ABB RED615 Product Manual page 10

Line Differential Protection and Control
RED615
Product version: 2.0
Figure 6. Line differential protection of an overhead line feeder using RED615 with the
standard configuration B. 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 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.
10
1MRS756500 B
Issued: 03.07.2009
ABB