2.12 Automatic Reclosure Function
125
7ST6 Manual
E50417-G1176-C251-A3
The integrated auto reclose function allows up to 8 reclosure attempts. The first two
interrupt cycles may operate with different parameters for action and dead times. The
parameters of the second cycle also apply for the third cycle and onwards.
Selectivity before
Reclosure
In order for the automatic reclosure to be successful, all faults on the entire overhead
line must be cleared at all line ends simultaneously — as fast as possible. In the dis-
tance protection, for example, the overreach zone Z1B may be released before the
first reclosure. This implies that faults up to the zone reach limit of Z1B are tripped
without delay for the first cycle. A limited unselectivity in favour of fast simultaneous
tripping is accepted here because a reclosure will be performed in any case. The
normal stages of the distance protection (Z1, Z2, etc.) and the normal grading of the
other short-circuit functions are independent of the automatic reclosure function.
Figure 2-38 applies for one reclosure cycle.
Figure 2-38
Reach control before first reclosure, using distance protection
The internal auto reclose function determines whether the overreach zone (Z1B for
distance protection) will be decisive for fast tripping. If no reclosure is expected (e.g.
circuit-breaker not ready) the normal grading of the distance protection (i.e. fast trip-
ping only for faults in zone Z1) must apply to retain selectivity.
If restart in a higher stage is permitted, the auto reclose function can also be used for
the back-up zones. The zone Z1L can in that case be used as an overreaching stage
for zone Z2.
If the auto reclose function is only to be used for the overhead contact line that is di-
rectly allocated to the 7ST6 device, the reach of zone Z1L can be set in the same way
as the reach of zone Z1B.
Zone Release for
the Distance Pro-
tection
In the initial state, with the distance protection switched on and the auto reclose func-
tion operative, zone Z1B is released. If the distance protection is switched off or the
auto reclose function is not operative, zone Z1 is released.
Before the 2nd reclosure cycle, the enable for zone Z1B is reset after the dead time
has expired, and the enable for zone Z1L is set with start of the blocking time and the
CLOSE command.
The pickup starts all action times which are enabled for initiation. When the 1st action
time has expired but the 2nd action time is still running, the zone enabling switches
from Z1B to Z1L.
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