ABB Relion 650 Series Technical Manual page 348

Section 11
Scheme communication
11.1.6.3 Permissive overreaching scheme
In a permissive overreaching scheme, a forward directed overreach measuring element (normally
zone2) sends a permissive signal CS to the remote end if a fault is detected in forward direction.
The received signal CR is used to allow an overreaching zone to trip after the settable
has elapsed. The
The logic for trip signal is the same as for permissive underreaching, as in figure 180.
The permissive overreaching scheme has the same blocking possibilities as mentioned for
blocking scheme.
11.1.6.4 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 181. 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 signalling purpose. The
unblocking function is reset 200 ms after that the guard signal is present again.
CR
CR_GUARD
ANSI05000746 V1 EN-US
Figure 181: Guard signal logic with unblocking scheme
The unblocking function can be set in three operation modes (setting
Disabled
No restart
Restart
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342
tCoord in permissive overreaching schemes is normally set to zero.
0-tSecurity
NOT
0
200 ms
OR
AND
0
The unblocking function is out of operation
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)
Communication failure shorter than
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OR
150 ms
AND
0
tSecurity will be ignored
tSecurity will be ignored
1MRK 506 326-UUS B
tCoord timer
CRL
LCG
en05000746_ansi.vsd
Unblock ):
Line distance protection REL650
Technical manual
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