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2.7 Teleprotection for Distance Protection (optional)
181
7SD5 Manual
C53000-G1176-C169-1
If at one line end there is weak or zero infeed, so that the distance protection does not
pick up, the circuit breaker can still be tripped. This „Weak-infeed tripping“ is referred
to in Section 2.10.1.
2.7.5 Direct Underreach Transfer Trip
The following scheme is suited for conventional transmission media.
Principle As is the case with PUTT (pickup) or PUTT with zone acceleration, a fault in the first
zone Z1 is transmitted to the opposite line end by means of a transfer trip signal. The
signal received there causes a trip without further queries after a short security margin
Tv (settable in address
2202 Trip Time DELAY
) (Figure 2-71). The transmit signal
can be prolonged by T
S
(settable in address
2103 Send Prolong.
), to compensate
for possible differences in the pickup time at the two line ends. The distance protection
is set such that the first zone reaches up to approximately 85% of the line length. On
three terminal lines Z1 is also set to approximately 85 % of the shorter line section, but
at least beyond the tee-off point. The overreaching zone Z1B is not required here. It
may, however, be activated by internal automatic reclosure or external criteria via the
binary input
„>Enable ARzones“
.
The advantage compared to the permissive underreach transfer trip with zone accel-
eration lies in the fact that both line ends are tripped without the necessity for any
further measures, even if one line end has no infeed. There is however no further su-
pervision of the trip signal at the receiving end.
The direct underreach transfer trip application is not provided by its own selectable
teleprotection scheme setting, but implemented by setting the teleprotection supple-
ment to operate in the permissive underreach transfer trip scheme (address
121
Teleprot. Dist.
=
PUTT (Z1B)
or
PUTT (Pickup)
), and using the binary inputs
for direct external trip at the receiving end. Correspondingly, the transmit circuit in
Section „The principle of PUTT“ (Figure 2-68) applies. For the receive circuit the logic
of the „external trip“ as described in Section 2.11 applies.
On two terminal lines, the signal transmission may be phase segregated. On three ter-
minal lines, the transmit signal is sent to both opposite line ends. The receive signals
are then combined with a logical OR function.
Figure 2-71 Function diagram of the direct underreach transfer trip scheme
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