Setting Notes - Siemens SIPROTEC 7SS522 V4.6 Manual

Functions
5.1.4

Setting Notes

STAB FAC:BZ 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".
• The burdening factor K
108
Iron-cored CTs transmit the DC component without any noticeable reduction,
whereas linearized transformers substantially reduce the DC component.
b
This factor is calculated from the maximum continuous short-circuit current I
and the current I at which CT saturation begins:
sat
= I
K / I
b scc max sat
The saturation current I
sat
fective factor of the symmetrical rated short-circuit current K'
called operational overcurrent factor n')
I = I * K'
sat pn ssc
I = primary rated current
pn
The factor K' can be calculated from the data and the actual burden of the current
ssc
transformers:
K' = (R +R ) / (R +R'
ssc ct b ct
with R' = R + R
b l relay
R = secondary winding resistance (75 °C)
ct
R = resistive rated burden
b
R' = connected burden
b
R = line resistance
l
R = protection burden
relay
K' = factor of the symmetrical rated short-circuit current
ssc
For burden factors K < 2, a k-factor of 0.6 is sufficient. For K
b
k-factor is:
K
b
>
with K
-----------------------
k
4 K – 1
b
The setting value k thus obtained comprises 20 % safety.
The basis for this fomula is summarized in the Chapter A.2, page 341.
of the current transformers
can be calculated from the rated current I
) * K
b ssc
> 2
b
scc max
and the ef-
pn
(which used to be
ssc
> 2, the minimum
b
7SS52 V4 Manual
C53000-G1176-C182-3