Siemens SIPROTEC 7SS523 V3.2

Busbar Protection
109
7SS52 V4 Manual
C53000-G1176-C182-1
Id> BZ - EF The parameter Id> BZ - EF (6109A/CU) is used to set the diff-current threshold 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.
Where due to low infeed conditions or to the type of starpoint earthing earth fault cur-
rents do not exceed the normal load range, the threshold must be set to less than nom-
inal value. A separate characteristic is provided for such cases. It should be noted,
however, that with this setting the failure of one current transformer in combination
with a high load can lead to a trip of the busbar. Additional criteria are required in such
cases to ensure sufficient stability. Such a criterion may be, for instance, additional re-
lease by a feeder protection device through detection of the offset voltage.
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%.
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 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 load
+ 30%.
1.3 I
max load
< 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.