ABB RED615 Product Manual page 12

Line Differential Protection and Control
RED615
Product version: 4.0
In figure 6 selectivity of earth-fault protection is
ensured using binary signal transfer (BST)
between the directional E/F protection stages of
the local and remote end. The lowest directional E/
F stages are not used for tripping purposes, but
set to detect earth-faults in the reverse direction.
Upon detection of an out-of-zone earth-fault, a
blocking signal is sent to the remote end
directional E/F protection stage preventing
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tripping of the circuit breaker. If the earth-fault is
within the protected zone, no blocking signal will
be issued, and the internal fault is cleared by the
tripping stages of the directional E/F protection.
To ensure simultaneous tripping of the local and
remote end circuit breakers, BST is also used for
sending an intertrip signal to the remote end
during earth-fault situations within the protected
zone.
1MRS756500 F
ABB