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
Summary of Contents for 6MD85
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