PU_37
BLUC
BLOCK
PU_UC
I3P
OR
t
tUC
AND
a<b
a
b
ANSI09000780-1-en.vsd
ANSI09000780 V1 EN
Figure 70: Low current criterion logic diagram
Security logic for differential protection
The configuration for the additional security logic for differential protection is shown
in fig 71. The function will release tripping of the line differential protection up to the
end of timer tStUpReset.
Phase-phase
current variation
STCV
i
U
LOW
<
I
0
>
27 PU
Pick Up 3IO
PU_UC
OR
Local side start-up
Send signal to
remote side
Zero sequence
current criterion
Low voltage
criterion
Low current
criterion
ANSI10000296-1-en.vsd
I
0
<
REMSTEP
t
tStUpReset
BFI_3P
ANSI10000296 V1 EN
Figure 71: Additional security logic for differential protection. Logic diagram for
start up element.
1MRK505222-UUS C Section 5
Differential protection
169
Technical reference manual
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