2.8 Earth Fault Protection in Earthed Systems (optional)
209
7SD5 Manual
C53000-G1176-C169-1
Figure 2-88
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 2-88 applies.
Definite Time Over-
current Stage 3
I
0
>
The logic of the high set current 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 re-
spects Figure 2-88 applies. This stage operates with a specially optimized digital filter
that completely suppresses all harmonic components beginning with the 2nd harmon-
ic. 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 a definite-time stage.
Inverse Time Over-
current Stage 3
I
0P
The logic of the stages with inverse time delay functions in the same way as the re-
maining stages. This stage operates with a specially optimized digital filter that com-
pletely suppresses all harmonic components beginning with the 2nd harmonic. There-
fore it is particularly suited for a highly-sensitive earth fault detection. However, the
time delay is calculated here based on the type of the set characteristic, the intensity
www
. ElectricalPartManuals
. com
