ABB Relion 670 Series Technical Reference Manual page 796

Section 13
Scheme communication
13.1.2
13.1.2.1
13.1.2.2
790
Phase segregated communication is also available for correct operation at simultaneous
faults when three distance protection communication channels are available between
the line ends.
Principle of operation
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.
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 tCoord has elapsed,
when no signal is 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 tCoord). The forward
overreaching zone to be accelerated is connected to the input PLTR_CRD, see
figure 386.
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 386.
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
AND
CR
ANSI05000512 V1 EN
Figure 386: Basic logic for trip signal in blocking scheme
Channels for communication in each direction must be available.
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
0-tCoord TRIP
0
en05000512_ansi.vsd
1MRK505222-UUS C
Technical reference manual