Directional Comparison Pickup - Siemens siprotec 7SD5 User Manual

2.7.7

Directional Comparison Pickup

The following scheme is suited for conventional transmission media.
Principle The directional comparison scheme is a permissive release scheme. Figure 2-74
shows the operation scheme.
Figure 2-74
If the distance protection detects a fault in line direction, it initially sends a release
signal to the opposite line end. If a release signal is also received from the opposite
line end, a trip signal is transmitted to the trip relay. This is only the case if the opposite
line end also detects a fault in line direction. A prerequisite for fast tripping is therefore
that the fault is recognized in both line ends in forward direction. The distance stages
operate independent from the directional comparison pickup.
The transmit signal can be prolonged by T
Prolong.). The prolongation of the send signal only comes into effect if the protec-
tion has already issued a trip command. This ensures release of the opposite line end
even when the short-circuit has been switched off rapidly by the independent zone Z1.
Sequence Figure 2-75 shows the logic diagram of the directional comparison scheme for one line
end.
On two terminal lines, the signal transmission may be phase segregated. Send and
receive circuits in this case are built up for each phase. On three terminal lines, the
transmit signal is sent to both opposite line ends. The receive signals are then com-
bined with a logical AND gate, as all three line ends must transmit a send signal during
an internal fault. With the setting parameter Type of Line (address 2102) the
device is informed as to whether it has one or two opposite line ends.
The occurrence of erroneous signals resulting from transients during clearance of ex-
ternal faults or from direction reversal resulting during the clearance of faults on par-
allel lines, is neutralized by the „Transient Blocking".
On feeders with single-sided infeed, the line end with no infeed cannot generate a
release signal, as no fault detection occurs there. To achieve tripping by the permis-
7SD5 Manual
C53000-G1176-C169-1
2.7 Teleprotection for Distance Protection (optional)
Function diagram of the directional comparison method
(settable under address 2103 Send
S
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