Parameter Value Description
w. 'CB pos. closed 3p.'
The auxiliary contacts are permitted as a further criterion in applications
(see the following examples) where the current is no reliable criterion for
determining the circuit-breaker position.
Parameter: 3I0 criterion
•
Recommended setting value (_:120) 3I0 criterion = Plausibility check
Parameter Value Description
Plausibility check
The ground current serves only for the plausibility check of the phase
currents. The threshold for the ground current uses the value set in the
Threshold sensitive parameter.
Direct release
The current-flow criterion can be satisfied only by the ground current
without the phase currents exceeding their set threshold value. The
threshold for the ground current uses the value set in the Threshold 3I0
dir. release parameter in this case.
If you have set the Threshold phase current to be larger than the maximum load current, overfunction
due to a false start is impossible. To have a Circuit-breaker failure protection for smaller ground faults also
with this setting, you can set the 3I0 criterion to Direct release and set the Threshold 3I0 dir.
release to be correspondingly smaller than the Threshold phase current.
Parameter: I2 criterion
•
Recommended setting value (_:121) I2 criterion = Plausibility check
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 load current, overfunction
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 parameter to half the permissible negative-sequence current (I2
min
) to achieve a fast fault
clearing in case of an undesired negative-sequence system component.
Protection and Automation Functions
6.41 Circuit-Breaker Failure Protection
SIPROTEC 5, Overcurrent Protection, Manual 847
C53000-G5040-C017-8, Edition 07.2017
To Next Page
Loading...
