Siemens SIPROTEC 7SS523 V3.2 Manual page 140

Functions
5.3.5.3 Circuit Breaker Failure Protection for Busbar Faults
124
The pulse mode is reserved for special applications. This operating mode may be
used if initiation of the CBF cannot be given by the corresponding feeder protection
(e.g. delayed fault recognition; feeder protection inoperative). In these specific cases
the CBF can be initiated by the protection at the remote end via a binary input
">CBF puls" (FNo. 7614/BU) of the bay unit.
The devices for transmission provide a signal (pulse) of variable duration. The mini-
mum signal duration of the binary input at the bay unit has to be 20 ms, the maximum
is 15 s. If the time monitoring of the impulse binary signal of the breaker failure protec-
tion picks up, the following alarm "BF BIImpErr $00" (FNo. 176.1104.xx) and the
general fault alarm "BF ImpBI errorM" (FNo. 10437) is issued by the central unit.
As soon as the delay time set with the parameter T-BF IMP (XX23A/CU) has elapsed,
a feeder-selective, three-pole TRIP command is issued. If the TRIP command does
not result in clearing the protection function, the second stage is started after a delay
time has elapsed. This delay time is set with the parameter T-BF-mP (XX21/CU).
Circuit Breaker failure can occur during a busbar short-circuit, too. In this case, the cur-
rent must be interrupted from the remote end (Figure 5-25, page 124).
The 7SS52 detects the breaker failure and allows a shorter tripping time by the trip sig-
nal sent to the opposite line end. If signal transmission equipment is used, the current
can be interrupted faster since signal transmission equipment trips the circuit breaker
at the remote end as soon as the delay time set with the parameter T-BF-mP (XX21/
CU) has elapsed.
On issuing a TRIP command, the currents are monitored in all feeders which are to be
tripped. If the current persists above the feeder-selective threshold set with the param-
eter I> BF (XX18/CU) after the delay time has elapsed, the corresponding bay unit
issues a transfer trip command (Figure 5-26, page 125).
Figure 5-25 Circuit breaker failure during a busbar fault
7SS52 V4 Manual
C53000-G1176-C182-1