Siemens siprotec 7SA6 User Manual page 356

Functions
Multiple Reclosure
Handling of
Sequential Faults
6-174
(adjustable) reclaim time is started. If the reclosure is blocked during the dead time
following a single-pole trip, optional immediate three-pole tripping can take place
(Forced Three-pole Trip, page 6-186).
If the fault is cleared (successful reclosure), the reclaim time expires and all functions
return to their quiescent state. The system disturbance has ended.
If the fault is not cleared (unsuccessful reclosure), the short-circuit protection initiates
a final three-pole trip with the protection stage that is valid when reclosure is not ready.
All faults during the reclaim time also lead to the issue of a final three-pole trip.
After unsuccessful reclosure (final tripping) the automatic reclosure function is blocked
dynamically (see also page 6-170, "Reclose Block").
The sequence above applies for single reclosure cycles. In the 7SA6 multiple
reclosure (up to 8 cycles) is also possible (see below).
If a short-circuit still exists after a reclosure attempt, further reclosure attempts can be
made. Up to 8 reclosure attempts are possible with the automatic reclosure function
integrated in the 7SA6.
The first four reclosure cycles are independent on each other. Each one has separate
action and dead times, can operate single or three pole and can be blocked separately
via binary inputs. The parameters and intervention possibilities of the fourth cycle also
apply to the fifth cycle and onwards.
The sequence is the same in principle as in the different reclosure programs described
above. However, if the first reclosure attempt was unsuccessful, the reclosure function
is not blocked, but instead the next reclose cycle is started. The appropriate dead time
starts with the reset of the trip command or opening of the circuit-breaker (pole)
(auxiliary contact criterion). The circuit-breaker receives a new close command after
expiry of the dead time. At the same time the reclaim time is started.
Until the set number of permissible reclose cycles is reached, the reclaim time is reset
with each new trip command after reclosure and started again with the next close
command.
If one of the cycles is successful, i.e. the fault no longer exists after reclosure, the
reclaim time expires and all functions return to their quiescent state. The system fault
has ended.
If none of the cycles is successful, a final three-pole trip is issued by the valid
protection stage selected to operate during the recloser not ready state following the
final permissible reclosure. The automatic reclosure is blocked dynamically (see also
"Reclose Block", page 6-170).
When single-pole or single- and three-pole reclose cycles are executed in the network,
particular attention must be paid to sequential faults.
Sequential faults are faults which occur during the dead time after clearance of the first
fault.
There are various ways of handling sequential faults in the 7SA6 depending on the
requirements of the network:
Detection of an sequential fault can be selected to occur either with a trip command
of a protection function during the dead time or with every further fault detection .
It is possible to select the desired response of the internal automatic recloser
following the detection of an sequential fault.
7SA6 Manual
C53000-G1176-C133-1