Functions
2.7 Teleprotection for Distance Protection (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
209
2.7.11
Reverse Interlocking
If the distance protection function of the 7SD5 is used as backup protection in single-end fed transformer feed-
ers, the reverse interlocking function ensures a fast protection of the busbar without endangering the selectivity
for faults on the outgoing feeders.
Figure 2-99 shows the logic for reverse interlocking.
Figure 2-99
Logic diagram of the reverse interlocking
According to Figure 2-100 the distance zones Z1 and Z2 serve as back-up stages for faults on the outgoing
lines, for example a fault in
F2
. For distance grading the shortest outgoing line is to be used.
The overreach zone Z1B, whose delay time T1B must be set longer than the pickup time Ta of the protection
devices of the outgoing lines, is blocked after the pickup of an inferior protection. The pickup signal is sent (ac-
cording to Figure 2-100) via the receive input (4006
„>DisTel Rec.Ch1“
) of the distance protection. If no
signal is received this zone guarantees fast tripping of the busbar for
• faults on the busbar, such as for example in
F1
,
• failure of the line protection during a fault, such as for example in
F2
.
The reverse interlocking of the distance protection is performed by specific release or blocking of the overreach
zone Z1B. It can be realized by the blocking mode (parallel connection of the NO contacts as illustrated in
Figure 2-100) or the release mode (series connection of the NC contacts).
To avoid transient false signals after clearance of external faults, the blocking condition of the reverse interlock-
ing is extended by a transient blocking time (TB in Figure 2-100).
