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Two-stage Breaker
Failure Protection
Normally, the breaker failure protection evaluates the current flow criteri-
on as well as the position of the breaker auxiliary contact(s). If the auxil-
iary contact(s) status is not available in the device, this criterion cannot
be processed. In this case, set address 3909 Chk BRK CONTACT to No .
The breaker failure protection in the 7SA6 can be operated single-stage
or two-stage:
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 single-pole trip is possible). This choice is made in address
3903 1p-RETRIP (T1) . Set this parameter to Yes if you wish single-
pole trip for the first stage, otherwise to No .
If the breaker does not respond to this first stage trip, the adjacent circuit
breakers must be tripped provided the fault has not yet been cleared. The
adjacent breakers are those of the other feeders on the bus-bar or bus-
bar section and — if signal transmission is possible — the breaker at the
remote end(s) of the protected object.
In the 7SA6, after a further delay time T2 (address 3906 ), the adjacent
circuit breakers (i.e. the breakers of the bus-bar zone and — if signal
transmission is possible — the breaker at the remote end) are tripped
provided the fault has not yet been cleared. An example of the time se-
quence is illustrated in Figure 6-136.
Separate delay times can be set:
− for single- or three-pole trip repetition to the local feeder circuit breaker
after 1 -pole trip of the feeder protection under address 3904 T1-
1pole ,
− for three-pole trip repetition to the local feeder circuit breaker after 3 -
pole trip of the feeder protection under address 3905 T1-3pole ,
− for trip of the adjacent circuit breakers (bus-bar zone and remote end
if applicable) under address 3906 T2 .
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 protection, plus a safety margin which allows for any tol-
erance of the delay timers. The time sequence is illustrated in Figure 6-
136. For sinusoidal currents one can assume that the reset time of the
current detectors is less than 12 ms but if current transformer saturation
is expected then 25 ms should be assumed.
7SA6 Manual
C53000-G1176-C156-2
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