Siemens SIPROTEC 7SD80 Manual page 109

Figure 2-43 Time sequence example for normal clearance of a fault, and with circuit-breaker failure, using
two-element breaker failure protection
Single-element Breaker Failure Protection
In single-element breaker failure protection, the adjacent circuit breakers, i.e. the breakers of the busbar or the
busbar section affected, and where applicable also the breaker at the remote end, are tripped after the time
delay 50BF-2 Delay (address 3906) has elapsed.
The time 50BF-1 Delay 3p (address 3905) is set to ∞ because it is not needed.
The time delay to be set should be based on the maximum circuit-breaker operating time plus the dropout time
of the current flow monitoring element plus a safety margin which takes into consideration the tolerance of the
time delay. Figure 2-44 illustrates the time sequences in an example. The dropout time for sinusoidal currents
is ≤ 15 ms. If current transformer saturation is anticipated, the time should be set to 25 ms.
Figure 2-44 Time sequence example for normal clearance of a fault, and with circuit-breaker failure, using
single-element breaker failure protection
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
2.6 Circuit-Breaker Failure Protection 50BF
Functions
109