ABB Relion 650 Series Technical Manual page 347

1MRK 506 326-UUS B
11.1.6 Operation principle
Depending on whether a reverse or forward directed impedance zone is used to issue the send
signal, the communication schemes are divided into Blocking and Permissive schemes,
respectively.
A permissive scheme is inherently faster and has better security against false tripping than a
blocking scheme. On the other hand, a permissive scheme depends on a received signal for a fast
trip, so its dependability is lower than that of a blocking scheme.
11.1.6.1 Blocking scheme
The principle of operation for a blocking scheme is that an overreaching zone is allowed to trip
instantaneously after the settable co-ordination time
received from the remote IED.
The received signal, which shall be connected to CR, is used to not release the zone to be
accelerated to clear the fault instantaneously (after time
accelerated is connected to the input PLTR_CRD, see figure 179.
In case of external faults, the blocking signal (CR) must be received before the settable timer
tCoord elapses, to prevent a false trip, see figure 179.
The function can be totally blocked by activating the input BLOCK, block of trip by activating the
input BLKTR, Block of signal send by activating the input BLKCS.
PLTR-CRD
CR
ANSI05000512 V1 EN-US
Figure 179: Basic logic for trip signal in blocking scheme
Channels for communication in each direction must be available.
11.1.6.2 Permissive underreaching scheme
In a permissive underreaching scheme, a forward directed underreach measuring element
(normally zone1) 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
timer has elapsed. The
The logic for trip signal in permissive scheme is shown in figure 180.
PLTR-CRD
CR
ANSI05000513 V1 EN-US
Figure 180: Logic for trip signal in permissive scheme
The permissive underreaching scheme has the same blocking possibilities as mentioned for
blocking scheme.
Line distance protection REL650
Technical manual
0-tCoord TRIP
AND
0
en05000512_ansi.vsd
tCoord in permissive underreaching schemes is normally set to zero.
0-tCoord
TRIP
AND
0
en05000513_ansi.vsd
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tCoord has elapsed, when no signal is
tCoord ). The overreaching zone to be
Section 11
Scheme communication
M13893-3 v2
M13893-6 v4
M13893-13 v3
tCoord
341