Functions
2.6 Circuit-Breaker Failure Protection 50BF
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
108
2.6.2 Setting Notes
General
The circuit-breaker failure protection and its ancillary functions (end fault protection, pole discrepancy supervi-
sion) can only operate if they were set during configuration of the scope of functions (address 139 50BF, setting
Enabled or enabled w/ 3I0>).
Breaker Failure Protection (50BF)
The breaker failure protection is switched ON or OFF at address 3901 FCT 50BF Break..
The current threshold 50BF PICKUP (address 3902) should be selected such that the protection will operate
with the smallest expected fault current. A setting of 10 % below the minimum fault current for which breaker
failure protection must operate is recommended. On the other hand, the value should not be set lower than
necessary.
If the breaker failure protection is configured with zero sequence current threshold (address 139 = enabled
w/ 3I0>), the pickup threshold for the zero sequence current 50NBF PICKUP (address 3912) can be set in-
dependently of 50BF PICKUP.
Normally, the breaker failure protection evaluates the current flow criterion as well as the position of the breaker
auxiliary contact(s). If the auxiliary contact(s) status is not available in the device, this criterion cannot be pro-
cessed. In this case, set address 3909 Chk BRK CONTACT to NO.
Two-Element Breaker Failure Protection
With two-element operation, the trip command is repeated after a time delay T1 to the local feeder breaker,
normally to a different set of trip coils of this breaker.
If the circuit breaker does not respond to this trip repetition, the adjacent circuit breakers are tripped after T2,
i.e. the circuit breakers of the busbar or of the concerned busbar section and, if necessary, also the circuit
breaker at the remote end unless the fault has been cleared.
The time delays can be set separately
• for trip repetition to the local feeder circuit breaker after a trip of the feeder protection 50BF-1 Delay 3p
(address 3905),
• for trip of the adjacent circuit breakers (busbar zone and remote end if applicable) 50BF-2 Delay at
address 3906.
The time delays 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 2-43 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.
Note
To prevent automatic reclosing after „50BF BusTrip“, you can set the time 3408 T-Start MONITOR so
that it elapses together with 50BF-2 Delay.
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