2.6 Teleprotection for distance protection
143
7SA522 Manual
C53000-G1176-C155-3
As soon as the distance protection has detected a fault in the reverse direction, a
blocking signal is transmitted (e.g. ´'LV76(1'µ, FNo 4056). The transmitted
signal may be prolonged by setting address accordingly. The blocking signal is
stopped if a fault is detected in the forward direction (e.g. ´'LV7%/6723µ, FNo
4070). Very rapid blocking is possible by transmitting also the output signal of the jump
detector for measured values. To do so, the output ´'LV-XPS%ORFNLQJµ (FNo 4060)
must also be allocated to the transmitter output relay. As this jump signal appears at
every measured value jump, it should only be used if the transmission channel can be
relied upon to respond promptly to the disappearance of the transmitted signal.
If there is a disturbance in the signal transmission path the overreaching zone can be
blocked via a binary input. The distance protection operates with the normal time
grading characteristic (non delayed trip in Z1). The overreach zone Z1B may however
be activated by internal automatic reclosure or external criteria via the binary input
´!(QDEOH$5]RQHVµ.
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”. It prolongs the blocking signal by
the transient blocking time 7U%ON%ORFN7LPH (address ), if it has been present
for the minimum duration equal to the waiting time 7U%ON:DLW7LPH (address
).
It lies in the nature of the blocking scheme that single end fed short circuits can also
be tripped rapidly without any special measures, as the non feeding end cannot gen-
erate a blocking signal.
2.6.8 Transient Blocking
In the overreach schemes, the transient blocking provides additional security against
erroneous signals due to transients caused by clearance of an external fault or by fault
direction reversal during clearance of a fault on a parallel line.
The principle of transient blocking scheme is that following the incidence of an external
fault, the formation of a release signal is prevented for a certain (settable) time. In the
case of permissive schemes, this is achieved by blocking of the transmit and receive
circuit.
Figure 2-60 shows the principle of the transient blocking for a directional comparison
and for a permissive scheme.
If, following fault detection, a non-directional fault or a fault in the reverse direction is
determined within the waiting time 7U%ON:DLW7LPH (address ), the transmit
circuit and the release of the overreaching zone Z1B are prevented. This blocking is
maintained for the duration of the transient blocking time 7U%ON%ORFN7LPH (ad-
dress ) also after the reset of the blocking criterion. But if a trip command is
already present in Z1, the transient blocking time 7U%ON%ORFN7LPH is terminated
and thus the blocking of the signal transmission scheme in the event of an internal fault
is prevented.
In the case of the blocking scheme, the transient blocking prolongs the received block
signal as shown in the logic diagram Figure 2-60.
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