Siemens Siprotec 7VK61 Manual page 127

Note
If the breaker failure protection is to perform a single-pole TRIP repetition, the time set for the AR, address
3408 T-Start MONITOR, has to be longer than the time set for address 3903 1p-RETRIP (T1) to prevent
3-pole coupling by the AR before T1 expires.
To prevent AR after „BF T2-TRIP(bus)", the time 3408 T-Start MONITOR can be set to expire together
with T2.
Figure 2-43
Single-stage breaker failure protection
With single-stage operation, the adjacent circuit breakers (i.e. the breakers of the busbar zone and, if applica-
ble, the breaker at the remote end) are tripped after a delay time T2 (address 3906) following initiation, should
the fault not have been cleared within this time.
The timers T1-1pole (address 3904) and T1-3pole (address 3905) are then set to ∞ since they are not
needed.
But you may use the T1 timers for single-stage protection if you wish to utilise the facility of setting different
delay times after single-pole trip and three-pole trip of the feeder protection. In this case set T1-1pole (ad-
dress 3904) and T1-3pole (address 3905) separately, but address 3903 1p-RETRIP (T1) to NO to avoid
a single-pole trip command to the busbar. Set T2 (address 3906) to ∞ or equal to T1-3pole (address 3905).
Be sure that the correct trip commands are assigned to the desired trip relay(s).
The delay time is determined from the maximum operating time of the feeder circuit breaker, the reset time of
the current detectors of the breaker failure protection, plus a safety margin which allows for any tolerance of
the delay timers. The time sequence is illustrated in Figure 2-44. The dropout time for sinusoidal currents is ≤
15 ms. If current transformer saturation is anticipated, the time should be set to 25 ms.
SIPROTEC, 7VK61, Manual
C53000-G1176-C159-3, Release date 05.2009
Time sequence example for normal clearance of a fault, and with circuit breaker failure, using
two-stage breaker failure protection
2.6 Circuit breaker failure protection (optional)
Functions
127