ABB Relion 670 series, Technical Reference Manual, Page: 803 / 1232

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.
The Phase segregated scheme communication logic for distance protection
(ZC1PPSCH ,85) function is a logical function built-up from logical elements. It is a
supplementary function to the distance protection, requiring for its operation inputs
from the distance protection and the communication equipment.
The type of communication-aided scheme to be used can be selected by way of the
settings.
The ability to select which distance protection zone is assigned to which input of
ZC1PPSCH (85) makes this logic able to support practically any scheme
communication requirements regardless of their basic operating principle. The outputs
to initiate tripping and sending of the teleprotection signal are given in accordance with
the type of communication-aided scheme selected and the zone(s) and phase(s) of the
distance protection which have operated.
When power line carrier communication channels are used for permissive schemes
communication, unblocking logic which uses the loss of guard signal as a receive
criteria is provided. This logic compensates for the lack of dependability due to the
transmission of the command signal over the faulted line.
13.2.2.1 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
tCoord has elapsed,
when no signal is received from the remote IED. The received signal (sent by a reverse
looking element in the remote IED), which shall be connected to CRLx, is used to not
release the zone to be accelerated to clear the fault instantaneously (after time
tCoord ).
The overreaching zone to be accelerated is connected to the input CACCLx, see
figure
391 . In case of external faults, the blocking signal (CRLx) must be received
before the settable timer tCoord elapses, to prevent an unneccesary trip, see figure 391 .
ZC1PPSCH (85) can be totally blocked by activating the input BLOCK, block of trip is
achieved by activating the input BLKTRLx, Block of carrier send is done by activating
the input BLKCSLx.
CACCLx
CRLx
AND
ANSI06000310_2_en.vsd
TRLx
0
0
25 ms
0
-
tCoord
ANSI06000310 V2 EN
Figure 391: Basic logic for trip carrier in one phase of a blocking scheme
1MRK505222-UUS C
Section 13
Scheme communication
797
Technical reference manual