2 Functions
212
7SA522 Manual
C53000-G1176-C155-3
Figure 2-95 Stub fault at an 1
1
/
2
circuit breaker arrangement
If a short circuit current I
A
and/or I
B
flows while the line isolator 1 is open, this implies
that a fault in the stub range between the current transformers I
A
, I
B
, and the line iso-
lator exists. The circuit breakers CBA and CBC that carry the short-circuit current can
be tripped without delay. The two sets of current transformers are connected in parallel
such that the current sum I
A
+ I
B
represents the current flowing towards the line isola-
tor.
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$%/(µ. The binary input must therefore be operated via an auxiliary contact of the
isolator. In the case of a closed line isolator, the stub protection is out of service. For
more information see the next logic diagram.
If the stub protection stage is to be used as a normal definite time overcurrent stage,
the binary input ´!%/2&.,678%µ, should be left without allocation or routing (ma-
trix). The enable input ´!,678%(1$%/(µ, 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.
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