ABB Relion 670 Series Technical Reference Manual page 804

Section 13
Scheme communication
13.2.2.2
13.2.2.3
13.2.2.4
798
Permissive underreach scheme
In a permissive underreach scheme, a forward directed underreach measuring element
(normally zone1) sends a permissive signal CSLx to the remote end if a fault is
detected in forward direction. The received signal CRLx is used to allow an
overreaching zone (connected to CACCLx) to trip after the tCoord timer has elapsed.
The tCoord is in permissive underreach schemes normally set to zero. The logic for
trip carrier in permissive scheme is shown in figure 392. Three channels for
communication in each direction must be available.
CACCLx
CRLx AND
ANSI07000088 V2 EN
Figure 392: Basic logic for trip carrier in one phase of a permissive underreach
scheme
Permissive overreach scheme
In a permissive overreach scheme, a forward directed overreach measuring element
(normally zone2) sends a permissive signal CSLx to the remote end if a fault is
detected in forward direction. The received signal CRLx is used to allow an
overreaching zone to trip after the settable tCoord timer has elapsed. The tCoord is in
permissive overreach schemes normally set to zero. The logic for trip carrier is the
same as for permissive underreach, see figure 391.
The permissive overreach scheme has the same blocking possibilities as mentioned for
blocking scheme above. The blocking inputs are activated from the current reversal
logic when this function is included.
Three channels for communication in each direction must be available.
Unblocking scheme
In an 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
carrier receive signal. It is common or suitable to use the function when older, less
reliable, power-line carrier (PLC) communication is used. As phase segregated
communication schemes uses phases individually and the PLC is typically connected
single-phase or phase-to-phase it is not possible to evaluate which of the phases to
release and the unblocking scheme has thus not been supported.
0
0-tCoord
25 ms
0
ANSI07000088_2_en.vsd
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Technical reference manual