In the overreaching alternative, an overreaching directional residual overcurrent
measurement element will be used as sending criterion of the permissive input
signal CSOR. Also the underreaching input signal CSUR can initiate sending.
BLOCK
CR
CACC
BLKCS
CRL
Overreach
CSOR
t
0 - 60 s
tCoord
t
25 ms
CSUR
TRIP
CS
IEC05000280.vsd
AND
AND AND
AND
AND
AND
OR
OR
t
50 ms
t
25 ms
IEC05000280 V4 EN-US
13.4.6.3 Unblocking scheme
M13922-45 v6
In unblocking scheme, the lower dependability in permissive scheme is overcome
by using the loss of guard signal from the communication equipment to locally
create a receive signal. It is common or suitable to use the function when older, less
reliable, power line carrier (PLC) communication is used.
The unblocking function uses a guard signal CRG, which must always be present,
even when no CR signal is received. The absence of the CRG signal for a time
longer than the setting tSecurity time is used as a CR signal, see figure
209. This
also enables a permissive scheme to operate when the line fault blocks the signal
transmission.
The received signal created by the unblocking function is reset 150 ms after the
security timer has elapsed. When that occurs an output signal LCG is activated for
signaling purpose. The unblocking function is reset 200 ms after that the guard
signal is present again.
Section 13 1MRK 505 394-UEN A
Scheme communication
422 Line differential protection RED650 2.2 IEC
Technical manual
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