Siemens siprotec 7SA522 User Manual page 284

Functions
Stub Protection
6-136
A further overcurrent stage is the stub protection. It can however also be used as a
normal additional definite time overcurrent stage, as it functions independent of the
other stages.
A stub fault is a short-circuit located between the current transformer set and the line
isolator. It is of particular importance with the 1
6-79).
Busbar A
I
A
CBA
= I +I
I
k A
CBC
I
B
CBB
busbar B
Figure 6-79 Stub fault at an 1
If a short circuit current I
that a fault in the stub range between the current transformers I
lator exists. The circuit breakers CBA and CBC which carry short-circuit current may
be tripped without delay.The two sets of current transformers are connected in parallel
such that the current sum I
lator.
The stub protection is an overcurrent protection which is only in service when the state
of the line isolator indicates the open condition via a binary input "!,678% (1$%/(".
The binary input must therefore be operated via an auxiliary contact of the isolator. In
the case of a closed line isolator, the stub protection is out of service. In Figure 6-80
shows the logic diagram.
If the stub protection stage is to be used as a normal definite time overcurrent stage,
the binary input "!%/2&. ,678%", should be left without allocation or routing (ma-
trix). The enable input "!,678% (1$%/(", however, has to be constantly activated
(either via a binary input or via integrated logic (CFC) functions which can be config-
ured by the user.
1
/
2
B
line isolator 1
stub fault
line isolator 2
1
/ –circuit breaker arrangement
2
and/or I flows while the line isolator 1 is open, this implies
A B
+ I represents the current flowing towards the line iso-
A B
–circuit breaker arrangement (Figure
, I , and the line iso-
A B
C53000-G1176-C119-2
7SA522 Manual