Functions
2.7 Teleprotection for Distance Protection (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
197
2.7.7
Directional Comparison
Principle
The directional comparison scheme is a permissive scheme. Figure 2-90 shows the operation scheme.
Figure 2-90
Operation scheme of the directional comparison pickup
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 at
both
line ends in forward direction. The distance stages operate in-
dependently of the directional comparison.
The transmit signal can be prolonged by T
S
(settable under address
2103
Send Prolong.
). The prolongation
of the send signal only comes into effect if the protection 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 2-91 shows the logic diagram of the directional comparison scheme for one line end.
On two terminal lines, the signal transmission may be phase segregated. In this case, send and receive circuits
operate separately for each phase. On three terminal lines, the transmit signals are sent to both opposite line
ends. The receive signals are then combined with a logical AND gate, as all three line ends must transmit a
send signal during an internal fault. With the 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 external faults or from direc-
tion reversal resulting during the clearance of faults on parallel lines, is neutralized by the „Transient Blocking“.
On feeders with single-end infeed, the line end with no infeed cannot generate a release signal as no fault de-
tection occurs there. To achieve tripping by the permissive overreach transfer scheme also in this case, the
device features a special function. This „Weak Infeed Function“ (echo function) is activated when a signal is
received from the opposite line end — in the case of three terminal lines from at least one of the opposite line
ends — without the device having detected a fault.
The circuit breaker can also be tripped at the line end with no or only weak infeed. This „weak-infeed tripping“
is described in Section 2.11.2.
