Functions
2.8 Earth Fault Protection in Earthed Systems (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
219
Figure 2-104
Logic diagram of the 3
I
0
>>> stage
Definite time high set current stage 3
I
0
>>
The logic of the high-set current stage 3
I
0
>> is the same as that of the 3
I
0
>>> stage. In all references
3I0>>>
must merely be replaced with
3I0>>
. In all other respects Figure 2-104 applies.
Definite time overcurrent stage 3
I
0
>
The logic of the overcurrent stage 3
I
0
>, too, is the same as that of the 3
I
0
>>> stage. In all references
3I0>>>
must merely be replaced with
3I0>
. In all other respects Figure 2-104 applies. This stage operates with a spe-
cially optimized digital filter that completely suppresses all harmonic components beginning with the 2nd har-
monic. Therefore it is particularly suited for a highly-sensitive earth fault detection.
A fourth definite-time stage can be implemented by setting the „inverse-time“ stage (refer to the next paragraph)
to definite-time stage.