendations -
Application
Example
NOTE Only select fuses suitable for a voltage of 600 V DC.
e.g.: Maximum short circuit current (I
SC
) of the solar module = 5.75 A
According to the criteria for selecting the correct fuse, the fuse must have
a nominal current greater than 1.5 times the short circuit current:
5.75 A x 1.5 = 8.625 A
The fuse that should be selected according to the ‘Fuses’ table: KLK D 9
with 9.0 A and 600 V AC / DC
General The use of string fuses in the inverter also adds fuse protection to the
solar modules.
A crucial factor for the fuse protection of solar modules is the maximum
short circuit current (I
SC
or STC) of the respective solar module.