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6.14.1 Method of Operation
Selectivity before
Reclosure
7SA6 Manual
C53000-G1176-C156-2
The integrated automatic reclosure circuit allows up to 8 reclosure attempts.
The first four interrupt cycles may operate with different parameters (action and dead
times, single/three-pole). The parameters of the fourth cycle also apply for the fifth
cycle and onwards.
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 overreaching zone Z1B may be released before the
first reclosure (zone extension). This implies that faults up to the zone reach limit of
Z1B are tripped without delay for the first cycle (figure 6-102). 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 automat-
ic reclosure function.
Line
Reach for 1st tripping before reclosure (overreach zone Z1B enabled)
Line
Reach after 1st reclosure (overreach zone Z1B disabled)
Figure 6-102 Reach control, before the first reclosure, in the distance protection
If the distance protection is operated with one of the signal transmission methods
described in section 6.6 the signal transmission logic controls the overreaching zone,
i.e. it determines whether an undelayed trip (or delayed with T1B) is permitted in the
event of faults in the overreaching zone (i.e. up to the reach limit of zone Z1B) at both
line ends simultaneously. Whether the automatic reclosure function is ready for reclos-
ure or not is irrelevant because the teleprotection function ensures the selectivity over
100 % of the line length and fast, simultaneous tripping. Similar considerations apply
for the earth fault direction comparison protection (section 6.8).
If, however, the signal transmission is switched off or the transmission path is dis-
turbed, the internal automatic reclosure function can determine whether the over-
reaching zone (Z1B in the distance protection) is released for fast tripping. If no reclos-
ure is expected (e.g. circuit-breaker not ready) the normal grading of the distance pro-
tection (i.e. fast tripping only for faults in zone Z1) must apply to retain selectivity.
Fast tripping before reclosure is also possible with multiple reclosures. Appropriate
links between the output signals (e.g. 2nd reclosure ready: " AR 2.CycZoneRel ") and
the inputs for enabling/releasing undelayed tripping of the protection functions can be
established via the binary inputs and outputs or the integrated user-definable logic
functions (CFC).
Z2
Z1
Z1B
Z2
Z1
Z1B
Functions
6-189
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