Functions
2.7 Teleprotection for Distance Protection (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
200
Sequence
Figure 2-93 shows the logic diagram of the unblocking scheme for one line end.
The unblock scheme only functions for faults in the „forward“ direction. Accordingly, the overreaching zone Z1B
of the distance protection must definitely be set to Forward: in Address 1651 Op. mode Z1B, see also Sub-
section 2.5.1 at margin heading „Controlled Zone Z1B“.
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 send signal is transmitted to both opposite 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.
An unblock logic is inserted before the receive logic, which in essence corresponds to that of the permissive
overreach transfer scheme, see Figure 2-94. If an interference free unblock signal is received, a receive signal,
e.g. „>Dis.T.UB ub 1“, appears and the blocking signal, e.g. „>Dis.T.UB bl 1“ disappears. The internal
signal „Unblock 1“ is passed on to the receive logic, where it initiates the release of the overreaching zone Z1B
of the distance protection (when all remaining conditions have been fulfilled).
If the transmitted signal does not reach the other line end because the short-circuit on the protected feeder
causes too much attenuation or reflection of the transmitted signal, neither the unblocking signal e.g.,
„>Dis.T.UB ub 1“, nor the blocking signal „>Dis.T.UB bl 1“ will appear on the receiving side. In this
case, the release „Unblock 1“ is issued after a security delay time of 20 ms and passed onto the receive logic.
This release is however removed after a further 100 ms via the timer stage 100/100 ms. When the transmission
is functional again, one of the two receive signals must appear again, either „>Dis.T.UB ub 1“or
„>Dis.T.UB bl 1“; after a further 100 ms (drop-off delay of the timer stage 100/100 ms) the quiescent state
is reached again, i.e. the direct release path to the signal „Unblock L1“ and thereby the usual release is possi-
ble.
If none of the signals is received for a period of more than 10 s the alarm „Dis.T.UB Fail1“ is generated.
During disturbance of the signal transmission path, the overreaching zone Z1B may be activated by an auto-
matic reclosure (internal or external) via the binary input „>Enable ARzones“.
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-sided infeed, the line end with no infeed cannot generate a release signal, as no fault
detection occurs there. To achieve tripping by the directional unblocking scheme also in this case, the device
features a special function. This „Weak Infeed Function“ (echo function) is described in Section „Measures for
Weak and Zero Infeed“. It 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.
If the parameter Mem.rec.sig. (address 2113) is set to YES and an own distance protection pickup is avail-
able in Z1B, the phase-selective release effected via the signal extension is stored. If the own distance protec-
tion pickup in Z1B drops out, it will be deleted.
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