Siemens siprotec 7SA6 User Manual page 421

Two-stage Breaker
Failure Protection
7SA6 Manual
C53000-G1176-C133-1
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 processed. In this case, set address
  &KN %5. &217$&7 to 1R.
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   S5(75,3 7 . Set this parameter to <HV if you
wish single-pole trip for the first stage, otherwise to 1R.
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 7 (address  ), 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 sequence is illustrated in Figure 6-127.
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   7SROH,
− for three-pole trip repetition to the local feeder circuit breaker after 3-pole trip of the
feeder protection under address   7SROH,
− for trip of the adjacent circuit breakers (bus-bar zone and remote end if applicable)
under address   7.
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 tolerance of the delay timers. The
time sequence is illustrated in Figure 6-127. 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.
Functions
6-239