ABB Relion 670 Series Applications Manual page 416

Section 15
Scheme communication
Permissive underreaching scheme
Permissive underreaching scheme is not suitable to use on short line length due to difficulties for
distance protection measurement in general to distinguish between internal and external faults in
those applications.
The underreaching zones at the local and remote end(s) must overlap in reach to prevent a gap
between the protection zones where faults would not be detected. If the underreaching zone do
not meet the required sensitivity due to for instance fault infeed from the remote end, a blocking
or permissive overreaching scheme should be considered.
The received signal (CR) must be received when the overreaching zone is activated to achieve an
instantaneous trip. In some cases, due to the fault current distribution, the overreaching zone can
operate only after the fault has been cleared at the terminal nearest to the fault. There is a certain
risk that in case of a trip from an independent tripping zone, the zone issuing the send signal (CS)
resets before the overreaching zone has started at the remote terminal. To assure a sufficient
duration of the received signal (CR), the send signal (CS) can be prolonged by a
timer. The recommended setting of
Since the received communication signal is combined with the output from an overreaching zone,
there is less concern about a false signal causing an incorrect trip. Therefore set the timer
to zero.
Failure of the communication channel does not affect the selectivity, but delays tripping at one
end(s) for certain fault locations.
OR
B
IEC09000013 V2 EN-US
Figure 196: Principle of Permissive underreaching scheme
UR: Underreaching
OR: Overreaching
CR: Communication signal received
CS: Communication signal send
Permissive overreaching scheme
In a permissive overreaching scheme there is an overreaching zone that issues the send signal. At
the remote end the received signal together with the start of an overreaching zone will give an
instantaneous trip. The scheme can be used for all line lengths.
410
tSendMin is 100 ms.
A
UR
B
CS
B
TRIP: UR or OR+CR
© Copyright 2017 ABB. All rights reserved
UR
A
CS
A
B
IEC09000013-2-en.vsd
1MRK 511 401-UUS F
M16866-53 v4
tSendMin reset
tCoord
OR
A
M16866-41 v4
Bay control REC670
Application manual