Siemens SIPROTEC 7SS523 V3.2 Manual page 123

5.1.3.7 Transfer Busbar Protection With Inside Transformers
5.1.4 Setting Notes
STAB FAC:BZ
If the protection of the transfer busbar is impossible because of internal transformers
or not required for outside transformers, PROT TR BUS (5401/CU) is to be configured
with No. Then, only the Q7 on the bus coupler side is required to start the transfer op-
eration. With the Q7 installed, the protected zone ends at the last coupling transformer
(T1). All system components "behind" the last coupling transformer are now outside
the protected zone of the busbar protection. Therefore, the protected zone of the
check zone also has to be transferred into the coupler (T1).
The following figure shows the correction of the check zone with an unprotected trans-
fer busbar.
Figure 5-14 Transfer operation without transfer busbar protection
1) configured and detected
2) existing but not configured
The STAB FAC:BZ (6101/CU) is used to match the stabilizing factor for the bus zone-
selective protection (common for all buses) to the service conditions.
A high setting provides for more stability against faults outside the protection system
but reduces the sensitivity for detecting busbar faults.
The stabilizing factor should therefore be set as low as possible and as high as nec-
essary.
Two aspects are of major importance for selecting the stabilizing factor STAB FAC:BZ
(6101/CU):
• Type of current transformers: "lineared" or "iron-cored".
Iron-cored CTs transmit the DC component without any noticeable reduction,
whereas linearized transformers substantially reduce the DC component.
• The burdening factor K
This factor is calculated from the maximum continuous short-circuit current I
and the current I
sat
of the current transformers
b
at which CT saturation begins:
C53000-G1176-C182-1
Busbar Protection
7SS52 V4 Manual
scc max
107