2.13 Circuit Breaker Failure Protection
189
7SD610 Manual
C53000-G1176-C145-4
Two-stage breaker
failure protection
With two-stage 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. A choice
can be made whether this trip repetition shall be single-pole or three-pole if the initial
feeder protection trip was single-pole (provided that single-pole trip is possible). This
choice is made in address 3903 1p-RETRIP (T1). Set this parameter to YES if the
first stage is to trip single-pole, otherwise set it to NO.
If the 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.
Separate delay times can be set
• for single- or three-pole trip repetition to the local feeder circuit breaker after a 1-
pole trip of the feeder protection T1-1pole at address 3904,
• for three-pole trip repetition to the local feeder circuit breaker after 3-pole trip of the
feeder protection T1-3pole (address 3905),
• for trip of the adjacent circuit breakers (busbar zone and remote end if applicable)
T2 at address 3906.
Note
If three-pole coupling is executed for a pending single-pole TRIP, the T2 delay is re-
started with the three-pole coupling.
The delay times are set dependant on the maximum operating time of the feeder
circuit breaker and the reset time of the current detectors of the breaker failure protec-
tion, plus a safety margin which allows for any tolerance of the delay timers. Figure 2-
77 illustrates the timing of a typical breaker failure scenario. The dropout time for si-
nusoidal currents is ≤ 15 ms. If current transformer saturation is anticipated, the time
should be set to 25 ms.
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 enable that the busbar is tripped by the breaker failure protection without preceding
three-pole coupling of the trip command (by AR or BF), the time set for 3408 T-Start
MONITOR also has to be longer than the time set for 3906 T2. In this case, the AR
must be blocked by a signal from the BF to prevent the AR from reclosing after a
busbar TRIP. It is recommended to connect the signal 1494 „BF T2-TRIP(bus)“ to
the AR input 2703 „>AR block“.
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