ABB Relion 670 Series Technical Reference Manual page 821

1MRK505222-UUS C
13.5.2.3
Technical reference manual
Unblocking scheme
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 CR_GUARD, which must always be
present, even when no CR signal is received. The absence of the CR_GUARD signal
for a time longer than the setting tSecurity time is used as a CR signal, see figure 403.
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.
CR
NOT
CR_GUARD
200 ms
0
ANSI05000746 V1 EN
Figure 403: Guard signal logic with unblocking scheme
The unblocking function can be set in three operation modes (setting Unblock):
Disabled: The unblocking function is out of operation
No restart: Communication failure shorter than
If CR_GUARD disappears, a CRL signal will be transferred to the trip logic
There will not be any information in case of communication failure (LCG)
Restart Communication failure shorter than
It sends a defined (150 ms) CRL after the disappearance of the CR_GUARD signal
The function will activate LCG output in case of communication failure
If the communication failure comes and goes (<200 ms) there will not be recurrent
signaling
0-tSecurity
0
150 ms
OR
AND
0
tSecurity will be ignored
tSecurity will be ignored
Section 13
Scheme communication
OR
AND
en05000746_ansi.vsd
CRL
LCG
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