Current variation
subfunction
I3P
t
ANSI10000295-1-en.vsd
t
t
Pick Up VAB
Pick Up VBC
Pick Up VCA
STCV
OR
Time Delay CV
cont
cont
Time Delay CV
Time Delay CV
i
ANSI10000295 V1 EN
Figure 67: Current variation logic diagram
Time Delay CV is the time setting for the change of current criterion. Phase current
samples are included in input signal I3P.
Zero sequence current criterion
Zero sequence criterion is mainly for detection of remote IED high resistance faults or
some gradual faults. The criterion takes the zero sequence current as input. Zero
sequence current is compared with PU 3I0 for the t3I0 time to generate the zero
sequence current startup signal.
a>b
a
b
AND
PU 3I0
B
L
K
3
I
0
BLOCK
Pick Up 3I0
I3P
OR
t
t3I0
ANSI09000778-2-en.vsd
ANSI09000778 V2 EN
Figure 68: Zero sequence current criterion logic diagram
Here PU 3I0 is the setting of the maximum possible non-faulted zero sequence current
for the protected line. The default value for this setting is 0.1 · IBase where IBase is the
rated current of the CT.
t3I0 is the time setting for the zero sequence current criterion.
1MRK505222-UUS C Section 5
Differential protection
167
Technical reference manual
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