Parameter Value Description
Plausibility check
The negative-sequence current serves only for the plausibility check of the
phase currents. The threshold for the negative-sequence current uses the
value set in the Threshold sensitive parameter.
Direct release
If a phase current exceeds 1/3 of the Threshold I2 dir. release, the
current-flow criterion can be satisfied just by the negative-sequence current
without the phase currents exceeding their set threshold value. The
threshold for the negative-sequence current uses the value set in the
Threshold I2 dir. release parameter in this case.
If you have set the Threshold phase current to be larger than the maximum usual load current, over-
function due to a false start is impossible. To have a Circuit-breaker failure protection function for smaller
unbalanced faults also with this setting, you can set the I2 criterion to Direct release and set the
Threshold 3I0 dir. release to be correspondingly smaller than the Threshold phase current.
Parameter: Threshold 3I0 dir. release
Recommended setting value (_:122)Threshold 3I0 dir. release = approx. 0.5 Isc
min
This parameter is effective only if the 3I0 criterion parameter is set to Direct release. Siemens
recommends setting the threshold to half the minimum short-circuit current (Isc
min
) to ensure that the discon-
nection of the fault is promptly detected and the function can drop out quickly.
Parameter: Threshold I2 dir. release
Recommended setting value (_:123)Threshold I2 dir. release = approx. 0.5 I2
min
This parameter is effective only if the I2 criterion parameter is set to Direct release. Siemens recom-
mends setting the threshold to half the permitted negative-sequence current (I2
min
) to achieve a fast fault
clearing in case of an undesired negative-sequence system component.
Parameter: Monit. time for BI ">Start"/Monit.tm. f.BI ">Release"
•
Default setting (_:124)Monit. time for BI ">Start" = 15 s
•
Default setting (_:125)Monit.tm. f.BI ">Release" = 15 s
With these parameters, you set the monitoring time of the binary inputs >Start/>Release. If the Circuit-
breaker failure protection function does not pick up during this monitoring time, a failure in the binary-input
circuit is assumed. Siemens recommends retaining the default setting of 15 s.
EXAMPLES
Applications which require you to permit the circuit-breaker auxiliary contact criterion:
•
Tripping of the high and low-voltage side CB on the transformer: If only one of the 2 CBs trips, there is no
more current flow.
•
Tripping of protection functions whose tripping decision is not based on current measurement in combi-
nation with low-load situations.
•
Injection of the tripping signal from Buchholz protection
Parameter: Dropout
•
Recommended setting value (_:104) Dropout = with effective criterion
The parameter Dropout is available if the circuit-breaker auxiliary contact criterion is permitted (see param-
eter CB aux.cont. crit. allowed).
Protection and Automation Functions
7.1 Circuit-Breaker Failure Protection
534 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017
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