Functions
110
7SS52 V4 Manual
C53000-G1176-C182-3
Is< BZ - EF The parameter Is< BZ - EF (6108A/CU) is used to set the stabilizing current thresh-
old I
s
/I
no
for the bus zone-selective protection in the presence of a 1-pole earth fault
This parameter is only displayed if the parameter EF charact. (6320A/CU) is re-
leased.
The setting of the parameter Is< BZ - EF (6108A/CU) depends on the maximum
stabilizing current to be expected and on the behaviour of the CTs.
Is< BZ - EF = 1.2 * (I
max load
+ I
EF
)
I
max load
= sum of the values of all load currents flowing in and out
STAB FAC:CZ The parameter STAB FAC:CZ (6103/CU) is used to match the stabilizing factor for
the check zone to the service conditions. For single busbars, please refer to the setting
hints for the parameter STAB FAC:BZ (6101/CU).
For multiple busbars, a stabilizing factor of 0.5 is recommended. This helps to prevent
overstabilization due to the load currents of bus zones which are not involved in the
fault.
Id> CZ The parameter Id> CZ (6104/CU) is used to set the threshold for the sensitivity of
the check zone in the presence of small fault currents.
For pickup and tripping of the protection, only those normalized currents I
d
are consid-
ered which exceed the diff-current threshold set in the parameter Id> CZ (6104/CU).
A current below this threshold causes the pickup to drop off.
To calculate the highest permissible setting, determine first the smallest fault current
to be expected in case of a busbar short-circuit. The set value should have an extra
response margin of about 20%.
The smallest permissible setting is I
max feeder
+ 30%.
1.3 I
max feeder
< Id> CZ < 0.8 I
scc min
Id> CZ - EF The parameter Id> CZ - EF (6111A/CU) is used to set the diff-current threshold I
d
/
I
no
for the check zone measuring system in the presence of a 1-pole earth fault.
This parameter is only displayed if the parameter EF charact. (6320A/CU) is re-
leased.
Siemens recommends to set the parameter Id> CZ - EF (6111A/CU) to 70% of the
smallest 1-pole earth fault current to be expected.
Is< CZ - EF The parameter Is< CZ - EF (6110A/CU) is used to set the stabilizing current thresh-
old I
s
/I
no
for the check zone measuring system in the presence of a 1-pole earth fault.
This parameter is only displayed if the parameter EF charact.
(6320A/CU) is released.
Due to the special treatment of the stabilizing current of the check zone, the parameter
Is< CZ - EF (6110A/CU) is to be set to the value
Is< BZ - EF = 1.2 * 0.5 * I
max load
.
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