2 Functions
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7SA522 Manual
C53000-G1176-C155-3
and the blocking signal e.g. ´!'LV78%EOµ disappears. The internal signal “Un-
block 1” is passed on to the receive logic, where it initiates the release of the over-
reaching 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 line causes too much attenuation or reflection of the transmitted signal,
neither the unblocking signal e.g., ´!'LV78%XEµ, nor the blocking signal
´!'LV78%EOµ will appear on the receiving side. In this case, the release “Un-
block 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 ´!'LV78%XEµ or ´!'LV78%EOµ; after a
further 100 ms (dropout 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 possible.
If none of the signals is received for a period of more than 10 s the alarm ´'LV78%
)DLOµ is generated.
During disturbance of the signal transmission path, the overreaching zone Z1B may
be activated by an automatic reclosure (internal or external) 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”.
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-
sive overreach transfer scheme even in this case, the device contains a special func-
tion. This “Weak-infeed tripping” (echo function) is referred to in Subsection “Mea-
sures 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 referred to in Section 2.9.1.
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