Siemens siprotec 7SD5 User Manual page 198

2 Functions
Figure 2-83 shows the logic for reverse interlocking.
Figure 2-83 Logic diagram of the reverse interlocking
According to Figure 2-84 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 (according to Figure 2-84) 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
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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 2-84) 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 interlocking is extended by a transient blocking time (TB in Figure 2-84).
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faults on the busbar, such as for example in F1,
failure of the line protection during a fault, such as for example in F2.
7SD5 Manual
C53000-G1176-C169-1