Permissive Overreaching Scheme; Unblocking Scheme - ABB REL650 Technical Manual

Section 12
Scheme communication
12.1.6.4
12.1.6.5
438
The function can be totally blocked by activating the input BLOCK. Tripping can
be blocked by activating the input BLKTR. Signal send can be blocked by
activating the input BLKCS.

Permissive overreaching scheme

In a permissive overreaching scheme, a forward directed overreaching 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 tCoord timer has elapsed. The tCoord in
permissive overreaching schemes is normally set to zero.
The logic for trip signal in permissive scheme is shown in figure 219.
CACC
AND
CR
IEC05000513 V1 EN-US
Figure 220: Logic for trip signal in permissive scheme
The function can be totally blocked by activating the input BLOCK. Tripping can
be blocked by activating the input BLKTR. Signal send can be blocked by
activating the input BLKCS.e.

Unblocking scheme

In unblocking scheme, the lower dependability of a 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 221. This
enables a permissive scheme to operate when the line fault blocks the signal
transmission. The CRG signal is only used in unblocking schemes.
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.
tCoord
t
TRIP
en05000513.vsd
1MRK 506 382-UEN A
Line distance protection REL650 2.2 IEC
Technical manual
M13893-22 v6
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