Siemens SIPROTEC 7SD80 Manual page 106

Functions
2.6 Circuit-Breaker Failure Protection 50BF
Figure 2-39 Logic diagram of the two-element circuit-breaker failure protection
Circuit-Breaker Malfunction
There may be cases when it is already obvious that the circuit breaker associated with a feeder protection relay
cannot clear a fault, e.g. when the tripping voltage or the tripping energy is not available.
In such a case it is not necessary to wait for the response of the feeder circuit breaker. If provision has been
made for the detection of such a condition (e.g. control voltage monitor or air pressure monitor), the monitor
alarm signal can be fed to the binary input „>52 faulty" of the 7SD80. On occurrence of this alarm and a
trip command by the feeder protection, a separate timer T3-BkrDefective, which is normally set to 0, is
started (Figure 2-40). Thus, the adjacent circuit breakers (bus-bar) are tripped immediately in case the feeder
circuit breaker is not operational.
Figure 2-40 Circuit-breaker faulty
Transfer Trip to the Remote End Circuit Breaker
The device has the facility to provide an additional intertrip signal to the circuit breaker at the remote line end
in the event that the local feeder circuit breaker fails. For this, a suitable protection signal transmission link is
required (e.g. via communication cable, power line carrier transmission, radio transmission, or optical fiber
transmission). With devices using digital transmission via protection interface, the remote commands can be
applied (see also Section 2.13).
To realize this intertrip, the desired command – usually the trip command which is intended to trip the adjacent
breakers — is assigned to a binary output of the device. The contact of this output triggers the transmission
device. When using digital signal transmission the command is connected to a remote command via the user-
defined logic (CFC).
106
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011