Functions
6-145
7SA522 Manual
C53000-G1176-C119-2
Stub Protection
When using the I STUB protection the pick-up thresholds
(address
)
and
(address
) are usually not critical, as this protection function is
only activated when the line isolator is open which implies that every measured current
should represents a fault current. With a 1
1
/
2
–circuit breaker arrangement similar to
Figure 6-79 it is possible that large short circuit currents flow from busbar A to busbar
B or to feeder 2 via the current transformers. These currents could cause different
transformation errors in the two current transformer sets
I
A
and
I
B
, especially in the
saturation range. The protection should therefore not be set unnecessarily sensitive.
If the minimum short circuit currents on the busbars are known, the pick-up threshold
is set somewhat (approx. 10 %) below the minimum two phase short cir-
cuit current,
is set below the minimum single-phase current.
The time settings
(address
(address
) are
set to
∞
for this application, to prevent the protection from operating while the line iso-
lator is closed. They may however also be used to implement an independent back-
up stage.
If this stage is applied differently, similar considerations as for the other overcurrent
stages apply.
The parameter
(address
) determines whether the delay
times
(address
) and
(address
) can be
bypassed via a binary input „
!2&,QVW75,3
“. The binary input (if allocated) is
applied to all stages of the time-overcurrent protection. With
=
<(6
you can set the
,6WXE
-stages to trip immediately after the pick-up, only if the
binary input is activated. Set time delays for
12
are always ac-
tivated.
If the
,6WXE
-stage is to trip when switching the line on to a fault with or without a
short delay,
, see above and refer to Sub-section
“General”), the parameter
(address
) is set to
<(6
. If using the
stub protection, then set to
12
as the effect of this protection function only depends on
the position of the isolator.
Summary of Contents for siprotec 7SA522
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Page 89: ...SIPROTEC 4 Devices 4 25 7SA522 Manual C53000 G1176 C119 2 Figure 4 20 CFC Logic example ...
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Page 620: ...Appendix B 48 ...
